The Influence of Wastewater Irrigation on the
Transcription
The Influence of Wastewater Irrigation on the
C H A P T E R F I V E The Influence of Wastewater Irrigation on the Transformation and Bioavailability of Heavy Metal (Loid)s in Soil Anitha Kunhikrishnan,*,†,} Nanthi S. Bolan,*,† Karin Müller,‡ Seth Laurenson,§ Ravi Naidu,*,† and Won-Il Kim} Contents 1. Introduction 2. Sources of Wastewater and Heavy Metal(Loid)s in Soils 2.1. Wastewater production and quality 2.2. Heavy metal(loid) sources 3. Effects of Wastewater Irrigation on Soil Properties Affecting Heavy Metal(Loid) Interactions 3.1. Soil chemistry 3.2. Soil biology 3.3. Soil physics 4. Effect of Wastewater Irrigation on Heavy Metal(Loid) Dynamics in Soils 4.1. Adsorption 4.2. Complexation 4.3. Redox reactions 4.4. Methylation/demethylation 4.5. Leaching and runoff 5. Bioavailability of Wastewater-Borne Heavy Metal(Loid)s in Soils 5.1. Chemical extraction 5.2. Bioassay 6. Conclusions and Research Needs References 216 219 219 227 231 231 242 245 248 248 249 253 256 258 261 262 265 271 273 * Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, Australia Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, Adelaide, Australia { Systems Modelling, The NZ Institute for Plant and Food Research Ltd., Hamilton, New Zealand } Land and Environment, AgResearch Ltd, Invermay, New Zealand } Chemical Safety Division, Department of Agro-Food Safety, National Academy of Agricultural Science, Suwon-si, Gyeonggi-do, Republic of Korea # 2012 Elsevier Inc. Advances in Agronomy, Volume 115 ISSN 0065-2113, DOI: 10.1016/B978-0-12-394276-0.00005-6 All rights reserved. { 215 216 Anitha Kunhikrishnan et al. Abstract With pressure increasing on potable water supplies worldwide, interest in using alternative water supplies including recycled wastewater for irrigation purposes is growing. Wastewater is derived from a number of sources including domestic sewage effluent or municipal wastewater, agricultural (farm effluents) and industrial effluents, and stormwater. Although wastewater irrigation has many positive effects like reliable water supply to farmers, better crop yield, pollution reduction of rivers, and other surface water resources, there are problems associated with it such as health risks to irrigators, build-up of chemical pollutants (e.g., heavy metal(loid)s and pesticides) in soils and contamination of groundwater. Since the environment comprises soil, plants, and soil organisms, wastewater use is directly associated with environmental quality due to its immediate contact with the soil–plant system and consequently can impact on it. For example, the presence of organic matter in wastewater-irrigated sites significantly affects the mobility and bioavailability of heavy metal(loid)s in the soil. Wastewater irrigation can also act as a source of heavy metal(loid) input to soils. In this chapter, first, the various sources of wastewater irrigation and heavy metal(loid) input to soil are identified; second, the effect of wastewater irrigation on soil properties affecting heavy metal(loid) interactions is described; and third and finally, the role of wastewater irrigation on heavy metal(loid) dynamics including adsorption and complexation, redox reactions, transport, and bioavailability is described in relation to strategies designed to mitigate wastewater-induced environmental impacts. 1. Introduction In many parts of the world, continued extraction of freshwater for various activities including irrigation have led to unsustainable rates of water consumption, which has not been assisted by declining rainfall and increased rationing of water to the ecosystem (Brown, 2007; Seckler et al., 1998). Considerable pressure is now being placed on communities, particularly primary producers, to improve water-use efficiency and use alternative water supplies including recycled wastewater sources for irrigation, in a much better way. Although using wastewater for irrigation raises concerns about public exposure to pathogens and contamination of soil, surface water, and groundwater, under controlled management these water sources can be employed safely and profitably for irrigation (Plate 1) (Qadir et al., 2007). Wastewaters originate from a number of sources including domestic sewage (municipal wastewater), agricultural, urban and industrial effluents, and stormwater. Wastewater irrigation has many beneficial effects, including groundwater recharging (Asano and Cotruvo, 2004) and nutrient supply to plants (Anderson, 2003). There are, however, some detrimental effects, such as build-up of salts, pesticides, and heavy metal(loid)s. At sites irrigated with Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 217 A B Plate 1 Recycled water irrigation in horticultural crops (A) Carrots, (B) Olives (Bolan et al., 2011a). wastewater, mobilization and transport of pesticides and heavy metal(loid)s into groundwater have been noted, as well as their enhanced bioavailability to soil biota and higher plants. For example, dissolved organic matter (DOM) present in wastewater and sewage sludge has been shown to facilitate the transport of both pesticides and heavy metal(loid)s (Ashworth and Alloway, 2004; Bolan et al., 2011a; Müller et al., 2007; Sedlak et al., 1997; Tam and Wong, 1996; Thevenot et al., 2009). Wastewater irrigation and sludge application have also been shown to act as a source of heavy metal(loid) input to soils (Barman et al., 2001; Eriksson and Donner, 2009; Murtaza et al., 2008). The term “heavy metal(loid)” in general includes elements (both metals and metalloids) with an atomic density greater than 6gcm3 [with the exception 218 Anitha Kunhikrishnan et al. of arsenic (As), boron (B), and selenium (Se)]. This group includes both biologically essential [e.g., cobalt (Co), copper (Cu), chromium (Cr), manganese (Mn), and zinc (Zn)] and nonessential [e.g., cadmium (Cd), lead (Pb), and mercury (Hg)] elements (Sparks, 2003). Heavy metal(loid)s reach the soil environment through both pedogenic (or geogenic) and anthropogenic processes. Anthropogenic activities, primarily associated with the disposal of industrial and domestic waste materials including wastewaters and biosolids, are the major sources of metal(loid) enrichment in soils (Adriano, 2001). Although the role of wastewater irrigation on the transport of pesticides has been reviewed recently (Müller et al., 2007), no comprehensive review has focused on its role in the mobilization, transport, and bioavailability of heavy metal(loid)s in soil. This review aims to classify the different sources of wastewater irrigation and heavy metal(loid) input to soil. It describes the influence of wastewater irrigation on soil properties affecting heavy metal (loid) interactions and explains the role of wastewater irrigation on heavy metal(loid) dynamics including adsorption and complexation, redox reactions and bioavailability (Fig. 1). Whilst some literature reviews have examined metal(loid) input through inorganic fertilizers, sewage sludge, Wastewater irrigation M+ Metal(loid) sink Adsorption Complexation Precipitation Redox reaction M+ M+ M+ M+ Treated sewage Stormwater Farm dairy effluent Piggery effluent Winery effluent Changes in soil properties + M+ M M+ M+ Metal(loid) source Plant uptake Microorganisms Earthworms Volatilization/demethylation Leaching pH, EC, CEC TOC, DOC Sodicity and salinity Aggregate stability BD and total porosity HC and infiltration Figure 1 Schematic representation of wastewater sources and their effect on metal (loid) transformation and fate in soils by acting as a source and sink for metal(loid)s and by altering soil properties. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 219 and atmospheric deposition (Adriano, 2001; Smith, 2009), most reviews on wastewater irrigation have focused on environmental issues of nutrients and salt accumulation (Bolan et al., 2009; Bond 1998; Carpenter, 1998). There has been no comprehensive review on the input of metal(loid)s via effluent and wastewater, and the subsequent transformation and bioavailability of effluent-borne metal(loid)s in soils. Unlike wastewater irrigation, a number of studies have assessed the environmental implications of metal(loid)s derived from sewage sludge and manure slurry application to soils (Cornu et al., 2001; McBride, 2002; McGrath et al., 1994). Since sewage sludge is derived during wastewater treatment and there are major resemblances in the composition and chemical properties between these two resources, some of the information on the distribution and bioavailability of metal(loid)s is inferred from sewage sludge and manure research. An improved knowledge of wastewater irrigation’s long-term effects on metal(loid) dynamics in soils can enhance the development of strategies to mitigate environmental impacts and maximize the benefits of wastewater as a viable irrigation source. 2. Sources of Wastewater and Heavy Metal(Loid)s in Soils 2.1. Wastewater production and quality As indicated above wastewaters originate from a number of sources including domestic sewage, agricultural and industrial effluents, and stormwater. Recycled water is defined as wastewater that is treated and reused to supplement water supply (US EPA, 1992). The beneficial utilization of treated wastewater for agriculture is the major water reuse application worldwide (US EPA, 2004). This water source can have the advantage of being a constant, reliable water source and furthermore reduces the amount of water extracted from the environment (Toze, 2006). Approximately 70% of the world’s water resources including all the water from underground and redirected from rivers is used for agricultural irrigation, so reusing treated wastewater for agricultural and landscape irrigation (Plate 1) reduces both the amount of water that has to be extracted from natural water sources and the uncontrolled discharge of wastewater to the environment (Pedrero et al., 2010). Thus, treated wastewater is a valuable water source for recycling and reuse, especially in the Mediterranean countries and other arid and semi-arid regions including Australia with increasing water shortages (Pedrero et al., 2010). Table 1 summarizes the amount of wastewater generated and reused annually in selected countries. For example, 88% and 70% of the recycled water in Spain and Israel, respectively, is used for agricultural purposes (Kanarek and Michail, 1996; Lallana et al., 2001). 220 Table 1 Anitha Kunhikrishnan et al. Wastewater generated and reused annually in selected countries Country Wastewater generated (GL) Wastewater reused (GL) % Reuse Argentina * Australia Bahrain Bolivia Chile Greece Egypt * India Jordan Kuwait Libya Mexico New Zealand Oman Peru Saudi Arabia Spain Syria Tunisia UAE US 200.3 1634 45 135.8 295.6 – 10,012 13,870 82 119 546 13,340 67 78 34.7 730 24,094 825 240 881 – 90.7 262.9 8 – – 0.7 200 1460 64.9 52 40 280 16 8.6 18.6 122.6 1100 550 33.8 185.3 2271 45.28 16.09 17.77 – – – 1.998 10.53 79.15 43.69 7.332 2.104 23.88 11.03 53.60 16.79 4.574 66.67 14.08 21.03 – Source: FAO AQUASTAT Database, *Mekala et al. (2008). By 2020, it is expected that 65% of the irrigation water used in Israeli agriculture will be sewage effluents (Assouline et al., 2002). Other arid and semi-arid countries, such as Jordan and Tunisia, reclaim the vast majority of municipal wastewater for agricultural irrigation. Wastewater has been recycled in agriculture for centuries as a means of disposal in cities such as Berlin, London, Milan, and Paris (AATSE, 2004). In Pakistan, 26% of national vegetable production is irrigated with wastewater (Ensink et al., 2004). In Hanoi, 80% of vegetable production is derived from urban and peri-urban areas that receive a secured supply of recycled water (Lai, 2000). In Ghana, irrigation involving diluted wastewater from rivers and streams has been reported (Keraita and Drechsel, 2004). In Mexico, about 260,000 ha are irrigated with wastewater (Mexico CAN, 2004). Agriculture, being the largest user of recycled water in Australia, accounts for approximately 66% (280 GL) of all recycled water used (ABS, 2006). In many countries, municipal wastewater is not collected and treated but discharged directly into surface water bodies or used in agriculture without appropriate consent. In most developing countries, 90% of all wastewater is Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 221 discharged untreated into local waterways (Johnston, 2003). In the rest of the world, most of the wastewater is collected and treated to remove solids, pathogens, oils, and other contaminants. Two main sets of regulations exist for wastewater treatment and reuse: the California Health Laws (Title 22, State of California, 2001) and the World Health Organization Guidelines (WHO, 1989). The WHO guidelines are frequently used in developing countries. Permissible water quality criteria stipulated are less restrictive than those described in the California Health Laws, which recommend waste stabilization pond systems as the preferred treatment method as opposed to a conventional energy intensive treatment system (Crook, 1991). Wastewater treatment can be grouped into three main processes: (i) primary treatment, which includes physical processes such as grit removal and settling out of coarse material to the bottom of the tank as primary sludge. In some treatment plants, flocculants such as aluminum sulfate (i.e., alum) are added; (ii) secondary treatment, which aims to remove soluble and colloidal biodegradable organic matter (OM) and suspended solids. Secondary treatment generally consists of an aerobic biological process whereby microorganisms oxidize OM in the wastewater; (iii) tertiary treatment or advanced treatment technologies, these referring to any physical, chemical, or biological treatment process used to accomplish a degree of treatment greater than that achieved by secondary treatment, such as ozonization, rapid gravity filtration, and ultraviolet radiation. The conditions in which wastewater is stored following treatment may further influence its chemical composition (Droste, 1997; Yu et al., 1997). Specific composition of a waste stream is dependent on its origin and the degree of treatment it receives. Heterogeneity in influent waste streams may include domestic, industrial sources (paper and printing manufacturing, timber processing plants, leather, and textile industries) and agricultural sources (dairy, poultry, meat, and vegetable processing operations). Wastewater quality defines certain biological, chemical, and physical characteristics that influence its suitability for a specific use (Ayers and Westcot, 1985; WHO, 2006). Nutrient loading (N, P, K, and S), organic loading, dissolved constituents, such as dissolved salts and solids, types and concentrations of microorganisms, and heavy metal(loid)s, trace organic compounds including pharmaceuticals, and pH are all quality criteria. Wastewater characterization is further complicated by daily and seasonal variation. There is a twofold risk associated with applying wastewaters to agricultural crops with respect to anthropogenic contaminants including metal(loid)s. First, wastewater-borne metal(loid)s can be assimilated by plants and subsequently enter the food chain. Second, application of wastewater can also impact on heavy metal(loid)s that have been applied to soil and crops prior to the wastewater irrigation. There is, however, limited information in the literature on both issues. In Tables 2 and 3, important wastewater types for agricultural irrigation and their main organic and inorganic components are summarized. Table 2 Metal (loid)s Heavy metal(loid) concentrations in various wastewater and waste sludge sources Treated sewage (mgL1) 0.035 0.012 Cd 0.002 0.0003 Pb 0.003 0.002 Ni 0.011 0.002 Cu 0.002 0.001 Zn 0.059 0.021 As – Hg – Reference Antanaitis and Antanaitis (2004) Cr a Storm water Dairy effluent Piggery effluent Pulp and paper secondary sludge 0.04 - – 20 0.04 – – 0.073– 1.78 0.053 – 0.022– 7.033 0.056– 0.929 0.058 3.22 Barrett et al. (1993) Dairy cattle slurry Beef cattle Poultry slurry litter Broiler litter Swine slurry Deep-pit poultry litter Threshold values LTVa (mgL1) – 5.64 4.69 – 9.9 2.82 6 0.1 4.5 – 0.33 0.26 3 4.93 0.3 2 0.01 – 42 – 5.87 7.07 11 - 2.48 13 2 – – 35 – 5.4 6.4 15 2.46 10.4 14 0.2 0.5–10.5 0.26 206 16.5 62.3 33.2 748 6.1 351 19 0.2 – 0.58 513 6480 209 133 718 743 575 252 2 – – Bolan et al. (2003a) – 0.17 – 0.3 Lowe Hart and (1993) Speir (1992), Carnus (1994) 1.44 – Wallingford et al. (1975) 2.6 – Nicholson et al. (1999) 43 – Nicholson et al. (1999) 34.6 – Moore et al. (1998) 1.68 – 0.1 – – – 0.002 Nicholson Nicholson Bomke Jackson et al. and et al. and (1999) Lowe (1999) Miller (1991) (2000) Feedlot manure (mgkg1) LTV (long-term trigger values) in irrigation water (long-term use—up to 100years) (ANZECC and ARMCANZ, 2000). Table 3 Composition of wastewaters or sludges from selected sources Parameter TDS Suspended solids BOD5 COD Total N Total P Fat Na K Ca Mg Free Chlorine Nitrate Phosphate Sulfide Reference Meat Milk processing Raw factory secondary meat wastewater effluent effluent Tannery secondary Dairy effluent effluent Piggery effluent Textile effluent Pulp and Preliminary- Primarypaper Untreated treated treated secondary wastewater wastewater wastewater sludges Biosolids – –– – 20–100 – 1155 – 120 – – – – 1480 471 1152 132 844.8 121 780 105 – – – 65 1700 – 70 35 400 560 13 8 1 – 20–100 80–400 40–200 5–30 0–30 50–250 20–150 3–250 3–10 – 646 1544 – – 110 – – – – – 30 410 130 1.6 – 2700 – 340 36 – – – 190 30 – 50 220 110 30 – – – 1300 600 8.3 – 500 – – – 645 2430 – – – – – 1.24 1.04 1.14 – – 1415 6.4 – 205 60 55 48 – – – 1260 5.10 – 193 52 51 – – – – 1124 5.14 – 154 42 47 – – – – 32,000 8075 – 4586 2905 17,000 2000 – – – 8.8 2.8 – – 1.8 4.9 1.7 – – – – Hart and Speir (1992), Carnus (1994) – – – Hart and Speir (1992), Carnus (1994) – – – Hart and Speir (1992), Carnus (1994) – – – Hart and Speir (1992), Carnus (1994) – – – Hart and Speir (1992), Carnus (1994) – – – Hart and Speir (1992), Carnus (1994) 7.97 2.63 0.58 Yusuff and Sonibare (2004) – – – Yusuff and Sonibare (2004) – – – Yusuff and Sonibare (2004) – – – Yusuff and Sonibare (2004) – – – Hart and Speir (1992), Carnus (1994) 420 – – Nash et al. (2011) Units are mgL1 except for pulp and paper sludges and biosolids (mgkg1). 224 Anitha Kunhikrishnan et al. 2.1.1. Municipal wastewater In both developed and developing countries, land application of municipal wastewater (both treated and untreated) is a common practice. Municipal wastewater is composed of domestic and industrial wastewater (Hussain et al., 2002; Pettygrove and Asano, 1984). Domestic wastewater consists of discharges from households, institutions, and commercial buildings. Where country or state legislation permits, this wastewater is applied to land. However, this depends on the crop it is applied to and the level of treatment. Secondary-treated wastewater typically contains low levels of contaminants as these tend to settle under gravitation with solid fractions in the treatment lagoons. Settling of suspended solids also lowers both the chemical and biochemical oxygen demand. Municipal wastewater also contains high concentrations of nutrients, especially nitrogen (N) and phosphorus (P), trace elements, such as iron (Fe) and Mn and dissolved salts, particularly sodium (Na), chloride (Cl), and in some cases bicarbonates. These parameters are critical when wastewater is reused in agriculture. 2.1.2. Farm wastewater Farm effluents such as those emanating from dairy sheds and piggeries are being increasingly employed as sources of irrigation water and nutrients (Bolan et al., 2009; McDonald, 2007). For example, in New Zealand, dairy and piggery effluents generate annually about 9000Mg of N, 1250Mg of P and 14,000Mg of K (Bolan et al., 2004a). Effluents from farms differ in their composition depending on the animal production system from which they are derived (chicken, pigs, beef, dairy). Generally, farm wastewater is rich in organic and inorganic components (Tables 2 and 3) (Wang et al., 2004). Copper and Zn are commonly used as feed additives, growth promoters, for disease prevention or treatment, and their concentration in the final wastewater can be significant (Bolan et al., 2004b; Sims and Wolf, 1994). In many countries including Australia and New Zealand, farm effluents have traditionally been treated biologically using two-pond systems and then discharged to land or stream. Bolan et al. (2009) have suggested that land application of farm effluent facilitates the recycling of valuable nutrients, carbon (C), and water, and if managed well, helps to mitigate surface water pollution. In many instances, this may be the cheapest and most socially/ culturally accepted form of final treatment. Application of farm effluents can increase pasture yield due to the net loading of nutrients and water (Bolan et al., 2004c; Wang et al., 2004). This, however, is influenced by the rate, method and time (season) of application, soil fertility, and climatic conditions (Ball and Field, 1982). According to Bolan et al. (2009) returning dairy and piggery effluents directly to land has become the most common method of treatment in most parts of the world. However, in many regions, the amount of farm effluents generated on a per farm basis exceeds the quantity that can be safely accommodated by the Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 225 available agricultural land and repeated annual applications of large amounts of effluent can cause soil nutritional side effects and environmental damage (Balota et al., 2010). For example, Giacomini et al. (2009) observed that half of the piggery effluent N is lost from soil–plant systems through leaching and volatilization, resulting in environmental pollution. Balota et al. (2010) and McDonald (2006) indicated that safe farm effluent application in agriculture is necessary to minimize the environmental damage. 2.1.3. Effluents from the agricultural industry Recycling of water from agricultural industry is another common source of wastewater. For example, in Australia, agricultural drainage effluent is collected and reused as a source of irrigation water (Dillon, 2000). Similarly, wastewater from farm animal treatment plants (abattoirs) is increasingly used as a source of irrigation water (Luo et al., 2004). Wastewater from intensive agricultural industries (fish processing plants) and rural industry (abattoirs) is characterized by high chemical and biological oxygen demand and nutrients relative to many other wastewaters (McLaren and Smith, 1996) (Tables 2 and 3). Mittal (2004) recently reviewed effluent wastewater from abattoirs and concluded that water quality depended on animal and processing type and water usage, that is, dilution. One concern associated with land application of abattoir waste is the high level of pathogens that have the potential to contaminate receiving water bodies either directly as point discharge or indirectly in runoff. These effluents also contain elevated levels of grease, blood, and organic chemicals added during processing and cleaning operations (Kretzschmar, 1990). In many countries including Australia and New Zealand, abattoir effluent is usually disposed of to land due to high costs associated with independent treatment systems and environmental concerns over surface water discharge (Quinn and Fabiansson, 2001). Afonso and Bórquez (2003) reported that the wastewaters generated during fish meal production contain a high organic load, but unlike other industrial effluents they do not contain any known toxic or carcinogenic materials. In some regions, winery wastewater is also a viable water source that is increasingly being recycled by grape growers and pastoralists for irrigation (Stevens, 2009). Reuse is driven primarily through the obligations of the winery to dispose of their wastewater, preferably in a sustainable and costeffective manner. Generally, winery wastewater is treated on-site through systems of only small flow volume capacity and the chemical composition of this wastewater source varies considerably between wineries and may require a management approach that is site specific when irrigated to land (Kumar and Christens, 2009). In general, winery wastewater contains high salt concentrations thereby accounting for a considerably greater salt loading relative to irrigating with river, ground, or town supply water. Specific ions, in particular Na and potassium (K), originating from cleaning products, grape lees, and waste juice may also have confounding effect on soils beyond 226 Anitha Kunhikrishnan et al. that imposed by salinity alone. A high concentration of either Na or K in irrigated waters is undesirable and when continually applied to soils can displace more desirable cations [i.e., calcium (Ca) and magnesium (Mg)] from the soil exchange complex (Pils et al., 2007). This in turn raises the potential for adverse changes to soil structure (Jayawardane et al., 2011). The management of salts is imperative so water conservation benefits are not compromised by a decline in soil and plant health and off-site pollution (McCarthy, 1981; Neilsen et al., 1989). 2.1.4. Effluents from pulp and paper mills Pulp and paper mill effluent either from thermomechanical pulp mill or chemi-thermomechanical pulp mill is often irrigated to land after primary treatment (Smith et al., 2003; Wang et al., 1999). Pulp mill effluent has high chemical and biochemical oxygen demand and some wood derived organic compounds, metal(loid)s, fatty and resin acids, and relatively high C:N ratios (Tables 2 and 3). Kookana and Rogers (1995) reviewed the effect of pulp mill effluents on soil properties. An extensive investigation into the different organic chemicals in pulp mill effluents and their behavior in soil can be found in this excellent review paper. Effluent from pulp mills is a rich source of OM, N, P, Ca, Mg, and trace elements (Kannan and Oblisami, 1990), and consequently the application of pulp mill effluents on land is becoming a common method for recycling nutrients (Rubilar et al., 2008). The presence of chlorinated organic compounds, most notably chlorine substituted phenolic compounds, chlorinated lignins, dioxins, chlorobenzenes, and non-chlorinated organic compounds (Deriziotis, 2004; Gergov et al., 1988), has raised concerns about land application (Kannan and Oblisami, 1990; Lavric et al., 2004). 2.1.5. Stormwater Urban stormwater harvesting has emerged in recent years as a viable option to reduce pressures on existing water sources and to alleviate adverse environmental impacts associated with stormwater runoff (Roy et al., 2008a). This is a relatively abundant, local source of water, available throughout most urban areas. In Australia, for instance, approximately 10,300 million liters of stormwater are generated annually (Laurenson et al., 2010). In many cases, urban stormwater runoff contains a broad range of pollutants that are transported to natural water systems (Aryal et al., 2010). Stormwater pollutants originate from many sources and activities and can occur as either particulate or dissolved forms. Many toxic chemicals, such as pesticides and herbicides are found in stormwater, along with oil, grease, and heavy metal(loid)s such as Cd, Cr, Cu, Ni, Pb, and Zn (Wong et al., 2000). Nutrients such as N and P are also important pollutants in stormwater. The harvesting of stormwater from industrial zones prior to its entry into natural waterways is likely to reduce the subsequent impact of point source Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 227 discharge on surface waters by reducing pollutant loads (Davis et al., 2009; Henderson et al., 2007). If suitably designed, a stormwater harvesting system will also provide urban stream health benefits by mitigating frequent flows to streams and serve as a public amenity (Bratieres et al., 2008; Hatt et al., 2009). Stormwater harvesting and storage can be achieved in a number of ways including biofiltration, porous pavement, rain garden, and groundwater recharge (Davis et al., 2009; Department of Planning and Local Government, 2009; Henderson et al., 2007; Kim et al., 2003; Laurenson et al., 2011). 2.2. Heavy metal(loid) sources Heavy metal(loid)s reach the soil environment through both pedogenic (geogenic) and anthropogenic processes. Most heavy metal(loid)s occur naturally in soil parent materials, chiefly in forms that are not readily available for plant uptake (Adriano, 2001; Alloway, 2004; Bolan et al., 2008). Due to their low solubility, the heavy metal(loid)s present in the parent materials are often not bioavailable and have a minimum impact on soil organisms. Apart from Se (Dhillon and Dhillon, 1990; Doblin et al., 2006) and As (Chakraborty and Saha, 1987; Mahimairaja et al., 2005; Mukherjee et al., 2008; Naidu and Skinner, 1999; Naidu et al., 2008), other heavy metal(loid)s (e.g., Cr, nickel (Ni), Pb) derived via geogenic processes have limited impact on the soil ecosystem. Unlike pedogenic inputs, heavy metal(loid)s added through anthropogenic activities typically have high bioavailability (Adriano et al., 2004; Lamb et al., 2009; Naidu et al., 1996). Anthropogenic activities primarily associated with industrial processes, manufacturing, and the disposal of domestic and industrial waste materials including wastewater are the major source of metal(loid) enrichment in soils (Adriano, 2001). Fertilizer, manure, effluents, and organic amendments addition to agricultural soils are considered to be the major sources of most minor elements including heavy metal (loid)s that are essential for plant growth (Bolan et al., 2004b; Loganathan et al., 2008; Park et al., 2011). 2.2.1. Fertilizer products Of the heavy metal(loid)s present in fertilizers, the presence of elevated concentrations of Cd is of greatest concern as it is highly toxic to humans and can accumulate in soils, plants and animals (Alloway 1990; USPHS 2000). Phosphate fertilizers are considered to be the major source of heavy metal (loid) input, especially Cd, in agricultural and pasture soils in Australia and New Zealand due to the extensive use of high Cd-containing phosphate fertilizers (Loganathan et al., 2003; McLaughlin et al., 1996; Naidu et al., 1997). Increased concentrations of Cd in fertilizers that are applied to land have been reported to result in increased Cd concentrations in grain crops (Bolan et al., 2011b; Grant et al., 2010; He and Singh 1994; McLaughlin et al., 1996). Results of studies in several countries have shown that some heavy 228 Anitha Kunhikrishnan et al. metal(loid)s in P fertilizers may be available to plants (Huang et al., 2003, 2005; Mortvedt, 1996). There have been increasing efforts to reduce the accumulation of Cd in soils by using low Cd-containing P fertilizers. This is achieved by either selective use of phosphate rocks (PRs) with low Cd or treating the PRs during processing to remove Cd. Superphosphate fertilizer manufacturers in many countries are introducing voluntary controls on the Cd content of P fertilizers. A number of PRs with low Cd contents are available which can be used for the manufacture of P fertilizers, but sources with higher Cd contents continue to be used in many countries for practical and economic reasons (Bolan and Duraisamy, 2003; Loganathan et al., 1995, 2003). 2.2.2. Biosolids Organic amendments such as biosolids (e.g., Cd) and poultry manure (e.g., As) have been regarded as a major source of heavy metal(loid) accumulation in soils, and a large volume of work has been carried out to examine the mobilization and bioavailability of heavy metal(loid)s derived from these sources (Bolan et al., 2004b; Haynes et al., 2009; McBride, 1995). The most commonly detectable heavy metal(loid)s in biosolids, Pb, Ni, Cd, Cr, Cu, and Zn originate primarily from the contamination of these wastes with industrial wastewater (Haynes et al., 2009). Heavy metal(loid) concentrations are governed by the nature and the intensity of the industrial activity, as well as the type of process employed during the biosolid treatment (Mattigod and Page, 1983; Oviasogie and Ndiokwere, 2008; Wang et al., 2003a). Gove et al. (2001) reported that biosolid application (250kgN ha1 1 yr ) to a sandy or sandy loam soil resulted in loadings of approximately 6, 2, 5, and 0.2mgkg1 Zn, Cu, Pb, and Ni, respectively. Illera et al. (2000) demonstrated that biosolid application to soil had little effect on the total concentration of Ni and Cr but resulted in Cd, Cu, Pb, and Zn increasing considerably as a consequence of the high content of these metal(loid)s in biosolids. It is known that these heavy metal(loid)s are typically immobilized in soils, but they can be toxic to soil micro flora and can accumulate in plants and grazing animals (Haynes et al., 2009). Kao et al. (2006) reported that the addition of biosolid accumulated Cu, Pb, and Zn but reduced microbial biomass, indicating that microbial activities were disrupted by the heavy metal(loid)s. 2.2.3. Manure Manures from intensive animal industries are a major source of organic amendments for agricultural land. In Australia, beef and dairy cattle alone produce approximately 4 million Mg of manure every year (Bünemann et al., 2006). Similarly, in USA, of about 0.9 billion Mg organic and inorganic agricultural recyclable by-products generated, approximately 45.4 million Mg are dairy and beef cattle manure, and 27 million Mg are poultry and swine Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 229 manure (Camberato et al., 1997; Walker et al., 1997). As heavy metal(loid)s are increasingly employed as a feed additive in intensive animal production systems, manure application is likely to be an important source of certain metal (loid) input to soils (Bolan et al., 2004b; Moscuzza and Fernández-Cirelli, 2009). Heavy metal(loid)s in manure by-products are also derived from ingestion of contaminated soil by the animal, and during manure collection and handling. Heavy metal(loid)s vary considerably between manure types, animal categories, and farms (Menzi et al., 1993). Heavy metal(loid) content in manures derived from intensive animal production systems is related to feed mineral content and the animal conversion efficiency (Nicholson et al., 1999). Increases in metal(loid) concentration in animal feed have often resulted in corresponding increases in their concentration in manure by-products (Mohanna et al., 1999; Moscuzza and Fernández-Cirelli, 2009; Nahm, 2002). A number of heavy metal(loid)s are added to livestock and poultry feedstuff not only as essential nutrients but also as supplement to improve health and feed efficiency. Diets of poultry and livestock include heavy metal(loid)s (As, Co, Cu, Fe, Mn, Se, Zn) to prevent diseases, improve weight gains, and increase egg production (Mondal et al., 2007; Tufft and Nockels, 1991). Not all of the heavy metal(loid)s consumed by animals are absorbed by their digestive tracts; consequently, the manure is often metal(loid) enriched (Sistani and Novak, 2006). For example, swine can excrete approximately 80–95% of the total daily Cu and Zn intake (Brumm, 1998; Moral et al., 2008). Adding As to feed as an additive to control coccidiosis in poultry has resulted in an increase in As level in poultry litter (Church et al., 2010; Garbarino et al., 2003; Morrison, 1969; Sims and Wolf, 1994). Regular application of manures and slurries has often been shown to result in the accumulation of heavy metal(loid)s. Brink et al. (2003) reported that application of swine effluent (annual mean of 10hacm) to Bermuda grass pasture added annual averages of 0.6, 2.2, 0.3, and 0.86kgha1 Cu, Fe, Mn, and Zn, respectively. Evers (2002) also reported application of 9Mg ha1 broiler litter added averages of 5.85, 5.0, 9.4, and 6.55kgha1 Zn, Fe and Cu, respectively. In another study, Jinadasa et al. (1997) reported that high Cd levels in soils and vegetables throughout Sydney, Australia, were due to repeated applications of poultry manures. In New Zealand, land application of dairy pond effluent, based on a N loading of 150kgN ha1, is likely to add a maximum of 31.5 and 73.7kg Cu ha1 through effluent and manure sludge application, respectively (Bolan et al., 2003a). 2.2.4. Wastewater Wastewaters act both as a source and sink for heavy metal(loid)s in soils. Depending on the source and level of treatment, wastewater may contain a range of heavy metal(loid)s (Table 2) and continuous application is likely to result in these heavy metal(loid)s accumulating in soils. Heavy metal(loid)s are usually removed during common treatment processes and most of them 230 Anitha Kunhikrishnan et al. end up in the biosolid fraction of the treatment process with very low metal (loid) concentrations present in the treated effluents (Kulbat et al., 2003; Sheikh et al., 1987; Ziolko et al., 2011). Generally therefore in highly treated wastewater, the concentration of heavy metal(loid)s is low and considered safe when used for irrigation and other recreational purposes. Consequently, heavy metal(loid)s are of little concern for irrigation of crops when using treated effluents as a source of wastewater. Irrigation with untreated or partially treated wastewaters has the potential to cause heavy metal(loid)s to accumulate in the soils and become bioavailable for crops (Cui et al., 2004; Qadir et al., 2000). If the wastewater is derived from an industrial source or is less treated, then the effect of heavy metal(loid)s would need to be inspected (Toze, 2006). Wastewater also contains a range of components including dissolved and particulate OM, soluble organic and inorganic anions which can interact with heavy metal(loid)s, thereby altering their mobility and subsequent bioavailability. Wastewater often contains high levels of nutrients, which can be beneficial to crop production (Liu et al., 2005) (Table 3). Bolan et al. (2004c) have indicated that the application of dairy farm effluent irrigation may provide an attractive means of increasing pasture growth through increased nutrient loading and a cost-effective amelioration technique, provided that the associated environmental risks of contamination of soils and groundwater by heavy metal(loid)s are minimized. Direct irrigation of untreated sewage effluents is a common practice especially in Asian countries and many studies have reported the risks associated with this system. Heavy metal(loid)s are easily accumulated in the edible parts of leafy vegetables, as compared to grain or fruit crops (Mapanda et al., 2005). Arora et al. (2008) assessed the levels of different heavy metal(loid)s like Fe, Mn, Cu, and Zn, in vegetables irrigated with water from different sources. The results indicated a substantial build-up of heavy metal(loid)s in vegetables and the range was 116–378, 12–69, 5.2– 16.8, and 22–46mgkg1 for Fe, Mn, Cu, and Zn, respectively. They reported that the highest mean levels of Fe and Mn were detected in mint and spinach, whereas the levels of Cu and Zn were highest in carrot. In another study, Latif et al. (2008) examined the heavy metal(loid) contamination of different water sources, soils, and vegetables and reported that the concentrations of heavy metal(loid)s in sewage and industrial effluentsirrigated vegetables were above critical levels. Similarly, Singh et al. (2010a) quantified the concentrations of heavy metal(loid)s (Cd, Cr, Cu, Ni, Pb, and Zn) in soil, vegetables, and the wastewater used for irrigation. Their study demonstrated that the wastewater used for irrigation had high concentrations of Zn followed by Pb, Cr, Ni, Cu, and Cd and its continuous application for more than 20years has led to accumulation of heavy metal (loid)s in the soil. They observed that concentrations of Cd, Pb, and Ni have crossed the safe limits for human consumption in all the vegetables. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 231 They also noticed that the percentage contribution of fruit and vegetables to daily human intake for Cu, Ni, Pb, and Cr was higher than that of leafy vegetables, while the reverse was true for Cd and Zn. 3. Effects of Wastewater Irrigation on Soil Properties Affecting Heavy Metal(Loid) Interactions Wastewater irrigation affects metal(loid) dynamics by directly influencing their reactions in soils and indirectly by altering soil properties controlling their fate. Research shows that wastewater irrigation can result in significant changes to soil physical, chemical, and biological properties (Müller et al., 2007). In the following section, an overview on the impacts of wastewater irrigation on soil properties relevant to the fate of metal(loid)s in the soil environment is provided. The effect of wastewater irrigation on metal(loid) reactions in soils will be discussed in Section 4. 3.1. Soil chemistry Soil chemistry plays an important role in the successful utilization of wastewater as a source of irrigation. On the one hand, the fertilization effect of wastewater and the resultant independence from costly fertilizers has enhanced the development of wastewater irrigation systems in many countries. On the other hand, induced salinity and sodicity often limit its viability. Consequently, the impact of wastewater irrigation on soil chemical properties is comparatively well investigated for a variety of soil types, climatic conditions, and crops (Tables 4 and 5). A selection of soil chemical properties affected by wastewater irrigation and relevant for the transformation, transport, and complexation of metal(loid)s, is described, viz. the soil pH, soil organic matter (SOM), cation exchange capacity (CEC), salinity, and sodicity. 3.1.1. Soil pH In the majority of studies, the soil pH significantly increased after long-term irrigation with wastewater from different sources (Friedel et al., 2000; Hassanli et al., 2008; Magesan et al., 1999; Qishlaqi et al., 2008; Roy et al., 2008b; Schipper et al., 1996; Walker and Lin, 2008). In some studies, however, soil pH was unaffected by long-term wastewater irrigation (Friedel et al., 2000; Gwenzi and Munondo, 2008; Magesan et al., 1999), while others reported decreased soil pH (Rattan et al., 2005; Rosabal et al., 2007; Xu et al., 2010). For example, vinasse irrigation (pH 5.02) for 40years significantly decreased the soil pH from 7.1 to 6.7 and from 6.2 to 5.9 in sampling depths of 0.1 and 1m, respectively (Rosabal et al., 2007). Angin et al. (2005) explained the Table 4 Selected references on the effect of wastewater on soil properties Site Location Soil type Land-use Wastewater (WW) Experiment Soil properties Type (years) (mm d1) Depth (m) Bulk density (gcm3) TSS SAR pH (gm3) Approach Total porosity (%) Ksat (mm h1) Suggested mechanism Different land management of control and treated area References Vogeler (2009) Taupo, New Zealand Silt loam Pasture WW 12 4.72 28 n.d. 7.2 0–0.05 Disc infiltrometer 0.75* (0.84) 71 (68) 16 (8) Levin, New Zealand Sand Pasture 185 n.d. 6.2 0–0.05 Disc infiltrometer 1.1* (1.2) 58 (54) 34* (13)* Levin, New Zealand Sand Pinus radiata 185 n.d. 6.2 0–0.1 Repacked column 1.1 (1.2) n.d. 35 (39) n.a. Magesan et al. (1999) Rotorua, New Zealand Sand Pinus radiata 6 n.d. 7.2 0–0.1 Repacked column 0.6 (0.6) n.d. 21 (23) n.a. Magesan et al. (1999) Amman, Jordan Clay Barley 111 5.4 7.6 0.1–0.2 Repacked column 1.3 1.3 1.3 1.3 n.d. 8* 7* 6* 3* Retention of DOC, clay dispersion, and change in pore size distribution Gharaibeh et al. (2007) Mizra, Israel Clay Orchard 170 5.1 7.6 0–0.2 Intact core 1.1 (0.9) n.d. 0.02 (0.06) Physical blocking of Bhardwaj et al. (2007) pores, clay swelling Rotorua, New Zealand Sandy loam Pinus radiata WW 22 9 Secondarytreated WW 7 8 Tertiarytreated WW 5 8 WW 0yr 2yr 5yr 15yr n.s. WW (drip irrigation) 23 15 WW 2.8 n.s. 25 1.5 7.5 2.3 Monolith n.d. (0.74–1) n.d. 6* (30)a Biological clogging of soil pores Vogeler (2009) Cook et al. (1994) Levin, New Zealand Sand Pinus radiata Primarytreated WW 4 8 185 n.d. 6.2 0–0.1 Intact cores 0.8* (1.2) 70* (54) 185 (159) Rotorua, New Zealand Sandy loam Pinus radiata Tertiarytreated WW 4 8 6 n.d. 7.2 0–0.1 Intact cores 0.7 (0.6) 72 (72) 114 (39) Farm WW 10 n.s. WW 15 n.s. WW 44 7 712 2.0 7.3 0–0.1b Intact cores 1.2 (1.3) 38 (35) 135 (91) 712 2.0 7.3 0–0.1b Intact cores 1.1 (1.3) 55 (35) 163 (91) 5 n.d. 7 0–0.2b Landscape approach 1.5* n.d. 38* (116) n.d. n.d. 7.8 0–0.15 0.15– 0.3 Double ring infiltrometer 1.3* (1.2) 1.3* (1.2) 49* (54) 49* (53) 35 (38) 35 (37) Sandy Madurai Corporation, loam India Sandy Madurai loam Corporation, India Diverse: Pennsylvania silt State loam– University, silty USA clay loam Isfahan, Iran Aridisol, silty clay a b Farm Farm Sugar beet, Secondarycorn, treated sunflower WW Increased macroporosity due to stimulation of microbial communities Increased macroporosity due to stimulation of microbial communities Input of OM improved structure Input of OM improved structure Excessive water, impact of water drops and machinery, soil transport across landscape Biological and physical clogging Ponded infiltration rate. Measured in increments for more than 1m depth in original paper. Values within brackets are from the control site (before irrigation of wastewater). Magesan (2001) Magesan (2001) Mathan (1994) Mathan (1994) Walker and Lin (2008) Abedi-Koupai et al. (2006) Table 5 Selected references on the effect of wastewater on soil properties (pH, SOC, and C-input) Location Soil type Shiraz, Iran – Marvdasht, Iran Silty clay Silty loam Silty loam Mezquital Valley, Mexico Silt loam, Mollic Leptosol Mezquital Valley, Mexico Clay loam, Eutric Vertisol Amman, Jordan Clay silt, Vertisol Wastewater Type (years) Untreated domestic WW, (20yr estimated) Treated municipal effluent, 25months (39 ML ha1 yr1) WW (11 ML ha1 yr1) 0 25 65 80 WW (11 ML ha1 yr1) 0 25 65 80 Municipal WW 0yr 2yr 5yr 15yr Land-use Depth (m) pH SOC (%) C-input (tha1 yr1) Wheat 0–0.2 8.4 (7.3) 15.9 (0.4) n.d. Qishlaqi et al. (2008) Trees 0–0.3 0.3–0.6 0.6–0.9 Hassanli et al. (2008) 0–0.15 0.0003 (<dL) 0.0006 (<dL) 0.0006 (<dL) 1.8 2.2 1.9 2.3 n.d. Maize 8.8 (8.0) 8.8 (8.2) 8.8 (8.1) 7.5 7.9 7.6 7.7. 1.5 Friedel et al. (2000) Maize 0–0.15 7.4 7.9 8.1 7.6. 1.1 1.7 2.2 2.7 1.5 Friedel et al. (2000) Barley 0–0.2 0.2–0.4 0–0.2 0.2–0.4 0–0.2 0.2–0.4 0–0.2 0.2–0.4 8 8.1 7.7 7.9 8.1 8.2 7.9 8.2 SOM 0.7 0.5 1.1 0.7 1.0 0.7 1.3 0.7 References Gharaibeh et al. (2007) 7.4 (7.1) 4.5 (4.5) 2.2 Magesan et al. (1999) 2.3 Magesan et al. (1999) n.d. Rosabal et al. (2007) 5.8 (5.6) 2.7 (2.4) 0.9 (0.4) 2.9 (2.0) 2.7 (1.6) 2.3 (0.9) 1.2 (0.5) 0.4 (0.2) 0.2 (0.3) þ164% þ109% þ118% 2.2 (0.6) 2.3 Filip et al. (2000) 0–0.15 7.5 (7.9) 0.65 (0.39) n.d. Rattan et al. (2005) 0–0.25 7.5 (7.2) 1.3 (0.6) OM n.d. Lado et al. (2005) 0–0.25 7.8 (7.5) 3.9 (3.4) OM n.d. Lado et al. (2005) Sand; Typic Udivitrand WW; 5yr (29 ML ha1 yr1) Forest plantation 0–0.1 0.1–0.2 Sand, Psamment WW, 7yr (31 ML ha1 yr1) Forest plantation 0–0.1 0.1–0.2 LaHabana, Cuba Ultisol Vinasse, 40yr; n.d. Sugarcane 0–0.1 0.1–0.2 0.2–0.3 0.3–0.4 0.4–0.5 0.5–0.6 6.7 (7.1) 7.0 (7.5) 6.9 (7.4) 6.8 (7.4) 6.9 (7.5) 5.9 (6.2) Erzurum, turkey n.s. Raw WW; long-term Cabbage, potato Decrease Berlin, Germany Haplic Luvisol Pasture Delhi, India RamatHacovech, Israel Mizra, Israel Loamy sand; sandy loam Sand Primary treated WW; 100yr (20 ML ha1 yr1) Sewage effluents 5, 10, 20yr Effluents, 10yr 0–0.3 0.3–0.6 0.6–0.9 Topsoil Rice, grain, vegetables Citrus Clay Effluents, 12yr Citrus Harare, Zimbabwe Loamy sand Gleyic Lixisol Rotorua, New Zealand Levin, New Zealand Pasture 6.9 (5.9) 6.7 (6.0) n.d. n.d. Angin et al. (2005) n.d. (Continued) Table 5 (Continued) Location Soil type Isfahan, Iran Silty clay Ebro Valley, Spain Xeric Petrocalcid Typic Xerofluvent Wastewater Type (years) Land-use Treated WW 26yr (15–37 ML ha1 yr1) Municipal WW (150, 300, 600t ha1 yr1) Vegetable canning WW; 4yr Annual rotation Values within brackets are from the control site (before irrigation of wastewater). Depth (m) pH SOC (%) 0–0.3 0.3–0.6 0.6–0.9 0–0.3 150t ha1 300t ha1 600t ha1 0.3–0.6 150t ha1 300t ha1 600t ha1 0–0.3 5.0 (3.9) 5.0 (3.9) 5.4 (3.8) (7.6) 7.4 7.3 7.2 (6.9) 6.6 6.5 6.3 n.d. n.d. 17.2 (7.1) 4.3 (3.8) 3.3 (2.9) (0.6) 0.9 0.9 1.1 (0.6) 0.7 0.8 0.8 1.2 (1.2) 0.8 (1.0) C-input (tha1 yr1) References 58 116 173 Gwenzi and Munondo (2008) Khoshgoftarmanesh and Kalbasi (2002) 0.06 0.26 Virto et al. (2006) Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 237 lower soil pH of a long-term wastewater-irrigated soil by the increased mineralization of OM, while Xu et al. (2010) ascribed the effect to the applied wastewater’s acidity. In general, the effect of wastewater irrigation on soil pH depends on the pH of the wastewater source and the pH buffering capacity of soil. pH is an important factor that controls the accumulation, mobility, and bioavailability of heavy metal(loid)s in wastewater-irrigated soils. The pH is often reported to show good correlation with soil adsorption of heavy metal (loid)s (Naidu et al., 1997; Tyler and McBride, 1982). Qishlaqi et al. (2008) examined the negative impacts of untreated wastewater irrigation on soils and crops and reported that pH increased by 2–3 units and heavy metal (loid)s (notably Pb and Ni) accumulated in topsoil above maximum permissible limits. Although they found a positive relationship (P<0.01) between pH and total contents of Pb and Ni in soils, they reported only 1.3–7.7% of Ni and 0.07–1.69% of Pb was phytoavailable. Roy et al. (2008b) reported that even though a higher pH in soils irrigated with paper mill wastewater was observed, the data did not show a significant positive correlation with the metal(loid) ions. 3.1.2. Soil organic matter Depending on the level of treatment, wastewater comprises about 0.1% suspended and dissolved organic and inorganic compounds (Feigin et al., 1991; Lado et al., 2005). Generally, therefore wastewater irrigation adds more OM to a soil than freshwater irrigation or rain. Hence, various studies conducted in long-term farm dairy/sewage effluent irrigated areas reported significantly increased SOM contents in the topsoil (Barkle et al., 2000; Bhandral et al., 2007; Filip et al., 2000; Friedel et al., 2000; Gwenzi and Munondo, 2008; Marecos do Monte, 1998; Qishlaqi et al., 2008; Rattan et al., 2005; Siebe and Fischer, 1996; Walker and Lin, 2008; Xu et al., 2010) and in the sub-soil (Walker and Lin, 2008). Such SOM-increases have also been attributed to indirect positive effect on biomass production through the nutritional benefit of wastewater irrigation leading to more residues in the soil (Ramı́rez-Fuentes et al., 2002). However, our attempts to correlate the C inputs associated with wastewater irrigation with the observed net C-increases failed because of: (i) the frequent lack of information on the C-input through wastewater application; and (ii) the difference in soil types, irrigation periods, effluent characteristics, and climate of the studies considered (Tables 4 and 5). In a short-term laboratory experiment of 40days, Travis et al. (2010) observed no change on SOM contents in three soil types irrigated with graywater. Falkiner and Smith (1997) even observed that total C in the top 0.1m of a sandy loam under forest plantation after 4years of irrigation with secondary-treated municipal wastewater was significantly reduced. This SOM loss was explained by accelerated decomposition rates caused by the 238 Anitha Kunhikrishnan et al. frequent wetting and drying cycles at the site. In three Luvisols and three Vertisols, long-term municipal wastewater irrigation led to SOM losses in 1m depth ranging between 0.6 and 4.9Mgha1 compared with freshwaterirrigated soils, while the impacts in the topsoils were inconsistent (Jueschke et al., 2008). Jueschke et al. (2008) postulated that the observed losses resulted from increased microbial activity stimulated through the application of easily degradable and complex organic substances with wastewater. In another study, the SOM content in 0–0.75m depth of a dairy factory effluent-irrigated allophanic soil was the same as in the non-irrigated control site after 22years, but a redistribution of SOM from the top 0.1m down to 0.50m depth was observed. This was partly attributed to leaching and the modified earthworm fauna, dominated by the earthworm Aporrectodea longa, a species that forms permanent burrows to lower depths (Degens et al., 2000). In a more detailed study, Herre et al. (2004) evaluated the impact of long-term wastewater irrigation (90years) on the quality of SOM in two soil types, Leptosols and Vertisols in the Mezquital valley in Mexico. They found that the quality of SOM (i.e., differences in carbon mineralization) had changed and carbon mineralization in the irrigated soils significantly increased. Consequently, the DOM concentrations in the irrigated soils also increased. This effect was more pronounced in the Leptosols than the Vertisols, suggesting the importance of clay (Leptosols: 26–35%, Vertisols: 39–56%) in stabilizing SOM (Friedel et al., 2000; Herre et al., 2004). Increased DOM concentrations in the soil solution of wastewater-irrigated sites have often been observed and explained by the direct input of wastewaterborne DOM and the indirect solubilization of SOM resulting from increased pH (Amiel et al., 1990; Fine et al., 2002; Menneer et al., 2001). Bhandral et al. (2007) noticed an increase in DOM concentration soon after effluent irrigation to a pasture soil, which varied with the type of effluent (Fig. 2). In another study, the DOM concentrations in wastewater-irrigated soils not only increased significantly but the aromaticity of the DOM in soil solutions decreased at the same time (Jueschke et al., 2008). Increased DOM concentrations in soil solutions may affect soil physical properties, such as soil aggregate stability and water binding potential (Frenkel et al., 1992). It also provides organic substrate for soil microorganisms and mobile sorbents to the system. OM content is also one of the most important factors that control the accumulation, mobility, and bioavailability of heavy metal(loid)s in wastewater-irrigated soils. Increase in SOM content can lead to increased soil adsorption capacity by which accumulation of heavy metal(loid)s will be enhanced. Qishlaqi and Moore (2007) carried out statistical analysis of the sources and accumulation of heavy metal(loid)s in agricultural soils and noticed that SOM was the most important factor controlling the distribution of heavy metal(loid)s. It was revealed that soil samples with high SOM content accumulated significantly higher concentrations of heavy metal 239 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil Concentration (mg kg–1 soil) 175 TFDE TPFE Water 150 UFDE TME Control 125 100 75 50 0 10 20 30 40 Days after treatment application 50 60 Figure 2 Soil DOM concentration at 10cm depth following the winter application of water and a range of effluents types to sheep grazed pasture (TFDE, treated farm dairy effluent; UFDE, untreated farm dairy effluent; TPFE, treated piggery dairy effluent; TME, treated meat effluent; Bhandral et al., 2007). (loid)s compared with other samples. Similarly, increase in DOM in soils as a result of wastewater irrigation controls the mobility and bioavailability of metal(loid)s (Bolan et al., 2011b; Jackson et al., 2006; Khan et al., 2006). 3.1.3. Cation exchange capacity A long-term increase in SOM content resulting from wastewater irrigation, which is sometimes accompanied by an increased soil pH, can result in an increase of the CEC (Angin et al., 2005; Falkiner and Smith, 1997). This has been observed, for example, in a 5-year study conducted in Portugal comparing the impact of potable water, primary effluent, and secondary effluent on various chemical parameters including CEC (Marecos do Monte, 1998). Qishlaqi et al. (2008) reported that the CEC of a sandy topsoil that has been irrigated with raw wastewater for about 20years increased by about 880%. Others, however, did not observe a significant increase in CEC in spite of significantly increased SOM contents through wastewater irrigation (Gharaibeh et al., 2007). Madyiwa et al. (2002) studied the effects of combined sewage sludge and effluent application on soil properties of a sandy soil under pasture. The relatively high metal(loid) (Cu, Ni, Pb, and Zn) concentrations within the top 10cm compared to the lower horizons in the irrigated area confirmed the immobility of most heavy metal(loid)s. They argued that considering the lower clay content in top 20cm, the high CEC resulting from high OM content of these layers attributed to metal(loid) immobilization. They confirmed that the four 240 Anitha Kunhikrishnan et al. metal(loid)s in their study were strongly correlated to CEC (R2 ¼0.94–0.99) and OM (R2 ¼0.88–0.99) in the sewage effluent irrigated soil. 3.1.4. Salinity Salinity is the most restricting factor for using wastewater as an irrigation source, especially in Australia’s arid climate conditions. It refers to the total concentration of all salts in the irrigation water or soil solution and is determined by measuring the electrical conductivity (EC) and/or the total dissolved solid (TDS) content in the water. Long-term wastewater irrigation adds large amounts of salts to a soil system (e.g., Bond, 1998; Falkiner and Smith, 1997; Gharaibeh et al., 2007; Gwenzi and Munondo, 2008; Menneer et al., 2001; Xu et al., 2010) as typical TDS concentrations in raw municipal sewage and tertiary-treated wastewater range from 200 to 3000 mgL1 (Feigin et al., 1991). Rana et al. (2010) indicated that long-term addition of sewage water to agricultural lands enhanced EC values from 0.99 dS m1 for well irrigated to 1.65 dS m1 for sewage irrigated soil. Salinity is likely to be at a minimum immediately after an irrigation event when the soil water content is maximal. Water removal through evapotranspiration can lead to salt accumulation in the topsoil (increased salinity), which may harm the crop depending on its salt tolerance (Mass and Hoffman, 1977). Salts in wastewater can also reduce water availability to the crop by changing the osmotic potential between plant and soil to the extent that the plant’s water, nutrient, and metal(loid) uptake and yield are affected. The annual variation of the water balance has to be taken into account when designing wastewater irrigation systems, and sufficient leaching for removal of excessive salts from the root zone has to be warranted (Smith et al., 1996). In addition to decreasing plant available water, salinity can also impact on soil structure through flocculation/deflocculation processes (Shainberg and Letey, 1984). McLaughlin et al. (1994) studied the causes of elevated Cd concentrations in field-grown potato tubers. They noticed that tuber Cd concentrations were positively related to soil EC and extractable Cl (R2 ¼ 0.62, P<0.001) in the topsoil, with extractable Cl accounting for more variation than EC. They observed that the tuber Cd was unrelated to tuber concentrations of P or sulfur (S) but was positively related to concentrations of Na. They concluded that the cause of elevated Cd concentrations in tubers was due to the effect of Cl mobilizing Cd within the soil and increasing the availability to plants irrigated with saline waters. 3.1.5. Sodicity Municipal wastewater, farm effluents, and effluents from agricultural industries usually have high Na concentrations (e.g., secondary municipal wastewater, 50–250mgL1; Feigin et al., 1991). Sodium has the opposite effect on soils to that of elevated salt concentrations (Sumner, 1993). While high levels Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 241 of salinity promote flocculation, elevated Na levels enhance clay swelling, clay dispersion, and aggregate slaking. Clay dispersion can lead to structural breakdown of a soil and can have adverse effects on soil physical properties, such as soil porosity and permeability (Bond, 1998). The sodicity of irrigation water can be quantified with the sodium adsorption ratio (SAR), which is the level of Na relative to other cations in the irrigation water: ðNaþ Þ SAR ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2þ ðCa ÞþðMg2þ Þ 2 ð1Þ with concentrations of Na, Ca, and Mg in meqL1. The SAR of wastewater can vary considerably, often within the range of 4.5–7.9 for secondary municipal wastewater (Arienzo et al., 2009; Feigin et al., 1991; Lado and Ben-Hur, 2009). The threshold level of SAR in relation to dispersion varies between soil types (Sumner, 1995). A measure of a soil’s sodicity is the exchangeable sodium percentage (ESP), the prevalence of exchangeable Na compared to other exchangeable cations, mainly Ca, Mg, K, hydrogen (H), and Aluminum (Al): ESP % ¼ 100ðexchangeable NaÞ CEC ð2Þ where the Na concentration and CEC are in cmolc kg1. Many studies demonstrated a positive correlation between a soil’s ESP and the SAR of the irrigation water (Harron et al., 1983; Jayawardane et al., 2011; Rengasamy and Marchuk, 2011). In Australia, soils that have more than 6% ESP are considered to have structural stability problems (Sumner, 1995). This threshold is 15% ESP under American conditions due principally to the differences in clay mineralogy (Halliwell et al., 2001), indicating that the thresholds are not absolute figures. The impact of increased ESP on soil physical properties is very complex and dependent on many other factors, such as clay content and mineralogy, EC of the soil solution, SOM, and DOM content, pH, and thus, cannot be readily predicted (Sumner, 1993). The opposing effects of salinity and sodicity of irrigation water on soil dispersion mean that while the likelihood of clay dispersion increases with high SAR-values, this may be mitigated by the increased flocculation due to high salt concentrations, an increased EC. Increases in EC and SAR in soil solutions have been observed with different types of effluents from municipal wastewater to pulp mill effluents (Patterson et al., 2008; Qian and Mecham, 2005; Seikh et al., 1998). In contrast, Hassanli et al. (2008) reported from a 25-month irrigation study in Iran that the soil SAR decreased significantly under effluent irrigation compared with borehole water irrigation. Curiously, the quality of the borehole water was often found to be inferior to the effluent quality (SAR, 242 Anitha Kunhikrishnan et al. 15 and 8, respectively). Stewart et al. (1990) reported an increase in ESP from 3.2% to 9.8% in 0.15–0.35m depth after effluents with an SAR of 5.4 have been irrigated to a plantation for 4years. Amongst several treatments, Falkiner and Smith (1997) observed a maximum increase in ESP from <2% to 25% in 0.3–0.4m depth under a plantation after 4years of weekly secondary-treated effluent irrigation (SAR of effluent, 4.8). Menneer et al. (2001) irrigated two different soil types with sodium-rich dairy factory wastewater over a period of 5 years and reported an increased ESP of 31% compared to 0.4% at the soil surface of unirrigated soils. A significant increase was also measured in an Iranian trial after 1-year irrigation of municipal waste leachate (Khoshgoftarmanesh and Kalbasi, 2002). The interrelationship between salinity and sodicity affects soil structure and thus, transport of heavy metal(loid)s. For example, Usman et al. (2005) investigated the effect of immobilizing substances (three clay minerals, iron oxides, and phosphate fertilizers) and NaCl salinity on the availability of heavy metal(loid)s Zn, Cd, Cu, Ni, and Pb to wheat grown in sewage sludge-amended soil. The plants were irrigated either with deionized or saline water containing 1600mgL1 NaCl. They reported that the addition of metal(loid) immobilizing substances—specifically bentonite clay— significantly decreased metal(loid) availability to wheat. They noticed that irrigation with saline water resulted in a significant increase in metal(loid) chloride species (MClþ and MCl02) with the highest concentration observed for Cd, which was about 53% of its total soil solution concentration. They concluded that saline water increased the availability of Cd and Pb to wheat and decreased the efficiency of bentonite to immobilize soluble Cd. 3.2. Soil biology Soil biological properties as affected by wastewater application have been investigated with variable results, depending on the experimental design and measurements monitored. For example, traditionally microbiological counts have been reported, whereas in more recent studies molecular biological approaches concentrating on gene expression and enzymatic activities, are employed. Controversial results can also be explained by the different nature of wastewater from different sources and the length of wastewater irrigation. For example, while wastewater irrigation is generally considered as a stimulant of microbial activities, long-term wastewater irrigation can lead to the accumulation of metal(loid)s, salts, and organic compounds such as pesticides in soils which might be toxic to soil fauna and flora (Müller et al., 2007). Antibiotics are bioactive compounds and can reach soils through wastewater irrigation, thereby affecting soil biological activity (Kinney et al., 2006). Moreover, wastewater-borne microorganisms might compete with indigenous microbial communities (Sidhu et al., 2001), thereby affecting the biotransformation of metal(loid)s. 243 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 3.2.1. Microbial communities A field trial using tertiary-treated domestic wastewater in a Pinus radiata forest on allophanic soils showed no significant differences in microbial biomass, basal respiration, and sulfatase activity relative to mains water irrigation possibly due to the low nutrient and carbon contents of the wastewater (Schipper et al., 1996). However, many other studies reported a positive impact of long-term wastewater irrigation on total microbial biomass and/or soil enzyme activities in different soils (Barkle et al., 2000; Brzezinska et al., 2006; Degens et al., 2000; Filip et al., 1999, 2000; Friedel et al., 2000; Goyal et al., 1995; Monnett et al., 1995; Ramı́rez-Fuentes et al., 2002). This phenomenon was ascribed to: first, the enrichment of the soils with microbial available carbon and nutrient sources stimulating the soil microbial populations; and second, to favorable pH and moisture conditions (Filip et al., 2000). Shapir et al. (2000) reported that wastewater irrigation mainly affected the soil microbial communities of the topsoil layers of a sandy soil. They emphasized that the observed increase in bacterial counts did not always correlate with similar changes in bacterial activity. Blume and Horn (1982) reported a shift in the microbiological population from aerobic to anaerobic microorganisms due to short-term oxygen depletion of the topsoil resulting from wastewater irrigation, as seen by a decrease in oxygen diffusion rate (Fig. 3; Bhandral et al., 2007). They also noticed a higher proportion of nitrifying and ammonifying microorganisms than in the control. The stimulation of copiotrophic bacteria was observed in the same long-term wastewater irrigation area (Filip et al., 1999). Similarly, increased denitrification rates under wastewater irrigation were Concentration (mg cm–2 min–1) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 TFDE UFDE TPFE TME Water Control Figure 3 Oxygen diffusion rate (ODR) values (mgcm2 min1) from the 10cm soil depth following the winter application of water and a range of effluent types to sheep grazed pasture (Bhandral et al., 2007). 244 Anitha Kunhikrishnan et al. reported and explained by higher substrate availability (Schipper et al., 1996) or denitrification enhancing surfactants (Friedel et al., 2000). Adenylate energy charge ratios were reduced and attributed to the addition of Na and salts with the wastewater irrigation (Friedel et al., 2000). Ramı́rez-Fuentes et al. (2002) assumed that the observed inhibition of N2O-oxidation in a long-term wastewater-irrigated soil was due to the accumulation of salts, heavy metal(loid)s, and toxic organic compounds. Others also observed changes in the structure and function of microbial communities due to wastewater irrigation (Faryal et al., 2007; Oved et al., 2001). These examples show that changed environmental conditions in the topsoil of long-term wastewater-irrigated sites can have a selective impact on the composition of microbial populations and soil functional diversity. It is noteworthy that the increase in microbial biomass in a long-term wastewater irrigation area in Berlin, Germany, remained detectable 20years after wastewater irrigation ceased (Filip et al., 1999). Additions of heavy metal(loid) salts to soils usually cause an immediate decrease in respiration rates, but long-term responses are determined by the properties of both the metal(loid) and the soil (Nwuche and Ugoji, 2008). According to Brookes (1995), high levels of Pb may have no effect on soil respiration rates in clay soils but may decrease respiration rates in sandy soils that may be attributed to the difference in bioavailability of Pb between soil types. It has been reported that a neutral soil may contain high levels of Mn, Al, or Pb without any sign of toxicity to microorganisms whereas toxicity may develop with certain organisms at much lower metal(loid) concentrations in acid soils (Marschner and Kalbitz, 2003; Utgikar et al., 2003). Some heavy metal(loid)s contained in the wastewater, for example Cu, Ni, and Zn, are essential trace elements for plants and microorganisms (Alloway, 1995). Even these trace elements, however, may become toxic at higher concentrations (Kosolapov et al., 2004). Copper at high concentration has a detrimental effect on soil microorganisms and modification to the population structure of microbial communities has been reported (Ranjard et al., 2006; Tom-Petersen et al., 2003). DOM is considered the most dynamic C fraction in soils and it represents a major source of energy and cellular C for the soil microbial community. Therefore, a close relationship exists between DOM and soil microbial activity and this C fraction contributes substantially to the total CO2 flux from soils (van Hees et al., 2005). Liu and Haynes (2010) investigated the microbial activity of soils that had received dairy factory wastewater irrigation for greater than 60years. Soil organic C content was unaffected by irrigation but the size (microbial biomass C and N) and activity (basal respiration) of the soil microbial community were increased. They concluded that these increases were attributed to regular inputs of soluble C (e.g., lactose) present as milk residues in the wastewater. Meli et al. (2002) investigated the dynamics of microbial biomass in the soil of a citrus orchard Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 245 which has been irrigated for 15years with lagooned municipal wastewater. They noticed that MBC, soluble C, cumulative respiration, and enzymatic activity were significantly higher in the soils irrigated with wastewater than soils irrigated with “clear” water; they also found that the metabolic quotient (qCO2) was significantly lower in wastewater-irrigated soil, indicating that the microbial biomass used the energy sources more efficiently. 3.2.2. Earthworms In a field trial, about 500mm dairy shed effluent applied during 270days to a silt loam soil under pasture had a positive effect on earthworm population (numbers, wet weight) compared with a control pasture (Yeates, 1976). This was explained by the increased moisture status of the irrigated soil leading to higher dry matter production and lower earthworm mortality during summer as a result of desiccation. The irrigation with dairy factory effluents for 22years to pasture on an allophanic soil led to lower earthworm numbers but a higher biomass of earthworms than in the control, which was accompanied by a modified abundance of the five species present (Degens et al., 2000). Increased earthworm numbers were also recorded by Yeates (1995) in a 7-year experiment of sewage application to a 17-year-old P. radiata plantation on a sandy soil. However, Blume and Horn (1982) warned that high wastewater irrigation rates have a detrimental impact on earthworms due to anaerobic soil conditions as observed under long-term wastewater irrigation “Rieselfelder” around Berlin. 3.3. Soil physics Long-term wastewater irrigation can affect soil physical and hydraulic properties (Daniel and Bouma, 1974; Jnad et al., 2000; Lado and BenHur, 2010; Mathan, 1994; Vinten et al., 1983a,b; Vogeler, 2009). Changes in soil physical properties are primarily caused by the impact of wastewater irrigation on soil chemical properties including soil pH, SOM content and quality, salinity, and sodicity. In this section, we considered potential risks of wastewater irrigation on soil structure, including changes in aggregate stability, bulk density, and hydraulic properties that in turn influence the retention and transport of heavy metal(loid)s. 3.3.1. Aggregate stability Aggregate stability is an important soil property because it affects water infiltration and flow through soils. Wastewater irrigation impacts on soil aggregate stability through the continuous addition of DOM and salts to the system (Assouline et al., 2002; Gharaibeh et al., 2007; Menneer et al., 2001; Vogeler, 2009). DOM stabilizes aggregates through its binding action and increases in microbiological activity (Vogeler, 2009), while Na accumulation through wastewater irrigation can lead to aggregate dispersion 246 Anitha Kunhikrishnan et al. (Misra and Sivongxay, 2009). Flocculation of fine soil particles under saline conditions has also been observed, highlighting the complex interactions between sodicity and salinity (Ghadiri et al., 2007). Others found no significant effect of wastewater irrigation on aggregates stability (Bhardwaj et al., 2007; Levy et al., 2003). Sodium in wastewater below critical coagulation concentration can cause a reduction in aggregate stability, decrease in infiltration rate, and an increase in the risk of runoff. Alvarez-Bernal et al. (2006) studied the effect of tannery wastewater on chemical and biological soil properties and observed that aggregate stability and infiltration properties were adversely affected by increased Na content in the effluent. 3.3.2. Bulk density and total porosity Changes in soil bulk density and porosity induced by wastewater irrigation are dependent on the wastewater quality, in particular, the concentration of dissolved and particulate constituents of the irrigation water. High concentrations of total suspended solids (TSS) tend to increase soil bulk density, while wastewater with lower TSS contents has no significant impact on bulk density (Magesan, 2001; Sopper and Richenderfer, 1979; Vogeler, 2009). Improvements in bulk density and soil porosity have been ascribed to the addition of DOM (Vogeler, 2009). Mathan (1994) reported significantly lower bulk density up to a depth of 0.6m after 15years of wastewater irrigation to a sandy loam. Total porosity was increased by 67% in the topsoil of the wastewater-irrigated soil. An improvement in total porosity was measurable up to a depth of 1.2m. Similarly, bulk density was significantly decreased and total porosity increased after irrigation of primary-treated wastewater to a sandy soil for 7 years at a rate of 55mm per week (Magesan, 2001). In contrast, the study by Jnad et al. (2000) demonstrated a decrease in the volume of large soil pores under subsurface drip irrigation with effluents. They attributed this shift in pore size distribution to an accumulation of suspended solids and an increased salt concentration leading to clay particle dispersion. Amongst 11 soil physical properties including bulk density, field water holding capacity, total porosity, clay content, and saturated hydraulic conductivity measured in the topsoil, Wang et al. (2003b) found that only total porosity was affected by long-term wastewater irrigation. Shahalam et al. (1998), however, demonstrated that the impact of short-term wastewater irrigation on porosity of a silt loam soil was not significant. Wastewater irrigation led to compaction and reduced total porosity, suggesting that total porosity might be a better soil quality indicator than bulk density (Wang et al., 2003b). 3.3.3. Soil hydraulic conductivity and infiltration rate The impact of wastewater irrigation on the hydraulic conductivity and infiltration rate is variable and depends on the soil type, clay content, presence of CaCO3, antecedent moisture content, the quality of the wastewater and Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 247 the irrigation technique (Lado and Ben-Hur, 2009; Lado et al., 2005). A compactive force, for instance the kinetic energy of water drops hitting the soil, may cause sealing of surface pores due to physical disintegration of soil aggregates (Mamedov et al., 2000), aggregate slaking controlled by the wetting rate of the soil (Mandal et al., 2008), TSS of the wastewater (de Vries, 1972) and/or by clay dispersion and the subsequent blocking of soil pores by clay particles (Agassi et al., 1981; Lado et al., 2005). For example, in wastewater-irrigated sites with a high ESP-value, the EC of the soil solution is reduced during rain events which can lead to clay dispersion at the soil surface, seal formation and subsequently to decreased infiltration rates (Lado et al., 2005; Mandal et al., 2008). In addition, DOM of wastewater can enhance soil water repellency (Assouline et al., 2002; Tarchitzky et al., 2007; Travis et al., 2010; Vogeler, 2009; Wallach et al., 2005). Soil water repellency inhibits water infiltration (Müller et al., 2010). Reduced infiltration rates have also been attributed to the collapse of soil structure caused by the dissolution of SOM (Jnad et al., 2000; Lieffering and McLay, 1996; Menneer et al., 2001), which can be initiated by alkaline wastewater (pH 11.5–13.5). In contrast, Magesan et al. (1996) showed increased infiltration rates due to increased macroporosity, which was explained by the increased biological activity following the wastewater applications. Gharaibeh et al. (2007) observed that the length of wastewater irrigation might play a role as well. In their study, up to 5years of wastewater irrigation significantly decreased the infiltration rate of Vertisol, but 15years of wastewater irrigation increased the infiltration rate due to the formation of large cracks. Similarly, it has been suggested that various mechanisms affect hydraulic conductivity as a result of wastewater irrigation (Table 4). Most studies reported reduced soil hydraulic conductivity for wastewater-irrigated soils (Cook et al., 1994; Gharaibeh et al., 2007; Sopper and Richenderfer, 1979; Vogeler, 2009). Suspended solids of the wastewater can block water-conducting soil pores (Vinten et al., 1983b). The higher the concentration of TSS in the wastewater, the higher the probability of decreased hydraulic conductivity due to blocking of soil pores. A decrease in soil hydraulic conductivity can also be due to biological (extracellular carbohydrates, cells, and microbiological waste products) clogging of soil pores following the stimulation of microbial communities by wastewater microbial growth. Magesan et al. (1999) indicated a decrease in the hydraulic conductivity of an allophanic soil after applying synthetic wastewater with a C:N ratio 50:1 for 14weeks in the laboratory. Yet no significant change was evident in field trials on the same soil irrigated with tertiary-treated wastewater with a C:N ratio 2:1 for 7 years. Wastewater with a high C:N led to net N immobilization, excess C and subsequently to an increase in microbial biomass and extracellular carbohydrates that blocked soil pores and reduced the hydraulic conductivity. The plugging of soil pores was shown to be more pronounced in fine textured soils due to the high initial microporosity (Vinten et al., 1983b). Further, wastewater irrigation can change 248 Anitha Kunhikrishnan et al. soil chemical properties, in particular the soil’s ESP, salinity, quantity, and quality of SOM and DOM, which impact on soil structure through clay swelling and dispersion, thereby affecting hydraulic properties (Jnad et al., 2000; Lado and Ben-Hur, 2009, 2010; Mandal et al., 2008). Balks et al. (1996) found at an effluent plantation project in Australia that the soil’s dispersion tendency increased after 5 years, but this did not impact on the hydraulic conductivity. No significant change in permeability was detected after 5 years of irrigation with tertiary-treated wastewater in a major Californian study (Seikh et al., 1998). In contrast, Magesan et al. (1996) reported that applying secondary-treated sewage effluents increased the macroporosity of a sandy loam soil from 11% to 19% and consequently, the hydraulic conductivity increased from 39 to 57mmh1. The infiltration rate influences the transport velocity of heavy metal(loid)s in soils. If the infiltration rate is small, transport of heavy metal(loid)s will also be limited or the transport time of heavy metal(loid)s to the groundwater will increase (Lu, 2005). 4. Effect of Wastewater Irrigation on Heavy Metal(Loid) Dynamics in Soils Heavy metal(loid)s introduced to soils undergo a number of reactions that include adsorption, complexation, precipitation, and reduction, that control their leaching and runoff losses, and bioavailability. In the case of wastewater irrigation, these reactions are manifested predominantly by the presence of high amounts of organic carbon (in particular DOM), soluble salt concentration (salinity), and acidification caused by the mineralization of organic N. 4.1. Adsorption The most important physicochemical process affecting the behavior of metal(loid)s in soils is its sorption from liquid to solid phase (Bolan et al., 1999; Li et al., 2006; Sparks, 2003). The retention and movement of heavy metal(loid)s in soils can be correlated with soil clays, surface area of particles, CEC/AEC, and soil pH (Kabata-Pendias and Pendias, 2001). For example, some studies have shown that the sorption of metal(loid)s by soils tends to increase with increasing pH (Naidu et al., 1996; Violante et al., 2010), OM (Lair et al., 2007), CEC (Buchter et al., 1989; Kwon et al., 2010), and the contents of Fe (Karpukhin and Ladonin, 2008) and Mn oxides (Brown and Parks, 2001; Stahl and James, 1991). It has often been observed that heavy metal(loid)s added through organic amendments, such as effluents, sewage sludge, and manures accumulate in Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 249 the surface layer, indicating a strong retention within surface soils enriched with carbon (Adriano, 2001). Table 6 shows selected references on the effect of wastewater/sludge addition on heavy metal(loid) adsorption. Zhu et al. (1991) observed that the Cu adsorption maxima by two soils which received 11 annual applications of Cu in the form of Cu-enriched swine manure or CuSO4 were higher for the manure-treated soil. This was due to an increase in OM-induced CEC. Addition of organic amendments has often been shown to increase the CEC of soils, thereby resulting in increased cation adsorption. The effect of effluent and manure addition on CEC-induced cation adsorption in soils is often inferred from literature in which the effects of other organic amendments, such as biosolid have been examined. Bolan et al. (2003b), for example, observed that CEC per unit organic carbon was higher for soils than for biosolid, which was attributed either to the difference in the nature of OM or to the significant contribution of negative charge by the mineral components in soils. Although a number of studies have shown general increases in metal(loid) adsorption with effluent and biosolid addition (Juste and Mench, 1992; Li et al., 2001), Zhou and Wong (2001) observed that with Cu, adsorption by both acidic and calcareous soils decreased with the addition of sewage sludge, which they attributed to the formation of soluble Cu-DOM complex. There is much evidence in the literature stating that DOM can reduce metal (loid) adsorption onto soils (Ashworth and Alloway, 2008; Baham and Sposito, 1994; Davis, 1984; Elliott and Denneny, 1982; Gove et al., 2001; Xu et al., 1989). A significant inverse relationship between the extent of Cu adsorption and the DOM in the soils treated with organic amendments was observed by Bolan et al. (2003c) and Hao et al. (2008). These Cu-DOM complexes are highly mobile in soils and may increase the leaching of Cu. Wong et al. (2007) noted that the addition of DOM through anaerobically digested dewatered sludge significantly reduced the Cd sorption capacity with a maximum inhibition on metal(loid) sorption occurring at pH 7–7.5. Al-Wabel et al. (2002) reported a positive correlation between increased soil DOM resulting from biosolid application and Pb and Cu concentrations indicating formation of soluble metal(loid)-DOM complexes. Kunhikrishnan (2011) examined the effect of farm dairy, winery, and piggery wastewaters on the adsorption of Cd, Cu, and Pb using batch experiments and showed that adsorption decreased in all the soils in the presence of wastewater sources. Results indicated that DOM in wastewater sources formed soluble metal(loid) complexes and consequently reduced the adsorption of Cu, Cd, and Pb. 4.2. Complexation Heavy metal(loid)s form both inorganic and organic complexes with a range of solutes. As might be expected, the organic component in wastewater has a high affinity for metal(loid)s due to the presence of ligands or functional Table 6 Selected references on the effect of wastewater and waste sludge on heavy metal(loid) adsorption and complexation reactions Metal(loid)s Wastewater/ sludge Cu, Fe, Mn, Ni, Pb, Zn Sewage effluent Cd, Cr, Cu, Ni, Pb, Zn Sewage water or sludge Cu, Cr, Ni, Zn Reclaimed wastewater Cr, Cu, Pb, Zn Municipal wastewater Cd, Cu, Fe, Mn Ni, Pb, Zn Untreated sewage effluent Observations References Sewage irrigation for 20years resulted into significant build-up of DTPA-extractable Zn (208%), Cu (170%), Fe (170%), Ni (63%), and Pb (29%) in sewage-irrigated soils over adjacent tube well water-irrigated soils, whereas Mn was depleted by 31%. Concentrations of Cr in the sewage-irrigated soils exceeded the permissible limits, the concentration of Zn in 55.6% of the samples, and 44.4% for Cu were above the limits, while Pb and Cd did not exhibit values beyond the allowable limits. Irrigation with effluents also increased both the total and EDTAextractable metals in the fields. Highest levels of EDTAextractable elements were at top 20-cm layers, and available fractions decreased with depth. Long-term irrigation (8 and 20 years) significantly increased EDTA-extractable Cu and Ni at top 50-cm profiles, while only increased EDTA-extractable Cr and Zn on top 30-cm soils. 3years after discontinuation of wastewater application on organic soils, heavy metals in soils were below the upper permissible limits. Also the basic soil properties (OM, pH, BD, WHC, and P2O5) were not changed. Organic carbon content showed positive correlation with all heavy metals except Zn. Degradation of sludge organic matter released heavy metals in sewage sludge-amended soils. Rattan et al. (2005) Chen et al. (2010) Xu et al. (2010) Brzezińska et al. (2010) Rana et al. (2010) Cu, Zn Sewage sludge Cu Sewage sludge Cd, Zn Anaerobically digested dewatered sludge Cu and Zn sorption capacity decreased in the presence of DOM. The kd values for Cu without and with DOM were 121.20 and 36.88 and for Zn the values were 33.58 and 14.825 for Zn, respectively. Complexation of Cu by sewage sludge-derived dissolved organic matter occurred due to reduced soil sorption and the complexation was greatest at intermediate pH values. The addition of DOM significantly reduced the Cd and Zn sorption capacity with a maximum inhibition on metal sorption occurring at pH 7–7.5. The kd values for acidic sandy loam soil in the absence and presence of DOM were 22.2 and 9.54 for Cd and 3.86 and 1.84 for Zn. The kd values for calcareous sandy loam soil in the absence and presence of DOM were 329 and 107 for Cd and 212 and 40.2 for Zn. Mesquita and Carranca (2005) Ashworth and Alloway (2007) Wong et al. (2007) 252 Anitha Kunhikrishnan et al. groups that chelate metal(loid)s (Harter and Naidu, 1995). With increasing pH, the carboxyl, phenolic, alcoholic, and carbonyl functional groups in OM dissociate, thereby increasing the affinity of ligand ions for metal(loid)s. It has been observed that addition of wastewater, sewage sludge, or manure by-products increases the complexation of metal(loid)s in soils, the extent of this relates to the DOM concentration (Hesterberg et al., 1993) (Table 6). Complexation can result in the formation of both soluble and insoluble metal(loid)-DOM complexes, thus affecting both movement and bioavailability of heavy metal(loid)s. While insoluble complexes result in the retardation of DOM and metal(loid) movement (Guggenberger and Kaiser, 2003; Jansen et al., 2005; Martin and Goldblatt, 2007), soluble metal (loid)-DOM complexes enhance their movement. Accordingly, in soils containing large amounts of OM, such as pasture soils and organic manure or wastewater-amended soils, only a small proportion of metal(loid)s in soil solution remains as free metal(loid) ion and a large portion are complexed with DOM (Bolan et al., 2003a,c; Haruna et al., 2009; McLaren and Ritchie, 1993). For example, del Castilho et al. (1993) observed that 30–70% of the dissolved Cu and all Cd in soils treated with cattle manure slurry was bound in relatively fast dissociating organic-metal(loid) complexes. Although the formation of soluble metal(loid)-organic complexes reduces the phytoavailability of heavy metal(loid)s, the mobility of the heavy metal (loid) may be greater in soils receiving alkaline-stabilized biosolid due to the reduction of metal(loid) adsorption and increased concentration of soluble metal(loid)-organic complex in solution (Brown et al., 1997; Gove et al., 2001). It has often been found that in manure- and effluent-amended soils, a large portion of Cd and Cu is complexed with DOM within soil solution (Buzier et al., 2006; del Castilho et al., 1993; van Veen et al., 2002). Similarly, Hyun et al. (1998) and Shan (2010) found a linear relationship between organic carbon and soluble Cd in solution for sludge-treated soils, indicating that most of the Cd remained as metal(loid)-organic complex. As reported by Bolan et al. (2003c), a decrease in Cu adsorption in the presence of DOM is likely to increase Cu mobility yet does not necessarily increase bioavailability. Application of effluent and manure has been shown to increase the soluble salt concentration of soils, as measured by EC (del Castilho et al., 1993; Rana et al., 2010; Rusan et al., 2007; Sutton et al., 1984). High concentration of inorganic anions, such as Cl and sulphate (SO2 4 ) in effluents and manure products induces the formation of metal(loid)-inorganic complexes (e.g., Cd– Cl complex) that are considered to be even more phytoavailable (Japenga and Harmsen, 1990; Khoshgoftarmenesh et al., 2002; McLaughlin et al., 1998; Smolders et al., 1998). Although a wide variety of organic compounds in DOM contribute to the formation of soluble complexes with metal(loid)s, Daum and Newland (1982), del Castilho et al. (1993), and Zhou and Wong (2001) observed that the low-molecular-weight fractions, such as hydrophilic bases have strong affinity for forming soluble complexes with Cd, Cu, and Zn. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 253 Thus, the formation of soluble aqueous metal(loid)-organic and to a lesser extent metal(loid)-inorganic complexes is expected to dominate the solution chemistry of metal(loid)s in wastewater and manure-amended soils (Hesterberg, 1998; Hesterberg et al., 1993; Lipoth and Schoenau, 2007). 4.3. Redox reactions As discussed above, adding biological waste materials, such as wastewater, livestock and poultry manures, and sewage sludge has often been shown to increase the amount of DOM in soils (Bolan et al., 2011b; Park et al., 2011; Schindler et al., 1992; Sleutel et al., 2006). These wastes of plant and animal origin contain large amounts of DOM, and the addition of certain organic manures, such as poultry manure increases the pH, thereby enhancing the solubilization of SOM (Jackson and Miller, 2000; Jackson et al., 1999). Such an increase in DOM may enhance microbial activity but lower the redox potential in the soil (Fig. 3; Bhandral et al., 2007; Luo et al., 2008; Redman et al., 2002). A number of studies have shown that addition of OM-rich soil amendments enhances the reduction or biotransformation of certain heavy metal (loid)s, such as As, Cr, and Se (Alexander, 1999; Frankenberger and Losi, 1995; Losi et al., 1994) (Table 7; Fig. 4). For example, Ajwa et al. (1998) noticed greater loss of Se from manure-borne Se than from inorganic fertilizer-borne Se, which they attributed to manure-facilitated volatilization due to the reduction of Se. Similarly, Banks et al. (2006), Cifuentes et al. (1996), Higgins et al. (1998), and Losi et al. (1994) reported a reduction of Cr(VI) to less toxic and less mobile Cr(III) in soils amended with cattle manure. Various reasons could be attributed to the enhanced reduction of Cr(VI) in the presence of organic amendments, including the supply of carbon and protons and the stimulation of microorganisms that mediate and facilitate the reduction of Cr(VI) to Cr(III) (Losi et al., 1994). Zhao et al. (2009) investigated the transport and fate of Cr(VI) and As(V) in soil zones derived from moderately contaminated farmland irrigated with industrial wastewater for 30years. A column test showed that the concentration of Cr(III) and As(III) in the leachate increased by 6% and 5.6%, respectively, indicating DOM-induced reduction of these metal(loid)s (Fig. 5). Under similar organic carbon loading, Bolan et al. (2003d) observed a significant difference in the extent of Cr(VI) reduction between various organic manure composts. Reduction increased with increasing level of DOM added through manure addition, which has been identified to facilitate the reduction of Cr(VI) to Cr(III) in soils (Jardine et al., 1999; Nakayasu et al., 1999). For example, the hydroquinone groups in OM have been identified as the major source of electron donor for the reduction of Cr(VI) to Cr(III) in soils (Elovitz and Fish, 1995). Table 7 Selected references on the effect of wastewater/manure addition on heavy metal(loid) reduction Metal (loid)s As and Cr As Wastewater/manure Observations References Industrial wastewater Poultry litter Cr(VI) and As(V) were reduced to Cr(III) and As(III) indicating DOC-induced reduction Poultry litter increased the solubility of As by complexation with DOC Enhanced the reduction of Cr(VI) to Cr(III) Enhanced the reduction of Cr(VI) to Cr(III) Chromate leaching was reduced in soils in the presence of elevated organic matter because of reduction followed by retention on cation exchange sites or precipitation The mixture of sewage sludge and poultry litter reduced As(V) to more mobile and toxic As(III) Zhao et al. (2009) Cr Cr Cr Cattle manure Cattle manure Composted cow manure As Sewage sludge and poultry litter Jackson et al. (2003) Cifuentes et al. (1996) Higgins et al. (1998) Banks et al. (2006) Jackson et al. (1999) 255 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 1200 Cr(VI) (mg L–1) 0 Mg OM ha–1 50 Mg OM ha–1 800 400 0 0 5 10 15 20 Time (weeks) Figure 4 1994). Effect of organic matter addition on Cr(VI) reduction in soils (Losi et al., Metal concentration (%) 120 100 80 60 40 20 0 After Before Chromium Cr(VI) Before After Arsenic Cr(III) As(V) As(III) Figure 5 Concentration of Cr(VI), Cr(III) and As (V), As(III) in wastewater-irrigated soil before and after column tests (Zhao et al., 2009). The increase in Cr(VI) reduction in the presence of manure and effluent addition may also result from enhanced microbial activity. Although Cr(VI) reduction can occur through both chemical and biological processes, the bioreduction is considered to be the dominant process in most arable soils that are low in Fe2þ ion. Losi et al. (1994) have reported that adding manure 256 Anitha Kunhikrishnan et al. compost generated a larger increase in the bioreduction than chemoreduction of Cr(VI), indicating that the supply of microorganisms is more important than the supply of organic carbon in enhancing the reduction of Cr(VI) when compost is added. It has often been reported that an increase in microbial activity will in turn increase the reduction of Cr(VI) to Cr(III) (Losi et al., 1994; Rajkumar et al., 2005; Sultan and Hasnain, 2006). Protons are required for the reduction of Cr(VI) to Cr(III) (Eq. (3)). Wastewater and manure compost are generally rich in N, part of which is in the ammoniacal form. Oxidation of ammoniacal nitrogen to nitrate nitrogen (nitrification) and ammonia volatilization result in the release of protons. It has often been observed that Cr(VI) reduction, being a proton consumption (or hydroxyl release) reaction, increases with a decrease in soil pH (Cary et al., 1977; Eary and Rai, 1991). 2Cr2 O7 þ 3C0 þ 16Hþ ! 4Cr3þ þ 3CO2 þ 8H2 O ð3Þ Increased concentration of Fe2þ and Mn2þ ions in drainage effluent from manure- and effluent-amended soil is related to reducing conditions with the consequent solubilization of these metal(loid)s in soils. Metal(loid)s, such as Co, are retained by Fe2þ and Mn2þ oxides under oxic conditions (McLaren et al., 1984) and the manure/effluent-induced reduction of these oxides results in the release of adsorbed metal(loid)s (L’Herroux et al., 1997; Siebe and Fischer, 1996). Wallingford et al. (1975) obtained a good correlation between Mn concentration in corn and cumulative level of feedlot manure application, which was attributed to enhanced solubilization of Mn due to reducing conditions in manure-treated soil. 4.4. Methylation/demethylation Methylated derivatives of As, Hg, and Se can arise as a result of chemical and biological processes that frequently alter their volatility, solubility, toxicity, and mobility. Biomethylation of these heavy metal(loid)s has emerged as a major process for their removal during wastewater treatment using natural and constructed wetlands (Kosolapov et al., 2004; Stasinakis and Thomaidis, 2010). The major microbial methylating agents are methylcobalamin (CH3CoB12), involved in the methylation of Hg, and S-adenosylmethionine, involved in the methylation of As and Se. Biomethylation may result in metal(loid) detoxification since methylated derivatives are excreted readily from cells, are often volatile, and may be less toxic, for example, organoarsenicals. Although methylation of heavy metal(loid)s occurs through both chemical (abiotic) and biological processes, biomethylation is considered to be the dominant process in soils and aquatic environments. At present there is substantial evidence for the biomethylation of As, Hg, and Se in soils and aquatic systems (Gadd, 2004; Masscheleyn and Patrick, 1993; Nicholas et al., 2003; Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 257 Oiffer and Siciliano, 2009) and during wastewater treatment (Stasinakis and Thomaidis, 2010). Microorganisms in soils and sediments act as biologically active methylators and OM derived from wastewater application provides the source of methyl donor for methylation (Kosolapov et al., 2004). Benthic microbes are capable of methylating As under both aerobic and anaerobic conditions to produce methylarsines and methyl-arsenic compounds (Maher, 1988). Methylation may play a significant role in the mobilization of As by releasing it from the sediments to the aqueous environment (Anderson and Bruland, 1991). Similarly, methylated Hg species that are highly toxic and biologically mobile have been observed in various wastewater sources including dental wastewater (Gbondo-tugbawa et al., 2010; Gustin et al., 2006; Zhao et al., 2008). When selenate [Se(VI)] and selenite [Se(IV)] are introduced into moderately reducing conditions they are quickly transformed through microbial processes to Se0 and/or organic Se compounds. Selenium biomethylation is of interest because it represents a potential mechanism for the removal of Se from contaminated environments, and it is believed that methylated compounds, such as dimethyl selenide are less toxic than dissolved Se oxyanions (Frankenberger and Losi, 1995). For example, biomethylation followed by volatilization is considered as one pathway by which high Se concentrations are dissipated from agricultural evaporation ponds in the San Joaquin Valley of California (Gao and Tanji, 1995). Literature reports that wastewater from some industries contains quite high concentrations of soluble Se, as high as 620mgL1 from the Se compounds industry and 20–60mgL1 from the Cu refining industry (Fujita et al., 2002). Moreover, in a recent study investigating the distribution of selenate, selenite, and selenocyanate (SeCN) in wastewater of an oil refinery plant (Miekeley et al., 2005), SeCN was by far the most abundant Se species, reaching concentrations of up to 90mgL1. The authors reported that selenite was detected only in one sample and selenate could not be identified in any of the analyzed samples. In a study investigating Se removal from selenitecontaminated oil refinery wastewater wetland, Hansen et al. (1998) found that 89% of the Se was removed. They found that most of the Se was immobilized into the sediment and plant tissues, whereas biological volatilization could have accounted for 10–30% of its removal. Ye et al. (2003) reported that 79% of initial Se mass contained in coal gasification plant wastewater was removed in a constructed wetland. The primary sink for Se retention was the sediment, which accounted for 63%, whereas accumulation in plant tissues and biological volatilization to the atmosphere were of minor importance (Ye et al., 2003). Frankenberger and Arshad (2001) observed that microorganisms, particularly Enterobacter cloacea, were very active in reduction of Se oxyanions present in irrigation drainage water, into insoluble Se0. Furthermore, by monitoring various environmental conditions and addition of organic amendments, they confirmed that the process could be stimulated manifold. 258 Anitha Kunhikrishnan et al. 4.5. Leaching and runoff Long-term application of wastewater to soils can potentially affect the quality of groundwater resources by excess nutrient loading and heavy metal(loid) mobilization beyond the plant root zone (Abaidoo et al., 2009; Hamilton et al., 2007). The impact depends on a number of factors including the depth of the water table, soil properties, soil drainage, management of wastewater irrigation, quality of groundwater, and the scale of wastewater irrigation. The capacity for heavy metal(loid)s to contaminate groundwater relies on the mobility of the heavy metal(loid) concerned, and the amounts and proportions of complexed and free metal(loid) forms within the soil solution. The leaching rate of heavy metal(loid)s is also influenced by the natural OM content of the soil, the concentration and quality of DOM, and pH of the leaching solution (Antoniadis and McKinley, 2003; van Zomeren and Comans, 2004). Many studies have examined the leaching behavior of heavy metal(loid)s from contaminated soils, industrial sludges, dredged sediments, and municipal solid wastes (Dijkstra et al., 2004; Meima and Comans, 1997; Voegelin et al., 2003) (Table 8). The potential risk of heavy metal(loid)s in soils, with respect to their mobility and ecotoxicological significance, is determined by their solid-solution partitioning rather than the total heavy metal(loid) content (Dijkstra et al., 2004; Shi et al., 2009). The release of heavy metal(loid)s to soil solution depends on their affinity to bind to reactive surfaces in the soil matrix (Dijkstra et al., 2004). Downward migration of heavy metal(loid)s in wastewater is facilitated by forming soluble complexes with DOM (Zhou and Wong, 2001). L’Herroux et al. (1997) observed that repeated applications of swine manure slurry increased the drainage water concentrations of Mn from 0.05 to 14mgL1, Co from 0.8 to 50mgL1, and Zn from 17.3 to 100mgL1. Studies on migration of metal(loid)s in soils after manure slurry applications have linked metal(loid) mobility with DOM (Amery et al., 2010; Japenga et al., 1992). Although the soluble organic metal(loid) fraction is not readily bioavailable to plants, it is relatively mobile and applying organic amendments including wastewater, biosolid, and animal manure has been shown to enhance the leaching of metal(loid)s in soils (Hsu and Lo, 2000). Del Castilho et al. (1993), for example, observed a positive relationship between soluble metal(loid) concentration and DOM in soils treated with cattle manure slurry. Li and Shuman (1997) observed that leaching metal(loid)contaminated soils with poultry litter extract increased the water-soluble fractions of Cu and Zn, with a corresponding decrease in exchangeable fractions, indicating that poultry manure application enhances the solubilization and mobilization of metal(loid)s. Acidification caused by manure application due to nitrification also results in the release of soil metal(loid)s (del Castilho et al., 1993; Japenga et al., 1992). Table 8 Selected references on the effect of wastewater and waste sludge on heavy metal(loid) leaching Metal(loid)s Wastewater Observations References Cd, Cu Treated wastewater Untreated wastewater Untreated wastewater Preferential flow and metal complexation with soluble organics apparently allowed leaching of heavy metals. Water extractable Cu and Cd concentrations and the metal leachates increase and correlate with DOC. Groundwater was not contaminated through vertical infiltrationinduced leaching. However, substantial build-up of metals in river sediments and wastewater-irrigated soils were observed. Zn, Cu, and Cd mobility was observed due to acidic soil pH. Behbahaninia et al. (2008) Herre et al. (2004) Cu, Cd Hg, Cd Zn, Cu, Cd, Treated sewage Cr effluent Cr, Zn, Cd, Poultry litter Cu, Pb Cd, Ni, Zn Sewage sludge Zn, Cd, Cu, Sewage sludge Ni, Cr Cu, Ni, and Sewage sludge Pb Cu, Cd, Pb, Pig manure and Zn amendment in mine soils Cu, Zn Poultry and livestock manures Wu and Cao (2010) Gwenzi and Munondo (2008) Leaching of metals increased with increasing rates of poultry litter. Paramasivam et al. (2009) DOM applications significantly increased the extractability of metals. Antoniadis and Alloway (2002) The concentrations of Zn, Cd, Cu, Ni, and Cr in the saturation extract Schaecke et al. (2002) closely correlated with the concentrations of DOM. Considerable amounts of Zn and Cd from sewage sludge were found in the mobile fractions of the soil with Cu, Ni, and Pb in organic particles. The solubility of the heavy metals showed a strong positive relationship Ashworth and to the solubility of organic matter, particularly at high pH. Alloway (2008) Pig manure amendment increased DOM in leachates, thereby Carmona et al. increasing the release of metals from mine soil. (2008) Total amounts of Cu and Zn eluted from the soil columns significantly Hao et al. (2008) correlated with the extracted soil Cu and Zn concentrations. 260 Anitha Kunhikrishnan et al. DOM plays an important role in facilitating the leaching of contaminants in soil (Haberhauer et al., 2002; van Zomeren and Comans, 2004) by forming soluble metal(loid) complexes (Bolan et al., 2011b; McCarthy and Zachara, 1989; Weng et al., 2002). Herre et al. (2004) did a column experiment to study the effect of wastewater on the leaching of metal(loid)s (Cu and Cd) and DOM. They found that the amount of Cu leached correlated well with the DOM concentrations in the leachates (Fig. 6A, B). This agrees well with many published reports emphasizing the importance of DOM for metal(loid) A B 10 Water extractable Cu (mg kg-1) Water extractable Cu (mg kg-1) 500 400 300 200 100 0 0 0.2 0.4 DOC (mg g-1) 0.6 8 6 4 2 0 0 0.1 0.2 0.3 0.4 0.5 DOC (mg g-1) Vertisol R 2 = 0.71 Vertisol R 2 = 0.75 Leptosol R = 0.54 Leptosol R 2 = 0.50 2 C Cd concentration (mg kg-1) 120 Arthrosol R 2 = 0.81 100 80 60 40 20 0 0 50 100 200 150 250 DOC concentration (mg C kg-1 soil) Figure 6 Relationship between DOC and water extractable Cu (A) and Cd (B, C) in different soils [(A, B): Herre et al., 2004; (C): Shan, 2010]. 261 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil mobility (Christensen et al., 1999; Ermakov et al., 2007; Kalbitz and Wennrich, 1998; Zhu and Alva, 1993) (Fig. 6C). The presence of wastewater DOM would maintain metal(loid)s in solution and thus limit adsorption onto the soil (Ashworth and Alloway, 2004; Harter and Naidu, 1995). Many researchers have viewed DOM as an important contributor to the elevated mobility of heavy metal(loid)s in soils treated with wastewater, manures, and biosolids (Al-Wabel et al., 2002; Haynes et al., 2009; Kunhikrishnan, 2011; Peckenham et al., 2008). For example, Kunhikrishnan (2011) examined the effect of piggery, farm dairy, and winery wastewaters on Cu leaching and noticed that leaching increased with increasing levels of Cu and was higher in soils treated with wastewater sources than Milli-Q water. Kunhikrishnan (2011) suggested that the DOM in wastewater sources formed soluble Cu-DOM complexes, thereby facilitating the movement of Cu in soils (Fig. 7). Thus, whilst free metal(loid) ions or readily dissociated inorganically complexed metal(loid)s added to a soil would be expected to become quickly adsorbed to soil solids (e.g., via cation exchange and complexation reactions), soluble organometal(loid) complexes may be maintained in the soil solution. 5. Bioavailability of Wastewater-Borne Heavy Metal(Loid)s in Soils Bioavailability of wastewater-, sludge-, and manure-borne metal(loid)s in soils can be examined using chemical extraction and bioassay tests. Chemical extraction tests include single extraction and sequential fractionation (Basta and Cumulative Cu concentration (mg kg-1) A B 0.8 1.6 PE WE FDE MQ 0.6 1.2 0.4 0.8 0.2 0.4 0 0 4 8 Pore volumes PE WE FDE MQ 12 0 0 4 8 Pore volumes 12 Figure 7 Effect of wastewater irrigation on cumulative Cu concentration of leachates in a silt loam soil, (A) 100mgkg1 and (B) 500mgkg1 (MQ, Milli-Q water; PE, piggery effluent; WE, winery effluent; FDE, farm dairy effluent; Kunhikrishnan, 2011). 262 Anitha Kunhikrishnan et al. Gradwohl, 2000; Ruby et al., 1996). Bioassay involves plants, animals, and microorganisms (Naidu et al., 2008; Yang et al., 1991). 5.1. Chemical extraction 5.1.1. Single extraction The feasibility of predicting the bioavailability of heavy metal(loid)s to higher plants and various organisms is assessed using selective chemical extractants (Kelsey et al., 1997; Loibner et al., 2000). Both single extractions (Beckett, 1989) and sequential extractions (Tessier et al., 1979) are used to identify those fractions of metal(loid)s in the soil that are more or less readily available (Kennedy et al., 1997). Bioavailability is organism- and speciesspecific and a single chemical test is insufficient to precisely assess bioavailability accurately (Reid et al., 2000). However, extraction with non-exhaustive selective extractants that mimics the bioavailability of pollutants is useful for providing predictors of exposure. Several methods have been used to evaluate the bioavailability of heavy metal(loid)s in soils which are based mainly on extractions by various solutions: (a) acids—mineral acids at various concentrations (e.g., 1N HCl), (b) chelating agents (e.g., EDTA, DTPA), (c) buffered salts (e.g., 1M NH4OAc), (d) neutral salts (CaCl2, NH4NO3), and (e) other extractants proposed for routine soil testing. These extractants have been used to predict the bioavailability of fertilizer-, wastewater-, manure-, and sludge-borne heavy metal(loid)s in soils (Gupta and Sinha, 2007; Marchi et al., 2009; Payne et al., 1988; van der Watt et al., 1994). Chelating agents such as EDTA and DTPA have often been found to be more reliable in predicting the plant availability of sludge- and wastewater-borne heavy metal(loid)s (Gupta and Sinha, 2007; Sims and Johnson, 1991), since they are more effective in removing soluble metal (loid)-organic complexes that are potentially bioavailable. However, it should not be readily assumed that these chelating agents actually measure availability (Beckett et al., 1983a, b; Peijnenburg et al., 2007). Jagtap et al. (2010) conducted a study to ascertain the addition of heavy metal(loid)s, Cr, Cd, Cu, Ni, Pb, and Zn into agricultural fields through municipal wastewater irrigation. They analyzed the available concentration of heavy metal(loid)s using DTPA extraction and found a maximum of 64.84% extraction in the case of Cr. They attributed the low extraction of other metal(loid)s to the formation of high-affinity complexes of metal (loid)s and soil particles. They reported that the extraction of heavy metal (loid)s is dependent on pH, EC, CaCO3, organic carbon, type of soil, and method of extraction. They also noticed that EDTA was more suitable for acidic soils, whereas DTPA was considered more suitable for neutral and near alkaline soils, as it buffered pH at 7.3 and therefore prevented CaCO3 from dissolution and release of occluded metal(loid)s (Chen et al., 2009; Lin and Zhou, 2009). Luo et al. (2003) studied the accumulation, chemical Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 263 fractionation, and availability of Cu to rice in a paddy soil irrigated with Cuenriched wastewater. They found that with irrigation the concentrations of Cu in the exchangeable (NH4OAc-extractable) and complexed (EDTAextractable) fractions increased rapidly, from 0.33 to 6.30mgkg1 and from 14.1 to 98.0mgkg1, respectively. EDTA-extractable Cu was much higher than NH4OAc-extractable Cu in the soils. Calcium chloride (CaCl2) soil extraction, although a neutral salt extraction, is a widely used and internationally recognized technique (Harmsen, 2007; Peijnenburg et al., 2007). van der Welle et al. (2007) reported that under aerobic conditions, plant heavy metal(loid) uptake was best predicted by the amount of CaCl2-extractable metal(loid)s. Metal(loid) extraction with CaCl2 solution was found to be effective, with Sauvé et al. (1996) and McBride (2001) reporting that Cu2þ in 0.01M CaCl2 correlated strongly with plant yields or tissue Cu concentrations of rye grass and crop species such as maize, lettuce, and radish. Wightwick et al. (2010) determined the environmental availability of Cu in Australian vineyard soils contaminated with fungicide derived Cu residues irrigated with treated sewage. They reported that differences in Cu availability determined by 0.01M CaCl2 extractable Cu concentrations were related to the total Cu concentration and soil properties, including pH, clay, exchangeable K, silt, and CaCO3. Kunhikrishnan et al. (2011) compared the free Cu2þ concentrations in CaCl2 extract and pore-water from soils in the presence of farm dairy and piggery wastewater sources. They reported that the free Cu2þ concentrations were lower in soils incubated when wastewater sources were present. These results suggest the formation of Cu-DOM complexes decreases the amount of free Cu2þ in the soil solution. 5.1.2. Sequential fractionation Fractionation studies are often used to examine the influence of amendments, such as wastewater, CaCO3, P compounds, and biosolid on the immobilization of heavy metal(loid)s. Following adsorption, irrespective of the nature of interaction between heavy metal(loid)s and soil colloidal particles, metal(loid) ions are redistributed amongst organic and mineral soil constituents (Bolan et al., 2003e; Fedotov and Mirò, 2008). Factors affecting the distribution of heavy metal(loid)s among different forms include pH, ionic strength of the soil solution, solid and solution components as well as their relative concentration and affinities for heavy metal(loid), and reaction time (Bolan et al., 2003e; Shuman, 1991). The various forms of the heavy metal(loid)s that are sequentially extracted can be classified as soluble, adsorbed/exchangeable, carbonate-bound, organic-bound, amorphous ferromanganese hydrous oxide-bound, crystalline ferromanganese hydrous oxide-bound, and residual or lattice mineral-bound. The phytoavailability of the different forms of the solid phase species generally decreases in the following order: soluble>adsorbed/exchangeable 264 Anitha Kunhikrishnan et al. >organic-bound>carbonate-bound>ferromanganese hydrous oxide-bound >residual or refractory (i.e., fixed in mineral lattice) (Tessier et al., 1979). Studies suggest treatment of soils with organic amendments such as sludge or wastewater shifts the solid phases of the heavy metal(loid)s away from immobile fractions to forms that are potentially more mobile, labile, and bioavailable. For example, Dudka and Chlopecka (1990) found with sewage sludge application the residual forms of Cd2þ, Cu2þ, and Zn2þ in soil decreased from 34–43% to 6–34%, with a corresponding increase in the readily phytoavailable forms. Through sequential extraction of Cu, Cd, Pb in four soils irrigated with wastewater, Flores et al. (1997) discovered metal(loid)s were predominantly associated with organic soil fractions. Bashir et al. (2007) studied the fractionation of heavy metal(loid) s (Cd, Mg, and Zn) in soils irrigated with untreated sewage effluent for a long period of time. Extraction procedure showed that most of the heavy metal(loid)s (>50%) was bound to residual fraction. Among nonresidual fractions, Cd and Mn were present in reducible fraction while Zn was present in oxidizable fraction. Luo et al. (2003) analyzed the fractionation of Cu in a paddy soil irrigated with Cu-enriched wastewater. They reported marked increases in the weak acid-soluble (HOAc-extractable), reducible Fe and Mn oxide-bound (NH2OHHCl-extractable), oxidizable OM-bound (H2O2-extractable), and residual fractions of Cu in the wastewater-irrigated soils, indicating an increase in mobility and bioavailability of Cu leading to Cu toxicity in the plants. Physiologically based in vitro chemical fractionation schemes are becoming increasingly popular for examining the bioavailability of heavy metal (loid)s (Basta and Gradwohl, 2000; Juhasz et al., 2009; Ruby et al., 1996). These schemes include physiologically based extraction tests (PBET), potentially bioavailable sequential extraction (PBASE), simplified bioaccessibility extraction test (SBET), Deutsches Institut für Normung (DIN), and gastrointestinal (GI) test. These improved tests make it possible to predict the bioavailability of heavy metal(loid)s in soil and sediments or when ingested by animals and humans (Bolan et al., 2008; Juhasz et al., 2009). The PBET and GI tests are in vitro screening-level assays used for predicting the bioaccessibility of contaminants from a soil matrix. While the PBET method has been applied to both organic and inorganic contaminants, it is more commonly recognized as an assay for assessing heavy metal(loid) bioaccessibility (Bolan et al., 2008). Assadian and Margez (2006) studied the bioaccessibility of heavy metal(loid)s (Cd, Cr, Ni, and Pb) using chemical fractionation and in vitro GI and PBET methods in soils blended with untreated effluent and biosolids. The results indicated that chemical fractionation of selected heavy metal(loid)s in soil did not reflect metal(loid) accumulation in oat forage or in sheep kidney, liver, or muscle tissue. However, PBET method was close to predicting Cd and Cr concentrations measured in sheep tissues. 265 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 5.2. Bioassay 5.2.1. Phytoavailability It can be expected that in wastewater-treated soils just like in sewage sludgeand manure-treated soils, plants may exhibit more tolerance to heavy metal (loid)s (Fig. 8; Table 9). Chang et al. (1992) and Logan et al. (1997), for example, have demonstrated that when maize and other crops were grown on Cu-contaminated sludge-amended soils, inconsequential changes in plant tissue Cu concentrations in response to substantial increases in total Cu loading in soils occurred. Organic amendments may also alleviate oxyanion phytotoxicity; for example, the uptake of Se was less in the presence of organic amendments (seleniferous plant tissues and manure) than that from inorganic sources (selenite) (Ajwa et al., 1998; Sharma et al., 2011). Singh et al. (2010b) examined the role of fertilizers (organic fertilizer as farmyard manure (FYM), commercial inorganic NPK, and a combination of FYMþNPK) in reducing the heavy metal(loid) availability in the soil, and subsequent uptake in Beta vulgaris L. (var. All green). They observed that phytoavailability of Cd, Cu, Pb, Zn, Mn, Ni, and Cr determined by bioconcentration factor (BF¼ Plant concentration/soil concentration) was lowest in FYM and highest in NPK treated soil, compared to the untreated control (Fig. 8). They also noticed that the yield of B. vulgaris was also highest in FYM-treated soil and suggested that application of FYM alone and in combination with NPK may Bioconcentration factor 2.5 2 1.5 1 0.5 0 Cd Cu Pb Zn Mn Ni Control NPK fertilizer Farmyard manure Farmyard manure+ NPK Cr Figure 8 Effect of organic and inorganic fertilizers on heavy metal(loid) uptake in Beta vulgaris L. grown in wastewater-irrigated soils (Singh et al., 2010b). Table 9 Selected references on the effect of wastewater irrigation on heavy metal(loid) phytoavailability Metal(loid)s Wastewater Plant species Observations References Cu, Cd, Pb, Zn, Fe, Mn Treated municipal wastewater Barley Rusan et al. (2007) Al, Cr, Mn, Fe Co, Ni, Cu, Zn, Cd, Pb Treated municipal wastewater Sunflower, Sorghum Zn, Cu, B, Mn, Fe, Mo Raw wastewater Cabbage Plant Cu, Zn, Fe, Mn increased with 2 years of wastewater irrigation, and then reduced with longer period. Plant Pb and Cd increased with longer periods of irrigation. Sorghum accumulated higher concentrations of Mn and Zn, whereas sunflower accumulated higher concentrations of Cr. It increased the metal content of cabbage plants. Cu, Zn, Mn, Fe Raw wastewater Increased build-up of metals in plants, high levels of Fe and Mn detected in mint and spinach, whereas Cu and Zn were highest in carrot. Mn, Zn, Cu, Pb, Ni, Cr, Cd Municipal wastewater Radish, spinach, turnip, brinjal, cauliflower, mint, coriander, carrot, lotus stem Leafy vegetable, palak Zn, Pb, Cr, Ni Water contaminated by industrial and domestic effluent Melilotus officinalis Pb, Cr, and Ni exceeded their permitted limits in roots of plants. Mn showed maximum uptake followed by other metals. Ahmed and Al-Hajri (2009) Kiziloglu et al. (2007) Arora et al. (2008) Singh and Agrawal (2010) Amiri et al. (2008) Cu Sewage sludge Fescue Pb, Cd, As, Zn, Hg Fermented pig slurry Tomato The effects of sewage sludge (SS) on Cu in solution and plants depended on the degree of weathering. In tailings with a low degree of sulfide oxidation, SS application resulted in increased solubility and shoot accumulation of Cu compared with NPK treated tailings, probably due to the DOC forming soluble complexes with Cu. All tomato samples were within the legislation limits of tested metals. Forsberg et al. (2009) Kouřimská et al. (2009) 268 Anitha Kunhikrishnan et al. be considered as an easy and cost-effective technique for reducing the levels of contamination in food crops. Addition of DOM to soils through wastewater irrigation and sludge addition can influence phytotoxic effectiveness of ions in at least two different ways. On the soil side, an increase in DOM will shift metal(loid) partitioning toward the soil solution and hence increase the content of soluble metal(loid) in solution. On the solution side, although the soluble metal(loid) increases, the free metal(loid) ion is decreased due to DOM complexation. While wastewater can act as a sink to reduce the heavy metal (loid) uptake it can also act as a source of heavy metal(loid)s (Table 9). Although metal(loid)-DOM complexes are more mobile in soils, potentially leading to groundwater contamination, these complexes have been shown to be less available for plant uptake, thereby alleviating phytotoxicity that may otherwise result from excessive metal(loid) accumulation in soils (Ashworth and Alloway, 2007; Bolan et al., 2003c; Han et al., 2001). In soils treated with wastewater and manure, only a small proportion of metal(loid)s dissolved in pore-water is likely to be available for plant uptake, the remainder is complexed with DOM (Huynh et al., 2008; Kunhikrishnan et al., 2011). Bolan et al. (2003c) studied Cu uptake in using mustard plants amended with biosolids plus various levels of Cu (0–400mgkg1 soil). They observed that adding manure compost increased the adsorption and complexation of Cu in soil, noting a significant inverse relationship between the extent of Cu adsorption and DOM in the manure-amended samples. This indicated that DOM formed soluble complexes with Cu. They reported that although soluble DOM complexes were formed, addition of biosolids was effective in reducing the phytotoxicity of Cu, especially at high levels of Cu addition. In mustard plants amended with farm dairy and piggery wastewaters, Kunhikrishnan et al. (2011) observed an increase in Cu uptake with increasing Cu input. However, at the same level of Cu application, plants took up less Cu from wastewater-amended soils than from Milli-Q water amended soils. They concluded that the presence of DOM in the wastewater sources was effective in reducing the phytotoxicity of Cu at high levels of Cu addition, indicating that the Cu-DOM complexes decreased the plant availability of Cu (Fig. 9a). Qishlaqi et al. (2008) assessed the negative impacts of wastewater irrigation on soils and crops collected from two wastewater-irrigated sites and a reference site where bore water was irrigated. The results showed that among the five heavy metal(loid)s (Ni, Pb, Cd, Zn, and Cr) studied, using untreated wastewater caused contamination of spinach and lettuce with Cd due to its high phytoavailability in topsoil and excessive accumulation of Ni and Pb in wheat. This scenario was due to the continual addition of heavy metal(loid)s through long-term wastewater application. They reported that accumulation of metal(loid)s strongly depended on the crop’s physiological properties (Liu et al., 2005) and the soil properties (Sharma et al., 2007). 269 Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil A B 40 MQ FDE PE 80 mg C-CO2 released g-1 soil h-1 Tissue Cu concentration (mg kg-1) 100 60 40 20 0 0 200 400 -1 Cu level (mg kg ) 600 MQ FDE WE PE 30 20 10 0 0 400 800 1200 Cu level (mg kg-1) Figure 9 Effect of Cu levels on (A) Cu concentration in plant tissue and (B) substrateinduced respiration in a silt loam soil in the presence of wastewater sources (PE, piggery effluent; WE, winery effluent; FDE, farm dairy effluent) and MQ water ((A): Kunhikrishnan et al., 2011; (B): Kunhikrishnan, 2011). Rusan et al. (2007) noticed that Cu, Zn, Fe, Mn increased with 2years of treated municipal wastewater irrigation in barley, and then declined with longer irrigation periods. However, Pb and Cd continued to increase with longer periods of irrigation. Several other studies report an increased uptake of heavy metal(loid)s by plants due to continuous loading of metal(loid)s to soil via irrigation (Abbas et al., 2007; Amiri et al., 2008; Kiziloglu et al., 2007; Moyo and Chimbira, 2009) (Table 9). Kiziloglu et al. (2008) compared the accumulation of heavy metal(loid)s (Fe, Cu, Mn, Zn, Pb, Ni, Cd) in cauliflower and cabbage species irrigated with either untreated or primarytreated wastewater. Metal(loid)s in vegetables irrigated with untreated wastewater were higher than those irrigated with primary-treated wastewater. 5.2.2. Microbial and earthworm availability As in the case of phytoavailability, the microbial availability of metal(loid)s is largely controlled by the activity of free ionic species in soil solution. Bolan et al. (2003a) observed the concentration of total Cu required to cause 50% reduction in basal respiration (microbial toxicity—MT50) was lower for CuSO4 (297mg Cu kg1) than for the dairy pond sludge-Cu (783mg Cu kg1), inferring that sludge-borne Cu was less detrimental to microbial activity than inorganic CuSO4. However, when the respiration value was plotted against the concentration of free ionic Cu2þ, a single smooth curve was obtained for both CuSO4 and sludge-Cu, and the MT50 value was found to be 18.37mgkg1. This indicates that the difference in the effect on 270 Anitha Kunhikrishnan et al. respiration between the two Cu sources (i.e., organic vs. inorganic) is due to the difference in bioavailable Cu content in soil. Soil microbial activity as measured by respiration and microbial biomass carbon was monitored by Kunhikrishnan (2011) following application of various levels of Cu (0–1000mgkg1), added as copper nitrate-spiked Milli-Q water, farm dairy, piggery, and winery wastewaters. The effect of Cu on soil microbial activity varied between Milli-Q water and wastewater sources and was attributed to the difference in the concentration of DOM. Metabolic quotient values were lower in soils in the presence of wastewater than in the Milli-Q water. The results indicated that wastewater sources decreased the inhibitory effect of Cu on microbial activity and suggested that it could be attributed to the formation of Cu-DOM complexes (Fig. 9B). Earthworms are also negatively influenced by the presence of heavy metal (loid)s in wastewater-irrigated soils. The bioaccumulation, however, depends on factors such as type and form of metal(loid) and concentration (Heikens et al., 2001; Hobbelen et al., 2006; Nahmani et al., 2007; Spurgeon et al., 2006), soil type and characteristics (Hendrickx et al., 2004; Hobbelen et al., 2006; Janssen et al., 1997; Kizilkaya, 2005; Spurgeon et al., 2006), test species (Heikens et al., 2001; Hendrickx et al., 2004; Nahmani et al., 2007), temperature (Olchawa et al., 2006), and exposure duration (Nahmani et al., 2007). Field observations have demonstrated that Cu is detrimental to lumbricid earthworms (Niklas and Kennel, 1978; van Rhee, 1975). This is supported by laboratory studies, which showed that the toxicity of Cu to earthworms is influenced by the pH and OM of the soil (Ma, 1984; Streit, 1984; Streit and Jaeggy, 1983). Aporrectodea tuberculata (Beyer et al., 1987) and Aporrectodea caliginosa (Perämäki et al., 1992) have been found to accumulate high Cd in acidic soils. This is largely related to the fact that most of the heavy metal(loid)s that accumulate in an earthworm’s body originate from pools of dissolved metal(loid)s which are bioavailable in the soil pores of acidic soils (Herms and Brummer, 1984). Kunhikrishnan (2011) examined the bioavailability of Cu to earthworms in the presence of farm dairy, piggery, and winery wastewaters varying in DOM. Bioavailability of Cu to earthworms as measured by mortality and avoidance test was monitored at various levels of Cu (0–1000mgkg1), added as copper nitrate-spiked Milli-Q water and wastewater sources. The results indicated that the wastewater sources decreased the inhibitory effect of Cu on the earthworm toxicity due to the formation of Cu-DOM complexes which are not readily available for uptake (Fig. 10). Metal(loid) concentrations of earthworms depended on CaCl2-extractable free Cu2þ concentrations in the soil. Kunhikrishnan (2011) also observed that the earthworms clearly avoided soils with high levels of Cu concentrations. Although DOM plays a protective role in reducing metal(loid) toxicity to earthworms, evidence suggests that earthworms play a humifying role in the soil because humic acids were detected in earthworm-worked soil that were not present in the non-humified starting material (Businelli et al., 271 Cu concentration in earthworms (mg kg–1) Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 70 60 50 40 30 20 10 0 0 100 500 MQ 0 100 500 FDE 0 100 500 WE 0 100 500 PE Figure 10 Effect of wastewater irrigation on Cu concentration in earthworms in a silt loam soil (PE, piggery effluent; WE, winery effluent; FDE, farm dairy effluent; Kunhikrishnan, 2011). 1984). Humic acids are known to transform the availability of metal(loid)s to plants by forming organometal(loid) complexes (Evangelou et al., 2004; Halim et al., 2003). Some authors suggest that increased uptake of heavy metal(loid)s by plants due to earthworm activity may be a direct result of metal(loid)-chelating organic materials released by earthworms forming organometal(loid) complexes (Currie et al., 2005; Udovic et al., 2007; Wang et al., 2006). A significant link has been found between the DOM increase in soils by earthworms Eisenia fetida and the concentration of water extractable metal(loid)s (Zn, Cu, Cr, Cd, Co, Ni, and Pb) (Wen et al., 2004). An increase in DOM in soil has also been noted in one study reporting that the presence of earthworms Metaphire guillelmi increased the availability of Cu to plants (Dandan et al., 2007). 6. Conclusions and Research Needs Growing population, increased urbanization, improved living conditions, and economic development have led to a considerable increase in the volume of wastewater generated by domestic, industrial, and commercial practices (Asano et al., 2007; Lazarova and Bahri, 2005; Qadir et al., 2010). Although water quality management is a high priority and a major concern for developing countries, most do not have sufficient resources to treat wastewater. Therefore, wastewater in a partially treated, diluted, or untreated 272 Anitha Kunhikrishnan et al. form is diverted and used by urban and peri-urban farmers to grow a range of crops (Ensink et al., 2002; Murtaza et al., 2010). Farmers consider wastewater to be a reliable or sometimes the only water source available for irrigation throughout the year and it often negates the need for fertilizer application since it provides a source of nutrients. Similarly, the use of treated wastewater for both agricultural production and environmental protection has increased in recent years in several continents including Australia, Europe, and North America (Qadir et al., 2007; US EPA, 2004). Like the supply of nutrients and OM through wastewater irrigation, it also contains different types and levels of undesirable constituents depending on the source and level of its treatment. On the positive side, OM added through wastewater improves soil structure, enhances charge characteristics of irrigated soils, such as CEC, which may retain undesirable metal(loid) ions rendering them less available for plants, and acts as a storehouse of essential nutrients for crop growth. On the negative side, heavy metal(loid) inputs to soils via wastewater irrigation are incommodious because, once accumulated, it is difficult to remove them. This situation may subsequently lead to toxicity-related issues in plants grown on contaminated soils, pose potential harm to people and animals who may consume contaminated crops and they can be transported from soils to groundwater or surface water, thereby rendering the water hazardous for other uses (Murtaza et al., 2010). Most wastewater sources are rich in DOM which influences the biological transformation processes of heavy metal(loid)s including their mobility and bioavailability. The transport and bioavailability of heavy metal(loid)s can be strongly influenced by forming soluble and insoluble complexes with DOM. Such interactions can alter the chemical speciation of the heavy metal(loid)s modifying their affinity for sorptive surfaces in the soil matrix or their uptake, accumulation, and eventual toxicity to organisms (Arnold et al., 2010; Boyd et al., 2005). While the insoluble complexes are not available to plants and other soil organisms, the question arises whether the soluble heavy metal(loid) complexes in wastewater become bioavailable or not. Anodic stripping voltammetry measurements and other speciation techniques have indicated that only a small percentage of the total dissolved heavy metal(loid)s exist as free ions and the remainder appears to be complexed with DOM. More research into this area is required to unravel the stability of such complexes, how they affect soil organisms and plants and long-term effects of application of DOM-enriched wastewater. Given the current knowledge on the influence of wastewater in the (im) mobilization and bioavailability of metal(loid)s in contaminated soils, the following research areas could be pursued: Long-term stability and biogeochemistry of metal(loid)s immobilized by wastewater sources. Influence of wastewater sources on rhizosphere biochemistry in relation to metal(loid) dynamics. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 273 Long-term leaching studies examining groundwater contamination through the movement of a wide range of chemical pollutants in wastewater, especially in the case of untreated industrial effluents. Influence of wastewater on the redox reactions of metal(loid)s such as Cr, As, and Hg in relation to their speciation, mobility, and bioavailability. Variation in wastewater-derived DOM composition and concentration can have a diverse effect on metal(loid) speciation in soil. Therefore, characterization of DOM, employing molecular weight determination, and fractionation is necessary in order to understand the influence of metal(loid)-DOM complexation on bioavailability and toxicity of heavy metal(loid)s. Although wastewater-borne metal(loid)s are reported to be less toxic to soil microorganisms, long-term studies are required to understand their dynamics in soils. In addition to the accretion of salts and nutrients, under certain conditions wastewater irrigation has the potential to translocate pathogenic bacteria and viruses to groundwater. It is therefore essential that other control options should be continued in parallel with ongoing efforts to identify key wastewater pollutants and suitable techniques for their treatment. Pragmatic approaches are required to protect water quality and ensure that wastewater is used in a sustainable way. Risk assessment conducted prior to wastewater irrigation is highly recommended to enable the safe use of wastewater for landscape and agricultural irrigation. There are several other opportunities for improving wastewater management through guidelines and policies, which would reduce potential environment and public health risk. For instance, governments should implement an integrated water management approach, promote public participation, disseminate existing knowledge, generate new knowledge, and monitor and administer imposed standards. REFERENCES AATSE (Australian Academy of Technological Sciences and Engineering). (2004). Water Recycling in Australia. AATSE, Victoria, Australia. Abaidoo, R., Keraita, B., Drechsel, P., Dissanayake, P., and Maxwell, A. (2009). Soil and crop contamination through wastewater irrigation and options for risk reduction in developing countries. In “Soil Biology and Agriculture in the Tropics” (P. Dion, Ed.). Springer-Verlag, Heidelberg. Abbas, S. T., Sarfraz, M., Mehdi, S. M., Hassan, G., and Obaid-Ur-Rehman (2007). Trace elements accumulation in soil and rice plants irrigated with the contaminated water. Soil Till. Res. 94, 503–509. Abedi-Koupai, J., Mostafazadeh-Fard, B., Afyuni, M., and Bagheri, M. R. (2006). Effect of treated wastewater on soil chemical and physical properties in an arid region. Plant Soil Environ. 52, 335–344. 274 Anitha Kunhikrishnan et al. ABS. (2006). Australian Bureau of Statistics, 4610.0-Water Account: 2004-05. Australian Commonwealth Government, Canberra, Australia. Adriano, D. C. (2001). Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability and Risks of Metals. 2nd edn. Springer, New York. Adriano, D. C., Wenzel, W., Vangronsveld, J., and Bolan, N. S. (2004). Role of assisted natural remediation in environmental cleanup. Geoderma 122, 121–142. Afonso, M. D., and Bórquez, R. (2003). Nanofiltration of wastewaters from the fish meal industry. Desalination 151, 131–138. Agassi, M., Shainberg, I., and Morin, J. (1981). Effect of electrolyte concentration and soil sodicity on infiltration rate and crust formation. Soil Sci. Soc. Am. J. 48, 848–851. Ahmed, T. A., and Al-Hajri, H. H. (2009). Effects of Treated Municipal Wastewater and Sea Water Irrigation on Soil and Plant Characteristics. Int. J. Environ. Res. 3, 503–510. Ajwa, H. A., Banuelos, G. S., and Mayland, H. F. (1998). Selenium uptake by plants from soils amended with inorganic and organic materials. J. Environ. Qual. 27, 1218–1227. Alexander, M. (1999). Biodegradation and Bioremediation. 2nd edn. Academic Press, San Diego, CA. Alloway, B. J. (1990). Heavy Metals in Soils. John Wiley and Sons, Inc, New York. Alloway, B. J. (1995). Soil processes and the behavior of heavy metals. In “Heavy Metals in Soils” (B. J. Alloway, Ed.), pp. 11–37. Blackie Academic and Professional, London. Alloway, B. J. (2004). Zinc in Soils and Crop Nutrition. International Zinc Association, Brussels, p 130. Alvarez-Bernal, D., Contreras-Ramos, S. M., Trujillo-Tapia, N., Olalde-Portugal, V., Frı´ as-Herna´ndez, J. T., and Dendooven, L. (2006). Effects of tanneries wastewater on chemical and biological soil characteristics. Appl. Soil Ecol. 33, 269–277. Al-Wabel, M. A., Heil, D. M., Westfall, D. G., and Barbarick, K. A. (2002). Solution chemistry influence on metal mobility in biosolids-amended soils. J. Environ. Qual. 31, 1157–1165. Amery, F., Degryse, F., Van Moorleghem, C., Duyck, M., and Smolders, E. (2010). The dissociation kinetics of Cu-dissolved organic matter complexes from soil and soil amendments. Anal. Chim. Acta 670, 24–32. Amiel, J. A., Magaritz, M., Ronen, D., and Lindstrand, O. (1990). Dissolved organic carbon in the unsaturated zone under land irrigated by wastewater effluent. Res. J. WPCF 62, 861–866. Amiri, S. S., Maralian, H., and Aghabarati, A. (2008). Heavy metal accumulation in Melilotus officinalis under crown Olea europaea L. forest irrigated with wastewater. Afr. J. Biotechnol. 7, 3912–3916. Anderson, J. (2003). The environmental benefits of water recycling and reuse. Water Sci. Technol. 3, 1–10. Anderson, L. C. D., and Bruland, K. W. (1991). Biogeochemistry of arsenic in natural waters: The importance of methylated species. Environ. Sci. Technol. 25, 420–427. Angin, I., Yaganoglu, A. V., and Turan, M. (2005). Effects of long-term wastewater irrigation on soil properties. J. Sustain. Agric. 26, 31–42. Antanaitis, D., and Antanaitis, A. (2004). Migration of heavy metals in soil and their concentration in sewage and sewage sludge. Ekologija 1, 42–45. Antoniadis, V., and Alloway, B. J. (2002). The role of dissolved organic carbon in the mobility of Cd, Ni, and Zn in sewage sludge-amended soils. Commun. Soil Sci. Plant Anal. 33, 273–286. Antoniadis, V., and McKinley, J. (2003). Measuring heavy metal migration rates in a lowpermeability soil. Environ. Chem. Lett. 1, 103–106. ANZECC & ARMCANZ. (2000). Australian and New Zealand Environment and Conservation Council & Agriculture and Resources Management Council of Australia and New Zealand. Australian and New Zealand Guidelines for Fresh and Marine Water Quality. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 275 Arienzo, M., Christen, E. W., Quayle, W., and Kumar, A. (2009). A review of the fate of potassium in the soil–plant system after land application of wastewaters. J. Hazard. Mater. 164, 415–422. Arnold, W. R., Cotsifas, J. S., Ogle, R. S., DePalma, S. G. S., and Smith, D. S. (2010). A comparison of the copper sensitivity of six invertebrate species in ambient salt water of varying dissolved organic matter concentrations. Environ. Toxicol. Chem. 29, 311–319. Arora, M., Kiran, B., Rani, S., Rani, A., Kaur, B., and Mittal, N. (2008). Heavy metal accumulation in vegetables irrigated with water from different sources. Food Chem. 111, 811–815. Aryal, R., Vigneswaran, S., Kandasamy, J., and Naidu, R. (2010). Urban stormwater quality and treatment. Korean J. Chem. Eng. 27, 1343–1359. Asano, T., and Cotruvo, J. A. (2004). Groundwater recharge with reclaimed municipal wastewater: Health and regulatory considerations. Water Res. 38, 1941–1951. Asano, T., Burton, F. L., Leverenz, H., Tsuchihashi, R., and Tchobanoglous, G. (2007). Water Reuse: Issues, Technologies, and Applications. McGraw-Hill, New York. Ashworth, D. J., and Alloway, B. J. (2004). Soil mobility of sewage sludge-derived dissolved organic matter, copper, nickel and zinc. Environ. Pollut. 127, 137–144. Ashworth, D. J., and Alloway, B. J. (2007). Complexation of copper by sewage sludgederived dissolved organic matter: Effects on soil sorption behaviour and plant uptake. Water Air Soil Pollut. 182, 187–196. Ashworth, D. J., and Alloway, B. J. (2008). Influence of dissolved organic matter on the solubility of heavy metals in sewage-sludge-amended soils. Commun. Soil Sci. Plant Anal. 39, 538–550. Assadian, N. W., and Margez, J. P. F. (2006). Bio-accessibility of Trace Metals Using Chemical Fractionation and In Vitro Extraction Methods. Lineae Terrarum Internacional Border Conference, El Paso, TX. Assouline, S., Ben-Hur, M., Chen, Y. L., Graber, E. R., Levy, G., Russo, D., and Tarchitzky, J. (2002). Effects of marginal water for irrigation on quality of soil and water resources. http://luna.tau.ac.il/_glowa/Munich/Poster_ARO.pdf. Ayers, R. S., and Westcot, D. W. (1985). Water Quality for Agriculture. Food and Agriculture Organization of the United Nations, Rome, Italy. Baham, J., and Sposito, G. (1994). Adsorption of dissolved organic carbon extracted from sewage sludge on montmorillonite and kaolinite in the presence of metal ions. J. Environ. Qual. 23, 147–153. Balks, M. R., Bond, W. J., and Smith, C. J. (1996). Effects of sodium accumulation on soil physical properties under an effluent-irrigated plantation. New Zealand Land Treatment Collective Proceedings of Technical Session. Aust. J. Soil Res. 14, 195–200. Ball, P. R., and Field, T. R. O. (1982). Responses to nitrogen as affected by pasture characteristics, season and grazing management. In “Nitrogen Fertilizer in New Zealand Agriculture” (P. B. Lynch, Ed.), pp. 45–64. New Zealand Institute of Agricultural Science, Auckland, New Zealand. Balota, E. L., Machineski, O., and Truber, P. V. (2010). Soil carbon and nitrogen mineralization caused by pig slurry application under different soil tillage systems. Pesq. agropec. bras., Brası´lia 45, 515–521. Banks, M. K., Schwab, A. P., and Henderson, C. (2006). Leaching and reduction of chromium in soil as affected by soil organic content and plants. Chemosphere 62, 255–264. Barkle, G. F., Stenger, R., Singleton, P., and Painter, D. J. (2000). Effect of regular irrigation with dairy farm effluent on soil organic matter and soil microbial biomass. Aust. J. Soil Res. 38, 1087–1097. Barman, S. C., Kisku, G. C., Salve, P. R., Misra, D., Sahu, R. K., Ramteke, P. W., and Bhargava, S. K. (2001). Assessment of industrial effluent and its impact on soil and plants. J. Environ. Biol. 22, 251–256. 276 Anitha Kunhikrishnan et al. Barrett, M. S., Zuber, R. D., Collins, E. R., Malina, J. F., Charbeneau, R. J., and Ward, G. H. (1993). A review and evaluation of literature pertaining to the quantity and control of pollution from highway runoff and construction. Center for Research in Water Resources, Bureau of Engineering Research, University of Texas, Austin. CRWR. 239. Bashir, F., Shafique, T., Kashmiri, M. A., and Tariq, M. (2007). Contents and fractionation of heavy metals in soils irrigated with sewage effluents. J. Chem. Soc. Pak. 29, 94–97. Basta, N. T., and Gradwohl, R. (2000). Estimation of Cd, Pb, and Zn bioavailability in smelter contaminated soils by a sequential extraction procedure. J. Soil. Contam. 9, 149–164. Beckett, P. H. T. (1989). The use of extractants in studies on trace metals in soils, sewage sludges and sludge-treated soils. Adv. Soil Sci. 9, 143–179. Beckett, P. H. T., Warr, E., and Brindley, P. (1983a). Changes in the extractabilities of the heavy metals in water-logged sludge-treated soils. Water Pollut. Control 82, 107–113. Beckett, P. H. T., Warr, E., and Davis, R. D. (1983b). Cu and Zn in soils treated with sewage sludge—Their extractability to reagents compared with their availability to plants. Plant Soil 70, 3–14. Behbahaninia, A., Mirbagheri, S. A., and Javid, A. H. (2008). Heavy metals transport in the soil profiles under the application of sludge and wastewater. World Academy Sci. Eng. Technol. 43. Beyer, W., Hensler, G., and Moore, J. (1987). Relation of pH and other soil variables to concentrations of Pb, Cu, Zn, Cd, and Se in earthworms. Pedobiologia 30, 167–172. Bhandral, R., Bolan, N. S., Saggar, S., and Hedley, M. J. (2007). Nitrogen transformation and nitrous oxide emissions from various types of farm effluents. Nutr. Cycl. Agroecosys. 79, 193–208. Bhardwaj, A. K., Goldstein, D., Azenkot, A., and Levy, G. J. (2007). Irrigation with treated wastewater under two different irrigation methods: Effects on hydraulic conductivity of a clay soil. Geoderma 140, 199–206. Blume, H. P., and Horn, R. (1982). Belastung und Belastbarkeit der Berliner Rieselfelder nach einem Jahrhundert Abwasserberieselung. Z. f. Kulturtechnik u. Flurbereinigung 23, 236–248. Bolan, N. S., and Duraisamy, V. P. (2003). Role of inorganic and organic soil amendments on immobilisation and phytoavailability of heavy metals: A review involving specific case studies. Aust. J. Soil Res. 41, 533–555. Bolan, N. S., Naidu, R., Syers, J. K., and Tillman, R. W. (1999). Surface charge and solute interactions in soils. Adv. Agron. 67, 88–141. Bolan, N. S., Khan, M. A., Donaldson, D. C., Adriano, D. C., and Matthew, C. (2003a). Distribution and bioavailability of copper in a farm effluent. Sci. Total Environ. 309, 225–236. Bolan, N. S., Adriano, D. C., Mani, P., Duraisamy, A., and Arulmozhiselvan, S. (2003b). Immobilization and phytoavailability of cadmium in variable charge soils: II. Effect of lime addition. Plant Soil 250, 187–198. Bolan, N. S., Adriano, D. C., Mani, S., and Khan, A. (2003c). Adsorption, complexation, and phytoavailability of copper as influenced by organic manure. Environ. Toxicol. Chem. 22, 450–456. Bolan, N. S., Adriano, D. C., Natesan, R., and Koo, B. J. (2003d). Effects of organic amendments on the reduction and phytoavailability of chromate in mineral soil. J. Environ. Qual. 32, 120–128. Bolan, N. S., Adriano, D. C., and Naidu, R. (2003e). Role of phosphorus in (im) mobilization and bioavailability of heavy metals in the soil-plant system. Rev. Environ. Contam. Toxicol. 177, 1–44. Bolan, N. S., Adriano, D. C., and Wong, C. (2004a). Nutrient removal from farm effluents. Bioresource Technol. 94, 251–260. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 277 Bolan, N. S., Adriano, D. C., and Mahimairaja, S. (2004b). Distribution and bioavailability of trace elements in livestock and poultry manure by-products. Crit. Rev. Environ. Sci. Tech. 34, 291–338. Bolan, N. S., Horne, D. J., and Currie, L. D. (2004c). Growth and chemical composition of legume-based pasture irrigated with dairy farm effluent. N. Z. J. Agric. Res. 47, 85–93. Bolan, N. S., Ko, B. G., Anderson, C. W. N., Vogeler, I., Mahimairaja, S., and Naidu, R. (2008). Manipulating bioavailability to manage remediation of metal contaminated soils. In “Chemical Bioavailability in Terrestrial Environment” (R. Naidu, Ed.), pp. 657–678. Elsevier, Amsterdam, The Netherlands. Bolan, N. S., Laurenson, S., Luo, J., and Sukias, J. (2009). Integrated treatment of farm effluents in New Zealand’s dairy operations. Bioresource Technol. 100, 5490–5497. Bolan, N. S., Bell, K., Kunhikrishnan, A., and Chung, J. W (2011a). Irrigating horticultural crops with recycled water: An Australian perspective. J. Hort. Sci. 6, 1–20. Bolan, N. S., Adriano, D. C., Kunhikrishnan, A., James, T., McDowell, R., and Senesi, N. (2011b). Dissolved organic matter: Biogeochemistry, dynamics and environmental significance in soils. Adv. Agron. 110, 1–75. Bomke, A. A., and Lowe, L. E. (1991). Trace-element uptake by two British Columbia forages as affected by poultry manure application. Can. J. Soil Sci. 71, 305–312. Bond, W. J. (1998). Effluent irrigation—An environmental challenge for soil science. Aust. J. Soil Res. 36, 543–555. Boyd, T. J., Wolgast, D. M., Rivera-Duarte, I., Holm-Hansen, O., Hewes, C. D., Zirino, A., and Chadwick, D. B. (2005). Effects of dissolved and complexed copper on heterotrophic bacterial production in San Diego Bay. Microbial Ecol. 49, 353–366. Bratieres, K., Fletcher, T., Deletic, A., and Zinger, Y. (2008). Nutrient and sediment removal by stormwater biofilters: A large-scale design optimisation study. Water Res. 42, 3930–3940. Brink, G. E., Rowe, D. E., Sistani, K. R., and Adeli, A. (2003). Bermudagrass cultivar response to swine effluent application. Agron. J. 95, 597. Brookes, P. (1995). The use of microbial parameters in monitoring soil pollution by heavy metals. Biol. Fert. Soils 19, 269–279. Brown, R. L. (2007). Global Fresh Water Supplies in Peril. Earth Policy Institute, http:// environmental-economics.blogspot.com/2007/07/global-fresh-water-supplies-in-peril. html. Brown, G. E., and Parks, G. A. (2001). Sorption of trace elements on mineral surfaces: Modern perspectives from spectroscopic studies, and comments on sorption in the marine environment. Int. Geol. Rev. 43, 963–1073. Brown, S., Chaney, R., and Angle, J. (1997). Subsurface liming and metal movement in soils amended with lime-stabilized biosolids. J. Environ. Qual. 26, 724–732. Brumm, M. C. (1998). Sources of manure: Swine. In “Animal Waste Utilization: Effective Use of Manure as a Soil Resource” ( J. L. Hatfield and B. A. Stewart, Eds.), pp. 49–64. Ann Arbor Press, Michigan. Brzezinska, M., Tiwari, S., Stepniewska, Z., Nosalewicz, M., Bennicelli, R., and Samborska, A. (2006). Variation of enzyme activities, CO2 evolution and redox potential in an Eutric Histosol irrigated with wastewater and tap water. Biol. Fert. Soils 43, 131. Brzezińska, M., Sokołowska, Z., Alekseeva, T., Alekseev, A., Hajnos, M., and Szarlip, P. (2011). Some characteristics of organic soils irrigated with municipal wastewater. Land Degrad. Dev. 22, 586–595. Buchter, B., Davidoff, B., Amacher, M., Hinz, C., Iskandar, I., and Selim, H. (1989). Correlation of Freundlich Kd and n retention parameters with soils and elements. Soil Sci. 148, 370–381. Bünemann, E. K., Schwenke, G. D., and Van Zwieten, L. (2006). Impact of agricultural inputs on soil organisms—A review. Aust. J. Soil Res. 44, 379–406. 278 Anitha Kunhikrishnan et al. Businelli, M., Perucci, P., Patumi, M., and Giusquiani, P. (1984). Chemical composition and enzymic activity of some worm casts. Plant Soil 80, 417–422. Buzier, R., Tusseau-Vuillemin, M. H., and Mouchel, J. M. (2006). Evaluation of DGT as a metal speciation tool in wastewater. Sci. Total Environ. 358, 277–285. Camberato, J. J., Vance, E. D., and Someshwar, A. V. (1997). Composition and land application of paper manufacturing residuals. In “Agricultural Uses of By-Products and Wastes” ( J. E. Rechcigl and H. C. MaKinnon, Eds.), pp. 185–202. ACS, Washington, DC. Carmona, D. M., Cano, Á.F., and Arocena, J. M. (2008). Dissolved organic carbon and metals release in amended mine soils. Resumen Workshop Macla 10, 115–117. Carnus, J. M. (1994). Land treatment of industrial wastes. Land Treatment Collective Technical Review No. 10. Carpenter, S. R. (1998). Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecol. Appl. 8, 559. Cary, E. E., Alloway, A. W., and Olson, O. E. (1977). Control of chromium concentration in food plants. 2. Chemistry of chromium in soils and its availability to plants. J. Agric. Food Chem. 25, 305–309. Chakraborty, A. K., and Saha, K. C. (1987). Arsenical dermatosis from tube well water in West Bengal. Indian J. Med. Res. 85, 326–334. Chang, A. C., Granato, T. C., and Page, A. L. (1992). A methodology for establishing phytotoxicity criteria for chromium, copper, nickel, and zinc in agricultural land application of municipal sewage sludge. J. Environ. Qual. 21, 521–536. Chen, S. L., Sun, L., Chao, L., Zhou, Q., and Sun, T. (2009). Estimation of lead bioavailability in smelter-contaminated soils by single and sequential extraction procedure. Bull. Environ. Contam. Toxicol. 82, 43–47. Chen, Z., Zhao, Y., Zhu, Y., Yang, X., Qiao, J., Tianc, Q., and Zhang, Q. (2010). Health risks of heavy metals in sewage-irrigated soils and edible seeds in Langfang of Hebei province, China. J. Sci. Food Agric. 90, 314–320. Christensen, J. B., Botma, J. J., and Christensen, T. H. (1999). Complexation of Cu and Pb by DOC in polluted groundwater: A comparison of experimental data and predictions by computer speciation models (WHAM and MINTEQA2). Water Res. 33, 3231–3238. Church, C. D., Kleinman, P. J., Bryant, R. B., Saporito, L. S., and Allen, A. L. (2010). Occurrence of arsenic and phosphorus in ditch flow from litter-amended soils and barn areas. J. Environ. Qual. 39, 2080–2088. Cifuentes, F. R., Lindemann, W. C., and Barton, L. L. (1996). Chromium sorption and reduction in soil with implications to bioremediation. Soil Sci. 161, 233–241. Cook, F. J., Kelliher, F. M., and McMohan, S. D. (1994). Changes in infiltration and drainage during wastewater irrigation of a highly permeable soil. J. Environ. Qual. 23, 476–482. Cornu, S., Neal, C., Ambrosi, J., Whitehead, P., Neal, M., Sigolo, J., and Vachier, P. (2001). The environmental impact of heavy metals from sewage sludge in ferralsols, (Sao Paulo, Brazil). Sci. Total Environ. 271, 27–48. Crook, J. (1991). Quality criteria for reclaimed water. Water Sci. Technol. 24, 109–121. Cui, Y. J., Zhu, Y. G., Zhai, R. H., Chen, D. Y., Huang, Y. Z., Qiu, Y., and Liang, J. Z. (2004). Transfer of metals from soil to vegetables in an area near a smelter in Nanning, China. Environ. Int. 30, 785–791. Currie, M., Hodson, M. E., Arnold, R. E., and Langdon, C. J. (2005). Single versus multiple occupancy—Effects on toxicity parameters measured on Eisenia fetida in lead nitratetreated soil. Environ. Toxicol. Chem. 24, 110–116. Dandan, W., Huixin, L., Feng, H., and Xia, W. (2007). Role of earthworm–straw interactions on phytoremediation of Cu contaminated soil by ryegrass. Acta Ecol. Sin. 27, 1292–1298. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 279 Daniel, T. C., and Bouma, J. (1974). Column studies of soil clogging in slowly permeable soil as a function of effluent quality. J. Environ. Qual. 3, 321–326. Daum, K. A., and Newland, L. W. (1982). Complexing effects on behavior of some metals. In “The Handbook of Environmental Chemistry: Reactions and Processes” (O. Huntzinger, Ed.), pp. 129–140. Springer-Verlag, New York. Davis, J. A. (1984). Complexation of trace metals by adsorbed natural organic matter. Geochim. Cosmochim. Acta 48, 679–691. Davis, A. P., Hunt, W. F., Traver, R. G., and Clar, M. (2009). Bioretention technology: Overview of current practice and future needs. J. Environ. Eng. 135, 109–117. de Vries, J. (1972). Soil filtration of wastewater effluent and the mechanism of pore clogging. J. Water Pollut. 44, 565–573. Degens, B. P., Schipper, L. A., Claydon, J. J., Russell, J. M., and Yeates, G. W. (2000). Irrigation of an allophanic soil with dairy factory effluent for 22 years: Responses of nutrient storage and soil biota. Aust. J. Soil Res. 38, 25–35. del Castilho, P., Chardon, W., and Salomons, W. (1993). Influence of cattle-manure slurry application on the solubility of cadmium, copper, and zinc in a manured acidic, loamysand oil. J. Environ. Qual. 22, 689–697. Department of Planning and Local Government (2009). Water Sensitive Urban Design Technical Manual for the Greater Adelaide Region. Government of South Australia, Adelaide, SA. Deriziotis, P. G. (2004). Substance and perceptions of environmental impacts of dioxin emissions. M.S. thesis, Earth Resources Engineering, Columbia University. Dhillon, K. S., and Dhillon, D. K. (1990). Selenium toxicity in soil-plant-animal system—A case study. In “Transactions of 14th International Congress of Soil Science, Comm. IV”, Vol VI, pp. 300–305. Dijkstra, J. J., Meeussen, J. C. L., and Comans, R. N. J. (2004). Leaching of heavy metals from contaminated soils: An experimental and modeling study. Environ. Sci. Technol. 38, 4390–4395. Dillon, P. (2000). Water reuse in Australia: Current status, projections and research. In “Proc. Water Recycling Australia 2000” (P. J. Dillon, Ed.), pp. 99–104. CSIRO Land & Water, Adelaide, Australia. Doblin, M. A., Baines, S. B., Cutter, L. S., and Cutter, G. A. (2006). Sources and biogeochemical cycling of particulate selenium in the San Francisco Bay estuary. Estuar. Coast. Shelf S. 67, 681–694. Droste, R. L. (1997). Theory and Practice of Water and Wastewater Treatment. John Wiley and Sons, New York, USA. Dudka, S. A., and Chlopecka, A. (1990). Effect of solid-phase speciation on metal mobility and phytoavailability in sludge-amended soil. Water Air Soil Pollut. 51, 153–160. Eary, L. E., and Rai, D. (1991). Chromate reduction by subsurface soils under acidic conditions. Soil Sci. Soc. Am. J. 55, 676–683. Elliott, H. A., and Denneny, C. M. (1982). Soil adsorption of cadmium from solutions containing organic ligands. J. Environ. Qual. 11, 658–663. Elovitz, M. S., and Fish, W. (1995). Redox interactions of Cr(VI) and substituted phenols: Products and mechanisms. Environ. Sci. Technol. 29, 1933–1943. Ensink, J. H. J., van der Hoek, W., Matsuno, Y., Munir, S., and Aslam, M. R. (2002). Use of untreated wastewater in peri-urban agriculture in Pakistan: Risks and opportunities. Research Report 64, International Water Management Institute (IWMI), Colombo, p.22. Ensink, H. H., Mehmood, T., Vand der Hoeck, W., Raschid-Sally, L., and Amerasinghe, F. P. (2004). A nation-wide assessment of wastewater use in Pakistan: An obscure activity or a vitally important one? Water Policy 6, 197–206. Eriksson, E., and Donner, E. (2009). Metals in greywater: Sources, presence and removal efficiencies. Desalination 248, 271–278. 280 Anitha Kunhikrishnan et al. Ermakov, I., Koptsik, S., Koptsik, G., and Lofts, S. (2007). Transport and accumulation of heavy metals in undisturbed soil columns. Global NEST J. 9, 187–194. Evangelou, M. W. H., Daghan, H., and Schaeffer, A. (2004). The influence of humic acids on the phytoextraction of cadmium from soil. Chemosphere 57, 207–213. Evers, G. W. (2002). Ryegrass-Bermuda grass production and nutrient uptake when combining nitrogen fertilizer with broiler litter. Agron. J. 94, 905–910. Falkiner, R. A., and Smith, C. J. (1997). Changes in soil chemistry in effluent-irrigated Pinus radiata and Eucalyptus grandis plantations. Aust. J. Soil. Res. 35, 131–147. FAO AQUASTAT Database. Global information system on water and agriculture. http:// www.fao.org/nr/water/aquastat/main/index.stm. Faryal, R., Tahir, F., and Hameed, A. (2007). Effect of wastewater irrigation on soil along with its micro and macro flora. Pakistan J. Bot. 39, 193–204. Fedotov, P. S., and Mirò, M. (2008). Fractionation and mobility of trace elements in soils and sediments. In “Biophysico-Chemical Processes of Heavy Metals and Metalloids in Soil Environments” (A. Violante, P. M. Huang, and G. M. Gadd, Eds.), WileyJupac Series, Vol. 1, pp. 467–520. John Wiley & Sons, Hoboken, NY. Feigin, A., Ravina, I., and Shalhevet, J. (1991). Irrigation with Treated Sewage Effluent: Management for Environmental Protection. Springer-Verlag, Berlin. pp. 224. Filip, Z., Kanazawa, S., and Berthelin, J. (1999). Characterization of effects of a long-term wastewater irrigation on soil quality by microbiological and biochemical parameters. J. Plant Nutr. Soil Sci. 162, 409–413. Filip, Z., Kanazawa, S., and Berthelin, J. (2000). Distribution of microorganisms, biomass ATP, and enzyme activities in organic and mineral particles of a long-term wastewater irrigated soil. J. Plant Nutr. Soil Sci. 163, 143–150. Fine, P., Hass, A., Prost, R., and Atzmon, N. (2002). Organic carbon leaching from effluent irrigated lysimeters as affected by residence time. Soil Sci. Soc. Am. J. 66, 1531–1539. Flores, L., Blas, G., Hernández, G., and Alcalá, R. (1997). Distribution and sequential extraction of some heavy metals from soils irrigated with wastewater from Mexico City. Water Air Soil Pollut. 98, 105–117. Forsberg, L. S., Kleja, D. B., Greger, M., and Ledin, S. (2009). Effects of sewage sludge on solution chemistry and plant uptake of Cu in sulphide mine tailings at different weathering stages. Appl. Geochem. 24, 475–482. Frankenberger, W. T., and Arshad, M. (2001). Bioremediation of selenium-contaminated sediments and water. Biofactors 14, 241–254. Frankenberger, W. T., and Losi, M. E. (1995). Application of bioremediation in the cleanup of heavy elements and metalloids. In “Bioremediation: Science and applications” (H. D. Skipper, and R. F. Turco, Eds.), pp. 173–210. Soil Science Special Publication No. 43, Madison, WI: Soil Science Society of America. Frenkel, H., Levy, G. J., and Fey, M. V. (1992). Organic and inorganic anion effects on reference and soil clay critical flocculation concentration. Soil Sci. Soc. Am. J. 56, 1762–1766. Friedel, J. K., Langer, T., Siebe, C., and Stahr, K. (2000). Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico. Biol. Fert. Soils 31, 414–421. Fujita, M., Ike, M., Kashiwa, M., Hashimoto, R., and Soda, S. (2002). Laboratory-scale continuous reactor for soluble selenium removal using selenite-reducing bacterium. Bacillus sp. SF-1. Biotechnol. Bioeng. 80, 755–761. Gadd, G. M. (2004). Microbial influence on metal mobility and application for bioremediation. Geoderma 122, 109–119. Gao, S. D., and Tanji, K. K. (1995). Model for biomethylation and volatilization of selenium from agricultural evaporation ponds. J. Environ. Qual. 24, 191–197. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 281 Garbarino, J. R., Bednar, A. J., Rutherford, D. W., Beyer, R. S., and Weshaw, R. L. (2003). Environmental fate of roxarsone in poultry litter. I. Degradation of roxarsone during composting. Environ. Sci. Technol. 15, 1509–1514. Gbondo-Tugbawa, S. S., McAlear, J. A., Driscoll, C. T., and Sharpe, C. W. (2010). Total and methyl mercury transformations and mass loadings within a wastewater treatment plant and the impact of the effluent discharge to an alkaline hypereutrophic lake. Water Res. 44, 2863–2875. Gergov, M., Priha, M., Talka, E., Valttila, O., Kangas, A., and Kukkonen, K. (1988). Chlorinated organic compounds in effluent treatment at kraft mills. Tappi J. 71, 175–184. Ghadiri, H., Hussein, J., and Rose, C. W. (2007). A study of the interactions between salinity, soil erosion, and pollutant transport on three Queensland soils. Aust. J. Soil Res. 45, 404–413. Gharaibeh, M. A., Eltaif, N. I., and Al-Abdullah, B. (2007). Impact of field application of treated wastewater on hydraulic properties of vertisols. Water Air Soil Pollut. 184, 347–353. Giacomini, S. J., Aita, C., Jantalia, C. P., and Urquiaga, S. (2009). Aproveitamento pelo milho do nitrogênio amoniacal de dejetos lı́quidos de suı́nos em plantio direto e preparo reduzido do solo. Pesquisa Agropecuária Brasileira 44, 761–768. Gove, L., Cooke, C. M., Nicholson, F. A., and Beck, A. J. (2001). Movement of water and heavy metals (Zn, Cu, Pb and Ni) through sand and sandy loam amended with biosolids under steady-state hydrological conditions. Bioresource Technol. 78, 171–179. Goyal, S., Chander, K., and Kapoor, K. (1995). Effect of distillery wastewater application on soil microbiological properties and plant growth. Environ. Ecol. 13, 89–93. Grant, C., Flaten, D., Tenuta, M., Gao, X., Malhi, S., and Gowalko, E. (2010). Impact of long-term application of phosphate fertilizer on cadmium accumulation in crops. In “19th World Congress of Soil Science Conference Proceedings,” Brisbane, Australia. Guggenberger, G., and Kaiser, K. (2003). Dissolved organic matter in soil: Challenging the paradigm of sorptive preservation. Geoderma 113, 293–310. Gupta, A. K., and Sinha, S. (2007). Assessment of single extraction methods for the prediction of bioavailability of metals to Brassica juncea L. Czern. (var. Vaibhav) grown on tannery waste contaminated soil. J. Hazard. Mater. 149, 144–150. Gustin, M. S., Chavan, P. V., Dennett, K. E., Donaldson, S., Marchand, E., and Fernanadez, G. (2006). Use of constructed wetlands with four different experimental designs to assess the potential for methyl and total Hg outputs. Appl. Geochem. 21, 2023–2035. Gwenzi, W., and Munondo, R. (2008). Long-term impacts of pasture irrigation with treated sewage effluent on nutrient status of a sandy soil in Zimbabwe. Nutr. Cycl. Agroecosyst. 82, 197–207. Haberhauer, G., Temmel, B., and Gerzabek, M. H. (2002). Influence of dissolved humic substances on the leaching of MCPA in a soil column experiment. Chemosphere 46, 495–499. Halim, M., Conte, P., and Piccolo, A. (2003). Potential availability of heavy metals to phytoextraction from contaminated soils induced by exogenous humic substances. Chemosphere 52, 265–275. Halliwell, D. J., Barlow, K. M., and Nash, D. M. (2001). A review of the effects of wastewater sodium on soil properties and their implications for irrigation systems. Aust. J. Soil Res. 39, 1259–1267. Hamilton, A. J., Stagnitti, F., Xiong, X., Kreidl, S. L., Benke, K. K., and Maher, P. (2007). Wastewater irrigation: The state of play. Vadose Zone J. 6, 823–840. Han, F., Kingery, W., and Selim, H. (2001). Accumulation, redistribution, transport and bioavailability of heavy metals in waste-amended soils. In “Trace Elements in Soil: Bioavailability, Flux, and Transfer” (I. K. Iskander and M. B. Kirkham, Eds.), pp. 141–168. CRC Press, Boca Raton, FL, USA. 282 Anitha Kunhikrishnan et al. Hansen, D., Duda, P. J., Zayed, A., and Terry, N. (1998). Selenium removal by contrcuted wetlands: Role of biological volatilization. Environ. Sci. Technol. 32, 591–597. Hao, X. Z., Zhou, D. M., Chen, H. M., and Dong, Y. H. (2008). Leaching of copper and zinc in a garden soil receiving poultry and livestock manures from intensive farming. Pedosphere 18, 69–76. Harmsen, J. (2007). Measuring bioavailability: From a scientific approach to standard methods. J. Environ. Qual. 36, 1420–1428. Harron, W. R. A., Webster, G. R., and Cairns, R. R. (1983). Relationship between exchangeable sodium and sodium adsorption ratio in a Solonetzic soil association. Can. J. Soil Sci. 63, 461–467. Hart, P. B. S., and Speir, T. W. (1992). Agricultural and industrial effluents and wastes as fertilizers and soil amendments in New Zealand. In “The Use of Wastes and Byproducts as Fertilizers and Soil Amendments for Pastures and Crops” (P.E.H. Gregg, and L.D. Currie, Eds.), Occasional Report No:6, pp. 69–90. Fertilizer and Lime Research Centre, Massey University, Palmerston North, NZ. Harter, R. D., and Naidu, R. (1995). Role of organic-metal complexation in metal sorption by soils. Adv. Agron. 55, 219–263. Haruna, A., Uzairu, A., and Harrison, G. F. S. (2009). Determination of levels of trace metals in sewage vegetation and sludge in Zaria city, Nigeria. EJEAFChe 8, 500–511. Hassanli, A. M., Javan, M., and Saadat, Y. (2008). Reuse of municipal effluent with drip irrigation and evaluation the effect on soil properties in a semi-arid area. Environ. Monit. Assess. 144, 151–158. Hatt, B. E., Fletcher, T. D., and Deletic, A. (2009). Hydrologic and pollutant removal performance of stormwater biofiltration systems at the field scale. J. Hydrol. 365, 310–321. Haynes, R. J., Murtaza, G., and Naidu, R. (2009). Inorganic and organic constituents and contaminants in biosolids: Implications for land application. Adv. Agron. 104, 165–267. He, Q. B., and Singh, B. R. (1994). Crop uptake of cadmium from phosphorus fertilisers. I. Yield and cadmium content. Water Air Soil Pollut. 74, 251–265. Heikens, A., Peijnenburg, W., and Hendriks, A. (2001). Bioaccumulation of heavy metals in terrestrial invertebrates. Environ. Pollut. 113, 385–393. Henderson, C., Greenway, M., and Phillips, I. (2007). Removal of dissolved nitrogen, phosphorus and carbon from stormwater by biofiltration mesocosms. Water Sci. Technol. 55, 183–191. Hendrickx, F., Maelfait, J. P., Bogaert, N., Tojal, C., Du Laing, G., Tack, F. M. G., and Verloo, M. G. (2004). The importance of biological factors affecting trace metal concentration as revealed from accumulation patterns in co-occurring terrestrial invertebrates. Environ. Pollut. 127, 335–341. Herms, U., and Brummer, G. (1984). Einflussgrößen der Schwermetalllöslichkeit und bindung in Bö-den. Z. Pflanzenernähr. Bodenkde. 147, 400–424. Herre, A., Siebe, C., and Kaupenjohann, M. (2004). Effect of irrigation water quality on organic matter, Cd and Cu mobility in soils of central Mexico. Water Sci. Technol. 50, 277–284. Hesterberg, D. (1998). Biogeochemical cycles and processes leading to changes in mobility of chemicals in soils. Agric. Ecosyst. Environ. 67, 121–133. Hesterberg, D., Bril, J., and del Castilho, P. (1993). Thermodynamic modeling of zinc, cadmium, and copper solubility in manure, acidic Loamy-sand topsoil. J. Environ. Qual. 22, 1100–1106. Higgins, T. E., Halloran, A. R., Dobbins, M. E., and Pittignano, A. J. (1998). In situ reduction of hexavalent chromium in alkaline soils enriched with chromites ore processing residue. J. Air Waste Manage. Assoc. 48, 100–1106. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 283 Hobbelen, P., Koolhaas, J., and Van Gestel, C. (2006). Bioaccumulation of heavy metals in the earthworms Lumbricus rubellus and Aporrectodea caliginosa in relation to total and available metal concentrations in field soils. Environ. Pollut. 144, 639–646. Hsu, J., and Lo, S. (2000). Effect of dissolved organic carbon on leaching of copper and zinc from swine manure compost. Water Sci. Technol. 42, 247–252. Huang, B., Kuo, S., and Bembenek, R. (2003). Cadmium uptake by lettuce from soil amended with phosphorus and trace element fertilizers. Water Air Soil Pollut. 147, 109–127. Huang, B., Kuo, S., and Bembenek, R. (2005). Availability to lettuce of arsenic and lead from trace element fertilizers in soil. Water Air Soil Pollut. 164, 223–239. Hussain, I., Raschid, L. M., Hanjra, A., Marikar, F., and van der Hoek, W. (2002). Wastewater use in agriculture: Review of impacts and methodological issues in valuing impacts.Working Paper 37 International Water Management Institute, Colombo, Sri Lanka. Huynh, T., Laidlaw, W., Singh, B., Gregory, D., and Baker, A. (2008). Effects of phytoextraction on heavy metal concentrations and pH of pore-water of biosolids determined using an in situ sampling technique. Environ. Pollut. 156, 874–882. Hyun, H. N., Chang, A., Parker, D., and Page, A. (1998). Cadmium solubility and phytoavailability in sludge-treated soil: Effects of soil organic carbon. J. Environ. Qual. 27, 329–334. Illera, V., Walter, I., Souza, P., and Cala, V. (2000). Short-term effects of biosolid and municipal solid waste applications on heavy metals distribution in a degraded soil under a semi-arid environment. Sci. Total Environ. 255, 29–44. Jackson, B. P., and Miller, W. P. (2000). Soil solution chemistry of a fly ash-, poultry litter-, and sewage sludge-amended soil. J. Environ. Qual. 29, 430–436. Jackson, B. P., Miller, W. P., Schumann, A. W., and Sumner, M. E. (1999). Trace element solubility from land application of fly ash/organic waste mixtures. J. Environ. Qual. 28, 639–647. Jackson, B. P., Bertsch, P. M., Cabrera, M. L., Camberato, J. J., Seaman, J. C., and Wood, C. W. (2003). Trace element speciation in poultry litter. J. Environ. Qual. 32, 535–540. Jackson, B. P., Seaman, J. C., and Bertsch, P. M. (2006). Fate of arsenic compounds in poultry litter upon land application. Chemosphere 65, 2028–2034. Jagtap, M. N., Kulkarni, M. V., and Puranik, P. R. (2010). Flux of heavy metals in soils irrigated with urban wastewaters. Am-Euras. J. Agric. Environ. Sci. 8, 487–493. Jansen, B., Nierop, K. G. J., and Verstraten, J. M. (2005). Mechanisms controlling the mobility of dissolved organic matter, aluminium and iron in podzol B horizons. Euro. J. Soil Sci. 56, 537–550. Janssen, R. P. T., Posthuma, L., Baerselman, R., Den Hollander, H. A., Van Veen, R. P. M., and Peijnenburg, W. J. G. M. (1997). Equilibrium partitioning of heavy metals in Dutch field soils. II. Prediction of metal accumulation in earthworms. Environ. Toxicol. Chem. 16, 2479–2488. Japenga, J., and Harmsen, K. (1990). Determination of mass balances and ionic balances in animal manures. Neth. J. Agric. Sci. 38, 353–367. Japenga, J., Dalenberg, J., Wiersma, D., Scheltens, S., Hesterberg, D., and Salomons, W. (1992). Effect of liquid animal manure application on the solubilization of heavy metals from soil. Int. J. Environ. Anal. Chem. 46, 25–39. Jardine, P. M., Fendorf, S. E., Mayes, M. A., Larsen, I. L., Brooks, S. C., and Bailey, W. B. (1999). Fate and transport of hexavalent chromium in undisturbed heterogeneous soil. Environ. Sci. Technol. 33, 2939–2944. Jayawardane, N. S., Christen, E. W., Arienzo, M., and Quayle, W. C. (2011). Evaluation of the effects of cation combinations on soil hydraulic conductivity. Aust J. Soil Res. 49, 56–64. 284 Anitha Kunhikrishnan et al. Jinadasa, K., Milham, P. J., Hawkins, C. A., Cornish, P. S., Williams, P. A., Kaldor, C. J., and Conroy, J. P. (1997). Survey of cadmium levels in vegetables and soils of Greater Sydney, Australia. J. Environ. Qual. 26, 924–933. Jnad, I., Lesikar, B., Sabbagh, G., and Kenimer, A. (2000). Characterizing soil hydraulic properties in a subsurface drip drain field. “National Irrigation Proceedings”, pp. 670– 676. Johnston, D. (2003). Improving water management. Recent OECD experience. Report 1-119. IWA Publishing. Jueschke, E., Marschner, B., Tarchitzky, J., and Chen, Y. (2008). Effects of treated wastewater irrigation on the dissolved and soil organic carbon in Israeli soils. Water Sci. Technol. 57, 727–733. Juhasz, A. L., Weber, J., Smith, E., Naidu, R., Rees, M., Rofe, A., Kuchel, T., and Sansom, L. (2009). Assessment of four commonly employed in vitro arsenic bioaccessibility assays for predicting in vivo relative arsenic bioavailability in contaminated soils. Environ. Sci. Technol. 43, 9487–9494. Juste, C., and Mench, M. (1992). Long-term application of sewage sludge and its effect of metal uptake by crops. In “Biogeochemistry of Trace Metals” (D. C. Adriano, Ed.), pp. 159–194. Lewis, Boca Raton, FL. Kabata-Pendias, A., and Pendias, H. (2001). Trace Elements in Soils and Plants. 3rd edn. CRC Press, Boca Raton. 432. Kalbitz, K., and Wennrich, R. (1998). Mobilization of heavy metals and arsenic in polluted wetland soils and its dependence on dissolved organic matter. Sci. Total Environ. 209, 27–39. Kanarek, A., and Michail, M. (1996). Groundwater recharge with municipal effluent: Dan region reclamation project, Israel. Water Sci. Technol. 34, 227–233. Kannan, K., and Oblisami, G. (1990). Effect of pulp and paper mill effluent irrigation on carbon dioxide evolution in soils. J. Agron. Crop Sci. 164, 116–119. Kao, P. H., Huang, C. C., and Hseu, Z. Y. (2006). Response of microbial activities to heavy metals in a neutral loamy soil treated with biosolid. Chemosphere 64, 63–70. Karpukhin, M., and Ladonin, D. (2008). Effect of soil components on the adsorption of heavy metals under technogenic contamination. Euras. Soil Sci. 41, 1228–1237. Kelsey, J. W., Kottler, B. D., and Alexander, M. (1997). Selective chemical extractants to predict bioavailability of soil-aged organic chemicals. Environ. Sci. Technol. 31, 214–217. Kennedy, V. H., Sanchez, A. L., Oughton, D. H., and Rowland, A. P. (1997). Use of single and sequential chemical extractants to assess radionuclides and heavy metal availability from soils for root uptake. Analyst 122, 89–100. Keraita, B. N., and Drechsel, P. (2004). Agricultural use of untreated urban wastewater in Ghana. In “Wastewater Use in Irrigated Agriculture” (C. A. Scott, N. I. Faruqui, and L. Raschid-Sally, Eds.), CABI Publishing, Wallingford, UK. Khan, S., Cao, Q., Chen, B., and Zhu, Y. G. (2006). Humic acids increase the phytoavailability of Cd and Pb to wheat plants cultivated in freshly spiked, contaminated soil. J. Soil Sediment. 6, 236–242. Khoshgoftarmanesh, A. H., and Kalbasi, M. (2002). Effect of municipal waste leachate on soil properties and growth and yield of rice. Commun. Soil Sci. Plant Anal. 33, 2011–2020. Khoshgoftarmenesh, A. H., Jaafari, B., and Shariathmadari, H. E. (2002). Effect of salinity on Cd and Zn availability. In “18th World Congress of Soil Science Conference Proceedings,” Thailand. Kim, H., Seagren, E. A., and Davis, A. P. (2003). Engineered bioretention for removal of nitrate from stormwater runoff. Water Environ. Res. 75, 355–367. Kinney, C. A., Furlong, E. T., Werner, S. L., and Cahill, J. D. (2006). Presence and distribution of wastewater-derived pharmaceuticals in soil irrigated with reclaimed water. Environ. Toxicol. Chem. 25, 317–326. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 285 Kizilkaya, R. I. (2005). The role of different organic wastes on zinc bioaccumulation by earthworm Lumbricus terrestris L. (Oligochaeta) in successive Zn added soil. Ecol. Eng. 25, 322–331. Kiziloglu, F. M., Turan, M., Sahin, U., Angin, I., Anapali, O., and Okuroglu, M. (2007). Effects of wastewater irrigation on soil and cabbage-plant (Brassica olerecea var. capitate cv. yalova- 1) chemical properties. J. Plant Nutr. Soil Sci. 170, 166–172. Kiziloglu, F. M., Turan, M., Sahin, U., Kuslu, Y., and Dursun, A. (2008). Effects of untreated and treated wastewater irrigation on some chemical properties of cauliflower (Brassica olerecea L. var. botrytis) and red cabbage (Brassica olerecea L. var. rubra) grown on calcareous soil in Turkey. Agric. Water Manage. 95, 716–724. Kookana, R. S., and Rogers, S. L. (1995). Effects of pulp mill effluent disposal on soil. Rev. Environ. Contam. Toxicol. 142, 13–64. Kosolapov, D. B., Kuschk, P., Vainshtein, M. B., Vatsourina, A. V., Wießner, A., Kästner, M., and Muller, R. A. (2004). Microbial processes of heavy metal removal from carbon-dericient effluents in constructed wetlands. Eng. Life Sci. 4, 403–411. Kouřimská, L., Babička, L., Václavı́ková, K., Miholová, D., Pacáková, Z., and Koudela, M. (2009). The effect of fertilisation with fermented pig slurry on the quantitative and qualitative parameters of tomatoes (Solanum lycopersicum). Soil Water Res. 4, 116–121. Kretzschmar, R. (1990). Abwasserverwertung. In “Handbuch des Bodenschutzes” (H. P. Blume, Ed.), pp. 425–439. ECOMED, Verlagsgesellschaft. Kulbat, E., Olańczuk-Neyman, K., Quant, B., Geneja, M., and Haustein, E. (2003). Heavy Metals Removal in the Mechanical-Biological Wastewater Treatment Plant “Wschód” in Gdańsk. Pol. J. Environ. Stud. 12, 635–641. Kumar, A., and Christen, E. (2009). Developing a Systematic Approach to Winery Wastewater Management. Report CSL05/02. Final report to Grape and Wine Research & Development Corporation, CSIRO Land and Water Science Report Adelaide. Kunhikrishnan, A. (2011). Role of recycled water sources in the (im)mobilization and bioavailability of copper in soils. PhD thesis, University of South Australia. Kunhikrishnan, A., Bolan, N. S., and Naidu, R. (2011). Phytoavailability of copper in the presence of recycled water sources. Plant Soil. 348, 425–438. Kwon, J. S., Yun, S. T., Lee, J. H., Kim, S. O., and Jo, H. Y. (2010). Removal of divalent heavy metals (Cd, Cu, Pb, and Zn) and arsenic (III) from aqueous solutions using scoria: Kinetics and equilibria of sorption. J. Hazard. Mater. 174, 307–313. L’Herroux, L., Le Roux, S., Appriou, P., and Martinez, J. (1997). Behaviors of metals following intensive pig slurry applications to natural filed treatment process in Brittany (France). Environ. Pollut. 97, 119–130. Lado, M., and Ben-Hur, M. (2009). Treated domestic sewage irrigation effects on soil hydraulic properties in arid and semiarid zones: A review. Soil Till. Res. 106, 152–163. Lado, M., and Ben-Hur, M. (2010). Effects of irrigation with different effluents on saturated hydraulic conductivity of arid and semiarid soils. Soil Sci. Soc. Am. J. 74, 23–32. Lado, M., Ben-Hur, M., and Assouline, S. (2005). Effects of effluent irrigation on seal formation, infiltration, and soil loss during rainfall. Soil Sci. Soc. Am. J. 69, 1432–1439. Lai, T. V. (2000). Perspectives of peri-urban vegetable production in Hanoi. In “Background paper prepared for the Action Planning Workshop of the CGIAR Strategic Initiative for Urban and Peri-urban Agriculture (SIUPA), Hanoi, 6–9 June,” Convened by International Potato Center (CIP), Lima. Lair, G., Gerzabek, M., and Haberhauer, G. (2007). Sorption of heavy metals on organic and inorganic soil constituents. Environ. Chem. Lett. 5, 23–27. Lallana, C., Krinner, W., and Estrela, T. (2001). Sustainable Water Use in Europe. European Environment Agency, Copenhagen. 286 Anitha Kunhikrishnan et al. Lamb, D. T., Ming, H., Megharaj, M., and Naidu, R. (2009). Heavy metal (Cu, Zn, Cd and Pb) partitioning and bioaccessibility in uncontaminated and long-term contaminated soils. J. Hazard. Mater. 171, 1150–1158. Latif, M. L., Lone, M. I., and Khan, K. S. (2008). Heavy metals contamination of different water sources, soils and vegetables in Rawalpindi area. Soil Environ. 27, 29–35. Laurenson, S., Kunhikrishnan, A., Bolan, N. S., Naidu, R., McKay, J., and Keremane, G. (2010). Management of recycled water for sustainable production and environmental protection: A case study with Northern Adelaide Plains recycling scheme. Int. J. Environ. Sci. Dev. 1, 176–180. Laurenson, G., Bolan, N. S., Simcock, R., Laurenson, S., and Beecham, S. (2011). The role of bioretention systems in the treatment of stormwater. Adv. Agron. (Communicated). Lavric, E. D., Konnov, A. A., and De Ruyck, J. (2004). Dioxin levels in wood combustion—A review. Biomass Bioenerg. 26, 115–145. Lazarova, V., and Bahri, A. (2005). Water Reuse for Irrigation: Agriculture, Landscapes, and Turf Grass. CRC Press, Boca Raton, FL. Levy, G. J., Mamedov, A. I., and Goldstein, D. (2003). Sodicity and water quality effects on slaking of aggregates from semi-arid soils. Soil Sci. 168, 552–562. Li, Z., and Shuman, L. M. (1997). Mobility of Zn, Cd and Pb in soils as affected by poultry litter extract–I. leaching in soil columns. Environ. Pollut. 95, 219–226. Li, Z. B., Ryan, J. A., Chen, J. L., and Al-Abed, S. R. (2001). Adsorption of cadmium on biosolids amended soils. J. Environ. Qual. 30, 903–911. Li, H., Wang, J., Teng, Y., and Wang, Z. (2006). Study on the mechanism of transport of heavy metals in soil in western suburb of Beijing. Chin. J. Geochem. 25, 173–177. Lieffering, R. E., and McLay, C. D. A. (1996). The effect of strong hydroxide solutions on the stability of aggregates and hydraulic conductivity of soil. Eur. J. Soil Sci. 47, 43–50. Lin, D., and Zhou, Q. (2009). Effects of soil amendments on the extractability and speciation of cadmium, lead and copper in a contaminated soils. Bull. Environ. Contam. Toxicol. 83, 136–140. Lipoth, S. L., and Schoenau, J. J. (2007). Copper, zinc, and cadmium accumulation in two prairie soils and crops as influenced by repeated applications of manure. J. Plant Nutr. Soil Sci. 170, 378–386. Liu, Y. Y., and Haynes, R. (2010). Effect of long-term irrigation with dairy factory wastewater on soil properties. “19th World Congress of Soil Science Conference Proceedings”, Brisbane, Australia. Liu, H., Probst, A., and Liao, B. (2005). Metal contamination of soils and crops affected by the Chenzhou lead/zinc mine spill (Hunan, China). Sci. Total Environ. 339, 153–166. Logan, T. J., Lindsay, B. J., Goins, L. E., and Ryan, J. A. (1997). Field assessment of sludge metal bioavailability to crops: Sludge rate response. J. Environ. Qual. 26, 534–550. Loganathan, P., MacKay, A. D., Lee, J., and Hedley, M. J. (1995). Cadmium distribution in hill pastures as influenced by 20 years of phosphate fertiliser application and sheep grazing. Aust. J. Soil Res. 33, 859–871. Loganathan, P., Hedley, M. J., Grace, N. D., Lee, J., Cronin, S. J., Bolan, N. S., and Zanders, J. M. (2003). Fertiliser contaminants in New Zealand grazed pasture with special reference to cadmium and fluorine: A review. Aust. J. Soil Res. 41, 501–532. Loganathan, P., Hedley, M. J., and Grace, N. D. (2008). Pasture soils contaminated with fertilizer-derived cadmium and fluorine: Livestock effects. Rev. Environ. Contam. Toxicol. 192, 29–66. Loibner, A. P., Holzer, M., Gartner, M., Szolar, O. H. J., and Braun, R. (2000). The use of sequential supercritical fluid extraction for bioavailability investigations of PAH in soil. Bodenkultur 51, 225–233. Losi, M. E., Amrhein, C., and Frankenberger, W. T. (1994). Factors affecting chemical and biological reduction of Cr(VI) in soil. Environ. Toxicol. Chem. 13, 1727–1735. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 287 Lowe, H. (1993). Accumulation and interim nutrient concentration of pasture irrigated with treated piggery effluent. “Proceedings of the New Zealand Land Treatment Collective Technical Session No. 9: Land application of farm wastes”, Palmerston North, New Zealand. Lu, X. (2005). The risk for heavy metal mobility from corrosion products to soil and groundwater. Trita-lwr Master Thesis. Luo, Y., Jianga, X., Wu, L., Song, J., Wu, S., Lu, R., and Christie, P. (2003). Accumulation and chemical fractionation of Cu in a paddy soil irrigated with Cu-rich wastewater. Geoderma 115, 113–120. Luo, J., Lindsey, S., and Xue, J. (2004). Irrigation of meat processing wastewater onto land. Agric. Ecosyt. Environ. 103, 123–148. Luo, J., Saggar, S., Bhandral, R., Bolan, N. S., Ledgard, S., and Sun, W. (2008). Effects of irrigating farm dairy effluent on nitrous oxide emissions. Plant Soil 309, 119–130. Ma, W. (1984). Sublethal toxic effects of copper on growth, reproduction and litter breakdown activity in the earthworm Lumbricus rubellus, with observations on the influence of temperature and soil pH. Environ. Pollut. A 33, 207–219. Madyiwa, S., Chimbari, M., Nyamangara, J., and Bangira, C. (2002). Cumulative effects of sewage sludge and effluent mixture application on soil properties of a sandy soil under a mixture of star and kikuyu grasses in Zimbabwe. Phys. Chem. Earth Pts A/B/C. 27, 747–753. Magesan, G. N. (2001). Changes in soil physical properties after irrigation of two forested soils with municipal wastewater. N. Z. J. For. Sci. 31, 188–195. Magesan, G. N., Claydon, J. J., and Harris, S. (1996). Influence of municipal effluent application on soil physical and hydraulic properties. In “1st International Conference—Contaminants and the soil environment—Extended abstracts,” pp. 269–270. Magesan, G. N., Williamson, J. C., Sparling, G. P., Schipper, L. A., and Lloyd-Jones, A. R. (1999). Hydraulic conductivity in soils irrigated with wastewaters of differing strengths: Field and laboratory studies. Aust. J. Soil. Res. 37, 391–402. Maher, W. A. (1988). Arsenic in the marine environment of south Australia. In “The Biological Alkylation of Heavy Elements”. (P. J. Craig and F. Glocking, Eds.), Proceedings of a conference, 17–18 September 1987, London, pp. 120–126. Special Publication no.66 Royal Society of Chemistry, Cambridge. Mahimairaja, S., Bolan, N. S., Adriano, D. C., and Robinson, B. (2005). Arsenic contamination and its risk management in complex environmental settings. Adv. Agron. 86, 1–82. Mamedov, A. I., Shainberg, I., and Levy, G. J. (2000). Irrigation with effluent water: Effects of rainfall energy on soil infiltration. Soil Sci. Soc. Am. J. 64, 732–737. Mandal, U. K., Bhardwaj, A. K., Warrington, D. N., Goldstein, D., Bar Tal, A., and Levy, G. J. (2008). Changes in soil hydraulic conductivity, runoff, and soil loss due to irrigation with different types of saline-sodic water. Geoderma 144, 509–516. Mapanda, F., Mangwayana, E. N., Nyamangara, J., and Giller, K. E. (2005). The effects of long-term irrigation using water on heavy metal contents of soils under vegetables. Agric. Ecosyst. Environ. 107, 151–156. Marchi, G., Guilherme, L. R. G., Chang, A. C., and do Nascimento, C. W. A. (2009). Heavy metals extractability in a soil amended with sewage sludge. Sci. Agric. 66, 643–649. Marecos do Monte, M. H. F. (1998). Agriculture irrigation with treated wastewater in Portugal. In “Wastewater Reclamation and Reuse” (T. Asano, Ed.), pp. 827–875. Technomic Publishing Company, Lancaster, Pennsylvania, USA. Marschner, B., and Kalbitz, K. (2003). Controls of bioavailability and biodegradability of dissolved organic matter in soils. Geoderma 113, 211–235. Martin, A. J., and Goldblatt, R. (2007). Speciation, behavior, and bioavailability of copper downstream of a mine-impacted lake. Environ. Toxicol. Chem. 26, 2594–2603. Mass, E. V., and Hoffman, G. J. (1977). Crop salt tolerance current assessment. ASCE J. Irrig. Drainage Div. 103, 115–134. 288 Anitha Kunhikrishnan et al. Masscheleyn, P. H., and Patrick, W. H. (1993). Biogeochemical processes affecting selenium cycling in wetlands. Environ. Toxicol. Chem. 12, 2235–2243. Mathan, K. K. (1994). Studies on the influence of long-term municipal sewage-effluent irrigation on soil physical properties. Bioresource Technol. 48, 275–276. Mattigod, S. V., and Page, A. L. (1983). Assessment of metal pollution in soil. In “Applied Environmental Geochemistry” (I. Thornton, Ed.), pp. 355–394. Academic Press, London. McBride, M. B. (1995). Toxic metal accumulation from agricultural use of sludge: Are USEPA regulations protective? J. Environ. Qual. 24, 5–18. McBride, M. B. (2001). Cupric ion activity in peat soil as a toxicity indicator for maize. J. Environ. Qual. 30, 78–84. McBride, M. B. (2002). Cadmium uptake by crops estimated from soil total Cd and pH. Soil Sci. 167, 62–67. McCarthy, M. G. (1981). Irrigation of grapevines with sewage effluent. 1. Effects on yield and petiole composition. Am. J. Enol. Viticult. 32, 189–196. McCarthy, J. F., and Zachara, J. M. (1989). Subsurface transport of contaminants. Environ. Sci. Technol. 23, 496–502. McDonald, S. (2006). Dairy effluent: building and operating a safe system. AG0444, Department of Primary Industries, Melbourne. McDonald, S. (2007). Dairy Effluent: Flood Irrigation of Dairy Shed Effluent. http://www .dpi.vic.gov.au/dpi/nreninf.nsf/AG0426_Jun07.pdf. McGrath, S. P., Chang, A. C., Page, A. L., and Witter, E. (1994). Land application of sewage sludge: Scientific perspectives of heavy metal loading limits in Europe and the United States. Environ. Rev. 2, 108–118. McLaren, R. G., and Ritchie, G. (1993). The long term fate of copper fertilizer applied to a lateritic sandy soil in Western Australia. Aust. J. Soil Res. 31, 39–50. McLaren, R. G., and Smith, C. J. (1996). Issues in the disposal of industrial and urban wastes. In “Contaminants and the Soil Environment in the Australasia-Pacific Region” (R. Naidu, R. S. Kookana, D. P. Oliver, S. Rogers, and M. J. McLaughlin, Eds.), pp. 183–212. Kluwer Academic Publishers, Dortrecht, The Netherlands. McLaren, R. G., Swift, R. S., and Quin, B. F. (1984). E.D.T.A.-extractable copper, zinc, and manganese in soils Canterbury Plains. N. Z. J. Agric. Res. 7, 207–217. McLaughlin, M. J., Palmer, L. T., Tiller, K. G., Beech, T. A., and Smart, M. K. (1994). Increased soil salinity causes elevated cadmium concentrations in field-grown potato tubers. J. Environ. Qual. 23, 1013–1018. McLaughlin, M. J., Tiller, K. G., Naidu, R., and Stevens, D. P. (1996). The behaviour and environmental impact of contaminants in fertilizers. Aust. J. Soil Res. 34, 1–54. McLaughlin, M. J., Lambrechts, R. M., Smolders, E., and Smart, M. K. (1998). Effects of sulfate on cadmium uptake by Swiss chard: II. Effects due to sulfate addition to soil. Plant Soil 202, 217–222. Meima, J. A., and Comans, R. N. J. (1997). Overview of geochemical processes controlling leaching characteristics of MSWI bottom ash. Stud. Environ. Sci. 71, 447–457. Mekala, G. D., Davidson, B., Samad, M., and Boland, A. (2008). Wastewater Reuse and Recycling Systems: A Perspective into India and Australia. International Water Management Institute, Colombo, Sri Lanka. Meli, S., Maurizio, M., Belligno, A., Bufo, S. A., Mazzatura, A., and Scopa, A. (2002). Influence of irrigation with lagooned urban wastewater on chemical and microbial soil parameters in a citrus orchard under Mediterranean condition. Sci. Total Environ. 285, 69–77. Menneer, J. C., McLay, C. D. A., and Lee, R. (2001). Effects of sodium-contaminated wastewater on soil permeability of two New Zealand soils. Aust. J. Soil Res. 39, 877–891. Menzi, H., Haldemann, C., and Kessler, J. (1993). Heavy metals in farmyard manures—A topic with knowledge gaps. Schweiz. Landwirtsch. Forsch. 32, 159–167. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 289 Mesquita, M. E., and Carranca, C. (2005). Effects of dissolved organic matter on copper– zinc competitive absorption by a sandy soil at different pH values. Environ. Technol. 26, 1065–1072. Mexico CAN. (2004). Water Statistics (Comision Nacional del Agua). Water Statistics National Water Commission, Mexico City. Miekeley, N., Pereira, R. C., Casartelli, E. A., Almeida, A. C., and Carvalho, M. D. (2005). Inorganic speciation analysis of selenium by ion chromatography-inductively coupled plasma-mass spectrometry and its application to effluents from a petroleum refinery. Spectrochim. Acta Part B 60, 633–641. Misra, R. K., and Sivongxay, A. (2009). Reuse of laundry greywater as affected by its interaction with saturated soil. J. Hydrol. 366, 55–61. Mittal, G. S. (2004). Characterization of effluent wastewater from abattoir for land application. Food Rev. Int. 20, 229–256. Mohanna, C., Carre, B., and Nys, Y. (1999). Incidence of dietary viscosity on growth performance and zinc and manganese bioavailability in broilers. Anim. Feed Sci. Technol. 77, 255–266. Mondal, M. K., Das, T. K., Biswas, P., Samanta, C. C., and Bairagi, B. (2007). Influence of dietary inorganic and organic copper salt and level of soybean oil on plasma lipids, metabolites and mineral balance of broiler chickens. Anim. Feed Sci. Technol. 139, 212–233. Monnett, G. T., Reneau, R. B. J., and Hagedom, C. (1995). Effects of domestic wastewater spray irrigation on denitrification rates. J. Environ. Qual. 24, 940–946. Moore, P. A. Jr., Daniel, T. C., Gilmour, J. T., Shreve, B. R., Edwards, D. R., and Wood, B. H. (1998). Decreasing metal runoff from poultry litter with aluminum sulfate. J. Environ. Qual. 27, 92–99. Moral, R., Perez-Murcia, M. D., Perez-Espinosa, A., Moreno-Caselles, J., Paredes, C., and Rufete, B. (2008). Salinity, organic content, micronutrients and heavy metals in pig slurries from South-eastern Spain. Waste Manage. 28, 367–371. Morrison, J. L. (1969). Distribution of arsenic from poultry litter in broiler chickens, soil, and crops. J. Agric. Food Chem. 17, 1288–1290. Mortvedt, J. J. (1996). Heavy metal contaminants in inorganic and organic fertilizers. Fertil. Res. 43, 55–61. Moscuzza, C. H., and Fernández-Cirelli, A. (2009). Trace elements in confined livestock production systems in the Pampean plains of Argentina. World Appl. Sci. J. 7, 1583–1590. Moyo, D. Z., and Chimbira, C. (2009). The effect of single and mixed treatments of lead and cadmium on soil bioavailability, uptake and yield of Lactuca sativa irrigated with sewage effluent under greenhouse conditions. Am. Euras. J. Agric. Environ. Sci. 6, 526–531. Mukherjee, A., Bhattacharya, P., Savage, K., Foster, A., and Bundschuh, J. (2008). Distribution of geogenic arsenic in hydrologic systems: Controls and challenges. J. Contam. Hydrol. 99, 1–7. Müller, K., Magesan, G. N., and Bolan, N. S. (2007). A critical review on the influence of effluent irrigation on the fate of pesticides in soil. Agric. Ecosyst. Environ. 120, 93–116. Müller, K., Deurer, M., Slay, M., Aslam, T., Carter, J. A., and Clothier, B. E. (2010). Environmental and economic consequences of soil water repellency under pasture. New Zealand Grassland Association. Murtaza, G., Ghafoor, A., and Qadir, M. (2008). Accumulation and implications of cadmium, cobalt and manganese in soils and vegetables irrigated with city effluent. J. Sci. Food Agric. 88, 100–107. Murtaza, G., Ghafoor, A., Qadir, M., Owens, G., Aziz, M., and Zia, M. (2010). Disposal and use of sewage on agricultural lands in Pakistan: A review. Pedosphere 20, 23–34. Nahm, K. (2002). Efficient feed nutrient utilization to reduce pollutants in poultry and swine manure. Crit. Rev. Environ. Sci. Technol. 32, 1–16. 290 Anitha Kunhikrishnan et al. Nahmani, J., Hodson, M. E., and Black, S. (2007). A review of studies performed to assess metal uptake by earthworms. Environ. Pollut. 145, 402–424. Naidu, R., and Skinner, H. C. W. (1999). Arsenic contamination of rural ground-water supplies in Bangladesh and India: Implications for soil quality, animal and human health. In “Proceedings of the International Conference on Diffuse Pollution” (C. Barber, B. Humphries, and J. Dixon, Eds.), pp. 407–417. CSIRO Publishing, Collingwood, Victoria. Naidu, R., Kookana, R. S., Oliver, D. P., Rogers, S., and McLaughlin, M. J. (1996). Contaminants and the Soil Environment in the Australasia-Pacific region. Kluwer Academic Publishers, Dordrecht, The Netherlands. Naidu, R., Kookana, R., Sumner, M., Harter, R., and Tiller, K. (1997). Cadmium sorption and transport in variable charge soils: A review. J. Environ. Qual. 26, 602–617. Naidu, R., Bolan, N. S., Megharaj, M., Juhasz, A. L., Gupta, S., Clothier, B., and Schulin, R. (2008). Chemical bioavailability in terrestrial environments. In “Chemical Bioavailability in Terrestrial Environment” (R. Naidu, Ed.), pp. 1–6. Elsevier, Amsterdam, The Netherlands. Nakayasu, K., Fukushima, M., Sasaki, K., Taraka, S., and Nakamura, H. (1999). Comparative study of the reduction behavior of chromium(VI) by humid substances and their precursors. Environ. Toxicol. Chem. 18, 1085–1090. Nash, D., Butler, C., Cody, J., Warne, M. J., McLaughlin, M. J., Heemsbergen, D., Broos, K., Bell, M., Barry, G., Pritchard, D., and Penny, N. (2011). Effects of biosolids application on pasture and grape vines in south-eastern Australia. Appl. Environ. Soil Sci. 2011, 11. Neilsen, G. H., Stevenson, D. S., and Fitzpatrick, J. J. (1989). The effect of municipal wastewater irrigation and rate of N fertilization on petiole composition, yield and quality of Okanagan Riesling grapes. Can. J. Plant Sci. 69, 1285–1294. Nicholas, D. R., Ramamoorthy, S., Palace, V., Spring, S., Moore, J. N., and Rosenzweig, R. F. (2003). Biogeochemical transformations of arsenic in circumneutral freshwater sediments. Biodegradation 14, 123–137. Nicholson, F., Chambers, B., Williams, J., and Unwin, R. (1999). Heavy metal contents of livestock feeds and animal manures in England and Wales. Bioresource Technol. 23, 23–31. Niklas, J., and Kennel, W. (1978). Lumbricidenpopulationen in Obstanlagen der Bundesrepublik Deutschland und ihre Beeinflussung durch Fungizide auf Basis von Kupferverbindungen und Benzimidazolderivaten. Zeitschr Pflanzenkrankh, Pflanzensch 85, 703–713. Nwuche, C., and Ugoji, E. (2008). Effects of heavy metal pollution on the soil microbial activity. Int. J. Environ. Sci. Tech. 5, 409–414. Oiffer, L., and Siciliano, S. D. (2009). Methyl mercury production and loss in Arctic soil. Sci. Total Environ. 407, 1691–1700. Olchawa, E., Bzowska, M., Stürzenbaum, S. R., Morgan, A. J., and Plytycz, B. (2006). Heavy metals affect the coelomocyte-bacteria balance in earthworms: Environmental interactions between abiotic and biotic stressors. Environ. Pollut. 142, 373–381. Oved, T., Shaviv, A., Goldrath, T., Mandelbaum, R. T., and Minz, D. (2001). Influence of effluent irrigation on community composition and function of ammonia-oxidizing bacteria in soil. Appl. Environ. Microbiol. 67, 3426–3433. Oviasogie, O. P., and Ndiokwere, C. L. (2008). Fractionation of lead and cadmium in refuse dump soil treated with cassava mill effluent. J. Agric. Environ. 9, 10–15. Paramasivam, S., Jayaraman, K., Wilson, T. C., Alva, A. K., Kelson, L., and Jones, L. B. (2009). Ammonia volatilization loss from surface applied livestock manure. J. Environ. Sci. Heal. B 44, 317–324. Park, J. H., Lamb, D., Paneerselvam, P., Choppala, G., Bolan, N., and Chung, J. W. (2011). Role of organic amendments on enhanced bioremediation of heavy metal(loid) contaminated soils. J. Hazard. Mater. 185, 549–574. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 291 Patterson, S. J., Chanasyk, D. S., Naeth, M. A., and Mapfumo, E. (2008). Effect of municipal and pulp mill effluents on the chemical properties and nutrient status of a coarse-textured Brunisol in a growth chamber. Can. J. Soil Sci. 88, 429–441. Payne, G. G., Martens, D. C., Kornegay, E. T., and Lindemann, M. D. (1988). Availability and form of copper in three soils following eight annual applications of copper enriched swine manure. J. Environ. Qual. 17, 740–746. Peckenham, J. M., Nadeau, J. A., Amirbahman, A., and Behr, R. S. (2008). Release of nitrogen and trace metal species from field stacked biosolids. Waste Manage. Res. 26, 163–172. Pedrero, F., Kalavrouziotis, I., Alarcón, J. J., Koukoulakis, P., and Asano, T. (2010). Use of treated municipal wastewater in irrigated agriculture—Review of some practices in Spain and Greece. Agric. Water Manage. 97, 1233–1241. Peijnenburg, W. J., Zablotskaja, M., and Vijver, M. G. (2007). Monitoring metals in terrestrial environments within a bioavailability framework and a focus on soil extraction. Ecotoxicol. Environ. Saf. 67, 163–179. Perämäki, P., Itämies, J., Karttunen, V., Lajunen, L., and Pulliainen, E. (1992). Influence of pH on the accumulation of cadmium and lead in earthworms (Aporrectodea caliginosa) under controlled conditions. Ann. Zool. Fenn. 29, 105–111. Pettygrove, G. S., and Asano, T. (1984). Irrigation with reclaimed municipal wastewater—A guidance manual. Rep. 84-1 wr, SWRCB, Sacramento, California. Pils, J. R. V., Laird, D. A., and Evangelou, V. P. (2007). Role of cation demixing and quasicrystal formation and breakup on the stability of smectitic colloids. Appl. Clay Sci. 35, 201–211. Qadir, M., Ghafoor, A., and Murtaza, G. (2000). Cadmium concentration in vegetables grown on urban soils irrigated with untreated municipal sewage. Environ. Dev. Sustain. 2, 11–19. Qadir, M., Wichelns, D., Raschid-Sally, L., Minhas, P. S., Drechsel, P., Bahri, A., and McCornick, P. (2007). Agricultural use of marginal-quality water—Opportunities and challenges. In “Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture” (D. Molden, Ed.), pp. 425–457. Earthscan, London. Qadir, M., Wichelns, D., Raschid-Sally, L., McCornick, P. G., Drechsel, P., Bahri, A., and Minhas, P. S. (2010). The challenges of wastewater irrigation in developing countries. Agric. Water Manage. 97, 561–568. Qian, Y. L., and Mecham, B. (2005). Long-term effects of recycled wastewater irrigation on soil chemical properties on golf course fairways. Agron. J. 97, 717–721. Qishlaqi, A., and Moore, F. (2007). Statistical analysis of accumulation and sources of heavy metals occurrence in agricultural soils of Khoshk River Banks, Shiraz, Iran. Am. Euras. J. Agric. Environ. Sci. 2, 565–573. Qishlaqi, A., Moore, F., and Forghani, G. (2008). Impact of untreated wastewater irrigation on soils and crops in Shiraz suburban area, SW Iran. Environ. Monit. Assess. 141, 257–273. Quinn, D. T., and Fabiansson, S. U. (2001). Risk Assessment of Abattoir Effluent Should BSE Be Found in Cattle in Australia. Bureau of Rural Sciences, Kingston. Rajkumar, M., Nagendran, R., Lee, K. J., and Lee, W. H. (2005). Characterization of a novel Cr6þ reducing Pseudomonas sp. with plant growth promoting potential. Curr. Microbiol. 50, 266–271. Ramı́rez-Fuentes, E., Lucho-Constantino, C., Escamilla-Silva, E., and Dendooven, L. (2002). Characteristics, and carbon and nitrogen dynamics in soil irrigated with wastewater for different lengths of time. Bioresource Technol. 85, 179–187. Rana, L., Dhankhar, R., and Chhikara, S. (2010). Soil characteristics affected by long term application of sewage wastewater. Int. J. Environ. Res. 4, 513–518. 292 Anitha Kunhikrishnan et al. Ranjard, L., Echairi, A., Nowak, V., Lejon, D. P. H., Nouaı̈m, R., and Chaussod, R. (2006). Field and microcosm experiments to evaluate the effects of agricultural Cu treatment on the density and genetic structure of microbial communities in two different soils. FEMS Microbiol. Ecol. 58, 303–315. Rattan, R. K., Datta, S. P., Chhonkar, P. K., Suribabu, K., and Singh, A. K. (2005). Longterm impact of irrigation with sewage effluents on heavy metal content in soils, crops and groundwater—A case study. Agric. Ecosyst. Environ. 109, 310–322. Redman, A. D., Macalady, D. L., and Ahmann, D. (2002). Natural organic matter affects arsenic speciation and sorption onto hematite. Environ. Sci. Technol. 36, 2889–2896. Reid, B. J., Jones, K. C., and Semple, K. T. (2000). Bioavailability of persistent organic pollutants in soils and sediments—A perspective on mechanisms, consequences and assessment. Environ. Pollut. 108, 103–112. Rengasamy, P., and Marchuk, A. (2011). Cation ratio of soil structural stability (CROSS). Soil Res. 49, 280–285. Rosabal, A., Morillo, E., Undabeytia, T., Maqueda, C., Justo, A., and Herencia, J. F. (2007). Long-term impacts of wastewater irrigation on Cuban soils. Soil Sci. Soc. Am. J. 71, 1292–1298. Roy, A. H., Wenger, S. J., Fletcher, T. D., Walsh, C. J., Ladson, A. R., Shuster, W. D., Thurston, H. W., and Brown, R. R. (2008a). Impediments and solutions to sustainable, watershed-scale urban stormwater management: Lessons from Australia and the United States. Environ. Manage. 42, 344–359. Roy, R. P., Prasad, J., and Joshi, A. P. (2008b). Changes in soil properties due to irrigation with paper industry wastewater. J. Environ. Sci. Eng. 50, 277–282. Rubilar, O., Diez, M. C., and Gianfreda, L. (2008). Transformation of chlorinated phenolic compounds by white rot fungi. Crit. Rev. Environ. Sci. Tech. 38, 227–268. Ruby, M. V., Davis, A., Schoof, R., Eberle, S., and Sellstone, C. M. (1996). Estimation of bioavailability using a physiologically based extraction test. Environ. Sci. Technol. 30, 420–430. Rusan, M. J., Hinnawi, S., and Rousan, L. (2007). Long term effect of wastewater irrigation of forage crops on soil and plant quality parameters. Chemosphere 215, 143–152. Sauvé, S., Cook, N., Hendershot, W. H., and McBride, M. B. (1996). Linking plant tissue concentrations and soil copper pools in urban contaminated soils. Environ. Pollut. 94, 153–157. Schaecke, W., Tanneberg, H., and Schilling, G. (2002). Behavior of heavy metals from sewage sludge in a Chernozem of the dry belt in Saxony-Anhalt/Germany. J. Plant Nutr. Soil Sci. 165, 609–617. Schindler, D. W., Bayley, S. E., Curtis, P. J., Parker, B. R., Stainton, M. P., and Kelly, C. A. (1992). Natural and man-caused factors affecting the abundance and cycling of dissolved organic substances in precambrian shield lakes. Hydrobiologia 229, 1–21. Schipper, L. A., Williamson, J. C., Kettles, H. A., and Speir, T. W. (1996). Impact of landapplied tertiary-treated effluent on soil biochemical properties. J. Environ. Qual. 25, 1073–1077. Seckler, D., Upali, A., Molden, D., de Silva, R., and Barker, R. (1998). World water demand and supply, 1990 to 2025: Scenarios and issues. Research Report 19. Colombo, Sri Lanka: International Water Management Institute. Sedlak, D. L., Phinney, J. T., and Bedsworth, W. W. (1997). Strongly complexed Cu and Ni in wastewater effluents and surface runoff. Environ. Sci. Technol. 31, 3010–3016. Seikh, B., Cort, R., Cooper, R., and Jaques, R. S. (1998). Tertiary-treated reclaimed water for irrigation of raw-eaten vegetables. In “Wastewater Reclamation and Reuse” (T. Asano, Ed.), pp. 779–826. Technomic Publishing Company, Lancaster, Pennsylvania, USA. Shahalam, A., Zahra, B. M. A., and Jaradat, A. (1998). Wastewater irrigation effect on soil, crop and environment: A pilot study in Irbid, Jordan. Water Air Soil Pollut. 106, 425–445. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 293 Shainberg, I., and Letey, J. (1984). Response of soils to sodic and saline conditions. Hilgardia 61, 21–57. Shan, Y. (2010). Enhancement of Cd solubility and bioavailability induced by straw incorporation in a Cd-polluted rice soil. In “19th World Congress of Soil Science Conference Proceedings,” Brisbane, Australia. Shapir, N., Mandelbaum, R. T., and Fine, P. (2000). Atrazine mineralization by indigeneous and introduced Pseudomonas sp strain ADP in sand irrigated with municipal wastewater and amended with composted sludge. Soil Biol. Biochem. 32, 887–897. Sharma, R. K., Agrawal, M., and Marshall, F. (2007). Heavy metal contamination of soil and vegetables in suburban areas of Varanasi, India. Ecotox. Environ. Safe. 66, 258–266. Sharma, S., Bansal, A., Dogra, R., Dhillon, S. K., and Dhillon, K. S. (2011). Effect of organic amendments on uptake of selenium and biochemical grain composition of wheat and rape grown on seleniferous soils in northwestern India. J. Plant Nutr. Soil Sci. 174, 269–275. Sheikh, B., Jaques, R. S., and Cort, R. P. (1987). Reuse of tertiary municipal wastewater effluent for irrigation of raw eaten food crops: A 5 year study. Desalination 67, 245–254. Shi, W., Shao, H., Li, H., Shao, M., and Du, S. (2009). Progress in the remediation of hazardous heavy metal-polluted soils by natural zeolite. J. Hazard. Mater. 170, 1–6. Shuman, L. M. (1991). Chemical forms of micronutrients in soils. In “Micronutrients in Agriculture” (J. J. Mortvedt, F. R. Fox, L. M. Shuman, and R. M. Welch, Eds.), 2nd edn. pp. 113–144. Soil Science Society of America, Madison, WI. Sidhu, J., Gibbs, R. A., Ho, G. E., and Unkovich, I. (2001). The role of indigenous microorganisms in suppression of Salmonella growth in composted biosolids. Water Res. 35, 913–920. Siebe, C., and Fischer, W. P. (1996). Effect of long-term irrigation with untreated sewage effluents on soil properties and heavy metal adsorption of Leptosols and Vertisols in Central Mexico. Z. Pflanz. Bodenkunde 159, 357–364. Sims, J. T., and Johnson, G. V. (1991). Micronutrient soil test. In “Micronutrients in Agriculture” (J. J. Mortvedt, F. R. Fox, L. M. Shuman, and R. M. Welch, Eds.), 2nd edn. pp. 427–476. Soil Science Society of America, Madison, WI. Sims, J. T., and Wolf, D. C. (1994). Poultry waste management: Agricultural and environmental issues. Adv. Agron. 52, 1–83. Singh, A., and Agrawal, M. (2010). Effects of municipal waste water irrigation on availability of heavy metals and morpho-physiological characteristics of Beta vulgaris L. J. Environ. Biol. 31, 727–736. Singh, A., Sharma, R. K., Agrawal, M., and Marshall, F. M. (2010a). Risk assessment of heavy metal toxicity through contaminated vegetables from waste water irrigated area of Varanasi, India. Trop. Ecol. 51, 375–387. Singh, A., Agrawal, M., and Marshall, F. M. (2010b). The role of organic vs. inorganic fertilizers in reducing phytoavailability of heavy metals in a wastewater-irrigated area. Ecol. Eng. 36, 1733–1740. Sistani, K. R., and Novak, J. M. (2006). Trace metal accumulation, movement, and remediation in soils receivinganimal manure. In “Trace Elements in the Environment” (M. V. Prasad, K. S. Sajwan, and R. Naidu, Eds.), CRC Press, New York. Sleutel, S., De Neve, S., Nemeth, T., Toth, T., and Hofman, G. (2006). Effect of manure and fertilizer application on the distribution of organic carbon in different soil fractions in long-term field experiments. Eur. J. Agron. 25, 280–288. Smith, S. R. (2009). A critical review of the bioavailability and impacts of heavy metals in municipal solid waste composts compared to sewage sludge. Environ. Int. 35, 142–156. Smith, C. J., Snow, V. O., Bond, W. J., and Falkiner, R. A. (1996). Salt dynamics in effluent irrigated soil. In “14th Land and Treatment Collective Meeting,” (P. J. Poglase and W. M. Tunningley, Eds.), pp. 175–180. 294 Anitha Kunhikrishnan et al. Smith, C. T., Carnus, J. M., Wang, H., Gielen, G. J. H. P., Stuthridge, T. R., and Tomer, M. D. (2003). Land application of chemi-thermo mechanical pulp and paper mill effluent in New Zealand: From research to practice. In “Environmental Impacts of Pulp and Paper Waste Streams” (T. Stuthridge, M. van den Heuval, N. Marvin, A. Slade, and J. Gifford, Eds.), pp. 177–187. Society of Environmental Toxicology and Chemistry, Pensacola, FL. Smolders, E., Lambregts, R. M., McLaughlin, M. J., and Tiller, K. G. (1998). Effect of soil solution chloride on cadmium availability to Swiss chard. J. Environ. Qual. 27, 426–431. Sopper, W. E., and Richenderfer, J. L. (1979). Effect of municipal wastewater irrigation on the physical properties of the soil. In “Utilization of Municipal Sewage Effluent and Sludge on Forest and Disturbed Land” (W. E. Sopper and S. N. Kerr, Eds.), The Pennsylvania State University Press, University Park. Sparks, D. L. (2003). Environmental Soil Chemistry. 2nd edn. Academic Press, San Diego. Spurgeon, D. J., Lofts, S., Hankard, P. K., Toal, M., McLellan, D., Fishwick, S., and Svendsen, C. (2006). Effect of pH on metal speciation and resulting metal uptake and toxicity for earthworms. Environ. Toxicol. Chem. 25, 788–796. Stahl, R. S., and James, B. R. (1991). Zinc sorption by manganese-oxide-coated sand as a function of pH. Soil Sci. Soc. Am. J. 55, 1291–1294. Stasinakis, A. S., and Thomaidis, N. S. (2010). Fate and biotransformation of metal and metalloid species in biological wastewater treatment processes. Crit. Rev. Environ. Sci. Technol. 40, 307–364. State of California. (2001). ‘Wastewater recycling criteria’, an excerpt from the California Code of Regulations. Title 22, Division 4, Environmental Health, Dept. of Health Services, Sacramento, California, June 2001 edition. Stevens, D. (2009). Irrigating with reclaimed water. A scoping study to investigate feasibility for the wine industry. Report to Grape and Wine Research Development Council. Arris Pty Ltd & South Australian Research and Development Institute, Adelaide. Stewart, H. T. L., Hopmans, P., Flinn, D. W., and Hillman, T. J. (1990). Nutrient accumulation in trees and soils following irrigation with municipal effluent in Australia. Environ. Pollut. 63, 155–177. Streit, B. (1984). Effects of high copper concentrations on soil invertebrates (earthworms and oribatid mites). Oecologia 64, 381–388. Streit, B., and Jaeggy, A. (1983). Effect of soil type on copper toxicity and copper uptake in Octolasium cyaneum (Lumbricidae). In “New Trends in Soil Biology” (P. H. Lebrun, A. André, C. D. Medts, C. Grégoire-Wibo, and G. Wauthy, Eds.), pp. 569–575. DieuBrichard, Ottignies-Louvain-la-Neuve. Sultan, S., and Hasnain, S. (2006). Characterization of an Ochrobactrum intermedium strain STCr-5 manifesting high level Cr(VI) resistance and reduction potential. Enzyme Microb. Technol. 39, 883–888. Sumner, M. E. (1993). Sodic soils: New pespectives. Aust. J. Soil. Res. 31, 683–750. Sumner, M. E. (1995). Sodic soils: New perspectives. In “Australian Sodic Soils: Distribution, Properties and Management” (R. Naidu, M. E. Sumner, and P. Rengasamy, Eds.), pp. 1–34. CSIRO Publications, Melbourne, Victoria. Sutton, A. L., Nelson, D. W., Mayrose, V. B., Kelly, D. T., and Nye, J. C. (1984). Effect of copper levels in swine manure on corn and soil. J. Environ. Qual. 13, 198–203. Tam, N. F. Y., and Wong, Y. S. (1996). Retention and distribution of heavy metals in mangrove soils receiving wastewater. Environ. Pollut. 94, 283–291. Tarchitzky, J., Lerner, O., Shani, U., Arye, G., Lowengart-Aycicegi, A., Brener, A., and Chen, Y. (2007). Water distribution pattern in treated wastewater irrigated soils: Hydrophobicity effect. Eur. J. Soil Sci. 58, 573–588. Tessier, A., Campbell, P. G. C., and Bisson, M. (1979). Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844–851. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 295 Thevenot, M., Dousset, S., Hertkorn, N., Schmitt-Kopplin, P., and Andreux, F. (2009). Interactions of diuron with dissolved organic matter from organic amendments. Sci. Total Environ. 407, 4297–4302. Tom-Petersen, A., Leser, T. D., Marsh, T. L., and Nybroe, O. (2003). Effects of copper amendment on the bacterial community in agricultural soil analyzed by the T-RFLP technique. FEMS Microbiol. Ecol. 46, 53–62. Toze, S. (2006). Reuse of effluent water—Benefits and risks. Agric. Water Manage. 80, 147–159. Travis, M. J., Wiel-Shafran, A., Weisbrod, N., Adar, E., and Gross, A. (2010). Greywater reuse for irrigation: Effect on soil properties. Sci. Total Environ. 408, 2501–2508. Tufft, L. S., and Nockels, C. F. (1991). The effects of stress, Escherichia coli, dietary ethylenediaminetetraacetic acid, and their interaction on tissue trace elements in chicks. Poult. Sci. 70, 2439–2449. Tyler, L. D., and McBride, M. B. (1982). Mobility and extractability of cadmium, copper, nickel, and mineral soil columns. Soil Sci. 134, 198–225. Udovic, M., Plavc, Z., and Lestan, D. (2007). The effect of earthworms on the fractionation, mobility and bioavailability of Pb, Zn and Cd before and after soil leaching with EDTA. Chemosphere 70, 126–134. US EPA. (1992). United States Environmental Protection Authority Guidelines for water reuse. EPA/625/R-92/004. Washington, DC. US EPA. (2004). Guidelines for Water Reuse. EPA/625/R-04/108. Camp Dresser and McKee Inc. for the US Environmental Protection Agency, Washington, DC002E. Usman, A. R. A., Kuzyakov, Y., and Stahr, K. (2005). Effect of immobilizing substances and salinity on heavy metals availability to wheat grown on sewage sludge-contaminated soil. Soil Sediment Contam. 14, 329–344. USPHS (2000). Toxicological profile on CD-ROM. Agency for Toxic Substances and Disease Registry. U.S. Public Health Service. Utgikar, V. P., Tabak, H. H., Haines, J. R., and Govind, R. (2003). Quantification of toxic and inhibitory impact of copper and zinc on mixed cultures of sulfate-reducing bacteria. Biotechnol. Bioeng. 82, 306–312. van der Watt, H. V. H., Sumner, M. E., and Cabrera, M. L. (1994). Bioavailability of copper, manganese and zinc in poultry manure. J. Environ. Qual. 23, 43–49. van der Welle, M. E. W., Roelofs, J. G. M., Op den Camp, H. J. M., and Lamers, L. P. M. (2007). Predicting metal uptake by wetland plants under aerobic and anaerobic conditions. Environ. Toxicol. Chem. 26, 686–694. van Hees, P. A. W., Jones, D. L., Finlay, R., Godbold, D. L., and Lundström, U. S. (2005). The carbon we do not see—The impact of low molecular weight compounds on carbon dynamics and respiration in forest soils: A review. Soil Biol. Biochem. 37, 1–13. van Rhee, J. (1975). Copper contamination effects on earthworms by disposal of pig waste in pastures. In “Progress in Soil Zoology”. (J. Vanek, Ed.), Proceedings of the 5th International Colloquium on Soil Zoology, pp. 451–457. Prague, Junk publishers, The Hague. van Veen, E., Burton, N., Comber, S., and Gardner, M. (2002). Speciation of copper in sewage effluents and its toxicity to Daphnia magna. Environ. Toxicol. Chem. 21, 275–280. van Zomeren, A., and Comans, R. N. J. (2004). Contribution of natural organic matter to copper leaching from municipal solid waste incinerator bottom ash. Environ. Sci. Technol. 38, 3927–3932. Vinten, A. J. A., Mingelgrin, U., and Yaron, B. (1983a). The effect of suspended solids in wastewater on soil hydraulic conductivity: I. Suspended solids labelling method. Soil Sci. Soc. Am. J. 47, 402–407. Vinten, A. J. A., Mingelgrin, U., and Yaron, B. (1983b). The effect of suspended solids in wastewater on soil hydraulic conductivity: II. Vertical distribution of suspended solids. Soil. Sci. Soc. Am. J. 47, 408–412. 296 Anitha Kunhikrishnan et al. Violante, A., Cozzolino, V., Perelomov, L., Caporale, A., and Pigna, M. (2010). Mobility and bioavailability of heavy metals and metalloids in soil environments. J. Soil Sci. Plant Nutr. 10, 268–292. Virto, I., Bescansa, P., Imaz, M. J., and Enrique, A. (2006). Soil quality under foodprocessing wastewater irrigation in semi-arid land, northern Spain: Aggregation and organic matter fractions. J. Soil Water Conserv. 61, 398. Voegelin, A., Barmettler, K., and Kretzschmar, R. (2003). Heavy metal release from contaminated soils: Comparison of column leaching and batch extraction results. J. Environ. Qual. 32, 865–875. Vogeler, I. (2009). Effect of long-term wastewater application on soi physical properties. Water Air Soil Pollut. 196, 385–392. Walker, C., and Lin, H. S. (2008). Soil property changes after four decades of wastewater irrigation: A landscape perspective. Catena 73, 63–74. Walker, J. M., Southworth, R. M., and Rubin, A. B. (1997). U.S. Environmental Protection Agency regulations and other stake holders activities affecting agricultural use of byproducts and wastes. In “Agricultural Uses of By-Products and Wastes” (J. E. Rechcigl and H. C. MaKinnon, Eds.), pp. 28–47. ACS, Washington, DC. Wallach, R., Ben-Arie, O., and Graber, E. R. (2005). Soil water repellency induced by long-term irrigation with treated sewage effluent. J. Environ. Qual. 34, 1910–1920. Wallingford, G. W., Murphy, L. S., Powers, W. L., and Manges, H. L. (1975). Effects of beef feedlot manure and lagoon water on iron, zinc, manganese and copper content in corn and in DTPA soil extracts. Soil Sci. Soc. J. Am. 39, 482–487. Wang, H., Gielen, G. J. H. P., Judd, M. L., Stuthridge, T. R., Blackwell, B., Tomer, M. D., and Perace, S. (1999). Treatment efficiency of land application for thermo-mechanical pulp mill (TMP) effluent constituents. Appita J. 52, 383–386. Wang, Q. R., Cui, Y. S., Liu, X. M., Dong, Y. T., and Christie, P. (2003a). Soil contamination and plant uptake of heavy metals at polluted sites in China. J. Environ. Sci. Health Tox. Hazard. Subst. Environ. Eng. 38, 823–838. Wang, Z., Chang, A. C., Wu, L., and Crowley, D. (2003b). Assessing the soil quality of long-term reclaimed wastewater-irrigated cropland. Geoderma 114, 261–278. Wang, H., Magesan, G. N., and Bolan, N. S. (2004). An overview of the environmental effects of land application of farm effluents. N. Z. J. Agric. Res. 47, 389–403. Wang, D., Li, H., Wei, Z., Wang, X., and Hu, F. (2006). Effect of earthworms on the phytoremediation of zinc-polluted soil by ryegrass and Indian mustard. Biol. Fert. Soils 43, 120–123. Wen, B., Hu, X., Liu, Y., Wang, W., Feng, M., and Shan, X. (2004). The role of earthworms (Eisenia fetida) in influencing bioavailability of heavy metals in soils. Biol. Fert. Soils 40, 181–187. Weng, L., Temminghoff, E. J. M., Lofts, S., Tipping, E., and Van Riemsdijk, W. H. (2002). Complexation with dissolved organic matter and solubility control of heavy metals in a sandy soil. Environ. Sci. Technol. 36, 4804–4810. WHO (1989). Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture. World Health Organization, Geneva. WHO (2006). Guidelines for the Safe Use of Wastewater, Excreta and Greywater, Volume 2: Wastewater Use in Agriculture. World Health Organization, Geneva. Wightwick, A. M., Salzman, S. A., Reichman, S. M., Allinson, G., and Menzies, N. W. (2010). Inter-Regional variability in environmental availability of fungicide derived copper in vineyard soils: An australian case study. J. Agric. Food Chem. 58, 449–457. Wong, T. H. F., Breen, P. F., and Lloyd, S. D. (2000). Water Sensitive Road Design— Design Options for Improving Stormwater Quality of Road Runoff. Co-operative Research Centre for Catchment Hydrology, Melbourne, VIC. Wastewater and Bioavailability of Heavy Metal(Loid)s in Soil 297 Wong, J. W. C., Li, K. L., Zhou, L. X., and Selvam, A. (2007). The sorption of Cd and Zn by different soils in the presence of dissolved organic matter from sludge. Geoderma 137, 310–317. Wu, G. H., and Cao, S. S. (2010). Mercury and cadmium contamination of irrigation water, sediment, soil and shallow groundwater in a wastewater-irrigated field in Tianjin, China. Bull. Environ. Contam. Toxicol. 84, 336–341. Xu, H., Ephraim, J., Ledin, A., and Allard, B. (1989). Effects of fulvic acid on the adsorption of Cd (II) on alumina. Sci. Total Environ. 81–82, 653–660. Xu, J., Wu, L., Chang, A. C., and Zhang, Y. (2010). Impact of long-term reclaimed wastewater irrigation on agricultural soils: A preliminary assessment. J. Hazard. Mater. 183, 780–786. Yang, J. E., Skogley, E. O., Georgitis, S. J., and Ferguson, A. H. (1991). Phytoavailability soil test: Development and verification of theory. Soil Sci. Soc. Am. J. 55, 1358–1365. Ye, Z. H., Lin, Z. Q., Whiting, S. N., de Souza, M. P., and Terry, N. (2003). Possible use of constructed wetland to remove selenocyanate, arsenic, and boron from electric utility wastewater. Chemosphere 52, 1571–1579. Yeates, G. W. (1976). Earthworm population of a pasture spray-irrigated with dairy shed effluent. N. Z J. Agric. Res. 19, 387–391. Yeates, G. W. (1995). Effect of sewage effluent on soil fauna in a Pinus radiata plantation. Aust. J. Soil Res. 33, 555–564. Yu, H., Tay, J., and Wilson, F. (1997). A sustainable municipal wastewater treatment process for tropical and subtropical regions in developing countries. Water Sci. Technol. 35, 191–198. Yusuff, R. O., and Sonibare, J. A. (2004). Characterization of textile industries’ effluents in Kaduna, Nigeria and pollution implications. Global Nest J. 6, 211–220. Zhao, X., Rockne, K. J., Drummond, J. L., Hurley, R. K., Shade, C. W., and Hudson, R. J. M. (2008). Characterization of methyl mercury in dental wastewater and correlation with sulfate-reducing bacterial DNA. Environ. Sci. Technol. 42, 2780– 2786. Zhao, X., Dong, D., Hua, X., and Dong, S. (2009). Investigation of the transport and fate of Pb, Cd, Cr(VI) and As(V) in soil zones derived from moderately contaminated farmland in Northeast, China. J. Hazard. Mater. 170, 570–577. Zhou, L. X., and Wong, J. W. (2001). Effect of dissolved organic matter from sludge and sludge compost on soil copper sorption. J. Environ. Qual. 30, 878–883. Zhu, B., and Alva, A. (1993). Effect of pH on growth and uptake of copper by Swingle citrumelo seedlings. J Plant Nutr. 16, 1837–1845. Zhu, Y. M., Berry, D. F., and Martens, D. C. (1991). Copper availability in two soils amended with 11 annual applications of copper-enriched hog manure. Commun. Soil Sci. Plant Anal. 22, 769–783. Ziolko, D., Martin, O. V., Scrimshaw, M. D., and Lester, J. N. (2011). An evaluation of metal removal during wastewater treatment: The potential to achieve more stringent final effluent standards. Crit. Rev. Environ . Sci. Tech. 41, 733–769.