Testing of SteriPEN™, a Portable Ultraviolet Light Water Purifier, On

Environmental Consulting ~ Drinking Water Analysis ~ Radon Testing
Testing of SteriPEN™, a Portable Ultraviolet Light Water
Purifier, On 3 Liter Hydration Bladders to NSF International
Protocol P248, Emergency Military Operations Microbiological
Water Purifiers
May 21st, 2008
Research Conducted For:
Miles Maiden
Hydro-Photon, Inc.
262 Ellsworth Road
Blue Hill, Maine 04614
Jonathan T. Dyer
Laboratory Director
Rebecca L. Lebrun
Quality Control Officer
A & L Laboratory Inc. 3100 Hotel Road P.O. Box 1507 Auburn, Maine 04211-1507
Telephone: (207) 784-5354 Fax: (207) 782-5561 Email: allabs@adelphia.net
NELAP CERT #250103
MAINE CERT #ME021
1
NH CERT #2501
Introduction
SteriPEN™ is a portable, handheld device designed to disinfect water by using a short wave
germicidal ultraviolet (UV) light. The device, unlike traditional flow through UV water purifiers,
treats batches of water up to 1 liter. Though the method of treatment is slightly different the
concept is the same. The SteriPEN™ produces ultraviolet energy that is used to destroy
microorganisms, without the use of chemicals. The SteriPEN™ is submerged in the water, where
microorganisms are exposed to a dose of ultraviolet light in the 254-nanometer range. Ultraviolet
light in this wavelength inactivates a wide range of microorganisms including bacteria, viruses
and protozoan cysts. This inactivation occurs as the ultraviolet light disrupts the organism's DNA
structure, making reproduction impossible. The intensity of the ultraviolet light and the
microorganism's exposure time to the ultraviolet light are factors that influence which
microorganisms are inactivated [6].
This study will examine the effects of the SteriPEN™ on 3 Liter Hydration Bladders {Figure #1}.
The bladders were tested as described in the NSF International Protocol P248. – Emergency
Military Operations Microbiological Water Purifiers. The P248 Protocol calls for use of both
General Test Water and a Challenge Test Water in the 3 Liter Hydration Bladders..
Test Organism
MS2 Coliphage is the test organism designated by the P248 protocol. MS2 offers a high linear
response over a wide range of UV dose levels, UV inactivation results are highly reproducible,
it’s easily propagated to high titers, and it is non-pathogenic to humans [9].
The MS2 Coliphage was provided by Clancy Environmental Consultants, P.O. Box 314, St.
Albans, VT, 05478. Thomas Hargy, Senior Scientist at Clancy Consultants ran a collimated beam
study on samples of this MS2 to determine the virus’s UV dose response curve. Testing
concluded that a 2.1-log reduction of MS2 correlated with a dose of 40mJ/sq.cm. (see attached
collimated beam study).
Test Procedure
The testing procedure was done in accordance with the NSF International P248 Protocol –
Emergency Military Operations Microbiological Water Purifiers. The complete protocol is found
in the U.S. Army Center for Health Promotion and Preventive Medicine publication entitled
“WATER SUPPLY MANAGEMENT PROGRAM NO. 31-EC-04TM, NSF PROTOCOL P248
PURIFIER SPECIFIC TEST PLAN, HYDRO-PHOTON STERIPEN”.
Samples of both General Test Water (EPA Test Water # 1) and Challenge Test Water (EPA Test
Water #4) were used to compare the effects of the SteriPEN™ on both visually clear water and
water of known contaminant levels. The General Test Waters and the Challenge Test Waters
were created from laboratory reagent water. The required physical and chemical characteristics
of both waters are listed in Table #1. Neither water contained chlorine or any other disinfectant
residuals. pH in both types of water was measured by a Denver Instruments pH-ISE Meter
2
model # 225. The pH was adjusted using a 1N solution of sodium hydroxide (NaOH) and/or
hydrochloric acid (HCL). Total organic carbon (TOC) analyzed on a Shimadzu TOC-V
Combustion Analyzer was adjusted in the challenge water using potassium hydrogen phthalate.
The turbidity in the challenge water was achieved through the addition of A.C. Fine Test Dust
Measurements of turbidity were taken on a Hach 2100A Turbidimeter. Total dissolved solids,
measured by a YSI Conductivity Meter, were increased in both waters to the appropriate
concentrations by the use of sea salts. The alkalinity value was obtained by following Standard
Methods Number 4500-CO3. The UV absorption was measured with a Shimadzu UV-2501PC
Spectrophotometer and then the percent transmittance was calculated. Proper water
temperatures were monitored (Sper Scientific Infrared Thermometer 800048) and maintained
throughout the entire experiment. Please refer to Table #2 for the actual readings of each
parameter used in the test.
Table #1. Required chemical and physical characteristics of test water per U.S.E.P.A . Guide Standard[7]
Parameter
General Test Water
Challenge Test Water
<0.1 mg/L
<0.1 mg/L
6.5 - 8.5
6.5 - 8.5
<0.1 mg/L
10.0 – 15.0 mg/L
0.1 NTU - 5 NTU
30 NTU – 50 NTU
Chlorine Residual
pH
Total Organic Carbon (TOC)
Turbidity
Temperature
Total Dissolved Solids (TDS)
20ºC +/- 5ºC
4º +/- 1ºC
50 mg/L - 500 mg/L
1500 mg/L +/- 300 mg/L
measure
measure
measure
80 mg/L – 120 mg/L
measure
80 mg/L – 120 mg/L
Color U.V. Absorption
Color U.V. Transmittance
Alkalinity
Table #2. Actual chemical and physical characteristics of test water.
Parameter
General Test Water
Challenge Test Water
<0.10 mg/L
<0.10 mg/L
7.3
6.9
Total Organic Carbon (TOC)
<1 mg/L
11 mg/L
Turbidity
1.3 NTU
42 NTU
20ºC
4ºC
Chlorine Residual
pH
Temperature
Total Dissolved Solids (TDS)
Color U.V. Absorption
Color U.V. Transmittance
Alkalinity
92 mg/L
1670 mg/L
0.0125//cm
0.5400/cm
97.16%
98 mg/L
28.84%
106 mg/L
1. General Test Water - Bladder Test 1st Draw Sample (200ml to waste) and Running Sample
(1,500mls)
3
Although the specified bladder (Source Vagabond MOLLE) is nominally 3.0L (3,000mls) it will
only hold 2.85L (2,850mls) for this testing scenario with the pre-filter attachment on the bladder
(Figure 1 and Figure 2).
The SteriPENs™ and General Test Water were kept at 20°C. The General Test Water was spiked
with test organism MS-2 coliphage (Escherichia coli bacteriophage ATCC® 15597-B1™).
The hydration bladder was filled with 2.85L of the General Test Water. An air compressor with
regulator and filter were attached to the bite valve on the end of the bite tube.. The water in the
bite tube was blown back into the bladder. Once the tube was empty of water the bite valve was
closed preventing water from re-entering the bite tube. No water re-entered the bite tube until
sampling was initiated.
A control sample was removed from each 3 liter bladder of water. Three UV doses for three
liters of water (270 seconds total) were applied to each sample.. The UV dose was administered
according to the manufacturers instructions for treating between 0.5 –1.0 liter of water [5]. The
on/off button was pushed once to begin the treatment scenario.. The green LED flashed
indicating the SteriPEN™ was ready for use. The UV lamp end was then inserted through the
pre-filter adapter into the bladder sufficiently to submerge the water sensors.[Figure #3 and
Figure #4] and creating a seal between the SteriPEN™ unit and the bladder. The bladder was
then held in such a way as to rock it back and forth creating a wave motion for mixing [Figure #5
and Figure #6] for the 90 second cycle. At the end of the 90 second cycle the SteriPEN™ unit was
removed, the on/off button was pressed again and the procedure was repeated again and then a
third time for a total of three doses.
Two samples were taken through the bite tube. The first sample is the “1st Draw” which extracts
200mls of water from the bladder to waste and prior to sampling. The cap was screwed tight and
the bladder was inverted several times to mix before the second sample was taken. The second
sample is the “Run” sample which extracts 1,500mls to waste and prior to sampling. These two
aliquots were made into several dilutions and plated according to the agar layer method
described by Adams using E. coli host (Escherichia coli ATCC® 15597™) [1].
The testing was run in triplicate (three bladders) with a total of three runs per bladder which
equals nine (9) test sample points.
2. Challenge Test Water - Bladder Test 1st Draw Sample (200ml to waste) and Running Sample
(1,500mls)
Although the specified bladder (Source Vagabond MOLLE) is nominally 3.0L (3,000mls) it will
only hold 2.85L (2,850mls) for this testing scenario with the pre-filter attachment on the bladder
(Figure 1 and Figure 2).
The SteriPENs™ and Challenge Test Water were kept at 4°C. The Challenge Test Water was
spiked with test organism MS-2 coliphage (Escherichia coli bacteriophage ATCC® 15597-B1™).
The hydration bladder was filled with 2.85L of the General Test Water. An air compressor with
regulator and filter were attached to the bite valve on the end of the bite tube.. The water in the
bite tube was blown back into the bladder. Once the tube was empty of water the bite valve was
closed preventing water from re-entering the bite tube. No water re-entered the bite tube until
sampling was initiated.
4
A control sample was removed from each 3 liter bladder of water. Three UV doses for three
liters of water (270 seconds total) were applied to each sample.. The UV dose was administered
according to the manufacturers instructions for treating between 0.5 –1.0 liter of water [5]. The
on/off button was pushed once to begin the treatment scenario.. The green LED flashed
indicating the SteriPEN™ was ready for use. The UV lamp end was then inserted through the
pre-filter adapter into the bladder sufficiently to submerge the water sensors.[Figure #3 and
Figure #4) and creating a seal between the SteriPEN™ unit and the bladder. The bladder was
then held in such a way as to rock it back and forth creating a wave motion for mixing [Figure #5
and Figure #6) for the 90 second cycle. At the end of the 90 second cycle the SteriPEN™ unit was
removed, the on/off button was pressed again and the procedure was repeated again and then a
third time for a total of three doses.
Two samples were taken through the bite tube. The first sample is the “1st Draw” which extracts
200mls of water from the bladder to waste and prior to sampling. The cap was screwed tight and
the bladder was inverted several times to mix before the second sample was taken. The second
sample is the “Run” sample which extracts 1,500mls to waste and prior to sampling. These two
aliquots were made into several dilutions and plated according to the agar layer method
described by Adams using E. coli host (Escherichia coli ATCC® 15597™) [1].
The testing was run in triplicate (three bladders) with a total of three runs per bladder which
equals nine (9) test sample points.
Results
Table #3. Hydration Bladder with General Test Water (Three 90 Second doses) MS-2 coliphage Titer (PFU/ml)st
logarithmic reductions and percent kill – 1 Draw Sample (200mls to waste)
Trial #1
SteriPEN
SteriPEN
SteriPEN
Trial #2
SteriPEN
SteriPEN
SteriPEN
Trial #3
SteriPEN
SteriPEN
SteriPEN
Mean
Control
Untreated (T=0)
General Test Water
Treated (T=270 Sec)
#1
#2
#3
8.82E+05
8.51E+05
8.34E+05
6.46E+02
6.28E+02
6.39E+02
#1
#2
#3
8.88E+05
8.20E+05
9.33E+05
1.61E+03
1.71E+03
1.53E+03
#1
#2
#3
8.13E+05
8.46E+05
8.38E+05
2.21E+03
2.09E+03
2.03E+03
Log Reduction
3.1276
3.1352
3.1320
3.1157
2.7359
2.7416
2.6808
2.7852
2.5958
2.5649
2.6064
2.6160
2.8197
% Kill
99.9254%
99.9268%
99.9262%
99.9234%
99.8154%
99.8187%
99.7915%
99.8360%
99.7460%
99.7277%
99.7525%
99.7579%
99.8289%
Table #4. Hydration Bladder with General Test Water (Three 90 Second doses) MS2 coliphage Titer (PFU/ml)logarithmic reductions and percent kill – Running Sample (1,500mls to waste)
Control
Untreated (T=0)
Challenge Test Water
Treated (T=270 Sec)
5
Log Reduction
% Kill
Trial #1
SteriPEN
SteriPEN
SteriPEN
Trial #2
SteriPEN
SteriPEN
SteriPEN
Trial #3
SteriPEN
SteriPEN
SteriPEN
Mean
#1
#2
#3
7.36E+05
7.61E+05
7.89E+05
2.11E+03
2.22E+03
2.31E+03
#1
#2
#3
8.38E+05
7.94E+05
7.83E+05
2.71E+03
2.56E+03
2.59E+03
#1
#2
#3
8.05E+05
8.38E+05
8.18E+05
1.93E+03
2.44E+03
2.23E+03
2.5370
2.5426
2.5350
2.5335
2.4874
2.4903
2.4916
2.4805
2.5735
2.6202
2.5359
2.5644
2.5329
99.7096%
99.7133%
99.7083%
99.7072%
99.6745%
99.6766%
99.6776%
99.6692%
99.7322%
99.7602%
99.7088%
99.7274%
99.7055%
Table #5. Hydration Bladder with Challenge Test Water (Six 90 Second doses) MS2 coliphage Titer (PFU/ml)st
logarithmic reductions and percent kill – 1 Draw Sample (200mls to waste)
Trial #1
SteriPEN
SteriPEN
SteriPEN
Trial #2
SteriPEN
SteriPEN
SteriPEN
Trial #3
SteriPEN
SteriPEN
SteriPEN
Control
Untreated (T=0)
General Test Water
Treated (T=540 Sec)
#1
#2
#3
1.36E+06
9.94E+05
1.27E+06
6.06E+03
6.33E+03
6.17E+03
#1
#2
#3
9.26E+05
9.14E+05
9.19E+05
6.23E+03
6.44E+03
6.36E+03
#1
#2
#3
9.61E+05
9.54E+05
9.35E+05
3.31E+03
3.05E+03
3.16E+03
Mean
Log Reduction
% Kill
2.2877
2.3523
2.1962
2.3145
2.1613
2.1721
2.1521
2.1599
2.4764
2.4629
2.4952
2.4711
99.4782%
99.5557%
99.3634%
99.5153%
99.3102%
99.3272%
99.2954%
99.3079%
99.6660%
99.6556%
99.6803%
99.6620%
2.3082
99.4845%
Table #6. Hydration Bladder with Challenge Test Water (Six 90 Second Doses) MS2 coliphage Titer (PFU/ml)logarithmic reductions and percent kill – Running Sample (1,500mls to waste)
Control
Untreated (T=0)
Challenge Test Water
Treated (T=540 Sec)
Trial #1
6
Log Reduction
% Kill
2.1483
99.2867%
SteriPEN
SteriPEN
SteriPEN
Trial #2
SteriPEN
SteriPEN
SteriPEN
Trial #3
SteriPEN
SteriPEN
SteriPEN
Mean
#1
#2
#3
1.52E+06
1.28E+06
1.41E+06
9.87E+03
1.02E+04
9.79E+03
#1
#2
#3
9.98E+05
9.92E+05
9.84E+05
6.14E+03
6.52E+03
6.43E+03
#1
#2
#3
9.52E+05
9.69E+05
9.97E+05
4.86E+03
5.75E+03
5.44E+03
2.1872
2.0991
2.1584
2.1925
2.2108
2.2820
2.1846
2.2606
2.2920
2.2267
2.2631
2.2004
99.3502%
99.2040%
99.3057%
99.3577%
99.3845%
99.3424%
99.3462%
99.4502%
99.4895%
99.4066%
99.4544%
99.3648%
Conclusion
The evaluation of SteriPEN™ on the General Test Water {Table #3} resulted in a 2.82-log
reduction (99.829 %) of MS-2 coliphage after three doses (90 seconds each) and running 200mls
of sample to waste. The use of SteriPEN™ on the Challenge Test Water {Table #5} resulted in a
2.31-log reduction (99.485%) of MS-2 coliphage after a six doses (90 seconds each) and running
200mls of sample to waste. The increased contaminants in the challenge test water slightly
reduced the effectiveness of SteriPEN™ but not enough to decrease the log reduction to an
inadequate level.
The evaluation of SteriPEN™ on the General Test Water {Table #4} resulted in a 2.53-log
reduction (99.706 %) of MS-2 coliphage after three doses (90 seconds each) and running 1,500mls
of sample to waste. The use of SteriPEN™ on the Challenge Test Water {Table #6} resulted in a
2.20-log reduction (99.365%) of MS-2 coliphage after a six doses (90 seconds each) and running
1,500mls of sample to waste. The increased contaminants in the challenge test water slightly
reduced the effectiveness of SteriPEN™ but not enough to decrease the log reduction to an
inadequate level.
The testing conducted on both General Test Waters (2.82- log reduction and 2.53-log reduction
respectively) and Challenge Test Waters (2.31- log reduction and 2.20-log reduction respectively)
indicates that SteriPEN™ delivered UV doses in excess of the required 40mJ/sq.cm. and
therefore meets the requirements of the NSF International P248 Protocol – Emergency Military
Operations Microbiological Water Purifiers.
Jonathan T. Dyer/ Laboratory Director
Rebecca Lebrun/ Quality Assurance Officer
Figure #1
7
Hydration Bladder Unit
Figure #2
Hydration Bladder Unit with SteriPEN™ Adapter
Figure #3
8
Photograph of SteriPEN™ Inserted Into The Bladder
Figure #4
Closer Photograph Of The UV light Inside The Bladder
9
Figure #5
Tipping the Hydration Bladder Down to Create “Wave” Motion
Figure #6
Tipping the Hydration Bladder Up to Create “Wave” Motion
10
References
1. Adams, M. H. 1959. Bacteriophages. Interscience Publishers, New York
2. Enriquez, C. and Gerba, c. 2001. Evaluation of the Steri-Pen® Water Treatment System
According to the US Environmental Protection Agency Guide Standard And Protocol For
Testing of Microbiological Water Purifiers.
3. Hanson, Anne 2000. Testing of Steri-Pen, a Hand-held Ultraviolet Water Treatment Device
using MS2 Coliphage.
4. Hanson, Anne 2001. Testing of Steri-Pen, a Hand-held Ultraviolet Water Treatment Device
using MS2 Coliphage on Visually Turbid Natural Water.
5. Hydro-Photon, Inc., 2005 SteriPEN™ Users Guide, Blue Hill, Maine
http://www.hydro-photon.com/PDF/SteriPENEnglish.pdf
6. Ultraviolet Light Disinfection Technology In Drinking Water Application - An Overview.
United States Environmental Protection Agency, Office of Water. EPA 811-R-96-002.
September, 1996
7. U.S.E.P.A. - Task Force Report, 1987. Guide Standard and Protocol for Testing
Microbiological Water Purifiers. United States Environmental Protection Agency,
Registration Division, Office of Pesticide Programs and Criteria and Standards Division,
Office of Drinking Water, Washington, DC
8. U.S. Army Center for Health Promotion and Preventive Medicine, 2005. Technical
Information Paper; Ultraviolet Light Disinfection in the Use of Individual Water Purification
Devices, Aberdeen Proving Ground, MD.
9. Wilson, B.R.P.F. Roessler, E. Van Dellen, M. Abbaszadegan and C.P. Gerba. Coliphage MS2
as a UV Water Disinfection Efficacy Test Surrogate for Bacterial and Viral Pathogens.
University of Arizona, Tuczon, AZ
11
Appendix
12
CEC Clancy Environmental Consultants, Inc.
Consulting and Microbiological Laboratory Services
May 15, 2008
Mr. Miles Maiden
Hydro-Photon
P.O. Box 675
262 Ellsworth Rd.
Blue Hill, ME 04614
Dear Miles,
Please find enclosed the results of collimated beam testing performed on the coliphage
MS2 lot that was shipped to A&L Laboratory for disinfection system testing.
If you have any questions concerning this information, please contact me.
Sincerely,
CLANCY ENVIRONMENTAL CONSULTANTS, INC.
Thomas M. Hargy
Senior Scientist
P.O. Box 314, St. Albans, VT 05478 Telephone (802) 527-2460 Fax (802) 524-3909
13
CEC Clancy Environmental Consultants, Inc.
Consulting and Microbiological Laboratory Services
MS2 UV Dose Response
For Hydro-Photon
Test date: May 1, 2008
Clancy Environmental Consultants, Inc.
Purpose:
This study was undertaken to determine the sensitivity of a specific lot of coliphage MS2
to UV irradiation.
Methods:
Challenge microorganism: MS-2 phage obtained from the American Type Culture
Collection (ATCC #15597-B1) were propagated in the host bacteria Escherichia coli HS
(pFamp)R (ATCC #700891) using a large volume liquid culture method.7 Bacteria were
maintained at Clancy Environmental Consultants, Inc. (CEC) under liquid nitrogen for
long-term storage. Working cultures were prepared regularly from archived sub-samples.
All stocks were maintained on trypticase soy agar plates containing ampicillin and
streptomycin. Stock MS2 phage was propagated in batches with titers of approximately 5
X 1011 plaque forming units (pfu) per mL.
Collimated beam dose-response determination: Stock MS2 was diluted to a working
volume of 100 mL containing approximately 1 x 106/mL, for dose response
determination. The process, known as a collimated beam test (refer to Fig. 1) was carried
out at CEC. The UV source used was a low-pressure mercury vapor lamp (Atlantic
Ultraviolet G12T6L). This lamp was housed above a shutter. When the shutter was
opened, light from the lamp passed through a 12 cm collimating tube to irradiate the test
organisms suspended in a 6 cm diameter Petri dish. Prior to irradiations, the lamp was
allowed to warm up for a minimum of 30 min. The UV incident to the surface of the
Petri dish was then measured using a radiometer and detector (model X-911, Gigahertz
Optik) calibrated at 254 nm. The incident irradiation across the surface of the Petri dish
was measured at 5 mm intervals along an X-Y grid originating at the center of the dish.
Overall irradiance distribution was then determined relative to the center reading, which
was confirmed using a second radiometer (model 1400A, International Light). This value
was then used in the calculation of average irradiation incident to the water surface.
Factors influencing average irradiation to the entire volume include reflection from the
water surface, divergence of the UV light, depth of the water, and UV absorption of the
inoculated test water. The latter was measured at 254 nm by spectrophotometry
(Spectronic Genesys 10uv™). UV dose was defined as the irradiation multiplied by the
exposure time.
P.O. Box 314, St. Albans, VT 05478 Telephone (802) 527-2460 Fax (802) 524-3909
14
CEC Clancy Environmental Consultants, Inc.
Consulting and Microbiological Laboratory Services
Figure 1 – Collimated Beam Apparatus
Irradiations of sub-samples of the test water were made across a range of exposure times
to provide UV doses of 0, 15 30, 45, 60, 75 and 90 mJ/cm2. Ten-milliliter subsamples
were transferred to 6 cm diameter Petri dishes containing a 12 mm stir bar. After 1 min
of stirring, the UV lamp shutter was opened and the suspension irradiated for a predetermined length of time. A 0 mJ/cm2 dose was run simultaneously with the irradiation
test for the highest mJ/cm2 dose, in the absence of UV. This 0 dose control provides the
base count for determination of log inactivation. Each dose was run in duplicate.
Results:
Concentrations of survivors and resulting log10 inactivations achieved at the above doses
are given in Table 1 and Figure 2. The best fit equation for the average inactivation
values is the polynomial equation:
y = 2.831x2 + 13.19 +0.214
Thus if a UV disinfection test achieves 2.1 log inactivation of this MS2, a UV dose of
40.4 mJ/cm2 would have been delivered.
P.O. Box 314, St. Albans, VT 05478 Telephone (802) 527-2460 Fax (802) 524-3909
15
CEC Clancy Environmental Consultants, Inc.
Consulting and Microbiological Laboratory Services
Table 1. MS2 surviving concentrations and log10 inactivations in collimated dose
response test.
Lot #: 120407F
Replicate:
A
Dose
PFU/mL
CB date:
log
UV dose
01-May-08
Replicate:
B
Dose
PFU/mL
log
UV dose
UV dose
A
B
average
0
1.2E+06
6.10
0
1.3E+06
6.12
0
0.00
0.00
0.00
15
1.5E+05
5.17
15
1.5E+05
5.19
15.0
0.93
0.93
0.93
30
2.9E+04
4.47
30
2.9E+04
4.47
30.0
1.63
1.65
1.64
45
6.6E+03
3.82
45
7.1E+03
3.85
45.0
2.28
2.27
2.27
60
1.7E+03
3.23
60
2.1E+03
3.32
60.0
2.87
2.80
2.83
75
5.3E+02
2.72
75
6.1E+02
2.78
75.0
3.37
3.34
3.36
90
1.8E+02
2.26
90
3.1E+02
2.49
90.0
3.84
3.63
3.73
Figure 2. UV Dose response of MS2 Lot 120407F
UV dose response, Lot 120407F
90
80
70
60
UV Dose 50
2) 40
(mJ/cm
30
20
10
0
0.00
2 + 13.19x + 0.214
y = 2.831x
1.00
2.00
Average
Log
3.00
4.00
Inactivation
P.O. Box 314, St. Albans, VT 05478 Telephone (802) 527-2460 Fax (802) 524-3909
16