Radon and Lung Cancer

Radon and Lung Cancer
Jing Chen
Radiation Protection Bureau, Health Canada
9th Annual Air Quality & Health Workshop:
“Radon: Threats, Challenges & Actions
March 7th 2012, Vancouver
What is Radon ?
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Radon is a radioactive gas that is colourless, odourless and tasteless.
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As a gas, radon escapes from the ground into the air.
It is formed by the breakdown of uranium, a natural radioactive
material found in soil, rock and groundwater.
Radon is present in the air everywhere in varying concentrations.
Indoors:
Radon can be elevated.
Outdoors:
Radon is generally very low.
2
The link between radon and lung cancer
Lung cancer, called “miners disease”, was identified in the late 1800s.
The link between radon exposure and lung cancer was suggested at the
beginning of 1900s and confirmed in 1950s.
Radon risk at high exposure levels
was determined by epidemiological
means, in particular,
11 major epidemiological
studies of underground
miners.
(Exposed Canadians in the cohorts: 31,412)
Studies of exposed miners have
consistently found associations
between radon and lung cancer.
Radon in Homes
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The connection between radon and lung cancer in miners raised
concern that radon levels typically found in homes might cause lung
cancer in the general population.
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Radon in homes is generally much lower than radon in mines.
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However, individually these studies have not been large enough to
assess moderate risks reliably.
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Large studies or pooling of multiple studies are needed to fully
evaluate radon effects.
To directly validate the risk of lung cancer associated with residential
radon exposure over several decades, about 40 studies have been
conducted in various countries.
Radon in Homes
Results of pooled analyses in China, Europe and North American became
available in recent years.
Pooled analysis
Chinese (Lubin et al., 2004)
European
(Darby et al., 2005) North American
(Krewski et al., 2006)
European
(Darby, 2011)*
Number of studies included
% increase per 100Bq/m3
95% CI
2
13%
(1.01, 1.36) 13
8%
(1.03, 1.16)
7
10%
(0.99, 1.26)
5
16%
(1.05, 1.31)
* Results after detailed stratification for smoking history, and allowing for year-to-year
variation in measured radon concentration (presented at ICRP Symposium 2011).
Strong direct evidence that radon causes lung cancer
in the general population.
Radon in Homes
Pooled analyses confirmed strong direct evidence that
radon causes lung cancer in the general population.
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Why Radon Affects Lung ?
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Radon decays naturally by emitting alpha particles.
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Radon health effects result from inhalation of alpha emitting particles in the air.
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The dead outer layers of human skin is sufficient to
stop alpha particles from reaching sensitive cells.
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However, if alpha emitters have been inhaled,
very thin and sensitive lung tissue can be exposed
to alpha radiation => damaged lung cells => lung cancer.
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Other health effects of radon have not consistently
been demonstrated.
Its decay products decay further and emit alpha particles as well.
Radon decay products are electrically charged and can attach themselves to
tiny dust particles in the air.
Most alpha particles have energies between 4 to 7 MeV, and
all their energies are deposited within ~ 40µm layer of human tissue.
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Risk Factors
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The only confirmed health risk associated with exposure to radon is an
increased risk of developing lung cancer.
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The risk from radon exposure is long term and depends on 3 things:
1) the level of radon,
2) the length of exposure,
3) smoking habits or environment.
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Although children have been reported to be at greater risk than adults of
developing certain types of cancer from radiation, currently there is no
conclusive evidence that radon exposure places children at any greater risk.
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For a given length of exposure to a given radon level (eg. 10 yrs at 100 Bq/m3)
the radon risk is comparable for a 10yr old child, a 30yr old man, or a 60yr old
woman.
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However, children have more years to live and have more time to develop
latent diseases. Because of the long latency period for lung cancer, individuals
who receive radon exposures in childhood are more likely to live long enough
to develop lung cancer than those who receive exposures in later life.
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Risk Factors
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There is no known threshold concentration below which radon
exposure presents no risk.
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Radon is much more likely to cause lung cancer in people who smoke,
or who have smoked in the past, than in lifelong non-smokers.
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Radon is the primary cause of lung cancer among people who have
never smoked.
(200Bq/m3 doubles the lung cancer risk for never-smokers)
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Although radon exposure alone may not place children at any greater
risk than adults, environmental tobacco smoke (ETS) could potentially
increase a child’s risk of radon related lung cancer.
Children's lungs are more susceptible to
harmful effects from ETS.
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Radon Surveys in Canada
In 2007, Health Canada lowered the acceptable level of radon from 800
to 200 Bq/m3 for dwellings.
To gain a better understanding of radon concentrations in homes across
Canada, second more comprehensive radon survey completed in 2011.
1970s survey:
5-minute grab sampling
14,000 homes in 19 cities
2009-2011 survey:
3-month alpha-track measurements
14,000 homes in 121 Health Regions
Radon Surveys in Canada
4% more Canadians live in homes of radon concentrations > 200 Bq/m3
than previously estimated.
Radon distribution in Canada
1970s survey: GM=11.2 Bq/m3, GSD=3.9
Homes of Rn>200Bq/m3: 2-3%
2009/11 survey:GM=41.9 Bq/m3, GSD=2.8
Homes of Rn>200Bq/m3: 6-7%
In BC: GM=24.2Bq/m3, GSD=2.2
Homes of Rn>200Bq/m3: < 1%
World average (UNSCEAR)
GM=30 Bq/m3, GSD=2.3
Homes of Rn>200Bq/m3: ~1%
It is very difficult to predict the radon level in
a home.
The only way to determine whether a home
has high radon levels is to test for it.
Population Radon Risk Assessment
Lung cancer risk increases with increased exposure concentration.
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Based on the more accurate radon distribution characteristics
(population weighted) obtained from the cross Canada radon survey
(2009-2011)
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lung cancers in Canada due to indoor radon exposure are 16%
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compared to the previous estimate of 10%
Based on the more accurate radon distribution characteristics in BC
(population weighted) obtained from the cross Canada radon survey
(2009-2011)
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lung cancers in BC attributable to indoor radon exposure are 9%
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Compared to the Canada average of 16%
Population Radon Risk Assessment
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In 2011 there were 20,600 deaths from lung cancer in Canada
(11,300 in men and 9,300 in women)
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16% of 20,600 => 3261 (1805 in men, 1456 in women)
More than 3000 lung cancer deaths are due to residential radon exposure
in 2011.
In 2011 there were 2500 deaths from lung cancer in BC
(1337 in men and 1163 in women)
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9% of 2500 => 219 (118 in men, 101 in women)
More than 200 lung cancer deaths are due to residential radon exposure in
2011.
The majority of radon-induced lung cancers are caused by low and moderate
radon concentrations rather than by high radon concentrations, because only
a few people are exposed to high indoor radon concentrations.
Conclusions
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Radon exposure is a serious public health concern.
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There is some risk at any radon level.
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Most people killed by radon induced lung cancer would never have
developed the disease if they hadn’t also smoked.
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There is strong & ongoing need for radon education and awareness by
all levels of government, and in partnership with medical professionals,
16% of lung cancer deaths among Canadians are attributable to indoor
radon exposure.
The lower the indoor radon level, the more radon-induced lung cancers
could potentially be prevented each year.
to encourage Canadians to take action
to reduce radon-related deaths
Thanks