Arsenic in Drinking Water 2001 Update (2001) / Chapter Skim
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From page 1... ...
In 198S, EPA conducted a risk assessment for arsenic in drinking water and, in 1996, requested that the National Research Council (NRC) , the operating arm of the National Academy of Sciences and the National Academy of Engineering, independently review the scientific database and evaluate the scientific validity of that risk assessment.
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From page 2... ...
The 2001 subcommittee was charged with the task of preparing a report updating the scientific analyses, uncertainties, and findings of the 1999 report on the basis of relevant toxicological and health-effects studies published and relevant data developed since the ~ 999 NRC report and to evaluate the analyses subsequently conducted by EPA in support of its regulatory decisionmaking for arsenic in drinking water. The subcommittee was charged and constituted to address only scientific topics relevant to toxicological risk and health effects of arsenic.
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From page 3... ...
It also heard presentations from the EPA administrator; other EPA representatives; the EPA Science Advisory Board; other scientists with expertise in arsenic toxicity; federal, state, and local government agencies; trade organizations; public-interest groups; and concerned individuals. The subcommittee evaluated the arsenic hazard assessment conducted by EPA for the pending arsenic standard published in the January 22, 2001, Federal Register and considered the comments made in the EPA Science Advisory Board's December 2000 report on the previously proposed rule.
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From page 4... ...
The strengths of the recent studies from Chile and northeastern Taiwan include the evaluation of some potential confounding factors affecting the observed association between arsenic ingestion and cancer in newly diagnosed cases. Although the recent study in southwestern Taiwan is limited in its exposure assessment, it addresses the issue of lifestyle differences (e.g., diet, smoking)
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From page 5... ...
The other recent studies of arsenic in humans, taken together with the many studies discussed in the 1999 NRC report, provide a sound and sufficient database showing an association between bladder and lung cancers and chronic arsenic exposure in drinking water, and they provide a basis for quantitative risk assessment. The subcommittee concludes that the early data from southwestern Taiwan remain appropriate for use in dose-response assessment of arsenic in Winking water.
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From page 6... ...
If an agent acts indirectly, the possibility of sublinear extrapolation is considered (i.e., such extrapolation has sometimes been interpreted to indicate a "threshold" for effects.) In the absence of definitive mode-of-action data, EPA's general policy is to use a linear extrapolation from the observed data range for its carcinogenic risk assessments.
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From page 7... ...
Furthermore, similar increases in risk have been associated with chronic arsenic exposure in many other countnes, including Chile and Argentina, where poor nutrition and low-protein diets are not issues. Therefore, the subcommittee concludes that the risk estimates based on the southwestern Taiwanese data are not substantially affected by differences in nutritional status or diet.
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From page 8... ...
There are no data available to indicate that smoking is a significant confounder of the observed association between exposure to arsenic in drinking water and an increase in lung or bladder cancer. However, several of the epidemiological studies reviewed by the subcommittee suggest the possibility of an interaction between smoking and arsenic on the risk of lung cancer or bladder cancer, but this potential effect requires further confirmation and characterization.
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From page 9... ...
The EDIT values estimated for the southwestern Taiwanese study ranged from 33 to 94 ,ug/L for lung cancer, and from 102 to 443 ,ug/L for bladder cancer, depending on the choice of statistical model. The previous NRC Subcommittee on Arsenic in Drinking Water estimated EDIT values for male bladder cancer mortality of 404 to 450 ~g/L, depending on the model used.
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From page 10... ...
The differences between these two approaches are discussed in a later section. The subcommittee investigated the extent ofthe variability among different types of statistical models using a model-weighting approach and also assessed the impact of differences in background incidence rates between different populations when using relative risks in a risk assessment.
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From page 11... ...
The corresponding risks estimated using Taiwanese background cancer rates would be approximately 2-fold lower for female bladder cancer, 3-fold lower for male bladder cancer, 3-fold Tower for female lung cancer, and 2-fold lower for mate lung
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Populations Exposed at Various Concentrations of Arsenic In Drinking Waterb C Arsenic Bladder Cancer Concentration Lung Cancer Females Males Females Males ~3 4 7 5 4 5 6 11 9 7 10 12 23 18 14 20 24 45 36 27 a The maximum-likelihood estimate is the central point estimate from the distribution of risk calculated using a particular statistical model and data set (see note b)
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From page 14... ...
The theoretical lifetime excess cancer risks estimated by the subcommittee and the uncertainties surrounding those estimates as presented in this report should be interpreted in a public-health context that uses an appropriate riskmanagement framework. In summary, the subcommittee concludes that recent studies and analyses enhance the confidence in risk estimates that suggest chronic arsenic exposure is associated with an increased incidence of bladder and lung cancer at arsenic concentrations in drinking water that are below the current MCL of 50 Egg.
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