Arsenic in Drinking Water (1999) / Chapter Skim
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2 The U.S. Environmental Protection Agency's 1988 Risk Assessment for Arsenic
2 The U.S. Environmental Protection Agency's 1988 Risk Assessment for Arsenic
Pages 16-26
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From page 16... ...
The risk assessment is then discussed in light of the events and information from the past 10 years that might affect its interpretation and utility. Overview Of The EPA 1988 Special Report EPA's 1988 risk assessment for arsenic is a special report of the EPA Risk Assessment Forum. Its development was motivated by major scientific controversies within EPA surrounding the health effects of ingested arsenic.
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From page 17... ...
. The forum also concluded that the Taiwanese studies provide a reasonable basis for quantitative risk assessment of skin cancer in the United States, despite many uncertainties.
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Hazard Identification The EPA forum based its 1988 risk assessment on skin cancer as the health-effects end point. Evidence of an association between arsenic and cancer at internal sites (e.g., liver, kidney, lung, and bladder)
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(That model is called the "generalized multistage model" in the report and is also commonly known as the "multistage Weibull model.") Using that model, the forum found that the estimated risk of skin cancer at low doses increased linearly with dose and stated that the estimate should be considered an "upper-bound estimate" because multiple hits or threshold considerations might apply.
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The concern is that food items, principally rice and yams grown in arsenic-contaminated water and fish, might also have been a source of inorganic arsenic. It is noted that arsenic intake from sources other than the drinking water would overestimate the unit arsenic risk calculated from the Taiwan study (EPA 1988, p.
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The remainder of this chapter focuses on the 1988 EPA risk assessment and the developments since 1988 that might affect its interpretation and current usefulness. Data Limitations As stated previously, the EPA forum based its risk assessment on the Tseng study.
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Assumptions about exposure to arsenic are generally indicated in the forum's risk assessment. Briefly, each individual's rate of exposure to arsenic was treated as constant since birth.
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population by rescaling dose to account for differences between Taiwan and the United States in average body weight and average rate of consumption of drinking water. The first step was accomplished by fitting the multistage Weibull model to the Tseng data by maximum likelihood and then evaluating the fitted curve at a specified age and arsenic dose for an estimate of the prevalence of skin cancer at that age and dose.
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From page 24... ...
This special report of the EPA Risk Assessment Forum was limited to the issues of skin cancer and nutritional essentiality. Quantification of skin-cancer risk for hazard identification and dose-response assessment was based on three studies in humans.
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Although recognized as a source of arsenic in the forum's report, dietary intake of arsenic in Taiwan and the United States was not sufficiently documented to be included in the 1988 risk assessment. Only sparse data are currently available, but estimates of lifetime risk of skin cancer from consumption of arsenic in drinking water show that estimates could be sensitive to differences in dietary intake of arsenic.
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From page 26... ...
1983. Risk Assessment in the Federal Government: Managing the Process.
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