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EPA's characterization of human health risks from ingestion of arsenic compounds found in food and drinking water and the uncertainties associated with that characterization; (2) review available data on cancer and noncancer health effects from exposure to arsenic compounds in drinking water and the implications of these effects on the assessment of the human health risks from arsenic exposure; (3) review data on the toxicokinetics, metabolism, and mechanism or mode of action of arsenic and ascertain how these data could assist in assessing human health risks from drinking-water exposures; and (4) identify research priorities to fill data gaps. EPA did not request, nor did the subcommittee endeavor to provide, a formal risk assessment for arsenic in drinking water.

The Subcommittee's Approach To Its Charge

The subcommittee evaluated data relating to key elements of the risk-assessment process—hazard identification, dose response, and risk characterization—that addresses the protective nature of the current MCL. Specifically, the subcommittee reviewed information on the health effects of arsenic exposure and data on the disposition and the mechanism or mode of action of arsenic. The subcommittee also evaluated other information that could affect the risk assessment, such as variations in human susceptibility, and current capabilities to measure arsenic in various media, including biological tissues. The major conclusions and recommendations of the subcommittee in each of those areas are discussed in the remainder of this summary. The implications of these findings on the assessment of human health risk is provided below in the section on risk characterization.

The Subcommittee's Evaluation

Health Effects

The subcommittee concludes that there is sufficient evidence from human epidemiological studies in Taiwan, Chile, and Argentina that chronic ingestion of inorganic arsenic causes bladder and lung cancer, as well as skin cancer. With minor exceptions, epidemiological studies for cancer are based on populations exposed to arsenic concentrations in drinking water of at least several hundred micrograms per liter. Few data address the degree of cancer risk at lower concentrations of ingested arsenic. Noncancer effects resulting from chronic ingestion of inorganic arsenic have been detected at doses of 0.01 milligram per kilogram (mg/kg) and higher per day. Of the noncancer

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