IN 1976 under the Safe Drinking Water Act, the U.S. Environmental
Protection Agency (EPA) proposed an interim maximum contaminant level
(MCL) for arsenic in drinking water of 50 micrograms per liter (μg/L) as part of
the National Interim Primary Drinking Water Standards. That standard will
apply until EPA adopts a new MCL. As part of a periodic review process, EPA
has been reviewing data on arsenic exposure and toxicity to determine the
adequacy of the 50-μg/L MCL for protecting public health. To ensure a solid
and unbiased scientific basis for its arsenic standard for drinking water and
surface waters, EPA requested that the National Research Council (NRC)
review and comment on the arsenic toxicity data base and evaluate the scientific
validity of EPA's 1988 risk assessment for arsenic in drinking water.
For this report, the Subcommittee on Arsenic in Drinking Water of the
NRC's Committee on Toxicology reviewed EPA's characterization of existing
human health risks from ingestion of arsenic found in drinking water and food;
determined the adequacy of the current EPA MCL for protecting human health
in the context of stated EPA policy; and identified priorities for research to fill
data gaps. The subcommittee evaluated the Taiwanese epidemiological data for
carcinogenic and noncarcinogenic health effects of arsenic exposure; compared
effects of arsenic exposure demonstrated in other countries, including the
United States, with those documented for Taiwanese populations; and reviewed
data on toxicokinetics, metabolism, and mechanism and mode of action of
arsenic to ascertain how these data could assist in assessing human health risks
from arsenic exposures. In areas where the subcommittee concluded that EPA
could improve the toxicity analysis and risk characterization, specific changes
are recommended, and the implications of the changes for EPA's current MCL
for arsenic are described in this report.