WASHINGTON -- The U.S. Environmental Protection Agency should develop a stricter standard for allowable levels of arsenic in the nation's drinking water supplies as soon as possible, says a new report by a committee of the National Research Council. Arsenic has long been identified as a toxicant, and in drinking water it has been associated with skin cancer and other disorders. But recent studies suggest that drinking water with high levels of arsenic also can lead to bladder and lung cancer, which are more likely to be fatal.
"New information on arsenic exposure and cancer indicate that EPA's current standard for acceptable levels of arsenic in drinking water does not sufficiently protect public health," said committee chair Robert Goyer, retired professor emeritus of pathology, University of Western Ontario, Chapel Hill, N.C. "Although additional research on arsenic is needed, available data indicate that EPA should set a new standard to ensure that amounts of arsenic in U.S. drinking water supplies are at levels that minimize potential health risks."
Inorganic arsenic, the form most likely to cause cancer, is a naturally occurring element in the Earth's crust. Arsenic is released into groundwater that travels through underground rocks and soil. Water from wells often has higher concentrations of arsenic than does surface water such as lakes and streams. Arsenic also can be found in plants, fish, and shellfish.
Serious health problems associated with very high levels of arsenic in drinking water have surfaced recently in India and Bangladesh. In the United States, water supplies rarely contain levels of arsenic above EPA's current maximum allowable amount of 50 micrograms of arsenic per liter of water. The standard was developed decades ago and remained in place after the EPA performed an assessment of skin cancer risks in 1988. However, the EPA assessment did not include risks for lung and bladder cancer.
New data and more precise models for estimating risk suggest that the likelihood of developing cancer from drinking water that contains the maximum allowable amount of arsenic greatly increases when lung and bladder cancers are included. For example, studies examining males who daily consume water that contains 50 micrograms of arsenic per liter show that they have about a 1 in 1,000 risk of developing bladder cancer, far exceeding EPA's goal of limiting cancer risks to 1 in 10,000. Moreover, the committee found that the choice of models used to estimate risks posed by arsenic in drinking water can significantly affect risk estimates.
Congress has required EPA to propose a new maximum allowable amount for arsenic in drinking water by January 2000, and to finalize the new standard by 2001. To help inform the agency's decision, the Research Council was asked to evaluate the latest information on the health effects of arsenic in drinking water and EPA's methods for assessing cancer risks. The Research Council committee was not charged with examining water treatment technologies or the economic impact of changing the standard.
EFFECTS OF ARSENIC
The committee examined clinical studies reported in medical literature and epidemiological data from several international studies, including research from Taiwan, Argentina, and Chile. These studies show that in addition to causing skin, bladder, and lung cancer, consuming arsenic in drinking water also can cause skin lesions, anemia, nerve damage, and circulatory problems.
Arsenic is readily absorbed from the gastrointestinal tract into the blood. The mechanisms through which arsenic causes cancer are not well understood, but data suggest that arsenic probably causes chromosomal abnormalities that lead to cancer. Sensitivity to arsenic's toxic effects -- including carcinogenic effects -- varies with each individual and appears to be influenced by such factors as nutrition and genetic susceptibility.
For many years, scientists have debated whether small amounts of arsenic could actually be beneficial in the human diet. Arsenic has not been tested as an essential nutrient for humans, and no evidence suggests that arsenic is required for any human biochemical processes, the committee said. Animal studies show that adding very high concentrations of arsenic to the diets of chicks, goats, and rats appears to affect growth, fertility, and litter size. But more research is needed to determine whether there are any nutritional effects in humans and animals.
UNCERTAINTIES IN ESTIMATES
No human studies of sufficient scope in the United States have directly examined whether regular consumption of arsenic in drinking water at EPA's current standard increases the risk of cancer or other adverse health effects. Rather, the committee's characterization of risk is based on findings from the international studies, experimental data on the mechanisms through which arsenic causes cancer, and available information on human susceptibility.
Problems in applying the data from the international studies were underscored by the committee. The studies measured exposure to arsenic in drinking water regionally, rather than assessing the amount of arsenic to which each individual was exposed. Moreover, most people in these studies were exposed to concentrations of more than 100 micrograms of arsenic per liter of water. More research is needed to assess how exposure to very small amounts of arsenic affects human health. However, these uncertainties do not change the committee's finding that exposure to arsenic in drinking water increases risks for developing bladder and lung cancer.
In addition, the committee identified several areas for further research, including:
The study was funded by the Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter.
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