New studies strengthen the evidence of a link between bladder and lung cancer and exposure to arsenic in drinking water, according to a report from the National Academies'' National Research Council.
"Even very low concentrations of arsenic in drinking water appear to be associated with a higher incidence of cancer," said Robert Goyer, chair of the committee that wrote the report and professor emeritus of pathology, University of Western Ontario, now living in Chapel Hill, N.C. "We estimated the risk of developing cancer at various arsenic concentrations, and now it is up to the federal government to determine an acceptable level to allow in drinking-water supplies."
The report''s findings are consistent with those of a 1999 National Research Council report that found high risks of cancer at EPA''s maximum allowable level for arsenic in drinking water, which at the time was 50 micrograms per liter, or parts per billion.
The agency lowered its standard to 10 parts per billion in January, but in March put the new rule on hold and asked the National Research Council to review research findings from the last two years on the health effects of arsenic. In particular, it asked for an evaluation of the cancer risk posed by daily consumption of water with arsenic levels of 3, 5, 10, and 20 parts per billion.
The committee found that men and women who daily consume water containing 3 parts per billion of arsenic have about a 1 in 1,000 increased risk of developing bladder or lung cancer during their lifetime.
At 5 parts per billion, the risk is about 1.5 in 1,000; at 10 parts per billion, it is greater than 3 in 1,000; and at 20 parts per billion, it is close to 7 in 1,000.
The committee''s risk estimates are greater than those on which EPA based its pending rule in January because the committee used some different estimation methods and assumptions.
For example, it compared cancer rates between people exposed to arsenic in southwestern Taiwan and a large, mostly unexposed Taiwanese population, whereas EPA only compared cancer rates within the study population itself. EPA also assumed that the Taiwanese consumed more food and cooking water that contain arsenic than the committee considered reasonable.
The committee addressed only the hazards from consuming water contaminated with arsenic, which can seep from natural sources or be discharged by agricultural and industrial processes.
It was not asked to evaluate current levels of arsenic in U.S. drinking water supplies or to make policy recommendations, nor was it asked to carry out any of the cost-benefit analyses the government will need in order to set a maximum allowable level for arsenic in drinking water.
At the time of the 1999 report, studies from southwestern Taiwan -- where people were exposed to large amounts of arsenic in drinking water -- were judged to provide the best data for estimating cancer risks.
Since then, additional studies in Taiwan, Bangladesh, Chile, China and Finland have shown an association between exposure to arsenic in drinking water and cancer.
The data showing a relationship between chronic exposure to arsenic in drinking water and cancer are abundant. However, more research is needed to study the extent to which exposure also causes diseases other than cancer, the committee said. Some studies overseas have linked arsenic exposure to diabetes, respiratory and cardiovascular ailments, and birth defects. Future studies also should be large enough to detect risks to potentially sensitive groups, such as children and smokers. In addition, the biological mechanisms by which arsenic causes cancer need to be better understood, according to the committee.
by Virginia Foran