National Academy of Sciences (NAS) panel has found that the cancer risks of arsenic in drinking water are even greater than had been thought. The panel's report, released 11 September, comes 6 months after the Bush Administration shelved the Environmental Protection Agency's (EPA's) proposal to clamp down on arsenic, sparking an outcry from environmentalists and some members of Congress (ScienceNOW, 21 March). EPA administrator Christie Whitman, who requested the NAS review, now appears to have little choice but to adopt a standard at least as tough as the one she had delayed.
Studies of people exposed to high levels of arsenic in water have linked the metal to elevated rates of internal cancers. After a 1999 NAS review found that the current standard of 50 parts per billion (ppb) wasn't sufficiently protective, the outgoing Clinton Administration proposed tightening it to 10 ppb, based on a study of arsenic and cancer in Taiwan. But officials from Western states with naturally high levels of arsenic protested that the cost of cleaning up the water would be overwhelming. In April, EPA asked the academy to review the latest science supporting levels between 3 ppb and 20 ppb.
This new panel concluded that the analysis on which EPA based the 10-ppb proposal had actually underestimated the risks. "Four new epidemiological studies were key," says panel chair Robert Goyer, a pathologist retired from the University of Western Ontario. New studies from Chile and Taiwan counter the suggestion that earlier results had been skewed by malnutrition. When panel members recalculated the risks in a slightly different way from an analysis EPA used, they concluded that the risks for lung and bladder cancer were higher. For example, at 10 ppb, the study that EPA relied on estimated up to 0.8 extra cases per 1000 people, while the panel found a risk of about 1.3 to 3.7 extra cases, depending on the background cancer rate.
An EPA spokesperson declined to speculate on whether the new standard would be 10 ppb or lower but said Whitman is now "more concerned, not less" about arsenic risks. Her decision is due out by February.