Washington

Toxic shock: the EPA's plans to reduce arsenic contamination of water have been dropped. Credit: AP

The US Environmental Protection Agency (EPA) is halting plans to lower the standard for arsenic in drinking water from 50 parts per billion (ppb) to 10 ppb, citing a lack of scientific evidence to justify the change.

The EPA says it will now seek an independent review of the science behind the lower standard, despite a 1999 study conducted by the National Academy of Sciences (NAS) at the EPA's request. In its report, the NAS recommended that the 50-ppb standard, set in 1942, be lowered “as promptly as possible” to an unspecified number.

A 10 ppb limit on inorganic arsenic is already recommended by the World Health Organization and by a 1998 directive from the European Union.

“Certainly the standard should be less than 50 ppb, but the scientific indicators are unclear as to whether the standard needs to go as low as 10 ppb,” said EPA Administrator Christie Whitman in a statement on the cancellation of the 10-ppb standard. She added that a new standard will quickly be devised to take its place.

But the former head of the EPA's water division, Chuck Fox, who was involved in drafting the 10-ppb rule, says that the available data could support a limit of as little as 5 ppb. “There's no question that there's enough science to justify bringing the standard down to 10 ppb,” he says.

The NAS report found that risks at low-level exposures to arsenic had not yet been directly established, but that extrapolation of existing data suggested a cancer risk of between 1 in 100 and 1 in 1,000 for people who regularly consumed water containing 50 ppb of arsenic.

A fresh study in this month's issue of the American Journal of Epidemiology (153, 411–418; 2001) is one of only a few that directly measure risk for arsenic levels around 10 ppb. It found that the risk of urinary tract cancer in Taiwanese farmers was significantly higher when consuming well water containing more than 100 ppb of arsenic compared with those consuming less than 10 ppb. But the increased risk among subjects drinking between 10 and 50 ppb was not statistically significant.

The 10-ppb arsenic rule was issued during the Clinton administration's last week in office, and Whitman considers it may have been a rushed decision. Fox disagrees, saying it is based on more than a decade of scientific and economic analysis.

→ http://www.nap.edu/books/0309063337/html/index.html

→ http://www.aje.oupjournals.org/content/vol153/issue5