Arsenic has long been used as a poison, most famously by the pair of elderly aunts in the play Arsenic and Old Lace. The murderous spinsters added a teaspoonful to a gallon of wine, but it takes a lot less than that to prove fatal. Scientists have discovered that arsenic may be hazardous even in the minute quantities found in many wells and municipal water systems in the U.S. In January, just before President George W. Bush took office, the Environmental Protection Agency finalized a long-awaited regulation reducing the amount of arsenic allowed in drinking water from 50 micrograms per liter—the U.S. standard since 1942—to 10 micrograms per liter, which is the standard used by the European Union and the World Health Organization. But in March the EPA—under the new leadership of Bush's appointee, Christie Whitman—withdrew the pending rule. And in April the agency asked the National Academy of Sciences (NAS) to reassess the research on arsenic, delaying a final decision until February 2002.

The scientists who have studied arsenic's health effects immediately assailed Whitman's decision. A growing number of epidemiological studies indicate that drinking arsenic-tainted water can cause skin, lung, liver and bladder cancers. A 1999 report by the NAS estimated that daily ingestion of water containing 50 micrograms of arsenic per liter would add about 1 percent to a person's lifetime risk of dying from cancer. That's about the same as the additional risk faced by a person who's living with a cigarette smoker. "The evidence against arsenic is very strong," says epidemiologist Allan H. Smith of the University of California at Berkeley. "But the EPA has created a false appearance of uncertainty."

Perhaps the best evidence comes from a long-term study of 40,000 villagers in southwestern Taiwan whose wells had high arsenic levels. (Because arsenic seeps into aquifers through the weathering of rocks and soils, it's generally more concentrated in groundwater than in lakes or streams.) In villages with the most severely contaminated wells, the death rates from bladder cancer were dozens of times above normal. Similar studies in Argentina and Chile later corroborated those findings. In a region of northern Chile, for example, researchers determined that 7 percent of all deaths among people over the age of 30 could be attributed to arsenic.

In the Taiwan study, the lowest median level of arsenic was 170 micrograms per liter. To determine the risk at the 50- and 10-microgram levels, epidemiologists extrapolated the health effects in a linear way (that is, half the exposure leads to half the cancer risk). Some toxicologists have criticized this approach, saying that arsenic concentrations may have to exceed a threshold level to cause cancer. But new research suggests that if this threshold exists, it is most likely well below 10 micrograms per liter.

In the U.S., most public water systems with high arsenic concentrations are in the western states [see table at left]. The EPA originally proposed lowering the arsenic standard to five micrograms per liter, but the agency doubled the allowable level after representatives of the water systems complained about the expense of removing the carcinogen. In the regulation issued in January, the agency estimated that 4,100 systems serving some 13 million people would have to pay a total of $180 million annually to implement the 10-microgram standard. The EPA claimed that the rule would prevent 21 to 30 deaths from lung and bladder cancer each year, but some epidemiologists say the standard could save 10 times as many lives.

So what prompted the EPA to suddenly call for a reassessment of the standard? Some environmentalists speculate that industry groups such as the National Mining Association, which filed a court petition in March to overturn the arsenic rule, put pressure on the Bush administration. The tailings from mines are often laced with arsenic. Because the EPA's cleanup regulations are based on drinking-water standards, tightening the restrictions on arsenic could vastly increase the cost of decontaminating abandoned mines, many of which are Superfund sites. Whitman has asked the NAS to review the EPA's risk analysis of arsenic. Many researchers fear that she will use the new report to justify a limit of 20 micrograms per liter, a standard that would cost about $110 million less than the stricter regulation but save only half as many lives. "The weaker standard would not be sufficient to protect public health," says Chuck Fox, who headed the EPA's Office of Water until the change of administrations. "The standard for arsenic should be as close to zero as feasible."

source: http://www.sciam.com/2001/0601issue/0601scicit2.html