A chemical from rocket fuel that has seeped into drinking-water supplies nationwide is safe at higher doses than federal environmental officials had concluded, according to a report released yesterday.
The chemical, perchlorate, can be ingested safely at doses more than 20 times those deemed safe by the Environmental Protection Agency, an expert panel convened by the National Academy of Sciences concluded.
The conclusion was praised by defense contractors facing potentially billions of dollars in cleanup costs but denounced by environmental activists, who accused the Defense Department, defense industry and White House of exerting undue influence on the panel.
The assessment is considered crucial for the EPA, which is establishing the first national standards for the pollutant, and for dozens of states that have been setting their own standards for cleaning up military and industrial sites to try to safeguard drinking water.
"[This] should protect even the most sensitive populations," said Richard B. Johnston Jr. of the University of Colorado School of Medicine in Denver, who chaired the panel.
Perchlorate is used in a variety of industrial processes, but contamination in the United States comes primarily from rocket fuel. Concern has been rising about its safety in recent years as the substance was detected in soil and drinking water around the country.
Perchlorate has been found in at least 35 states, and more than 11 million people have significant levels in their drinking water. The Food and Drug Administration also recently found the substance in milk and lettuce.
At high doses, perchlorate can interfere with the thyroid gland, which helps regulate many bodily functions. Animal studies have suggested it could cause thyroid tumors. In children, the thyroid plays a major role in development, raising fears that exposure to perchlorate by pregnant women and young children could cause brain damage.
The health concerns prompted the EPA to begin drafting the first national standard for safe levels, and in 2002 the agency concluded in a draft assessment that perchlorate levels in drinking water should be no higher than 1 part per billion. That prompted protests from the Defense Department and defense contractors, which face potentially billions of dollars in cleanup costs.
They maintained that the substance posed no danger even at levels several hundred times as high.
In an attempt to resolve the dispute, the federal government asked the National Research Council, an arm of the National Academy of Sciences, to convene an expert panel to examine the issue.
After spending months reviewing all available scientific evidence, the 15-member panel concluded that humans could safely ingest levels as high as 0.0007 milligrams per kilogram of body weight, which is more than 20 times the dose of 0.00003 milligrams per kilogram that the EPA had recommended. The committee did not translate that into parts per billion of drinking water.
The committee said it concluded that perchlorate was much less likely to cause thyroid tumors in humans than the EPA had determined because humans are much less susceptible to disruption of thyroid functions and formation of thyroid tumors than are rats, the subjects of earlier studies.
"The committee concludes that the development of thyroid tumors, as an ultimate result of perchlorate-caused inhibition of thyroid iodide uptake, is unlikely in humans," the report said.