Senator Dianne Feinstein's concern about perchlorate, a chemical that has contaminated the Colorado River and several Inland water supplies, follows recent reports in The Press-Enterprise and a scientific journal that raised questions about the study.

The research, sponsored by perchlorate manufacturers and users, became a cornerstone of the EPA's policy on how much of the chemical people can safely consume.

Feinstein released a letter Wednesday that she wrote to EPA Administrator Stephen Johnson reiterating some scientists' concerns about uncertainties in the study's data and how it has been interpreted.

Perchlorate is an oxidizer in rocket fuel, munitions, road flares and other products. It has been found in drinking water sources in at least 34 states and in samples of lettuce, cows' milk and human breast milk. In sufficient doses, the chemical can impair thyroid function and result in neurological impairment of fetuses and babies, metabolic disorders and other problems, scientists say.

"With such widespread contamination in my state and across the country, I have serious concerns over the health and well-being of the most vulnerable among the population -- infants, toddlers, pregnant women and their unborn children, and those with compromised immune systems," Feinstein wrote. Feinstein could not be reached for comment Wednesday.

An EPA press officer, Suzanne Ackerman, said the agency had received Feinstein's letter and is reviewing it.

In 2002, EPA scientists concluded that 1 part per billion of perchlorate was known to be safe in drinking water. The lower Colorado River and several Inland drinking-water supplies have higher levels.

Independent Study Sought

The next year, under pressure from the U.S. Department of Defense and defense contractors responsible for perchlorate contamination, the Bush administration asked the independent National Academy of Sciences to review perchlorate science.

In January, a National Academy panel concluded that people can safely consume 24 times more perchlorate than the amount reflected in the EPA's analysis in 2002.

The National Academy recommendation was based, in part, on a study by the late Dr. Monte Greer and industry consultants who concluded that seven people given water laced with about 245 parts per billion were unaffected by the chemical.

Unpublished data from the study, however, showed the thyroid function in two of the seven people appeared to be affected by the chemical, The Press-Enterprise reported last week.

Study co-author Richard Pleus, a Seattle-based toxicologist, has said the conclusions published in the Greer study were statistically and biologically significant. He could not be reached on Wednesday.

Scientists from California, Massachusetts, Connecticut, Maine and the EPA who reviewed the data all concluded perchlorate might affect people at lower doses than the Greer study reported.

National Academy panelists said in interviews last month that they relied on the Greer study's published conclusions -- and not the raw data about the seven adults who drank perchlorate-laced water for two weeks.

Dr. Richard Johnston, chairman of the academy's perchlorate panel and associate dean of research and development at the University of Colorado Medical School, defended the panel's work during a radio interview Tuesday on Pasadena-based KPCC (FM 89.3).

'Weakest Point'

The panel members were conservative and careful to protect everyone, including fetuses and babies, he said. Their conclusions were based on reviews of many studies, he said.

"If you want to attack the weakest point, it would be the Greer study and the seven individuals in that study, and the committee would agree," Johnston said.

Feinstein's letter also raised concerns about of the EPA's decision to accept the National Academy's recommendations without input from the public.

Gary Ginsberg is a Connecticut state toxicologist who co-wrote a scientific journal article, published last month, that was critical of the Greer study. He said in a telephone interview that the EPA allowed for much more input in 2000 when it set safe levels for methyl mercury, a chemical found in fish.

The EPA proposed a safe dose, then had a National Academy panel review relevant studies. EPA scientists then analyzed the panel's recommendations, rewrote the proposal and opened a public comment period.

"That was in stark contrast to what happened with perchlorate," Ginsberg said.

Kevin Mayer, the EPA's perchlorate coordinator for the Southwest region, said the agency's scientists were not asked to re-evaluate their 2002 proposed safe dose to incorporate the National Academy recommendation. Instead, EPA administrators adopted the National Academy's recommendation.