Chemical in drinking water harms female thyroid

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Scientists have linked exposure to small levels of a chemical found in public drinking water supplies in 26 states to suppressed thyroid function in more than a third of women and girls 12 and older.

The exposure to perchlorate, a study showed, was most acute in women with low levels of iodine in their systems, said Dr. James L. Pirkle, director of sciences in the federal Centers for Disease Control (CDC) and Prevention's Environmental Health laboratory and the study's author.

"It's already been known that high levels of exposure to perchlorate [reduce] thyroid function, but this large study of more than 1,100 women marks the first time this effect has been shown from exposure to perchlorate at lower levels found in the general population ... the effect is not trivial," Dr. Pirkle said.

Levels of perchlorate commonly found in the population range from 0.2 micrograms per liter up to 100 micrograms per liter.

Perchlorate, both a naturally occurring and man-made chemical primarily used in making rocket fuel, may not be a household world across the nation, but it is well-known in California, where it seeped into the ground from operations of defense contractors and military bases. The chemical contaminated more than 450 wells and other water sources in Los Angeles, Sacramento and four other counties.

Perchlorate also is found in milk, cheese and lettuce, as well as in human breast milk and baby formula.

A report last year by the National Academy of Sciences found that perchlorate has been detected in the public drinking water supplies of more than 11 million Americans in 26 states.

In the new research, published online in the journal Environmental Health Perspectives, investigators explained that perchlorate blocks the thyroid gland's uptake of iodine, slowing metabolism and causing medical problems such as fatigue, depression and weight gain, especially in women with low levels of iodine. Infants and fetuses are also at risk from perchlorate exposure.

The CDC said the new research shows "that even small increases in perchlorate exposure may inhibit the thyroid's ability to absorb iodine from the bloodstream."

Findings from the CDC research indicate perchlorate puts women at much greater risk of thyroid disorders than they had previously thought. However, no such association was found with men.

The new data may help the Environmental Protection Agency as it considers whether to impose a drinking water standard. Such a standard is opposed by the Pentagon and its contractors, because they say cleaning up perchlorate could cost billions and there are no proven health benefits.

The CDC researchers are not calling their findings definitive. They plan another trial involving 1,200 to 1,400 women to try to duplicate their results.

If confirmed in the second study, their findings would be significant, given that 36 percent of U.S. women have low iodine levels.

"It would mean 36 percent of regular women in the U.S. population have a relationship between thyroid function and levels of perchlorate in the environment," Dr. Pirkle said.