Debate Is Over Safe Levels Of Toxin Causes Harm. Perchlorate is one of a newly recognized group of toxins called endocrine disrupters chemicals such as dioxin and PCBs that can alter hormonal balances and thus impede human reproduction and development.
The debate is over how much perchlorate causes harm, and whether fetuses and infants are more susceptible than adults to perchlorate’s effects at very low doses.
The EPA, citing experiments on rats and epidemiological studies in Arizona and California, says perchlorate is dangerous in drinking water at levels above one part per billion. The Pentagon and defense industry, citing human experiments and epidemiological studies in Chile, say perchlorate is safe in drinking water below 200 ppb. Billions of dollars in cleanup and liability costs may hang in the balance, since most perchlorate plumes in the U.S., including the Colorado River, range between four and 100 ppb.
In 1993, several defense contractors, backed by the Pentagon, created the Perchlorate Study Group to research toxicity. The group’s “goal,” according to an internal document written in 1996 by GenCorp’s Aerojet subsidiary, was “to provide EPA with a scientific-based argument to justify a higher [reference dose] and thus a more reasonable remediation standard.” The industry group has spent roughly $7 million on toxicity studies.
In Your Backyard?
Perchlorate has been found in local drinking wells across the country in amounts that could be causing the slow spread of serious disease. Read the full article.
Yet, as with other contentious toxins such as arsenic and lead, the more information EPA scientists learned about perchlorate, the more they worried about its effects. Their main concern focuses on changes found in the brain size of laboratory rat pups exposed to low doses of perchlorate in utero. Such changes in so-called brain morphometry indicate perchlorate’s thyroid effects may cause permanent neurological damage in rats as well as people, the EPA says, because the thyroid system works similarly in both species.
The Pentagon and its allies say the rat studies, which the industry’s study group directed and sponsored, used poor autopsy techniques on the rats. And why trust rat data, they argue, when human data are available? The Pentagon and its allies cite an Oregon study that found small doses of perchlorate, given orally to adult volunteers, had little effect on thyroid-hormone levels.
The EPA says the human study didn’t examine the most-sensitive subgroups pregnant mothers and infants and was much too brief to measure the effects of long-term exposure.
To counter, the defense establishment cites an epidemiological study of three Chilean villages with varying levels of naturally occurring perchlorate in their drinking water. The study’s conclusion: Perchlorate had little effect on the thyroid-hormone levels of newborns and children in the three villages studied.
The EPA prefers a different epidemiological study that it claims shows “strong evidence” of perchlorate’s danger to infants. That study found California babies born to mothers exposed to trace amounts of perchlorate in drinking water had lower thyroid-hormone levels at birth than did infants of nonexposed moms. California’s Office of Environmental Health Hazard Assessment recently used that study, and other human data, to derive its own “health goal” for perchlorate in drinking water of two ppb.