Food is the primary source of perchlorate for most Americans, and U.S. toddlers on average are being exposed to more than half of the U.S. EPA's safe dose from food alone, according to a new U.S. Food and Drug Administration (FDA) diet survey designed to provide perchlorate and iodine intake averages from food for the entire U.S. Even though the new study is silent on intake by highly exposed populations, several lawmakers and environmental advocates renew their calls for a national perchlorate drinking-water standard, EPA is not divulging its plans.
The agency, which has been waiting for the results from the FDA study to help it decide whether to set a national drinking-water standard for perchlorate, intends to issue a preliminary determination on whether to regulate the substance soon, according to Benjamin Grumbles, assistant administrator of EPA's Office of Water. EPA has been investigating the contaminant for almost a decade.
Perchlorate is well known as a major component in rocket fuel, but the chemical also forms naturally. In sufficient amounts it disrupts the thyroid by inhibiting the uptake of iodide, an essential component of thyroid hormones. Because these hormones direct brain development, health concerns have focused on fetuses and young infants. A National Academy of Sciences (NAS) committee in 2005 recommended a safe dose of 0.7 micrograms per kilogram of body weight per day, and EPA adopted this as its reference dose.
As part of FDA's existing Total Diet Study, agency scientists measured perchlorate levels in 285 foods obtained from grocery stores and fast-food outlets in different parts of the U.S. between 2003 and 2006. To estimate exposure, they combined the analytical results with food consumption estimates. Drinking water was excluded from the survey.
Other studies have found perchlorate in food, but this is the first to estimate exposure for the U.S. population. Toxicologist Gary Ginsberg of the Connecticut Department of Public Health notes that the FDA estimates for adult exposure to perchlorate from food, about 10% of the reference dose, agree well with biomonitoring data collected by the Centers for Disease Control and Prevention (CDC). But the FDA survey cannot estimate extremes of exposure. "The CDC study found a fourfold increase from the average to the extremely exposed. . . . If this holds for toddlers, then some are likely to be way above the safe dose," he says.
FDA toxicologist and study author Michael Bolger acknowledges that the survey on its own provides no information about the distribution of perchlorate exposures.
For iodine, the FDA study has similar limitations. CDC data indicate that about one-third of American women are deficient in iodine. "But those people don't show up in the FDA study," says Robert Utiger of the Harvard Institute of Medicine.
Although some lawmakers and environmental groups argue that the new study emphasizes the need for a national drinking-water standard, EPA has not declared its intentions. The Safe Drinking Water Act requires that a contaminant be capable of causing adverse health effects and occur in public water systems at a frequency and level of public-health concern. In addition, the proposed regulation must provide a meaningful opportunity for reducing health risks, says Alan Roberson, director of regulatory affairs at the American Water Works Association.
EPA is considering health effects studies published after the NAS study, according to a May 2007 Federal Register notice (72, 24,016-24,058). These include the CDC study, which found that women with low iodine levels who are exposed to perchlorate may have impaired thyroid function even when their exposure level is below the EPA safe dose.
Perchlorate has been found in drinking water from 4% of major water supply systems in 28 states at levels of at least 4 parts per billion (ppb). Scientists with the Environmental Working Group calculate that perchlorate concentrations in drinking water would need to be lower than 2 ppb to keep toddlers' exposure below the safe-dose level.
As for providing a meaningful opportunity to reduce health risks, Ginsberg notes that water companies know how to get perchlorate out of drinking water. "But we really don't know how to get perchlorate out of food. By getting it out of the water we can reduce the health risk," he adds. -REBECCA RENNER
Perchlorate In Food
A new FDA study provides averages but doesn't include highly exposed populations
By Rebecca Renner
Environmental Science & Technology, February 13, 2008
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