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Perceptions Of Perchlorate

July 30, 2007 | A version of this story appeared in Volume 85, Issue 31

Concerning perchlorate, the horse has already left the barn (C&EN, May 14, page 39). We have been exposed to perchlorate for decades with no adverse effects on infants or children. The problem is one of public health, such as the iodide supplementation of food.

Epidemiological studies involving thousands of children show no significant effects from perchlorate exposure (about 5-120 µg/L in water). Additionally, all newborn infants are tested for thyroid function. Skeptics will insist breast milk still presents risks to infants of iodide-deficient mothers. But urinary iodide levels in U.S. women are half of 1970 levels, so the problem is not perchlorate ingestion. Rather, the problem is more likely a decrease in dietary iodide (a result of the substitution of iodide with bromide in bread in the 1980s). The article states that "an estimated 43 million women in the U.S. have iodide levels low enough to put them at increased risk of developing goiter." Wouldn't it make more sense to resupplement iodide in staple foods, as we did in the past?

Studies show that iodide and perchlorate compete reversibly in the thyroid and are effectively excreted (half-life of about seven hours or >98% excreted in 48 hours). The National Research Council developed a no-observed-effect-level (NOEL) of 0.007 mg/kg/day using a human study (the "Greer study") rather than extrapolating from laboratory animals to evaluate the most sensitive endpoint (uptake of iodide by the thyroid gland). This dose was then divided by a safety factor of 10 to protect sensitive individuals such as nursing mothers and infants (the Environmental Protection Agency adopted 0.0007 mg/kg/day as its "reference dose").

But regulatory agencies are now double-dipping: Massachusetts adds two more safety factors of 3, calling the NOEL a lowest-observed-effect-adverse-level and correcting for "database deficiencies." My research has found a safe level 100 times lower than the NOEL—extremely conservative.

This is reminiscent of the use of Alar pesticide on apples (remember Meryl Streep testifying before Congress?) and EPA's caution on eating fish to avoid exposure to dioxins (I now eat more apples and fish). Evidence showing that perchlorate does not pose risks to humans is overwhelming: There have been hundreds of articles, an NRC expert report, and landmark epidemiological studies involving newborns and children. Application of Chilean fertilizer has made perchlorate ubiquitous in the U.S. for almost a century. Mothers should, therefore, continue breastfeeding.

Stephen R. Clough
Manchester, N.H.



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