A small survey in 2005 reported high levels of perchlorate in the breast milk of nursing mothers in the U.S. Now, in a study published online December 12 in the Proceedings of the National Academy of Sciences U.S.A., molecular biologists uncover the mechanism that can concentrate perchlorate in breast milk.
"This is important because it suggests that infants are the most vulnerable population, and the effects of perchlorate exposure through breast milk have not been studied," says thyroid researcher Tom Zoeller at the University of Massachusetts Amherst. Perchlorate is both a naturally occurring and anthropogenic chemical that has been detected in drinking water and food. High levels of contamination have been found near some military bases and manufacturing sites. A recent Centers for Disease Control and Prevention study revealed that low levels of perchlorate exposure appear to have a negative effect on the thyroid, particularly for women with low levels of iodide.
Perchlorate can impair the ability of a specific protein to transport iodide into the thyroid gland and breast milk. The protein, called the sodium iodine symporter (NIS), actively pulls iodide from the bloodstream into cells. Symporter studies that use electrochemical methods failed to reveal perchlorate's role. But now, Nancy Carrasco of the Albert Einstein College of Medicine and colleagues show that perchlorate is actively concentrated in breast milk by the NIS.
Carrasco, who discovered the NIS in 1996, and her colleagues injected lactating female rats with perchlorate. They found that perchlorate concentrations in the rats' milk were more than six times higher than the concentrations in their blood. They also conducted a series of innovative in vitro experiments to elucidate the mechanism. The scientists discovered that NIS has a higher affinity for perchlorate than it does for iodine.
"Our study suggests that high levels of perchlorate may pose a particular risk to infants," says Carrasco. Iodide is essential to synthesize the thyroid hormones necessary for normal development of the central nervous system. "Nursing mothers exposed to high levels of perchlorate in drinking water may not only provide less iodide to their babies, but their milk may actually pass on perchlorate, which could further deprive the infants' thyroid glands of iodide," she adds.
Copyright © 2007 American Chemical Society
Study: Perchlorate Concentrates in Breast Milk
Perchlorate concentrates in breast milk
Infants may be most vulnerable to thyroid effects
By -REBECCA RENNER
Science News, December 19, 2007
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