Perchlorate is an industrial pollutant known to interfere with the ability of the thyroid, mammary glands and certain other tissues to absorb iodide from the bloodstream. A study by researchers at the Albert Einstein College of Medicine at Yeshiva University suggest that perchlorate contamination of drinking water is resulting in concentrations of perchlorate in breast milk.

‘High levels of perchlorate may pose a particular risk to infants,’ says Dr Nancy Carrasco, senior author of the study and professor of
molecular pharmacology at Einstein. ‘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. The thyroid equires iodide to synthesise the hormones T3 and T4 that are essential for normal development of the central nervous system. Babies who don't make enough of these thyroid hormones may
become mentally impaired.’

Iodide is relatively scarce in the diet, and tissues that need to accumulate it – the breast and thyroid in particular – are equipped with a cell-surface protein called NIS (sodium/iodide symporter) that actively pulls iodide from the bloodstream and into the cells. NIS was first identified and cloned by Dr Carrasco's team in 1996. In the current study, Dr Carrasco and her colleagues injected female rats with perchlorate and then extracted the animals' breast milk and tested it on cells that express NIS. The milk inhibited iodide transport in NIS-expressing cells, indicating that perchlorate had become concentrated in the milk.

‘We found that the same protein – NIS – that actively recruits iodide into cells does the same thing for perchlorate,’ says Dr Carrasco. ‘In fact, NIS has a higher affinity for perchlorate than it does for iodide, which certainly heightens the risk posed by this contaminant.’

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First Published in January 2008

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