breast NIS to perchlorate inhibition, the role of iodide status in these effects, and the effects of perchlorate on development independently of effects on iodide transport. The committee notes that other tissues contain NIS, such as the salivary glands, gastric mucosa, and perhaps the choroid plexus. Studies of NIS in those tissues, and possible effects of perchlorate on them, might be done but at a much lower priority than studies of the placenta and mammary gland.

The primary sources of uncertainty in estimating an RfD for perchlorate in drinking water arise from the absence of data on possible effects of exposure among populations at greatest risk of adverse effects of iodide deficiency (pregnant women and their fetuses and newborns). Therefore, new epidemiologic research should assess the possible health effects of perchlorate exposure in those populations. Future epidemiologic research should focus on additional analyses of existing data, new studies of health effects in selected populations, and monitoring of frequencies of specific conditions in communities affected by efforts to reduce perchlorate in drinking water.

Finally, in its deliberations on the health effects of perchlorate in drinking water, the committee considered pregnant women and their fetuses to be particularly sensitive populations. Although iodide deficiency is believed to be rare in the United States, some pregnant women may have a low iodide intake. The committee believes that further research is needed to measure more precisely the extent of, and risk factors for, iodide deficiency, particularly in pregnant women and their offspring. However, while studies are being conducted, the committee emphasizes the importance of ensuring that all pregnant women have adequate iodide intake and, as a first step, recommends that consideration be given to adding iodide to all prenatal vitamins.

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