The committee recognizes that its recommendations would lead to an RfD of 0.0007 mg/kg per day.5 That value is supported by other clinical studies, occupational and environmental epidemiologic studies, and studies of long-term perchlorate administration to patients with hyperthyroidism. The committee concludes that an RfD of 0.0007 mg/kg per day should protect the health of even the most sensitive populations. The committee acknowledges that the RfD may need to be adjusted upward or downward on the basis of future research, such as that suggested in this report.

RESEARCH RECOMMENDATIONS

The committee was asked to suggest scientific research that could reduce the uncertainty in the understanding of human health effects associated with perchlorate ingestion at low concentrations, especially research that could clarify “safe” exposure for sensitive populations. Although the committee found that available data are sufficient to derive an RfD for perchlorate, new research could provide a more complete understanding of the array of effects of perchlorate, especially regarding the effects of chronic exposure and the effects on sensitive populations. Therefore, the committee recommends a series of interrelated clinical, mechanistic, and epidemiologic studies that have the potential to define more precisely “safe” perchlorate exposures.

The committee recommends a clinical study designed to provide information on the potential chronic effects of low-dose perchlorate exposure on thyroid function, with a special focus on the ability and mechanisms of thyroid compensation. If long-term studies of humans are not possible, chronic studies in nonhuman primates could provide useful information. Studies of pregnant monkeys could also provide useful information on the effects of perchlorate on fetal and neonatal development. Further toxicology studies of perchlorate in rats would be less useful for clarifying the health effects of perchlorate in humans.

Especially critical issues in perchlorate risk assessment have been the effect of perchlorate on placental and breast iodide transport and the influence of iodide status on the effects of perchlorate. The committee recommends a series of in vitro studies using human tissues and animal studies to determine the role of NIS in placental iodide transport, the susceptibility of

5  

For comparison, EPA’s draft RfD in its 2002 draft risk assessment was 0.00003 mg/kg per day.



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