Does perchlorate cause cancer?

The salt within perchlorate is a toxin, but there is disagreement about how much is bad for you when ingested. The U.S. Environmental Protection Agency is creating drinking water standards for the pollutant. There is general agreement that exposure to perchlorate is a big risk. The question is at what level do you avoid that risk?

Scientists know it interferes with the way the body takes iodide into the thyroid and can disrupt the gland's regulation of metabolism. In adults, the thyroid helps to regulate metabolism. In children, the thyroid plays a major role in proper development in addition to metabolism. Impairment of thyroid function in expectant mothers may impact the fetus and newborn and result in effects including changes in behavior, delayed development and decreased learning capability. Changes in thyroid hormone levels may also result in thyroid gland tumors. EPA's draft analysis of perchlorate toxicity is that perchlorate's disruption of iodide uptake is the key event leading to changes in development or tumor formation.

Further more, a 2000 Arizona study found an increase in abnormal thyroid levels in Yuma, Ariz., newborns whose mothers drank water from the Colorado River that contained five to seven parts per billion perchlorate. Dr. Ross Brechner, author of the study and now Maryland's state epidemiologist, said he could show only an association between perchlorate exposure and abnormal thyroid function. Further work is needed, but he said his personal recommendation would be that pregnant women be conservative and not drink the water. Other perchlorate research, most of it funded by industry and the Pentagon, suggests moderate doses might not affect healthy adults. ''At very low levels, I think levels below 200 parts per billion, you wouldn't have any effect on human health,'' said Dr. John Gibbs, medical director for former perchlorate manufacturer Kerr-McGee Corp.

What are the sources for perchlorate contamination of water? One major source of contamination is improper disposal of ammonium perchlorate that is used as the primary component in solid propellant for rockets, missiles, and fireworks. Perchlorate salts are also used on a large scale as a component of air bag inflators. Other potential sources include chemical fertilizers and wastes from a number of chemical and industrial facilities that use chlorates.

The EPA's National Center for Environmental Assessment released a document on the toxicological review and risk characterization for perchlorate in 1999. A complete externally peer reviewed document titled "Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization" was completed in 2002 and incorporates results from extensive laboratory and field studies performed since 1999. This document is now available through the Internet. More information on perchlorate is also available from EPA's Office of Ground Water and Drinking Water at http://www.epa.gov/safewater/ccl/perchlor/perchlo.html).