The EPA has established an official reference dose (RfD) of 0.0007 mg/kg/day of perchlorate, which is consistent with the recommended reference dose included in the National Academy of Science’s January 2005 report. A reference dose is defined by the EPA as a scientific estimate of a daily exposure level that is not expected to cause adverse health effects in humans. According to the agency, the established reference dose, which assumes total intake from both water and food sources, is appropriate and protective for all populations, including the most sensitive subgroups. The selected reference dose contains a full ten-fold uncertainty factor to protect the most sensitive population, fetuses of women with potential hypothyroidism or iodide deficiency. This uncertainty factor also covers variability among other human life stages, gender and individual sensitivities, protecting not only adults, but also other sensitive subpopulations such as premature neonates, infants and developing children.

The EPA’s reference dose for perchlorate will be posted on the agency’s online IRIS database, which contains risk information on possible human health effects from exposure to chemical substances in the environment.

The agency’s new RfD translates to a Drinking Water Equivalent Level (DWEL) of 24.5 ppb. This standard, which assumes that all of a contaminant comes from drinking water, would represent the concentration of a contaminant in drinking water that should have no adverse effect with a margin of safety. Because there is a margin of safety built into the RfD and the DWEL, according to the risk calculation texts, exposures above the DWEL would not necessarily be considered unsafe. The EPA’s Superfund cleanup program plans to issue guidance based on the new RfD. The perchlorate summary is available on the IRIS web site at www.epa.gov/iris and www.epa.gov/perchlorate.