In the water. This EPA map shows locations where perchlorate has been found.

NAS Enters Perchlorate Fray

How much of a rocket fuel ingredient is safe to have in drinking water? That question--currently being mulled over by the Environmental Protection Agency (EPA)--has huge implications for the potential scale of cleaning up groundwater, which is contaminated with the chemical perchlorate in many parts of the country. A new report by the National Academies of Sciences has now found that the EPA's draft risk assessment of safe oral intake of perchlorate was roughly 20 times too stringent.

The potential danger of perchlorate is that it can prevent the thyroid from making hormones, leading to hypothyroidism. Adults can store a supply of thyroid hormones, which are important for brain development, but children need iodine every day to make them. The major worry, then, is that perchlorate could harm fetuses and young children. In 2002, the EPA released a draft risk assessment that proposed that the safe oral intake of perchlorate was 0.00003 milligrams per kilogram of body weight. Given certain preliminary assumptions, this indicated to EPA that groundwater concentrations would need to be less than 1 part per billion--which would mean billions of dollars to clean up contamination.

Perchlorate manufacturers and users, such as the Department of Defense (DOD), which manages many contaminated sites, objected to aspects of the EPA's assessment, such as its reliance on studies of perchlorate's effects on rat brains. The EPA, DOD, and other agencies then commissioned the NAS to review the science and EPA's assessment.

After reviewing animal studies, human clinical studies, and epidemiological studies, the NAS panel determined that 0.0007 mg/kg would be a safe level for oral intake. "This should protect the health of even the most sensitive populations," says panel chair Richard Johnston of the University of Colorado School of Medicine in Denver. The panel did not convert this into a drinking water standard, because that depends on making assumptions like what fraction of perchlorate is consumed from food versus water, which may vary from place to place.

Renee Sharp, an analyst with the Environmental Working Group, an advocacy group in Washington, D.C., says she's generally pleased with the outcome, and that the NAS's oral intake level implies a safe water level of a few parts per billion.

Related sites
The report
The NAS project webpage
EPA's webpage on perchlorate
The source of the map
A report on perchlorate from the Environmental Working Group
Perchlorate information from Toxicology Excellence for Risk Assessment (TERA), which receives industry funding.