Perchlorate

Perchlorate is a man-made anion commonly associated with the solid salts of ammonium, potassium, and sodium. Ammonium perchlorate is the mostly widely used perchlorate compound. It has also been found to occur naturally in certain highly arid environments. These salts are highly soluble in water, and because perchlorate adheres poorly to mineral surfaces and organic material, it can be very mobile in surface and subsurface aqueous systems. Also, since it is relatively inert in typical groundwater and surface water conditions, perchlorate contamination may persist for extended periods of time.

Perchlorate interferes with iodide uptake into the thyroid gland. Because iodide is an essential component of thyroid hormones, perchlorate disrupts how the thyroid functions. In adults, the thyroid helps to regulate the metabolism. In children, the thyroid plays a major role in proper development, in addition to metabolism. Impairment of thyroid function in pregnant mothers may impact the fetus and result in such effects as changes in behavior, delayed development and decreased learning capability. Drinking water contaminated with perchlorate is the most likely way that perchlorate can be ingested.

Recent studies conducted by the U.S. Department of Agriculture (Nov. 2004) and the Environmental Working Group (Apr. 2003) have detected perchlorate in samples of lettuce in California. Several other studies also detected perchlorate in milk samples taken from California and Texas. Additional studies of perchlorate uptake in food crops are currently being conducted by the U.S. Food and Drug Administration.

Production of ammonium perchlorate first began in the United States in the mid-1940s, primarily for use by the U.S. military. The most common uses for ammonium perchlorate are in explosives and rocket propellants, which have been widely used in military munitions items, such as mortars, grenades and flares and solid fuel rocket. Based on production data from two perchlorate manufacturers, it is estimated that 90 percent of perchlorate compounds are manufactured for use in defense activities and the aerospace industry. While occurring most frequently at domestic Air Force installations, ammonium perchlorate has been detected at Army and Navy sites too. The National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) also have a small number of facilities with perchlorate (specific information on known perchlorate releases in the U.S. (XLS) (PDF, 7 pages, 515KB), as of September 23, 2004). In addition, ammonium perchlorate and the other perchlorate salts have been or are used in a wide range of applications, including pyrotechnics and fireworks, blasting agents, solid rocket fuel, matches, lubricating oils, nuclear reactors, air bags and certain types of fertilizers. Improper storage and/or disposal related to the uses mentioned above are the most typical route for perchlorate to enter into the environment.

The EPA has been working with states, federal agencies, tribes, water suppliers and the private sector for several years to address perchlorate. In 1998, EPA released an Interim Assessment Guidance for Perchlorate (PDF, 4 pages, 224KB), which was then subject to peer review in 1999. The external review draft of the revised document "Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization," (November, 2002) responds to those recommendations emanating from the peer review.

The National Research Council of the National Academies published its technical review of the Health Implications of Perchlorate Ingestion in January 2005. From this review, EPA has established an official reference dose of 0.0007 mg/kg/day of perchlorate. This level is consistent with the recommended reference dose included in the National Academy of Science’s report. A reference dose is a scientific estimate of a daily exposure level that is not expected to cause adverse health effects in humans.

Molecular Structure of a Perchlorate (ClO4-1) Ion