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Perchlorate (ClO4-) is an anion that originates as a contaminant in ground water and surface waters when the salts of ammonium, potassium, magnesium, or sodium dissolve in water. One major source of contamination is the manufacture or improper disposal of ammonium perchlorate that is used as the primary component in solid propellant for rockets, missiles, and fireworks. Appreciation of widespread contamination in the United States emerged in the Spring of 1997 when development of an analytical method with a quantitation level at 4 ppb became available. By May of that same year EPA was engaged in developing a targeted testing strategy to evaluate the potential human health and ecotoxicological effects of potential perchlorate exposures. The National Center for Environmental Assessment (NCEA) first released an external review draft in 1998 and recommendations for additional studies and analyses were made at a 1999 scientific peer review. The external review draft of the revised document, Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization responds to those recommendations and incorporates results from extensive laboratory and field studies performed since 1999. For more information on perchlorate and the external review draft, including Frequently Asked Questions, see the Office of Ground Water and Drinking Water's website at

External Peer Review
An external scientific peer review workshop to review the revised draft report, Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization (2002 external review draft) took place on March 5 and 6, 2002, in Sacramento, CA. All questions regarding workshop registration and logistics were directed to EPA's contractor, the Eastern Research Group, Inc. For contact information, please refer to the January 2, 2002, Federal Register notice (and corrections to this notice on the address to submit comments published in the Federal Register on January 14, 2002).

Public Comment
EPA's January 2, 2002, Federal Register notice (67 FR 75) announced the beginning of a 30-day public comment period for the revised draft perchlorate assessment. Because of an approximately one-week delay in public release and availability of the draft document, EPA extended the public comment period to February 19, 2002 (67 FR 3493, January 24, 2002). In response to the high level of interest in this draft document and because of several requests for extension of the comment period, EPA has extended the public comment period by an additional 45 days to April 5, 2002. Comments on the draft document should be in writing and must be received (not postmarked) by April 5, 2002 (67 FR 9271, Feb. 28, 2002). As is the EPA's normal procedure, the Agency will summarize and indicate the disposition of all major comments provided by April 5, 2002, in preparation for its release of the assessment in final form.


U.S. EPA. PERCHLORATE ENVIRONMENTAL CONTAMINATION: TOXICOLOGICAL REVIEW AND RISK CHARACTERIZATION (EXTERNAL REVIEW DRAFT) 2002. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington Office, Washington, DC, NCEA-1-0503, 2002.

Additional Information

Copies of the following thesis is available from Jackie Schwartz at the University of California at Berkeley ( Schwartz, J. (2001). Gestational exposure to perchlorate is associated with measures of decreased thyroid function in a population of California neonates [thesis]. Berkeley, CA: University of California.