J. Environ. Monit., 1999, 1 37N US Focus Perchlorate rockets to US national attention Ground and surface water contaminated with ammonium perchlorate, a component of solid rocket fuel, has placed drinking water supplies at risk in a number of communities throughout the US, especially in the West. An expedited research agenda is providing many answers about this new environmental problem, but important questions remain.In late 1996, groundwater migration of perchlorate was discovered in California following an improvement in the ion chromatographic (IC) method used for its detection.1 The discovery caused immediate and intense concern among water utility companies, regulators and environmental groups for many reasons. Although it is a component of rocket fuel, ammonium perchlorate reacts explosively only at elevated temperatures (380 °C); it is stable at 110 °C.2 At high doses, the perchlorate anion is known to block iodide uptake by the thyroid, but the eVects of chronic low-level exposures are poorly defined.This oxidising agent is exceedingly mobile in aqueous systems and can persist for many decades under The image was obtained from IMSI’s MasterClipsA and MasterPhotosTM Premium Image Collection.typical ground- and surface water conditions. In addition, there was, and still is, no proven treatment method for cleaning up contaminated drinking water. To top matters oV, no-one was aware of the extent of the contamination due to unregulated eZuent discharges. Faced with these uncertainties, the California Department of Health Services (CDHS), together with the California Environmental Protection Agency, compiled available health data and set a provisional action level of 18 mg L-1 in drinking water.3 Over 20 water utilities closed wells contaminated above this level.This action prompted local concern about the safety of drinking water. For example, hundreds of people who live near Los Angeles are involved in law suits over health risks believed to be associated with intake of perchlorate and volatile organic compounds.In Nevada, the perchlorate anion has been detected in the Colorado River—waters that are used for drinking, irrigation and recreation by millions of people in the South-West. As a result, the US Congress committed $2 million for research into water treatment methods.The US Department of Defense, a major user of perchlorate, and a coalition of perchlorate manufacturers and users, put up another $2.2 million to fund an expedited toxicological assessment under the oversight of the US Environmental Protection Agency (EPA). Then the EPA began assessing the likelihood of perchlorate contamination throughout the country. These initiatives have begun to pay oV.The EPA produced a draft toxicological risk assessment in December 1998—in just one year rather than the customary seven. There is a now a large body of analytical and chemical data, and interlaboratory validation of the California DHS IC method for water samples is underway.4 Pilot testing for some water clean-up technologies has already started.The extent of the groundwater contamination problem is also better understood. Concentrations ranging from 8 mg L-1 to 3 700 000 mg L-1 have been found. The latter value corresponded to samples collected at a former munitions site. The Colorado River and several California wells show concentrations in the range of 8–30 mg L-1. To date, most of the sites where perchlorate has been detected in ground or surface waters are primarily in areas associated with the development, testing or manufacture of aerospace materials. For the country as a whole, EPA now estimates that perchlorate has been either manufactured or used in 44 states.There are 14 states with confirmed releases in ground or surface waters.5 Huge monitoring task ahead There is still a huge monitoring task ahead because only a small number of water supplies have been monitored using techniques capable of measuring perchlorate at low levels.5 In addition to the interlaboratory validation which is being conducted by the US Air Force Research Laboratory and EPA’s National Exposure Research Laboratory,4 other methods are being developed involving gravimetry, capillary electrophoresis or spectrophotometry.Potentiometric measurements employing ion selective38N J. Environ. Monit., 1999, 1 electrodes (ISE) constitute another approach.6 This method, well established for research, has potential for field monitoring and for continuous monitoring within treatment facilities. Health concerns persist EPA’s new draft toxicological assessment substantiates concerns about the health eVects of chronic exposure to low levels of perchlorate. The December 1998 draft supports an action level of 32 mg L-1, almost double the 18 mg L-1 value that California used to shut down drinking water sources.5 However, an order-of-magnitude uncertainty associated with this standard indicates that the updated draft does not dramatically alter the perchlorate problem.The draft toxicological assessment was based on animal testing expressly designed and conducted to evaluate human health. A final toxicological assessment is due in 2000, on completion of further toxicological assessments (including human exposure) and peer review. Treatment challenges Perchlorate’s chemistry and physical properties prevent the use of standard water-treatment methods.7 Although the perchlorate ion (ClO4-) is the most oxidised form of chlorine that can exist in water, it is remarkably unreactive and its salts are extremely soluble.Common reducing agents do not react with it and common cations do not precipitate it. As a result, standard water treatment methods neither remove nor destroy it. Methods under consideration for the treatment of perchlorate-contaminated waters include: ion exchange, membrane filtration, electrodialysis and biological techniques.Bioremediation and biological or biochemical methods appear to be the most economically feasible, fastest and easiest means of dealing with perchlorate at all concentrations.7 Several genera of microorganisms are capable of using perchlorate as an oxidant for metabolism.8 A significant barrier to the implementation of any biological method is that such techniques have never been used to treat drinking water in the US.A pilot project that uses a biological treatment system to remove perchlorate from groundwater began early this year in Baldwin Park, near Los Angeles, CA.4 No federal regulations There are currently no federal regulations for perchlorate.Perchlorate was placed on the DrinkingWater Contaminant Candidate List in March 1998.5 The list is a source for priority contaminants, defined as either known or anticipated to occur in drinking water, for research, regulatory determinations and monitoring by the states. Perchlorate was listed as a contaminant that required additional research and occurrence information before regulatory determinations could be considered.Action under the Safe DrinkingWater Act would not even begin before 2001,5 but EPA could issue a health advisory if the toxicity results warranted it. Perchlorate is the topic of an upcoming symposium at the American Chemical Society national meeting in US Focus August, 1999, in New Orleans, LA. For details see: http://www.epa.gov/ OGWDW/ccl/perchlo.html Notes 1 California Department of Health Services, Perchlorate in California Drinking Water, September, 1997.http://www.dhs.cahwnet.gov/prevsrv/ ddwem/perch.htm#advice. 2 A. A. Schilt, Perchloric Acid and Perchlorates, The G. Frederick Smith Chemical Company, Columbus, OH, 1979. 3 California Department of Health Services, Determination of Perchlorate by Ion Chromatography, Rev. 0, June 3, 1997. Sanitation and Radiation Laboratories Branch. 4 D. Tsui and S. Pia, Analytical T echniques and Pending Interlaboratory Study, presented at the Perchlorate Stakeholders Forum, May 19–21, 1998, Henderson, Nevada. 5 U.S. EPA OYce ofWater perchlorate web site, Overview of Perchlorate Issues, United States Environmental Protection Agency OYce of GroundWater and Drinking Water, 1998. http://www.epa.gov/OGWDW/ccl/ perchlo.html 6 United States Environmental Protection Agency, Perchlorate Environmental Contamination: T oxicological Review and Risk Characterization. Based on Emerging Information (external review draft), National Center for Environmental Assessment NCEA-1–0503, 1998. http://www.epa.gov/OGWDW/ccl/ perchlor.html 7 E. T. Urbansky, Perchlorate Chemistry: Implications for Analysis and Remediation, Biorem. J., 1998, 2, 81. 8 B. E. Logan, A review of chlorate- and perchlorate-respiring microorganisms Biorem. J., 1998, 2, 69. Rebecca Renner Science writer and editor based in the US Tel:+1 570 321 8640; Fax: +1 570 321 9028, e-mail: applepie@sunlink.net