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What is Perchlorate?
Perchlorate (ClO4-) is the soluble anion associated with the solid salts of ammonium, potassium, and sodium perchlorate. Ammonium perchlorate is used as an energetics booster or oxidant in solid propellant for rockets and missiles. It is, therefore, a national technical asset integral to the Nation's strategic defense system and space exploration. Ammonium perchlorate is also used in certain fireworks, the manufacture of matches, as a component of air bag inflators, and in analytical chemistry to preserve ionic strength. Large-scale production of ammonium perchlorate began in the United States in the mid-1940's. Ammonium perchlorate has a limited shelf life, and must be periodically replaced in munitions and rockets, or in inventory. This has lead to the disposal of large volumes of the compound since the 1940's in Nevada, California, Utah, and likely other states. In addition, the Military Departments have jointly identified a need for an environmentally responsible method to dispose of rocket propellant that complies with arms control treaties (Cooperative Threat Reduction Program, START I and START II) and requirements of the Clean Air Act (CAA). Disposal and demilitarization of solid rocket motors from large propulsion systems is a major task facing DoD.Potassium perchlorate until recently was used to treat hyperthyroidism resulting from Grave's disease, and is still used diagnostically to test thyroid hormone production in some clinical settings. In addition, potassium perchlorate is used in protective breathing equipment on Air National Guard (ANG) aircraft for use in the event of depressurization, and in naval emergency escape breathing devices. Other uses of perchlorate salts include in nuclear reactors and electronic tubes, as additives in lubricating oils, in tanning and finishing leather, as a fixer for fabrics and dyes, and in electoplating, aluminum refining, rubber manufacture, and production of paints and enamels. Areas of natural occurrence of perchlorate are rare; however, one natural source of solid perchlorate is found in potassium nitrate from Chile (Chile saltpeter), which may be used in chemical fertilizers originating from Chile. Additional areas of natural occurrence of perchlorate have not been identified, but are speculated to exist, based on the confirmed existence of several genera of perchlorate-reducing organisms. The toxicity of perchlorate is an active area of research, with most activity focused on the potential of perchlorate to hinder the synthesis of thyroid hormones and/or subsequent consequences resulting from decreases in thyroid hormones. Based on an EPA reference dose (RfD) range of 0.0001 to 0.0005 mg/kg-day revised in 1995, and applying standard default body weights and water consumption levels, provisional cleanup or action levels would range from 4 to 18 parts per billion (ppb). In April 1997 the California Department of Health Services developed an ion chromatography analytical method capable of detecting perchlorate in water at the 4 ppb detection limit; prior to this, analytical techniques were reliable only to a 100 ppb detection limit. Since April 1997, perchlorate has been found in the drinking water supplies of over 15 million people in California, Nevada, and Arizona, and in surface or groundwater throughout the U.S., including Arizona, Iowa, Indiana, Kansas, Maryland, New Mexico, New York, Pennsylvania, Texas, Utah, and West Virginia. Several ongoing projects are now being conducted by various federal and state agencies and research institutions to fully determine the extent of perchlorate occurrence in the environment. The EPA is continuing the process to more completely and accurately characterize human and ecotoxicological risks associated with perchlorate contamination, which will likely result in a change to the human and ecotoxicology benchmarks. A revised oral risk benchmark of 0.0009 mg/kg-day that combines noncancer and cancer approaches has been proposed in an external review document prepared by the EPA Office of Research and Development (ORD) and National Center for Environmental Assessment (NCEA). Applying standard default body weights and water consumption levels to this revised benchmark would yield a drinking water equivalent level (assuming all perchlorate comes from drinking water) of 31.5 ppb. At this time, EPA Office of Research and Development (ORD) recommends that the 1995 provisional RfD continue to be used by risk assessors as the more conservative estimate. The state of California has established 18 ppb as an action level, resulting in water suppliers without perchlorate treatment capabilities having to shut down wells or blend water in order to meet this 18 ppb action level. Water utilities in California and Nevada have expressed interest in treating perchlorate to non-detectable levels, and some environmentalist organizations believe treated potable water should have zero ppb perchlorate. The majority of the work being conducted in perchlorate treatability research, testing, and application uses 4 to 18 ppb as benchmark treatment goals. |
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