PERCHLORATE

Concern about environmental perchlorate exposure centers on its inhibition of iodide uptake into the thyroid. Decreased iodine intake may decrease thyroid hormone production. In the last few years, perchlorate has become a major inorganic contaminant in drinking water and has been detected in a number of public drinking water systems throughout the Unites States. In 1998, the US EPA added perchlorate to the Drinking Water Candidate Contaminant List.

The primary source of perchlorate is the ammonium salt. Ammonium perchlorate is the oxidizer ingredient in solid propellant mixtures for rockets, missiles, and munitions. Other uses of perchlorate salts include medicine, matches, metal cation chemistry, and pyrotechnics (illuminating and signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, photo-flash compounds, and fireworks). Perchlorate is also found in lubricating oils, finished leather, fabric fixer, dyes, electroplating, aluminum refining, manufacture of rubber, paint, and enamel production, as an additive in cattle feed and magnesium batteries, and as a component of automobile airbag inflators.

Perchlorate is a soluble oxychloro anion most commonly used as a solid salt in the form of ammonium perchlorate, potassium perchlorate, lithium perchlorate, or sodium per- chlorate, all of which are highly soluble. Ammonium perchlorate is the most widely used perchlorate compound. In their pure forms, these salts are white or colorless crystals or powders. Perchlorate salts dissolve in water and readily move from surface to groundwater. Perchlorate is known to originate from both natural and man-made sources.
The most common uses for ammonium perchlorate are in explosives, military munitions, and rocket propellants. In addition, perchlorate salts are used in a wide range of nonmilitary 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 disposal related to these uses is the most typical route for perchlorate to enter into the environment. Monitoring data show that more than 4% of public water systems, serving between 5 million and 17 million people, have detected perchlorate in their finished water.

ChEBI: Perchlorate is a monovalent inorganic anion obtained by deprotonation of perchloric acid. It is a monovalent inorganic anion and a chlorine oxoanion. It is a conjugate base of a perchloric acid.

Crystalline or powdered solids. May explode under exposure to heat or fire. If available, obtain the technical name from the shipping papers and contact CHEMTREC, 800-424-9300 for specific response information.

Water soluble.

PERCHLORATE is a strong oxidizing agents. May be self-reactive (e.g., ammonium perchlorate, glycol perchlorate) and liable to violent decomposition. The violence of decomposition of some perchlorates exceeds that of nitroglycerine. Noncombustible but able to accelerate the burning of combustible materials. If large quantities are involved in a fire or the combustible material is finely divided, then an explosion may result.

Inhalation, ingestion or contact (skin, eyes) with vapors or substance may cause severe injury, burns or death. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause pollution.

These substances will accelerate burning when involved in a fire. Some may decompose explosively when heated or involved in a fire. May explode from heat or contamination. Some will react explosively with hydrocarbons (fuels). May ignite combustibles (wood, paper, oil, clothing, etc.). Containers may explode when heated. Runoff may create fire or explosion hazard.

Environmental Persistency (Degradation and Speciation): Perchlorate salts such as ammonium perchlorate are expected to exist as a solid aerosol or be absorbed to suspended particulate matter. Therefore, removal from the atmosphere is expected to occur by both wet and dry depositions. Perchlorates are not expected to undergo direct photolysis in air. If released in soil, the perchlorate ion is only weakly absorbed to mineral surfaces of moderate ionic strength. The ion exhibits high aqueous solubility, and together these properties contribute to its ability to readily migrate in groundwater systems. The ion is not expected to volatilize from soil to the atmosphere because perchlorates exhibit very low vapor pressures. If released to water, ammonium perchlorate readily dissolves and dissociates to the perchlorate ion. Perchlorate is an ion; therefore, volatilization from water surfaces is not expected to be an important fate process. Hydrolysis does not occur for inorganic salts such as ammonium perchlorate, which ionizes in aqueous solution.
Handling and storage: Keep the container tightly closed. Keep the container in a cool, well-ventilated area, separate from acids, alkalies, reducing agents, and combustibles.
Bioaccumulation and biomagnifications: Significant decomposition of perchlorate does not occur in nature, making human interventions necessary for efficient environmental cleanup.

The perchlorate ion, because of its similarity to iodide in ionic size and charge,competes with iodide for uptake into the thyroid gland. At therapeutic dosage levels (100–1000 mg day°1), this competitive inhibition results in reduced production of the thyroid hormones T3 and T4 and a consequent increase in TSH via a negative feedback loop involving the thyroid, pituitary, and hypothalamus.
The competitive inhibition of iodide uptake is the only direct perchlorate effect on the thyroid, leading to a reversible chemical- induced iodine deficiency. Inhibition of iodide uptake in the thyroid of adult male rats dosed intravenously was detected at a dose as low as 0.01 mg kg^-1 perchlorate. Perchlorate has not been shown to produce iodine deficiency in humans.
The effects of perchlorate on iodine availability should be interpreted in the context of other sodium iodide symporter inhibitors. These include thiocyanate, a metabolite of cyanide that is produced as a byproduct of cigarette smoke and found in a large variety of foods, and nitrate, which is produced naturally. Comparatively, perchlorate is a very potent inhibitor of the sodium iodide symporter; its effects are 15-fold greater than thiocyanate, 30-fold compared with iodide, and 240-fold compared with nitrate.