Environmental Significance of Perchlorate in Aqueous Systems and its Removal Technologies

Perchlorate (ClO4-) is a naturally occurring anion, commonly found in ammonium, potassium, and sodium salts. It is extensively used as an oxidizer in solid rocket propellant, fireworks, batteries and automobile air-bags. Its contamination to environment is generally associated with the release of ammonium perchlorate by defense contractors, military operations and aerospace programs. This anion is very much persistent in the environment due to high activation energy associated with its reduction. At high concentration perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodine. Also, perchlorate has recently been added to the U.S. Environmental Protection Agency's (EPA) drinking water Candidate Contaminant List. It has been found at high concentrations (>1000 mg/L) in surface water and groundwater. Due to the stability in water systems it is difficult to remove by existing physico-chemical techniques such as adsorption, anion exchange and membrane filtration, therefore bioremediation is a promising method to reduce perchlorate from water systems. Biological perchlorate degradation depends on several environmental factors such as presence of nitrate and chlorate, dissolved oxygen, carbon-source and temperature. In this review, environmental occurrence of perchlorate, it's toxicity in various living organism and remediation processes from water environment have been discussed.