Perchlorate is a hazardous industrial pollutant that does not occur naturally.
Perchlorate consists of an atom of chlorine surrounded by four atoms of oxygen.
It occurs as ammonium, potassium, magnesium or sodium salts. These perchlorate salts bind weakly to soil particles and are not significantly broken down in the environment (EPA, 1998).
In water, however, perchlorate salts are extremely soluble and highly mobile, migrating faster and farther than many other water contaminants. Together, these properties make perchlorate a particularly persistent and problematic pollutant once it contaminates groundwater.
Perchlorate salts are used in a variety of products as diverse as electronic tubes, car air bags, leather tanning and fireworks. Perchlorate's main use is as an explosive propellant: Ninety percent of the perchlorate produced goes into solid rocket fuel for Air Force missiles and the NASA space shuttle.
Perchlorate impairs normal thyroid function because it is taken up preferentially by the thyroid gland in place of iodide. The thyroid gland is therefore deprived of iodide, a necessary nutrient which it is designed to concentrate; and without iodine, thyroid hormone is inactive. As a result, perchlorate can disrupt the delicate balance of hormone levels in the body which are crucial for healthy metabolism, growth and development.
Perchlorate-reducing bacteria use perchlorate ion as a terminal electron acceptor during the anaerobic oxidation of acetate (Coates et al., 1999). Molybdenum is required as a cofactor.
The overall stoichiometry of the pathway shown here is: CH3COO- + ClO4- -------> 2HCO3- + H+ + Cl-
It is shown here as three discrete steps. However Dr. Coates states (personal communication, 2004) that presently:
The perchlorate reductase and chlorate reductase enzymes are not consecutive in any organism. Some organisms reduce chlorate to chlorite using the chlorate reductase while some (the majority) reduce perchlorate to chlorite using the perchlorate reductase. It is unknown whether or not chlorate is produced as a transient intermediate in this reductive step.The following is a text-format perchlorate pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic format: graphic(15k).
Perchlorate Dechlorosoma suillum | | perchlorate | reductase | v Chlorate | | chlorate | reductase | v Chlorite | | chlorite | dismutase | v Chloride
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