Perchlorate is a regulated drinking water contaminant in California, with a maximum contaminant level of 6 micrograms per liter (µg/L), effective October 18, 2007.
The use of perchlorate and its salts in solid propellant for rockets, missiles, and fireworks, and elsewhere (e.g., production of matches, flares, pyrotechnics, ordnance, and explosives) can lead to releases of perchlorate into the environment. Perchlorate's interference with iodide uptake by the thyroid gland can decrease production of thyroid hormones, which are needed for prenatal and postnatal growth and development, as well as for normal metabolism and mental function in the adult.
Initial testing in 1997 by the California Department of Health Services (now the California Department of Public Health, CDPH) and subsequent monitoring showed perchlorate to be a widespread drinking water contaminant in several hundred wells, primarily in southern California counties. Perchlorate is also found in the Colorado River, an important source of water for drinking and irrigation, where its presence results from contamination from ammonium perchlorate manufacturing facilities in Nevada.