Using biomonitoring to assess human exposure to perchlorate

Abstract

Perchlorate (C104-) is an inorganic anion used primarily as an oxidant in solid rocket fuel. Perchlorate salts are also used in a variety of products such as road flares, air bags, explosives, and pyrotechnics. 1 It can also form naturally in the atmosphere, 2 producing C104-; in precipitation. This natural process is thought to geologically concentrate C104- in certain regions such as west Texas2 and northern Chile3 A. combination of human and nonhuman activities has led to the widespread presence of C104- in the environment. Concerns about this led the U.S. Environmental Protection Agency (EPA) to include perchlorate on the Drinking Water Candidate Contaminant List4and to monitor perchlorate levels in public water systems. As of August 2005, C10 4- was detected in 5.4% of public water utility samples in 34 different states, with levels ranging from the method detection limit (4 μg/L) to a maximum of 420 μg /L.5 The majority of this drinking water contamination is likely due to polluted source water, although in certain rare instances electrolytic C1O4- formation can occur in situ in water distribution systems.6 Dietary perchlorate exposure is also likely, because of the contamination of vegetable7 and forage 8-10 crops irrigated with perchlorate-containing water or fertilized with Chilean nitrate. 3 Although C104-: contamination is a national problem, it is most severe in California, Nevada, and Arizona, where it routinely occurs in the lower Colorado River at parts-per-billion levels. 11 The prevalence of trace levels of C104- in the environment almost certainly leads to human exposure. Environmental perchlorate exposure is of potential health concern because large clinical and experimental doses of C104- competitively inhibit iodide take12,13 and sustained inhibition of iodide uptake could potentially lead to hypothyroidism. The thyroid plays a crucial role in homeostasis and neurological development. Hypothyroidism can cause metabolic problems in adults and abnormal development in children. 14 Severe hypothyroidism due to iodine deficiency during pregnancy is a cause of cretinism, a permanent cognitive impairment of the developing fetus. 14 Even mild hypothyroidism during pregnancy is associated with measurable cognitive deficits in children. 15.l6 The key question is whether or not exposure to environmental amounts of perchlorate impairs thyroid function, especially in sensitive subpopulations such as pregnant women. © 2006 Springer Science+Business Media, Inc.