Perchlorate human exposure

Abstract We have reviewed the human exposure to selected emerging organic contaminants, such new brominated flame retardants, organophosphate flame retardants, phthalate substitutes, triclosan, synthetic musks, bisphenol-A, perchlorate, and polycyclic siloxanes. Levels of these emerging contaminants in matrices relevant for human exposure (air, dust, food, water, etc.) and in human matrices (blood, urine, or tissues) have been reviewed, together with some of the relevant health effects reported recently. 

Exposure of humans to perchlorate via foodstuffs and drinking water has been documented [241]. Urine, breast milk, amniotic fluid, saliva, and blood have been used as matrices in biomonitoring of human exposures to perchlorate [233, 242-253] (Table 10). Assessment of human exposures to perchlorate is important, since this compound blocks iodine uptake in the thyroid gland, which can lead to a decrease in the production of thyroid hormones (T3 and T4) essential for neurodevelopment [260]. 

Urine Urine is the principal route by which nonlactating humans excrete perchlorate [261, 262]. Urinary perchlorate provides a reasonable measure of human exposure because 70-95% of perchlorate dose is excreted unchanged in the urine with a half-life of 8 h [261-263]. Creatinine (CR) adjustment is typically used to minimize the effects of variation of analyte concentration in urine either among samples produced by different individuals or among samples produced by the same individual. 

Extraction procedure. For AAS and ICE wet chemistry is required. Methods range from a cold, dilute nitric acid extraction to a total dissolution with nitric and hydrofluoric acids. Hydrochloric and perchloric acids have also been used, but these are less common. There is no standard extraction procedure designed to simulate human exposure. 

Breast milk During lactation human mammary tissue expresses the sodium iodide symporter [260], and thus significant transfer of perchlorate into human milk is likely. The presence of micrograms per liter concentrations of perchlorate in milk collected fi om US women [233] confirms lactation as a relevant perchlorate excretion path. If lactating women are secreting perchlorate in milk, then urine-based estimates of total perchlorate exposure for these individuals are likely to be lower than actual [242]. 

Studies of low-dose perchlorate exposure in healthy human subjects A small number of studies have been published investigating the effects of low doses of perchlorate in thyroid function in healthy adults (without thyroid disease). One study was conducted in healthy male volunteers, involving the administration of 10 mg of perchlorate in drinking water for 14 days. A significant decrease in the uptake of iodine by the thyroid was observed at this dose, but there was no evidence of adverse effects on thyroid hormones or TSH concentrations [262]. Another recent study was conducted in healthy adults to determine the highest dose of perchlorate at which there is no effect on the uptake of iodine by the thyroid gland [263]. 

Another 14 day study employed 10 subjects (5 male/5 female) for each dose (0.5, 0.1, 0.02, and 0.007mgkg day ) who also served as their own control. The parameters measured were iodide-123 uptake in the thyroid for inhibition data and iodide and perchlorate in blood and urine for kinetic data. There were no changes seen in TSH or thyroid hormone levels in the blood. The result of the iodide inhibition measurements was a NOAEL of 0.007 mg kg day resulting in 4.8% iodide inhibition (equivalent to 0.5 mg day perchlorate exposure). Data from these studies were used to develop the human PBPK model for perchlorate. 

Perchloric acid s corrosive properties and ability to cause tissue oxidation are mechanisms of toxicity. Perchlorate (CIOT) disrupts endocrine homeostasis by competitively inhibiting the transport of iodide (I ) into the thyroid through the sodium iodide symporter. Potential human health risks exist from chronic exposure to perchlorate via drinking water. Such risks may include hypothyroidism, goiter, and mental retardation (if exposure occurs during critical periods in neurodevelopment). 

Perchlorates pose a serious risk to humans because they are unstable and have a tendency to explode spontaneously. They are also human health hazards, with harmful effects on both the brain and the thyroid. They have a tendency to prevent the uptake of iodine by the thyroid, thus interfering with the synthesis of hormones normally produced by that organ. Health officials believe that exposure to perchlorates may cause infertility in women or may have harmful effects on their newborn children. These effects include mental retardation and delays in their normal development. As a consequence, efforts are underway to locate areas where perchlorates may have entered the public water supply causing potential health problems for people living in the region. 

Obviously, then, the major opportunity for ground contamination with perchlorate occurs at manufacturing sites. As a result, manufacturers of propellants and pyrotechnics have proceeded to take appropriate measures and institute best management practices to prevent the release of perchlorate materials into groundwater systems, while research is under way to find replacement formulations that are perchlorate-free, as well as to better determine hazardous exposure levels for humans. ... 

---