Direct Measurement of Perchlorate Exposure Biomarkers in a Highly Exposed Population: A Pilot Study

Abstract

Exposure to perchlorate is ubiquitous in the United States and has been found to be widespread in food and drinking water. People living in the lower Colorado River region may have perchlorate exposure because of perchlorate in ground water and locally-grown produce. Relatively high doses of perchlorate can inhibit iodine uptake and impair thyroid function, and thus could impair neurological development in utero. We examined human exposures to perchlorate in the Imperial Valley among individuals consuming locally grown produce and compared perchlorate exposure doses to state and federal reference doses. We collected 24-hour urine specimen from a convenience sample of 31 individuals and measured urinary excretion rates of perchlorate, thiocyanate, nitrate, and iodide. In addition, drinking water and local produce were also sampled for perchlorate. All but two of the water samples tested negative for perchlorate. Perchlorate levels in 79 produce samples ranged from non-detect to 1816 ppb. Estimated perchlorate doses ranged from 0.02 to 0.51 µg/kg of body weight/day. Perchlorate dose increased with the number of servings of dairy products consumed and with estimated perchlorate levels in produce consumed. The geometric mean perchlorate dose was 70% higher than for the NHANES reference population. Our sample of 31 Imperial Valley residents had higher perchlorate dose levels compared with national reference ranges. Although none of our exposure estimates exceeded the U. S. EPA reference dose, three participants exceeded the acceptable daily dose as defined by bench mark dose methods used by the California Office of Environmental Health Hazard Assessment.

Urinary perchlorate as a measure of dietary and drinking water exposure in a representative sample of the United States population 2001–2008

“…17,26,30,[45][46][47] The adolescent and adult food models also show that consumption of vegetables and fruits were significant sources of perchlorate, which is consistent with earlier studies. 21,22,44 In addition, the contribution of dark-green leafy vegetables, which was significant in the adult food model, is well-supported by other studies. 11,22,27,28 Although egg consumption was a significant predictor of increased urinary perchlorate on a unit mass basis in the adult food model, it did not contribute to perchlorate exposure in the median diet because the median mass consumed was zero (Table 3), 21 likewise reported that perchlorate in eggs contributes minimally to average perchlorate intakes in the United States.…”

“…The milk products food group was significantly associated with increased urinary perchlorate in the food models, which is consistent with studies of perchlorate exposure from dairy products. 18,21,43,44 Perchlorate can bioaccumulate in milk because perchlorate absorbed from consumption of forage crops is actively transported during lactation by the sodium-iodide symporter present in the mammary gland. 17,26,30,[45][46][47] The adolescent and adult food models also show that consumption of vegetables and fruits were significant sources of perchlorate, which is consistent with earlier studies.…”

Thyroid antagonists and thyroid indicators in U.S. pregnant women in the Vanguard Study of the National Children's Study

“…That the adjusted GM urinary perchlorate was highest in Hispanic compared to other racial/ethnic categories is likely the result of dietary differences, but the small subsample size limited further analysis. The highest adjusted urinary perchlorate concentrations were observed in winter, possibly because fresh vegetables available and consumed at that time of year came from arid regions where perchlorate from natural and anthropogenic sources result in higher food crop levels (English et al, 2011; Sanchez et al, 2008 and 2009). Leafy green vegetable intake was predictive of urine SCN, consistent with the observation that various foods, including root and cruciferous vegetables (e.g., kale, broccoli, cauliflower) contain SCN or cyanide that is subsequently metabolized to SCN (Clements, 1960).…”

Implications of the Reanalysis and Weight of Evidence Determination of Human Health Studies for Exposure to Perchlorates under Cumulative and Aggregate Risk Assessment

“…In all instances, water concentrations are converted (where necessary) to Average Daily Rate of Intake (ADRI) by use of the age-specific body weights and water ingestion rates used in Crawford-Brown [18] for the perchlorate Monte Carlo analysis performed in that paper. For studies using urinary perchlorate as the exposure metric, the conversion to dietary intake rate uses the results of Leung et al [54], English et al [55] and Lau et al [56], with a mean conversion factor of 0.015 µg/kg-day per µg/L(urine). These conversions allow comparison with the results of Greer et al [14] summarised in Figure 1 by expressing all exposures in units of ADRI, although note should be taken of the differences between the dosing regime and timing of measurements of the Greer et al [14] and the large majority of epidemiological studies (the latter being primarily chronic exposures at environmentally relevant dose-rates).…”