Crump et al. Study Among School Children in Chile: Subsequent Urine and Serum Perchlorate Levels Are Consistent With Perchlorate in Water in Taltal

Perchlorate contamination in Chile: Legacy, challenges, and potential solutions

This paper reviews the unique situation of perchlorate contamination in Chile, including its sources, presence in environmental media and in the human population, and possible steps to mitigate its health impacts. Perchlorate is a ubiquitous water contaminant that inhibits thyroid function. Standards for drinking water range from 2 to 18 µg L^-1 in United States and Europe. A major natural source of perchlorate contamination is Chile saltpeter, found in the Atacama Desert. High concentrations of perchlorate have presumably existed in this region, in soils, sediments, surface waters and groundwaters, for millions of years. As a result of this presence, and the use of Chile saltpeter as a nitrogen fertilizer, perchlorate in Chile has been found at concentrations as high as 1480 µg L^-1 in drinking water, 140 µg/kg^-1 in fruits, and 30 µg L^-1 in wine. Health studies in Chile have shown concentrations of 100 µg L^-1 in breast milk and 20 µg L^-1 in neonatal serum. It is important to acknowledge perchlorate as a potential health concern in Chile, and assess mitigation strategies. A more thorough survey of perchlorate in Chilean soils, sediments, surface waters, groundwaters, and food products can help better assess the risks and potentially develop standards. Also, perchlorate treatment technologies should be more closely assessed for relevance to Chile. The Atacama Desert is a unique biogeochemical environment, with millions of years of perchlorate exposure, which can be mined for novel perchlorate-reducing microorganisms, potentially leading to new biological treatment processes for perchlorate-containing waters, brines, and fertilizers.

A review of perchlorate (ClO4-) occurrence in fruits and vegetables

Since the 1990s, a large number of studies around the world have reported the presence of perchlorate in different types of environmental matrices. In view of their inherent characteristics, such as high solubility, mobility, persistence, and low affinity for the surface of soil, perchlorates are mobilized through the water-soil system and accumulate in edible plant species of high human consumption. However, the ingestion of food products containing perchlorate represents a potential health risk to people due to their adverse effects on thyroid, hormone, and neuronal development, mainly in infants and fetuses. At present, research has been centered on determining sources, fates, and remediation methods and not on its real extension in vegetables under farming conditions. This review presents a comprehensive overview and update of the frequent detection of perchlorate in fruits and vegetables produced and marketed around the world. Additionally, the impact of fertilizer on the potential addition of perchlorate to soil and its mobility in the water-soil-plant system is discussed. This review is organized into the following sections: sources of perchlorate, mobility in the water-soil system, presence in fruits and vegetables in different countries, international regulations, and toxicological studies. Finally, recommendations for future studies concerning perchlorate in fruits and vegetables are presented.

Gestational exposure to high perchlorate concentrations in drinking water and neonatal thyroxine levels

OBJECTIVE

To assess the effect of gestational perchlorate exposure through drinking water on neonatal thyroxine (T(4)).

DESIGN

T(4) values were compared among newborns in Ramat Hasharon, Israel, whose mothers resided in suburbs where drinking water contained perchlorate < or = 340 microg/L (very high exposure, n = 97), 42-94 microg/L (high exposure, n = 216), and < 3 microg/L (low exposure, n = 843). In the very high and high exposure areas, T(4) values in newborns whose mothers drank tap water exclusively (as determined by a telephone interview) were analyzed as a subset. Serum perchlorate levels in blood from donors residing in the area were used as proxy indicators of exposure.

MAIN OUTCOME

Neonatal T(4) values (mean +/- SD) in the very high, high, and low exposure groups were 13.9 +/- 3.8, 13.9 +/- 3.4, and 14.0 +/- 3.5 microg/dL, respectively (p = NS). Serum perchlorate concentrations in blood from donors residing in areas corresponding to these groups were 5.99 +/- 3.89, 1.19 +/- 1.37, and 0.44 +/- 0.55 microg/L, respectively. T(4) levels of neonates with putative gestational exposure to perchlorate in drinking water were not statistically different from controls.

CONCLUSION

This study finds no change in neonatal T(4) levels despite maternal consumption of drinking water that contains perchlorate at levels in excess of the Environmental Protection Agency (EPA) drinking water equivalent level (24.5 microg/L) based on the National Research Council reference dose (RfD) [0.7 microg/(kg.day)]. Therefore the perchlorate RfD is likely to be protective of thyroid function in neonates of mothers with adequate iodide intake.

Perchlorate exposure of the US Population, 2001-2002

Perchlorate is commonly found in the environment and can impair thyroid function at pharmacological doses. As a result of the potential for widespread human exposure to this biologically active chemical, we assessed perchlorate exposure in a nationally representative population of 2,820 US residents, ages 6 years and older, during 2001 and 2002 as part of the National Health and Nutrition Examination Survey (NHANES). We found detectable levels of perchlorate (>0.05 microg/l) in all 2,820 urine samples tested, indicating widespread human exposure to perchlorate. Urinary perchlorate levels were distributed in a log normal fashion with a median of 3.6 microg/l (3.38 microg/g creatinine) and a 95th percentile of 14 microg/l (12.7 microg/g creatinine). When geometric means of urinary perchlorate levels were adjusted for age, fasting, sex and race-ethnicity, we found significantly higher levels of urinary perchlorate in children compared with adolescents and adults. We estimated total daily perchlorate dose for each adult (ages 20 years and older), based on urinary perchlorate, urinary creatinine concentration and physiological parameters predictive of creatinine excretion rate. The 95th percentile of the distribution of estimated daily perchlorate doses in the adult population was 0.234 microg/kg-day [CI 0.202-0.268 microg/kg-day] and is below the EPA reference dose (0.7 microg/kg-day), a dose estimated to be without appreciable risk of adverse effects during a lifetime of exposure. These data provide the first population-based assessment of the magnitude and prevalence of perchlorate exposure in the US.

Perchlorate and radioiodide kinetics across life stages in the human: using PBPK models to predict dosimetry and thyroid inhibition and sensitive subpopulations based on developmental stage

Perchlorate (ClO4(-)) is a drinking-water contaminant, known to disrupt thyroid hormone homeostasis in rats. This effect has only been seen in humans at high doses, yet the potential for long term effects from developmental endocrine disruption emphasizes the need for improved understanding of perchlorate's effect during the perinatal period. Physiologically based pharmacokinetic/dynamic (PBPK/PD) models for ClO4(-) and its effect on thyroid iodide uptake were constructed for human gestation and lactation data. Chemical specific parameters were estimated from life-stage and species-specific relationships established in previously published models for various life-stages in the rat and nonpregnant adult human. With the appropriate physiological descriptions, these kinetic models successfully simulate radioiodide data culled from the literature for gestation and lactation, as well as ClO4(-) data from populations exposed to contaminated drinking water. These models provide a framework for extrapolating from chemical exposure in laboratory animals to human response, and support a more quantitative understanding of life-stage-specific susceptibility to ClO4(-). The pregnant and lactating woman, fetus, and nursing infant were predicted to have higher blood ClO4(-) concentrations and greater thyroid iodide uptake inhibition at a given drinking-water concentration than either the nonpregnant adult or the older child. The fetus is predicted to receive the greatest dose (per kilogram body weight) due to several factors, including placental sodium-iodide symporter (NIS) activity and reduced maternal urinary clearance of ClO4(-). The predicted extent of iodide inhibition in the most sensitive population (fetus) is not significant (approximately 1%) at the U.S. Environmental Protection Agency reference dose (0.0007 mg/kg-d).

Perchlorate in dairy milk. Comparison of Japan versus the United States

Perchlorate has been considered a potential threat to human health, especially to developing infants and children due to its ability to inhibit iodide uptake by the sodium iodide symporter (NIS) of the thyroid. Although the U.S. has been the prime focus of perchlorate contamination, at least some of the similar sources of perchlorate exist across the world, and it has been detected in many types of foods and beverages worldwide. We present here perchlorate data from cow's milk samples from Japan (mean 9.4 +/-2.7 microg/L, n = 54), which are higher on average than those found in U.S. dairy milk samples reported by a 2004 Food and Drug Administration (FDA) study (5.9+/-1.8 microg/L, n= 104).

Analysis of Perchlorate in Human Urine Using Ion Chromatography and Electrospray Tandem Mass Spectrometry

Because of health concerns surrounding widespread exposure to perchlorate, we developed a sensitive and selective method for quantifying perchlorate in human urine using ion chromatography coupled with electrospray ionization tandem mass spectrometry. Perchlorate was quantified using a stable isotope-labeled internal standard ((18)O(4)-perchlorate) with excellent assay precision (coefficient of variation <5% for repetitively analyzed quality control material). Analytical accuracy was established by blind analysis of certified proficiency testing materials prepared in synthetic urine matrix; calculated amounts deviated minimally from true amounts, with percent differences ranging from 2% to 5%. Selective chromatography and tandem mass spectrometry reduced the need for sample cleanup, resulting in a rugged and rapid method capable of routinely analyzing 75 samples/day. The lowest reportable level (0.025 ng/mL) was sufficiently sensitive to detect perchlorate in all human urine samples evaluated to date, with a linear response range from 0.025 to 100 ng/mL. This selective, sensitive, and rapid method will help elucidate any potential associations between human exposure to low levels of perchlorate and adverse health effects.