Temporal variability in urinary concentrations of perchlorate, nitrate, thiocyanate and iodide among children

Urinary perchlorate, thiocyanate, and nitrate and their associated risk factors among Chinese pregnant women

Perchlorate, nitrate, and thiocyanate are well-known inhibitors of iodide uptake and thyroid-disrupting chemicals. Widespread human exposure to them has been identified, whereas studies on their internal exposure levels among Chinese pregnant women are scarce and factors associated with them are not well recognized. The objective of this study is to determine their levels and identify the associated factors among pregnant women (n = 1120), based on a prospective birth cohort in Wuhan, central China, using repeated urine samples of three trimesters. Urinary perchlorate, thiocyanate, and nitrate were 100% detected in the samples, and specific gravity-adjusted median concentrations of them in all the samples were 12.6 ng/mL, 367 ng/mL, and 63.7 μg/mL, respectively. Their concentrations were weakly-to-moderately correlated with each other, with Spearman correlation coefficients ranging from 0.27 to 0.54. Poor reproducibility were observed for the three analytes over the three trimesters, with intraclass correlation coefficient of 0.07, 0.19, 0.04 for perchlorate, thiocyanate, and nitrate, respectively. The women who were overweight or used tap water as drinking water had significantly higher perchlorate concentrations, while those with excessive gestational weight gain had significantly higher thiocyanate concentrations (p < 0.05). The women with a college degree or above had lower nitrate concentrations (p < 0.05). Meanwhile, the median concentration of perchlorate in urine samples collected in spring, thiocyanate in those collected in winter, and nitrate in those collected in autumn, was significantly higher compared to their median concentrations in the samples collected in other three seasons (p < 0.05), respectively. Urinary perchlorate and nitrate concentrations of pregnant women in this study were higher than the concentrations of pregnant women in other countries, while thiocyanate concentrations were lower than that of most other countries. This study suggested potential covariates for future epidemiological analyses.

Associations of perchlorate, nitrate, and thiocyanate with metabolic syndrome and its components among US adults: A cross-sectional study from NHANES

Perchlorate, nitrate and thiocyanate are common endocrine disruptors. Herein, this study was undertaken to evaluate the associations between perchlorate, nitrate, and thiocyanate exposures (alone or in combination) and risk of metabolic syndrome (MetS) among adults, which has not been explored so far. Analytical data were extracted from different datasets in the National Health and Nutrition Examination Survey (NHANES) database. Multivariate logistic regression models were constructed to investigate the associations between perchlorate, nitrate, and thiocyanate exposures, and the prevalence of MetS. Subsequently, odds ratios (OR) and their corresponding 95 % confidence intervals (CIs) were adopted to represent the magnitude of the effect size. We performed a series of subgroup analyses and sensitivity analyses as well. Moreover, three commonly used mixture modeling strategies [Weighted quantile sum (WQS) regression, quantile-based g-computation (Qgcomp), and Bayesian kernel machine regression (BKMR)] were utilized to evaluate the joint mixture effect on MetS. This study included 12,007 participants in the subsequent analyses. After adjustment for confounding factors, higher levels of perchlorate, and thiocyanate concentrations were significantly associated with the risk of MetS (OR = 1.15, 95%CI:1.00, 1.32; OR = 1.21, 95%CI:1.04, 1.41, respectively). Analyses of WQS and Qgcomp showed that a quartile increase in chemical mixture was correlated with the occurrence of MetS with ORs of 1.07 (95%CI: 0.99, 1.16) and 1.07 (95%CI: 1.00, 1.14), respectively. This positive association was mainly driven by perchlorate and thiocyanate. Analysis of BKMR revealed that perchlorate, nitrate, and thiocyanate mixture was positively associated with the risk of MetS while perchlorate, and thiocyanate were major predictors in the mixture. In summary, our study reveals positive relationships between perchlorate, thiocyanate and MetS. Co-exposure to perchlorate, nitrate and thiocyanate is positively associated with the risk of MetS, with perchlorate and thiocyanate contributing the most to the overall mixture effect.

Association of perchlorate, thiocyanate, and nitrate with dyslexic risk

Perchlorate, thiocyanate, and nitrate are sodium iodide symporter (NIS) inhibitors that disturb iodide uptake into the thyroid and have been implicated in child development. However, no data are available on the association between exposure to/related with them and dyslexia. Here, we examined the association of exposure to/related with the three NIS inhibitors with the risk of dyslexia in a case-control study. The three chemicals were detected in urine samples of 355 children with dyslexia and 390 children without dyslexia from three cities in China. The adjusted odds ratios for dyslexia were examined using logistic regression models. The detection frequencies of all the targeted compounds were 100%. After adjusting for multiple covariates, urinary thiocyanate was significantly associated with the risk of dyslexia (P-trend = 0.02). Compared with the lowest quartile, children within the highest quartile had a 2.66-fold risk of dyslexia (95% confidence interval: 1.32, 5.36]. Stratified analyses showed that the association between urinary thiocyanate level and the risk of dyslexia was more pronounced among boys, children with fixed reading time, and those without maternal depression or anxiety during pregnancy. Urinary perchlorate and nitrate levels were not associated with the risk of dyslexia. This study suggests the possible neurotoxicity of thiocyanate or its parent compounds in dyslexia. Further investigation is warranted to confirm our findings and clarify the potential mechanisms.

Biomonitoring Equivalents for cyanide

Exposure to cyanide is widespread in human populations due to a variety of natural and anthropogenic sources. The potential health risks of excess cyanide exposure are dose-dependent and include effects on the thyroid, the male reproductive system, developmental effects, neuropathies and death. Many organizations have derived exposure guideline values for cyanide, which represent maximum recommended exposure levels for inhalation and oral routes of exposure. Biomonitoring Equivalents (BEs) are estimates of the average biomarker concentrations that correspond to these reference doses. Here, we determine BE values for cyanide. The literature on the pharmacokinetics of cyanide was reviewed to identify a biomarker of exposure. Despite issues with biomarker specificity, thiocyanate (SCN-) in the urine or plasma was identified as the most practical biomarker. BE values were produced that correspond to previously published critical effect levels. These BE values range from 0.0008 to 0.8 mg/L and 0.0005-2.5 mg/L for SCN- in urine and plasma, respectively. Confidence in these BE values varies, depending on route of exposure, biomarker, and health endpoint of interest. We anticipate that these BE values will be useful for lower tier (screening level) chemical risk assessment; however due to issues with biomarker specificity and uncertainty in background levels of SCN-, this approach requires refinement to be useful at higher tiers.

A cross sectional study of urinary phthalates, phenols and perchlorate on thyroid hormones in US adults using structural equation models (NHANES 2007-2008)

BACKGROUND

Biomonitoring data shows that people are exposed to phthalates, phenols and perchlorates. Many of these compounds are endocrine disrupting compounds that affect thyroid hormone levels. Yet the effect of these compounds on thyroid hormone levels are often evaluated individually rather than as a mixture. Our objective was to examine the association between 11 urinary endocrine disrupting compounds and thyroid hormones using structural equation models.

METHODS

Using data from the National Health and Nutrition and Examination Survey 2007-2008, we fit a latent variable utilizing urinary measurements of 9 compounds in females (perchlorate, bisphenol A, benzophenone-3, mono-2ethyl5carboxypentyl phthalate, mono-n-butyl phthalate, mono-(3-carboxypropyl) phthalate, mono(2ethyl5hydroxyhexyl) phthalate, mono-benzyl phthalate, and mono-isobutyl phthalate) and 8 compounds in males (without benzophenone-3). The association of the latent variable with serum thyroid hormones (Total T3, Total T4, and Thyroid Stimulating Hormones) was assessed in females (N = 710) and males (N = 850) over the age of 12 controlling for age, race, and urinary creatinine.

RESULTS

In males, urinary endocrine disrupting compound levels were negatively associated with thyroxine (β: -0.19, 95% Confidence Interval (95% CI): -0.31, -0.05). In females, urinary endocrine disrupting compound levels were positively associated with triiodothyronine serum concentrations (β: 0.09, 95% CI: -0.03, 0.21) however this association was not statistically significant.

CONCLUSIONS

This cross-sectional analysis provides additional evidence that environmental exposure to phthalates and phenols is associated with endocrine-related processes. Furthermore, these results suggested sex-specific differences in exposure to endocrine disrupting mixtures, and the exposure-response between endocrine disrupting mixtures and thyroid hormone levels. Specifically, higher exposure to a mixture of endocrine disrupting compounds was associated with lower levels of total T4 in males but not in females. While a structural methodological framework was used to assess these complex relationships, the cross sectional nature of this analysis limits causal inference and further research is needed to determine the clinical significance of these findings.

Neighborhood Factors and Urinary Metabolites of Nicotine, Phthalates, and Dichlorobenzene

BACKGROUND AND OBJECTIVES

Exposures to environmental chemicals are ubiquitous in the US. Little is known about how neighborhood factors contribute to exposures.

METHODS

Growing Up Healthy is a prospective cohort study of environmental exposures and growth and development among Hispanic and African American children (n = 506) in New York City. We sought to determine associations between neighborhood-level factors (eg, housing type, school, time spent indoors versus outdoors) and urinary biomarkers of chemical exposures suspected to be associated with these characteristics (cotinine, 2,5-dichlorophenol, and phthalate metabolites) adjusted by age, sex, race, and caregiver education and language.

RESULTS

Urinary cotinine concentrations revealed a prevalent exposure to secondhand smoke; children living in public housing had higher concentrations than those in private housing. In homes with 1 smoker versus none, we found significant differences in urinary cotinine concentrations by housing, although not in homes with 2 or more smokers. Children in charter or public schools had higher urinary cotinine concentrations than those in private schools. School type was associated with exposures to both low- and high-molecular-weight phthalates, and concentrations of both exposure biomarkers were higher for children attending public versus private school. 2,5-Dichlorophenol concentrations declined from 2004 to 2007 (P = .038) and were higher among charter school children.

CONCLUSIONS

Housing and school type are associated with chemical exposures in this minority, inner city population. Understanding the role of neighborhood on environmental exposures can lead to targeted community-level interventions, with the goal of reducing environmental chemical exposures disproportionately seen in urban minority communities.

Exposure to perchlorate, nitrate and thiocyanate, and prevalence of diabetes mellitus

Background

It is known that perchlorate, nitrate and thiocyanate have the property of inhibiting sodium iodide symporter. Animal studies have suggested that these compounds, especially perchlorate, might also interfere with insulin secretion. However, the association between their exposure and diabetes risk is largely unknown in humans.

Methods

Among 11 443 participants (mean age 42.3 years) from the National Health and Nutritional Examination Survey 2001-14, urinary perchlorate, nitrate and thiocyanate were measured by using ion chromatography coupled with electrospray tandem mass spectrometry. Diabetes was defined as self-reported doctor diagnosis, use of oral hypoglycaemic medication or insulin, fasting plasma glucose ≥ 126 mg/dl or glycated haemoglobin A1c (HbA1c) ≥ 6.5%.

Results

The median (interquartile range) levels of urinary perchlorate, nitrate and thiocyanate were 3.32 (1.84, 5.70) μg/l, 46.4 (27.9, 72.0) mg/l and 1.23 (0.59, 2.78) mg/l, respectively. Higher levels of urinary perchlorate were associated with elevated levels of fasting glucose, HbA1c, insulin and homeostatic model assessment of insulin resistance (all Ptrend < 0.001). After multivariate adjustment including urinary creatinine, smoking status and body mass index (BMI), higher urinary perchlorate, but not nitrate or thiocyanate, was associated with an increased prevalence of diabetes mellitus. Comparing extreme quintiles, the odds ratio (95% confidence interval) of diabetes was 1.53 (1.21, 1.93; Ptrend < 0.001) for perchlorate, 1.01 (0.77, 1.32; Ptrend = 0.44) for nitrate and 0.98 (0.73, 1.31; Ptrend = 0.64) for thiocyanate. When urinary perchlorate, nitrate and thiocyanate were further mutually adjusted, the results did not materially change. Similar results were observed when analyses were stratified by smoking status, as well as by age, gender, kidney function and BMI.

Conclusions

Higher urinary perchlorate levels are associated with an increased prevalence of diabetes mellitus, independent of traditional risk factors. Future prospective studies are needed to confirm these findings.

Maternal perchlorate exposure in pregnancy and altered birth outcomes

BACKGROUND

At high medicinal doses perchlorate is known to decrease the production of thyroid hormone, a critical factor for fetal development. In a large and uniquely exposed cohort of pregnant women, we recently identified associations between environmental perchlorate exposures and decreased maternal thyroid hormone during pregnancy. Here, we investigate whether perchlorate might be associated with birthweight or preterm birth in the offspring of these women.

METHODS

Maternal urinary perchlorate, serum thyroid hormone concentrations, birthweight, gestational age, and urinary nitrate, thiocyanate, and iodide were collected in 1957 mother-infant pairs from San Diego County during 2000-2003, a period when the county's water supply was contaminated with perchlorate. Associations between perchlorate exposure and birth outcomes were examined using linear and logistic regression analyses adjusted for maternal age, weight, race/ethnicity, and other factors.

RESULTS

Perchlorate was not associated with birth outcomes in the overall population. However, in analyses confined to male infants, log₁₀ maternal perchlorate concentrations were associated with increasing birthweight (β=143.1gm, p=0.01), especially among preterm births (β=829.1g, p<0.001). Perchlorate was associated with male preterm births ≥2500g (odds ratio=3.03, 95% confidence interval=1.09-8.40, p-trend=0.03). Similar associations were not seen in females.

CONCLUSIONS

This is the first study to identify associations between perchlorate and increasing birthweight. Further research is needed to explore the differences we identified related to infant sex, preterm birth, and other factors. Given that perchlorate exposure is ubiquitous, and that long-term impacts can follow altered birth outcomes, future research on perchlorate could have widespread public health importance.

Phenol Concentrations During Childhood and Subsequent Measures of Adiposity Among Young Girls

Phenolic compounds represent a class of environmental chemicals with potentially endocrine-disrupting capabilities. We investigated longitudinal associations between childhood exposure to phenols, from both manmade and natural sources, and subsequent measures of adiposity among girls enrolled in the Breast Cancer and the Environment Research Program between 2004 and 2007. Baseline (ages 6-8 years) urinary concentrations were obtained for creatinine and phenol metabolites: enterolactone, genistein, daidzein, benzophenone-3, bisphenol A, the sum of parabens (methyl, ethyl, and propyl parabens), 2,5-dichlorophenol, and triclosan. Body mass index (weight (kg)/height (m)2), waist circumference, and percent body fat were measured at annual or semiannual examinations through 2015 (n = 1,017). Linear mixed-effects regression was used to estimate how baseline concentrations of phenols (tertile groups) were related to changes in girls' adiposity measurements from ages 7 through 15 years. Enterolactone was inversely associated with body mass index, waist circumference, and percent body fat, while 2,5-dichlorophenol was positively associated with these measurements. A nonmonotonic association was observed for triclosan and girls' adiposity; however, it was due to effect modification by baseline overweight status. Triclosan was positively associated with adiposity only among overweight girls. These results suggest that exposure to specific phenols during childhood may influence adiposity through adolescence.

Effect of Nitrates, Thiocyanates and Selenium on the Iron and Iodine Status of Postpartum Women

AIM

To find correlations between high thiocyanate and nitrate levels and low selenium levels and the indicators of the iodine and iron status of postpartum women.

MATERIALS AND METHODS

The study included 41 mothers aged 26.4±5.9 yrs from Asenovgrad and nearby villages. Urinary iodine was determined by the Sandell-Kolthoff reaction and thiocyanate - by the interaction of these ions with acidic solution of KMnO4; for serum nitrates we used the colorimetric method; serum selenium was assessed by electro-thermal atomic-absorption spectrophotometry; thyroxin (FT4), the thyroid stimulating hormone (TSH), serum ferritin (SF), and serum transferrin receptor (sTfR) were determined using ELISA; Hb levels were determined by hematology analyzer.

RESULTS

Assessing the iodine status, we found a negative correlation between the levels of iodine and thiocyanates in urine (R=-0.717, р<0.0001), a positive correlation between nitrates and TSH (R=0.487, р=0.003) and a negative correlation between nitrates and FT4 (R=-0.312, р=0.06). For the iron status, we found a negative correlation between nitrates and SF (R=-0.429, р=0.009) and between nitrates and Hb (R=-0.383, р=0.021). The Mann-Whitney U-test showed that in women with nitrate levels higher than the mean value there was low FT4 level (р=0.06), high TSH level (р=0.013), low Hb concentration (р=0.061) and low SF concentration (р=0.005). The combined effects of environmental factors (elevated nitrate levels and low selenium level) on the iodine and iron status are manifested by low concentrations of FT4 (р=0.033), Hb (р=0.06) and SF (р=0.05) and high level of TSH (р=0.05). In conclusion, we found that environmental factors, especially when combined, have a negative impact on the iron and iodine status of females.

Perchlorate in Water Supplies: Sources, Exposures, and Health Effects

Perchlorate exposure occurs from ingestion of natural or man-made perchlorate in food or water. Perchlorate is used in a variety of industrial products including missile fuel, fireworks, and fertilizers, and industrial contamination of drinking water supplies has occurred in a number of areas. Perchlorate blocks iodide uptake into the thyroid and decreases the production of thyroid hormone, a critical hormone for metabolism, neurodevelopment, and other physiologic functions. Occupational and clinical dosing studies have not identified clear adverse effects, but may be limited by small sample sizes, short study durations, and the inclusion of mostly healthy adults. Expanding evidence suggests that young children, pregnant women, fetuses, and people co-exposed to similarly acting agents may be especially susceptible to perchlorate. Given the ubiquitous nature of perchlorate exposure, and the importance of thyroid hormone for brain development, studying the impact of perchlorate on human health could have far-reaching public health implications.

Thyroid Hormones and Moderate Exposure to Perchlorate during Pregnancy in Women in Southern California

BACKGROUND

Findings from national surveys suggest that everyone in the United States is exposed to perchlorate. At high doses, perchlorate, thiocyanate, and nitrate inhibit iodide uptake into the thyroid and decrease thyroid hormone production. Small changes in thyroid hormones during pregnancy, including changes within normal reference ranges, have been linked to cognitive function declines in the offspring.

OBJECTIVES

We evaluated the potential effects of low environmental exposures to perchlorate on thyroid function.

METHODS

Serum thyroid hormones and anti-thyroid antibodies and urinary perchlorate, thiocyanate, nitrate, and iodide concentrations were measured in 1,880 pregnant women from San Diego County, California, during 2000-2003, a period when much of the area's water supply was contaminated from an industrial plant with perchlorate at levels near the 2007 California regulatory standard of 6 μg/L. Linear regression was used to evaluate associations between urinary perchlorate and serum thyroid hormone concentrations in models adjusted for urinary creatinine and thiocyanate, maternal age and education, ethnicity, and gestational age at serum collection.

RESULTS

The median urinary perchlorate concentration was 6.5 μg/L, about two times higher than in the general U.S.

POPULATION

Adjusted associations were identified between increasing log10 perchlorate and decreasing total thyroxine (T4) [regression coefficient (β) = -0.70; 95% CI: -1.06, -0.34], decreasing free thyroxine (fT4) (β = -0.053; 95% CI: -0.092, -0.013), and increasing log10 thyroid-stimulating hormone (β = 0.071; 95% CI: 0.008, 0.133).

CONCLUSIONS

These results suggest that environmental perchlorate exposures may affect thyroid hormone production during pregnancy. This could have implications for public health given widespread perchlorate exposure and the importance of thyroid hormone in fetal neurodevelopment.

CITATION

Steinmaus C, Pearl M, Kharrazi M, Blount BC, Miller MD, Pearce EN, Valentin-Blasini L, DeLorenze G, Hoofnagle AN, Liaw J. 2016. Thyroid hormones and moderate exposure to perchlorate during pregnancy in women in Southern California. Environ Health Perspect 124:861-867; http://dx.doi.org/10.1289/ehp.1409614.

Thyroid Antagonists (Perchlorate, Thiocyanate, and Nitrate) and Childhood Growth in a Longitudinal Study of U.S. Girls

BACKGROUND

Perchlorate, thiocyanate, and nitrate are sodium/iodide symporter (NIS) inhibitors that block iodide uptake into the thyroid, thus affecting thyroid function. Thyroid dysfunction can adversely affect somatic growth and development in children. To our knowledge, no studies have examined effects of NIS inhibitors on body size measures.

OBJECTIVE

We investigated associations between NIS inhibitors and childhood growth in 940 girls from the Puberty Study of the Breast Cancer and Environment Research Program.

METHODS

Urine samples collected from girls 6-8 years of age at enrollment (2004-2007) from New York City, greater Cincinnati, Ohio, and the Bay Area in California were analyzed for NIS inhibitors and creatinine (C). The longitudinal association between NIS inhibitors and anthropometric measures [height, waist circumference, and body mass index (BMI)] during at least three visits was examined using mixed effects linear models, adjusted for race and site.

RESULTS

Compared with girls in the low-exposure group (3.6, 626, and 500 mg/gC, median perchlorate, thiocyanate, and nitrate, respectively) girls with the highest NIS inhibitor exposure (9.6, 2,343, and 955 mg/gC, median perchlorate, thiocyanate, and nitrate, respectively) had slower growth in waist circumference and BMI but not height. Significant differences in the predicted mean waist circumference and BMI between the low- and high-exposure groups were observed beginning at 11 years of age.

CONCLUSIONS

Higher NIS inhibitor exposure biomarkers were associated with reductions in waist circumference and BMI. These findings underscore the need to assess exposure to NIS inhibitors with respect to their influence on childhood growth.

CITATION

Mervish NA, Pajak A, Teitelbaum SL, Pinney SM, Windham GC, Kushi LH, Biro FM, Valentin-Blasini L, Blount BC, Wolff MS, for the Breast Cancer and Environment Research Project (BCERP). 2016. Thyroid antagonists (perchlorate, thiocyanate, and nitrate) and childhood growth in a longitudinal study of U.S. girls. Environ Health Perspect 124:542-549; http://dx.doi.org/10.1289/ehp.1409309.

Daily intake of bisphenol A and triclosan and their association with anthropometric data, thyroid hormones and weight loss in overweight and obese individuals

Bisphenol A (BPA) and triclosan (TCS) were determined in urine of Belgian overweight and obese (n=151) and lean (n=43) individuals. After the first urine collection (0M), obese patients started a diet program or have undergone bariatric surgery. Hereafter, three additional urine samples from obese patients were collected after 3 (3M), 6 (6M) and 12 (12M) months. Both compounds were detected in >99% of the samples. BPA had median concentrations of 1.7 and 1.2ng/mL in obese and lean groups, respectively, while TCS had median concentrations of 1.5 and 0.9ng/mL in the obese and lean groups, respectively. The obese group had higher urinary concentrations (ng/mL) of BPA (p<0.5), while no significant differences were found for TCS between the obese and lean groups. No time trends between the different collection moments were observed. The BPA concentrations in the obese group were negatively associated with age, while no gender difference or relationship with body mass index was observed. For TCS, no relationships with gender, BMI, or age were found. The temporal variability of BPA and TCS was assessed with calculation of the intraclass correlation coefficient, Spearman rank correlation coefficients, and surrogate category analysis. We observed evidence that single spot urine samples might be predictive of exposure over a longer period of time. Dietary intakes of BPA and TCS did not differ significantly among the time points considered after obese individuals started losing weight (6 and 12months). Multiple linear regression analyses after adjusting for age and weight loss revealed negative associations between urinary TCS and serum FT4 in the 0M and 3M female obese individuals and positive associations between urinary BPA and serum TSH in the lean group.

Negative association between serum parathyroid hormone levels and urinary perchlorate, nitrate, and thiocyanate concentrations in U.S. adults: the National Health and Nutrition Examination Survey 2005-2006

OBJECTIVES

Perchlorate, nitrate, and thiocyanate are well-known inhibitors of the sodium-iodide symporter and may disrupt thyroid function. This exploratory study investigated the association among urinary perchlorate, nitrate, and thiocyanate concentrations and parathyroid hormone (PTH) levels in the general U.S. population.

METHODS

We analyzed data on 4265 adults (aged 20 years and older) from the National Health and Nutrition Examination Survey in 2005 through 2006 to evaluate the relationship among urinary perchlorate, nitrate, and thiocyanate concentration and PTH levels and the presence of hyperparathyroidism cross-sectionally.

RESULTS

The geometric means and 95% confidence interval (95% CI) concentrations of urinary perchlorate, nitrate, and thiocyanate were 3.38 (3.15-3.62), 40363 (37512-43431), and 1129 (1029-1239) ng/mL, respectively. After adjusting for confounding variables and sample weights, creatinine-corrected urinary perchlorate was negatively associated with serum PTH levels in women (P = 0.001), and creatinine-corrected urinary nitrate and thiocyanate were negatively associated with serum PTH levels in both sex groups (P = 0.001 and P<0.001 for men, P = 0.018 and P<0.001 for women, respectively). Similar results were obtained from sensitivity analyses performed for exposure variables unadjusted for creatinine with urinary creatinine added as a separate covariate. There was a negative relationship between hyperparathyroidism and urinary nitrate and thiocyanate [odds ratio (95% CI) = 0.77 (0.60-0.98) and 0.69 (0.61-0.79), respectively].

CONCLUSIONS

A higher urinary concentration of perchlorate, nitrate, and thiocyanate is associated with lower serum PTH levels. Future studies are needed to determine the pathophysiological background of the observation.

The effects of perchlorate, nitrate, and thiocyanate on free thyroxine for potentially sensitive subpopulations of the 2001-2002 and 2007-2008 National Health and Nutrition Examination Surveys

Among women with urinary iodine concentration <100 μg/l in the 2001-2002 National Health and Nutrition Examination Survey (NHANES), urinary perchlorate was associated with significant changes in thyroid stimulating hormone and total thyroxine (T4). Although perchlorate, nitrate, and thiocyanate all potentially act to inhibit iodide uptake, free T4 was not found to be associated with exposure to these chemicals in the same data. Fetuses of pregnant mothers with iodine deficiency are thought to be a sensitive subpopulation for perchlorate exposure, but the potential associations between free T4 and exposure to these chemicals among pregnant mothers in NHANES 2001-2002 and 2007-2008 have not been specifically evaluated to date. This study investigates the potential associations between urinary perchlorate, nitrate, and thiocyanate and serum free T4 in individuals with low urinary iodine levels and pregnant women. Multivariate regression models of free T4 were conducted and included urinary perchlorate, nitrate, thiocyanate, and covariates known to have an impact on the thyroid (anti-thyroid peroxidase (TPO) antibodies, age, race/ethnicity, body mass index, and hours of fasting). Meta-analyses were also conducted on non-pregnant and on pregnant women from the two survey cycles. Urinary nitrate was associated with serum free T4 in non-pregnant women of NHANES 2001-2002 who had urinary iodine ≥100 μg/l. In the meta-analysis, urinary perchlorate, nitrate, and thiocyanate were significant predictors of serum free T4 in non-pregnant women. No association was found in men and pregnant women. TPO antibodies were significant predictors of free T4 among non-pregnant women only when the models included urinary perchlorate, nitrate, or thiocyanate. Risk assessment for perchlorate exposure should consider co-exposure to nitrate and thiocyanate.

A robust method for iodine status determination in epidemiological studies by capillary electrophoresis

Iodine deficiency is the most common preventable cause of intellectual disabilities in children. Global health initiatives to ensure optimum nutrition thus require continuous monitoring of population-wide iodine intake as determined by urinary excretion of iodide. Current methods to analyze urinary iodide are limited by complicated sample pretreatment, costly infrastructure, and/or poor selectivity, posing restrictions to large-scale epidemiological studies. We describe a simple yet selective method to analyze iodide in volume-restricted human urine specimens stored in biorepositories by capillary electrophoresis (CE) with UV detection. Excellent selectivity is achieved when using an acidic background electrolyte in conjunction with dynamic complexation via α-cyclodextrin in an unmodified fused-silica capillary under reversed polarity. Sample self-stacking is developed as a novel online sample preconcentration method to boost sensitivity with submicromolar detection limits for iodide (S/N ≈ 3, 0.06 μM) directly in urine. This assay also allows for simultaneous analysis of environmental iodide uptake inhibitors, including thiocyanate and nitrate. Rigorous method validation confirmed good linearity (R(2) = 0.9998), dynamic range (0.20 to 4.0 μM), accuracy (average recovery of 93% at three concentration levels) and precision for reliable iodide determination in pooled urine specimens over 29 days of analysis (RSD = 11%, n = 87).

Environmental perchlorate exposure: potential adverse thyroid effects

PURPOSE OF REVIEW

This review will present a general overview of the sources, human studies, and proposed regulatory action regarding environmental perchlorate exposure.

RECENT FINDINGS

Some recent studies have reported significant associations between urinary perchlorate concentrations, thyroid dysfunction, and decreased infant intelligence quotient in groups who would be particularly susceptible to perchlorate effects. An update regarding the recently proposed regulatory actions and potential costs surrounding amelioration of perchlorate contamination is provided.

SUMMARY

The potential adverse thyroidal effects of environmental perchlorate exposure remain controversial, and further research is needed to further define its relationship to human health among pregnant and lactating women and their infants.

Perchlorate exposure and thyroid function in ammonium perchlorate workers in Yicheng, China

The impact of low level dust on the thyroid function of workers chronically exposed to ammonium perchlorate (AP) is uncertain and controversial. The aim of this study was to examine whether workers in China with long-term (>3 years) occupational exposure to low levels of AP dust had affected thyroid homeostasis. Mean occupational exposures to AP dust ranged from 0.43 to 1.17 mg/m³. Geometric means of post-shift urinary perchlorate levels were 20.5 µg/L for those exposed and 12.8 µg/L for the controls. No significant differences were found for thyroid function parameters of FT₃, FT₄, or log TSH or for TPO prevalence or thyroglobulin levels. Additionally, no differences in findings were observed for complete blood count (CBC), serum biochemical profile, or pulmonary function test. Median urinary iodine levels of 172 and 184 µg/L showed that the workers had sufficient iodine intake. This study found no effect on thyroid function from long term, low-level documented exposure to ammonium perchlorate. It is the first study to report both thyroid status parameters and urinary perchlorate, a biomarker of internal perchlorate exposure, in occupationally exposed workers in China.