Environmental Perchlorate and Thiocyanate Exposures and Infant Serum Thyroid Function

Abstract

Background: Breastfed infants rely on maternal iodine for thyroid hormone production required for neurodevelopment. Dietary iodine among women of childbearing age in the United States may be insufficient. Perchlorate (competitive inhibitor of the sodium/iodide symporter [NIS]) exposure is ubiquitous. Thiocyanate, from cigarettes and diet, is a weaker NIS inhibitor. Environmental perchlorate and thiocyanate exposures could decrease breast milk iodine by competitively inhibiting NIS in lactating breasts (thus impairing infants' iodine availability), and/or infants' thyroidal NIS to directly decrease infant thyroid function. The current study assessed the relationships between environmental perchlorate and thiocyanate exposures and infant serum thyroid function. Methods: Iodine, perchlorate, and thiocyanate in breast milk, maternal and infant urine, and infant serum thyroid function tests were cross-sectionally measured in Boston-area women and their 1-3 month-old breastfed infants. Univariate and multivariable analyses assessed relationships between iodine, perchlorate, thiocyanate, thyroid-stimulating hormone (TSH), and free thyroxine (FT4) levels. Results: In 64 mothers and infants, median (range) iodine levels were 45.6 lg/L (4.3-1080) in breast milk, 101.9 lg/L (27-570) in maternal urine, and 197.5 lg/L (40-785) in infant urine. Median perchlorate concentrations were 4.4 lg/L (0.5-29.5) in breast milk, 3.1 lg/L (0.2-22.4) in maternal urine, and 4.7 lg/L (0.3-25.3) in infant urine. There were no correlations between infant TSH or FT4 and iodine, perchlorate, and thiocyanate levels in breast milk, maternal urine, and infant urine. In multivariable analyses, perchlorate and thiocyanate levels in breast milk, maternal urine, and infant urine were not significant predictors of infant TSH or FT4. Conclusions: Boston-area mothers and their breastfed infants are generally iodine sufficient. Although environmental perchlorate and thiocyanate are ubiquitous, these results do not support the concern that maternal and infant environmental perchlorate and thiocyanate exposures affect infant thyroid function.

Placental transfer of and infantile exposure to perchlorate

“…2). Furthermore, our DOSE M values were an order of magnitude greater than those reported in the U.S. (Leung et al, 2012;Valentin-Blasini et al, 2011), however, our results on the influence of dietary habits on perchlorate exposure by infants are similar to that found in the U.S. . Although the majority of studied infants in this study had exposure dose of perchlorate exceeding RfD, the estimations of DOSE U and DOSE M has certain uncertainty by using spot urine and breast milk samples, respectively.…”

“…Similarly, the concentrations of perchlorate found in breast milk in Nanchang, China were 3e8 times greater than the values reported from the U.S. (Fig. 1, mean: 5.80e10.6 ng mL À1 , median: 2.50e7.30 ng mL À1 ) (Borjan et al, 2011;Dasgupta et al, 2008;Kirk et al, 2007Kirk et al, , 2012Kirk et al, , 2005Leung et al, 2012;Leung et al, 2009). It is a tradition in China to display fireworks and firecrackers during celebration; in Nanchang city, approximately 376 tons of fireworks trashes were generated in 2012 during the 7-day Chinese New Year celebration.…”

“…1), but were much lower than those in maternal (mean: 13.2 ± 1.70 ng mL À1 ) and cord serum (19.9 ± 5.00 ng mL À1 ) samples obtained in a city of Chile (Lumen et al, 2013). However, it should (Asami et al, 2013;Blount et al, 2009;Borjan et al, 2011;Dasgupta et al, 2008;Her et al, 2010;Kirk et al, 2007;Kirk et al, 2005;Kirk et al, 2012;Lee et al, 2012;Leung et al, 2012;Leung et al, 2009;Lumen et al, 2013;Pearce et al, 2007;Wang et al, 2011;Valentin-Blasini et al, 2011). In this study, breast milk and infants' urine were recruited in Nanchang; cord blood samples were obtained in Tianjin; infant formula samples from ten manufacturers representing >80% of the Chinese market were purchased from retail stores.…”

“…1. To our knowledge, nearly all previously studies on perchlorate in the breast milk, infant formula and urine of infants were from the U.S. (Borjan et al, 2011;Dasgupta et al, 2008;Kirk et al, 2007Kirk et al, , 2012Kirk et al, , 2005Leung et al, 2012;Leung et al, 2009;Pearce et al, 2007;Valentin-Blasini et al, 2011), but several studies reported perchlorate concentrations in infant formula from Canada (Wang et al, 2011), Korea (Her et al, 2010;Lee et al, 2012) and Japan (Asami et al, 2013). The urinary concentrations of perchlorate that were detected among all infants from Nanchang, China were up to 20 (range: 2e20) fold higher than those of American infants (Fig.…”

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

“…18) Leung et al [43]. This epidemiological study examined the relationship between exposure to perchlorate and thiocyanate in breast milk and indices of infant serum thyroid functions in 64 breast-fed infants.…”