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 (T₄). Design: T₄ values were compared among newborns in Ramat Hasharon, Israel, whose mothers resided in suburbs where drinking water contained perchlorate ≤340 μg/L (very high exposure, n = 97), 42-94 μg/L (high exposure, n = 216), and <3 μg/L (low exposure, n = 843). In the very high and high exposure areas, T₄ 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 T₄ 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 μg/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 μg/L, respectively. T₄ 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 T₄ 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 μg/L) based on the National Research Council reference dose (RfD) [0.7 μg/(kg·day)]. Therefore the perchlorate RfD is likely to be protective of thyroid function in neonates of mothers with adequate iodide intake.