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Exposure to perchlorate, nitrate, and thiocyanate among pregnant women in Norway
Kjersti S Bakken1, Tim I M Korevaar2, Johannes G Krabbe3
1Women's Clinic, Innlandet Hospital Trust, PO.Box 990, Lillehammer, N-2609, Norway; Center for International Health, University of Bergen, Bergen, N-5020, Norway.
Background:
The sodium-iodide symporter (NIS) inhibitors perchlorate, thiocyanate, and nitrate are ubiquitous environmental contaminants that competitively inhibit iodine uptake into the thyroid gland as well as iodine transport across the placenta. Globally, iodine deficiency remains common, and inhibition of NIS, reducing iodine transport, may increase the risk of impaired thyroid function.
Aim:
To characterize pregnant women's exposure to NIS inhibitors by measuring the urine concentrations of perchlorate, thiocyanate, and nitrate, and explore their determinants. We also examined individual variability by repeating the measurements in a sub-sample.
Method:
Pregnant women were included from December 1st, 2021 to August 31st, 2023. Urinary concentrations of NIS inhibitors were determined by Liquid Chromatography - Tandem Mass Spectrometry and were adjusted for creatinine to account for urinary dilution. Intraclass correlation between repeated samples was assessed using one-way analysis of variance. Generalized linear models and quantile regression were used to examine the association between potential determinants and NIS inhibitor concentrations.
Results:
A total of 197 women were included, of whom 53 had repeated urine samples. Median interquartile range (IQR) urinary concentrations of perchlorate, thiocyanate, and nitrate were 0.43 µg/L (0.07-1.24), 1365 µg/L (844-2132), and 41.8 mg/L (31.7-59.0), respectively. The intraclass correlation between the 53 repeated samples was poor for all three analytes, with an intraclass correlation (ICC) (95% CI) of 0.19 (0.0-0.5), 0.05 (0.0-0.4), and 0.19 (0.0-0.5) for perchlorate, thiocyanate, and nitrate, respectively. Women with daily tobacco use (snus) had 28% higher geometric mean of thiocyanate concentrations compared to non-users (95% CI: 7-52%).
Conclusion:
Norwegian women are exposed to perchlorate, thiocyanate, and nitrate, and the levels of these anions vary substantially within individuals, which has implications for the interpretation of exposure.