Perchlorate and thiocyanate environmental contaminants in a mother-baby cohort in a Northern European population

Background Sufficient iodine intake is essential for thyroid hormone synthesis and foetal neurodevelopment. Perchlorate and thiocyanate inhibit iodine uptake into thyroid cells and may adversely affect thyroid function. This study reports perchlorate and thiocyanate exposure in a mother-infant cohort. Methods A prospective cohort of 241 mothers in Northern Ireland provided spot urine samples for storage during each trimester of pregnancy and postpartum, with a subset of 80 providing an offspring sample (6-24 weeks old). Urinary iodine concentration was measured in all women and infants. Urinary perchlorate and thiocyanate were measured in a subset of 159 women and 72 infants. Results Mothers were iodine deficient while babies were iodine replete, as previously reported. Perchlorate was detected in 95% of maternal and 65% of infant samples, whilst thiocyanate was detected in all samples. Maternal median perchlorate level was 3.7 µg/L, and 1.9 µg/L in offspring. Maternal median thiocyanate level was 585.8 µg/L, and 136 µg/L in offspring. Smoking was associated with a four-fold higher level of maternal thiocyanate in the second trimester (2970 vs 657 µg/L, p < 0.001). Breastfeeding was associated with lower perchlorate levels in infants. No significant perchlorate or thiocyanate contamination was detected in contemporaneous water samples across the island of Ireland (median <0.05 and <0.5 µg/L respectively). Conclusion This study demonstrates widespread exposure to perchlorate and thiocyanate in this cohort of mothers and infants, alongside maternal iodine deficiency. This may have an adverse impact on thyroid hormone synthesis and neurocognitive development of offspring in this geographical region with no iodine fortification programme.