Perchlorate Exposure in Pregnancy and Cognitive Outcomes in Children: It's Not Your Mother's Thyroid

Perchlorate (ClO−4) is utilized in manufacturing rocket fuel, fireworks, and airbag inflation systems as well as being formed naturally in the atmosphere (1). It is stable and soluble in water and has been detected in drinking water, vegetables, and even breast milk. Perchlorate is a direct inhibitor of iodine transport and is the best characterized toxicant with respect to mechanism of action, although a range of environmental toxicants have been identified that disrupt thyroid hormone synthesis, metabolism, and action (2). At a sufficient dose and duration of exposure, perchlorate can reduce thyroid hormone production by reducing iodine uptake into the thyroid. Iodine is essential for thyroid hormone production and must be derived from dietary sources (3). Perchlorate antagonism of iodine transport is additive with other inhibitors, such as thiocyanate, found in cigarette smoke. The impact of perchlorate on thyroid function, especially in pregnancy, has led to intense focus on determining acceptable levels of perchlorate and other iodine inhibitors in the water supply (4, 5).