The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term.

Perchlorate (ClO4−) and thiocyanate (SCN−) are potent and nitrate (NO3−) a weak competitive inhibitor of the thyroid sodium-iodide symporter. To determine the effects of long-term, high ClO4− exposure on thyroid function, we conducted a study of 29 workers employed for at least 1.7 yr (50% over 5.9 yr) in an ammonium ClO4− production plant in Utah. Serum ClO4−, SCN−, and NO3−; serum T4, free T4 index, total T3, thyroglobulin (Tg), and TSH; 14-h thyroid radioactive iodine uptake (RAIU); and urine iodine (I) and ClO4− were assessed after 3 d off (Pre) and during the last of three 12-h night shifts in the plant (During) and in 12 volunteers (C) not working in the plant. Serum and urine ClO4− were not detected in C; urine ClO4− was not detected in 12 of 29 and was 272 μg/liter in 17 Pre workers; serum ClO4− was not detected in 27 of 29 Pre; and serum and urine ClO4− were markedly elevated during ClO4− exposure to 868 μg/liter and 43 mg/g creatinine, respectively. Serum SCN− and NO3− concentrations were simila...