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Submitted on September 14, 2004
Accepted on November 17, 2004
Section of Endocrinology, Diabetes, and Nutrition, Boston Medical Center, Boston, MA, USA; Section of Endocrinology, Diabetes & Nutrition, Boston Medical Center, Boston, MA, USA; Section of Endocrinology, Diabetes & Nutrition, Boston Medical Center, Boston, MA, USA; Department of Radiology, Boston Medical Center, Boston, MA, USA; Department of Laboratory Medicine, Boston Medical Center, Boston, MA, USA; Consultants in Epidemiology and Occupational Health, Washington, DC, USA; Consultants in Epidemiology and Occupational Health, Inc., Washington, DC, USA; Consultants in Epidemiology and Occupational Health, Inc., Washington, DC, USA; Environ, Ruston, LA, USA; Health Management Division, Kerr-McGee Shared Services LLC, Oklahoma City, OK, USA
* To whom correspondence should be addressed.
Lewis E. Braverman, E-mail: Lewis.Braverman{at}bmc.org
Perchlorate (ClO4-) and thiocyanate (SCN-) are potent and nitrate (NO3-) a weak competitive inhibitor of the thyroid NIS. 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, FTI, TT3, Tg and TSH; 14-hour thyroid radioactive iodine uptake (RAIU); and urine iodine (I) and ClO4- were assessed after three days off (Pre) and during the last of three, 12-hour 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 Pre workers and was 272 µg/L in 17; serum ClO4- was not detected in 27/29 Pre; and serum and urine ClO4- were markedly elevated during ClO4- exposure to 868 µg/L and 43 mg/g creatinine respectively. Serum SCN- and NO3- concentrations were similar in all groups. Thyroid RAIUs were markedly decreased in During compared with Pre (13.5 vs. 21.5%, P < 0.01, paired t) and were associated with an increase in urine I excretion (230 vs. 148 µgI/g Cr, P = 0.02, paired t) but were similar to those in the C group (14.4%). Serum TSH and Tg concentrations were normal and similar in the three groups. Serum T4 (8.3 vs. 7.7 µg/dl), FTI (2.4 vs. 2.2) and TT3 (147 vs. 134 ng/dl) were slightly, but significantly increased in the During vs. Pre workers (P < 0.01, paired t). Thyroid volumes and patterns by ultrasound were similar in the 29 workers and 12 community volunteers. Conclusion: High ClO4- absorption during three nights work exposure decreased the 14-hour thyroid RAIU by 38% in ClO4- production workers compared with the RAIU after three days off. However, serum TSH and Tg concentrations and thyroid volume by ultrasound were not affected by ClO4- suggesting that long-term, intermittent, high exposure to ClO4- does not induce hypothyroidism or goiter in adults.
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