THYROID-FUNCTION IN LEAD SMELTER WORKERS - ABSENCE OF SUBACUTE OR CUMULATIVE EFFECTS WITH MODERATE LEAD BURDENS

Objective: To evaluate the effect of low to moderate occupational lead exposure on thyroid function we conducted a cross-sectional study of 151 male lead smelter workers. Methods: Parameters of thyroid function were assessed in relation to both subacute and cumulative lead exposu re over a 10-year employment period. Blood lead levels, obtained from plant surveillance records, were used to establish four ordinal levels of current and cumulative exposure (<15, 15-24, 25-39, and greater th an or equal to 40 mu g/dl). Results: Mean values for the lowest as com pared with the highest current exposure group were similar for thyroxi ne (T-4: 6.8 versus 6.1 mu g/dl), estimated free thyroxine (EFT4: 1.6 ng/dl in both groups), and thyroid-stimulating hormone (TSH: 1.8 versu s 1.7 mIU/l); there was no evidence of a significant trend for diminis hed thyroid function associated with increasing current lead exposure. Similarly, no significant difference was observed for T-4, EFT4, or T SH in relation to the 10-year cumulative exposure or for adjusted anal yses controlling for potential confounders, including age and alcohol use. Conclusion: In contrast to studies observing thyroid dysfunction in the setting of high lead exposure and related clinical poisoning, o ur findings weigh against a significant physiologic effect on thyroid function at lower levels (<60 mu g/dl) of occupational lead exposure.