Polychlorinated biphenyl (PCB) exposure in relation to thyroid hormone levels in neonates

Polychlorinated biphenyls (PCBs) are industrially produced environmentally persistent compounds. In developed countries all humans have detectable lev els in blood and other tissues. PCBs alter thyroid hormone metabolism in an imal experiments, and human data suggest background-level exposure may have similar effects in neonates. We evaluated this possible effect among 160 N orth Carolina children whose in utero PCB exposure was estimated on the bas is of the mother's PCB levels in milk and blood, in 1978-1982 (estimated me dian PCB level in milk at birth, 1.8 mg/kg lipid). Their umbilical cord ser a were thawed in 1998 and assayed for total thyroxine, free thyroxine, and thyroid stimulating hormone. We found that PCB exposure was not strongly re lated to any of the thyroid measures. For example, for a one unit change in milk PCB concentration (mg/kg lipid), the associated multivariate-adjusted increase in thyroid stimulating hormone level was 7% (95% confidence limit s (CL) = -6, 21), Despite the possibility of sample degradation, these data suggest that within the range of background-level exposure in the United S tates, in utero PCB exposure is only slightly related to serum concentratio n of total thyroxine, free thyroxine, and thyroid stimulating hormone at bi rth.