EFFECTS OF DIOXINS AND POLYCHLORINATED-BIPHENYLS ON THYROID-HORMONE STATUS OF PREGNANT-WOMEN AND THEIR INFANTS

Dioxins [polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF )] and polychlorinated biphenyls (PCB) are potentially hazardous compo unds. Animal studies have demonstrated that PCDD, PCDF, and PCB can al ter thyroid hormone homeostasis. We investigated thyroid hormone level s in 105 mother-infant pairs. To estimate maternal and infant exposure , four nonplanar PCB congeners were measured in maternal plasma during the last month of pregnancy and in umbilical cord plasma. Seventeen P CDD and PCDF congeners, three planar PCB congeners, and 23 nonplanar P CB congeners were measured in human milk. Higher PCDD, PCDF, and PCB l evels in human milk, expressed as toxic equivalents, correlated signif icantly with lower plasma levels of maternal total triiodothyronine an d total thyroxine, and with higher plasma levels of TSH in the infants in the 2nd wk and 3rd mo after birth. Infants exposed to higher toxic equivalents levels had also lower plasma free thyroxine and total thy roxine levels in the 2nd wk after birth. We conclude that elevated lev els of dioxins and PCB can alter the human thyroid hormone status.