McNABB, F.M.A.*; FOWLER, L.A.; PARSONS, C.M.; GRASMAN, K.A.; FOX, G.A.: Thyroid Function in Herring Gulls from PCB-contaminated Great Lakes sites.

We have investigated thyroid function in pipped embryos and prefledglings of herring gulls sampled in 1998 and 1999 at several Great Lakes sites with different amounts of PCB contamination and have compared them with gulls from the reference site, Kent Island in the Bay of Fundy. Previous studies found alterations in thyroid gland histology and size in gulls from PCB-polluted Great Lakes sites, suggesting thyroid disruption in these birds. Gulls collected in 1992 had decreased organ masses (liver, kidney, spleen, adrenals) and thyroid gland hypertrophy correlated with the sum of PCBs in pooled egg homogenates from different sites. In 1998 and 1999, there was no consistent pattern of differences in plasma thyroid hormones (THs) or T4 to T3 conversion in brain of either embryos or prefledglings across sites. However, thyroid glands tended to be larger in embryos and were significantly hypertrophied in prefledglings from the high PCB sites compared to the reference site. Weight-specific thyroid gland TH content was significantly decreased in both embryos and prefledglings at high PCB sites in both 1998 and 1999. Thus, despite thyroid gland depletion of stored THs with high PCB exposure, developing herring gulls are able to maintain their circulating THs at concentrations comparable to those in gulls from the reference site. Supported by EPA grant #827400-01-0.