LEVELS OF POLYCHLORINATED-BIPHENYLS, INCLUDING COPLANAR CONGENERS, AND 2,3,7,8-T-4 CDD TOXIC EQUIVALENTS IN DOUBLE-CRESTED CORMORANT AND HERRING GULL EGGS FROM LAKE ERIE AND LAKE ONTARIO - A COMPARISON BETWEEN1981 AND 1992

Eggs of double-crested cormorants and herring gulls collected from Lak es Erie and Ontario during 1981 and 1992 were analyzed for PCB congene r concentrations, including non-ortho congeners 77, 126, and 169. Tota l PCB in herring gulls, measured as Aroclor 1254/1260, was significant ly lower in 1992, although differences in chemical concentrations in L ake Erie birds were not of the same magnitude as those observed in Lak e Ontario. Changes in concentration of total PCB in cormorant populati ons were not significant in Lake Ontario, and only a small change was observed in Lake Erie cormorants. In 1981, cormorants and herring gull eggs were similarly contaminated in Lake Ontario and Lake Erie, but i n 1992, Lake Erie eggs were significantly more contaminated than those from Lake Ontario. An examination of changes in concentrations of ind ividual congeners suggested that in cormorants, the decrease in PCB co ncentrations was due primarily to the loss of low K-ow congeners. All congeners, however, contributed to the decline of PCBs in herring gull s. Toxic equivalents (TEQs) estimates revealed that congener 126 domin ated the TEQs in both species in Lake Ontario and Lake Erie, and were highest in herring gulls. Although estimates of total TEQs in herring gulls in both lakes were lower in 1992, there was little change in TEQ s in double-crested cormorants. These results support the conclusion t hat chemical accumulation patterns are regulated to some degree by bot h ecological and limnological processes.