Historical changes in PCB patterns in Lake Ontario and Green Bay, Lake Michigan, 1971 to 1982, from herring gull egg monitoring data

Patterns of PCB congener bioaccumulation were examined in archived herring gull (Larus argentatus) eggs collected from Big Sister Island in Green Bay, Lake Michigan, and Scotch Bonnet Island in Lake Ontario from 1971 to 1982 as part of the Canadian Wildlife Service's Great Lakes Herring Gull Monitor ing Program. Concentrations of 97 PCB congeners were measured. From 1971 to 1982, ecological half-lives of most congeners, particularly the tri- throu gh hexachlorobiphenyls, were greater in eggs from Green Bay than Lake Ontar io. Comparing sum PCB levels in eggs collected in 1971 and 1982, concentrat ions declined 80% at Scotch Bonnet Island and 74% at Big Sister Island. PCB congener patterns were different in eggs from the two colonies. Principal components analysis showed that inter-site differences in congener patterns became more apparent after 1976. This indicated that regional PCB sources were the most influential in determining patterns of biologically-available PCBs during the 1971 to 1982 period in: these two lakes, via recycling of historical PCBs from sediments or gradually decreasing loading. Trend analy sis of selected congeners specific to Aroclors 1242, 1254, and 1260 reveale d that the rapid decline of less chlorinated congeners,observed from 1971 t o 1976 in Lake Ontario, was explained by a decrease in loading of Aroclor 1 242 to the lake. At both colonies, ecological half life of the congeners wa s significantly (p < 0.001) correlated with log K-ow and with -log HLC. Cha nges in PCB composition, after 1976 in Lake Ontario and from 1971 to 1982 i n Green Bay, could be explained by differences in the physical behavior of individual congeners affecting removal by volatilization and sedimentation.