TEMPORAL AND GEOGRAPHIC-VARIATION OF ORGANOCHLORINE RESIDUES IN EGGS OF THE COMMON SNAPPING TURTLE (CHELYDRA-SERPENTINA-SERPENTINA) (1981-1991) AND COMPARISONS TO TRENDS IN THE HERRING GULL (LARUS-ARGENTATUS) IN THE GREAT-LAKES BASIN IN ONTARIO, CANADA

Common snapping turtle (Chelydra serpentina serpentina) eggs from five sites within the Great Lakes basin, and from a reference site in nort h-central Ontario were collected during 1981-1991 and analyzed for fou r oganochlorine pesticides, polychlorinated biphenyls (PCBs) including six non-ortho PCBs, polychlorinated dibenzodioxins (PCDDs), and polyc hlorinated dibenzofurans (PCDFs). The pattern of geographic variation was consistent over time in eggs with Cootes Paradise/Hamilton Harbour and Lynde Creek eggs on Lake Ontario containing the highest concentra tions and most PCDD and PCDF congeners among all sites. Eggs from Cran berry Marsh on Lake Ontario contained organochlorine concentrations si milar to those from Big Creek Marsh and Rondeau Provincial Park on Lak e Erie except PCDDs and PCDFs which occurred at higher concentrations and more congeners were detectable in Cranbeny Marsh eggs. Concentrati ons of most contaminants in turtle eggs from Algonquin Park, the refer ence site, have significantly decreased in the past decade. Dieldrin c oncentrations, however, increased in Algonquin Park eggs from 1981 to 1989. Significant decreases in concentrations of hexachlorobenzene, mi rex and PCBs occurred between turtle eggs collected in 1981/84 and 198 9 at Big Creek Marsh and Rondeau Provincial Park, whereas there was no significant change in concentrations of p,p'-DDE and dieldrin. In Lak e Ontario eggs, concentrations of PCBs, p,p'-DDE and dieldrin increase d significantly between 1984 and 1991. Differences were also found in patterns of temporal variation in contamination between herring gulls (Larus argentatus) and snapping turtles which were attributed to diffe rences in diet. Elevated and continued contamination in turtle eggs fr om Lake Ontario is probably due to a combination of local sources of c hemicals and consumption of large migratory fish that spawn in wetland s inhabited by these turtles.