ORGANOCHLORINE CONTAMINANT LEVELS IN WATERBIRD SPECIES FROM HAMILTON HARBOR, LAKE-ONTARIO - AN IJC AREA OF CONCERN

The levels of organochlorine (OC) contaminants in eggs and tissues of waterbird species nesting in Hamilton Harbour, Ontario, an Internation al Joint Commission Area of Concern, were monitored between 1981 and 1 992. PCBs, DDE, and mirex were present at the highest concentrations o f the 29 organochlorines and one trace metal measured. Most contaminan ts in the various species tested showed a declining temporal pattern d uring that period. Double-crested cormorant eggs generally had higher concentrations of contaminants than those in herring gull eggs which i n turn were higher than those in eggs of black-crowned night-herons, C aspian terns and common terns. The levels of contaminants in the eggs reflect the dietary preferences of the species with the fish-eating bi rds containing consistently higher accumulations of contaminants when compared to the herbivorous Canada goose for which the levels were con sistently much lower for all compounds. The concentrations of contamin ants detected are among some of the highest in the Great Lakes but whe n compared to other sites on Lake Ontario, the levels in Hamilton Harb our are generally equal or lower. Elevated levels of contaminants such as PCBs, mirex, and DDE were also detected in liver and muscle tissue s of migrant waterfowl species from the harbor. Despite habitat degrad ation and continued presence of contaminants, the harbor supports a la rge number and wide variety of waterbird species. Except for black-cro wned night herons, the nesting populations of colonial waterbirds have increased between 21 and 1061 % since the East survey in 1987.