Contaminant concentrations in eggs of Black Terns (Chlidonias niger) from southern Ontario and southern Quebec, 1989-1996

Eggs of Black Terns (Chlidonias niger) were collected from 8 sites in southern Quebec (6 sites in 1989, 1 in 1992 and 1 in 1993) and from 5 sites in southern Ontario (1 in 1993 and 4 in 1996). Four to 16 eggs per site were pooled and analyzed for organochlorines (OCs). Eggs collected from Quebec were analyzed also for mercury, lead and cadmium. Thickness measurements were taken on all eggshells. The ranges of OC contaminant values tug g(-1), wet weight) for the 13 site pools were as follows: total (Sum) PCBs = 0.46 to 3.72, PCBs (1:1) = 0.94 to 5.13, DDE = 0.14 to 0.83, total chlordanes = 0.021 to 0.138, dieldrin = 0.012 to 0.072, mirex = 0.005 to 0.106, b-HCH = Nondetect to 0.026, heptachlor epoxide = 0.004 to 0.021 and HCB = 0.005 to 0.013. There were no significant differences in levels of OCs in eggs between Quebec and Ontario except for PCBs (I:1), which were significantly higher in Quebec samples (2.82 ug.g(-1) vs 1.44 ug.g(-1)). In eggs from 11 of 13 sites PCB congeners # 118, 138, 153 and 180 were 4 of the 5 most prevalent. Two sites (1 in Ontario and 1 in Quebec) had different congener "signatures", suggesting localized sources within the eastern Great Lakes-St. Lawrence River Basin. OC contaminant levels in Black Tern eggs measured in this study were lower than those reported previously. The ranges of metal concentrations were: total mercury = 0.24 to 0.40, methyl mercury = 0.24 to 0.37, lead = 0.09 to 0.65 and cadmium = 0.02 to 0.11. Eggshells from Quebec were significantly thicker than those from Ontario. Eggshells from Quebec and Ontario were 3.2 and 9.0% thinner, respectively, than pre-1947 values. The levels of contaminants found in this study were low compared to those known in other colonially nesting waterbirds. The biological effects of contaminants on Black Terns have not been studied in detail and the species' sensitivity should be evaluated on a biochemical level.