| Year | DDE | Dieldrin | Mirex | HCB | PCBs |
| parts per million in whole egg samples, wet weight | |||||
| 1974 | 7.13 | 0.35 | 0.64 | 0.29 | 72.46 |
| 1975 | 7.41 | 0.33 | 0.32 | 0.19 | 62.30 |
| 1976 | na | na | na | na | na |
| 1977 | 7.49 | 0.40 | 0.45 | 0.37 | 68.70 |
| 1978 | 4.29 | 0.24 | 0.20 | 0.09 | 44.43 |
| 1979 | 3.10 | 0.25 | 0.17 | 0.11 | 48.44 |
| 1980 | 2.98 | 0.21 | 0.18 | 0.09 | 46.38 |
| 1981 | 3.90 | 0.22 | 0.25 | 0.09 | 56.49 |
| 1982 | 3.07 | 0.25 | 0.13 | 0.08 | 58.89 |
| 1983 | 2.39 | 0.20 | 0.17 | 0.05 | 37.31 |
| 1984 | 3.23 | 0.33 | 0.22 | 0.06 | 46.20 |
| 1985 | 2.83 | 0.19 | 0.14 | 0.06 | 38.41 |
| 1986 | 2.77 | 0.23 | 0.14 | 0.06 | 33.35 |
| 1987 | 1.77 | 0.14 | 0.12 | 0.03 | 23.16 |
| 1988 | 2.07 | 0.17 | 0.10 | 0.05 | 27.50 |
| 1989 | 2.69 | 0.17 | 0.18 | 0.05 | 39.21 |
| 1990 | 2.01 | 0.10 | 0.11 | 0.03 | 30.09 |
| 1991 | 2.12 | 0.08 | 0.07 | 0.02 | 26.55 |
| 1992 | 1.68 | 0.13 | 0.05 | 0.04 | 24.44 |
| 1993 | 1.49 | 0.10 | 0.07 | 0.02 | 21.69 |
| 1994 | 1.55 | 0.08 | 0.08 | 0.03 | 22.89 |
| 1995 | 1.42 | 0.08 | 0.07 | 0.03 | 23.57 |
| 1996 | 1.25 | 0.06 | 0.09 | 0.03 | 15.51 |
| 1997 | 0.74 | 0.05 | 0.02 | 0.01 | 13.58 |
| 1998 | 0.83 | 0.03 | 0.03 | 0.01 | 15.59 |
| 1999 | 0.76 | 0.05 | 0.02 | 0.01 | 12.81 |
Source: Environment Canada, Canadian Wildlife Service, Canada Centre for Inland Waters, Organochlorine Contaminant Concentrations in Herring Gull Eggs from Great Lakes Colonies, unpublished, Burlington, ON, 2000.
Notes: DDE = Derivative of Dichloro-diphenyl-trichloro ethane (DDT). HCB = Hexachloro-benzene. PCBs = Polychlorinated biphenyls. na = not available. Eggs were not sampled in eastern Lake Erie in 1994. Therefore, for that year, lakewide averages were calculated by averaging contaminant levels measured in 1993 and 1995 in the eastern basin with those measured in 1994 in the western basin.
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