| Year | DDE | Dieldrin | Mirex | HCB | PCBs |
| parts per million in whole egg samples, wet weight | |||||
| 1974 | 16.59 | 0.51 | 1.04 | 0.26 | 62.08 |
| 1975 | 23.10 | 0.38 | 0.96 | 0.18 | 76.24 |
| 1976 | na | na | na | na | na |
| 1977 | 11.92 | 0.38 | 0.33 | 0.24 | 55.22 |
| 1978 | 9.64 | 0.39 | 0.28 | 0.12 | 41.57 |
| 1979 | 6.83 | 0.60 | 0.26 | 0.14 | 58.74 |
| 1980 | 3.67 | 0.34 | 0.13 | 0.08 | 25.58 |
| 1981 | 5.74 | 0.44 | 0.14 | 0.12 | 33.84 |
| 1982 | 6.29 | 0.39 | 0.37 | 0.08 | 34.74 |
| 1983 | 3.17 | 0.33 | 0.15 | 0.05 | 21.42 |
| 1984 | 2.94 | 0.36 | 0.12 | 0.05 | 16.91 |
| 1985 | 3.13 | 0.32 | 0.11 | 0.05 | 15.89 |
| 1986 | 3.22 | 0.34 | 0.11 | 0.05 | 14.10 |
| 1987 | 2.52 | 0.20 | 0.10 | 0.04 | 12.35 |
| 1988 | 2.94 | 0.34 | 0.06 | 0.05 | 13.43 |
| 1989 | 2.50 | 0.34 | 0.07 | 0.05 | 15.09 |
| 1990 | 2.64 | 0.30 | 0.06 | 0.03 | 11.62 |
| 1991 | 3.60 | 0.27 | 0.07 | 0.04 | 14.09 |
| 1992 | 3.68 | 0.40 | 0.07 | 0.05 | 13.96 |
| 1993 | 4.08 | 0.19 | 0.07 | 0.03 | 15.68 |
| 1994 | 2.39 | 0.15 | 0.10 | 0.03 | 12.31 |
| 1995 | 2.48 | 0.11 | 0.08 | 0.02 | 11.17 |
| 1996 | 2.79 | 0.13 | 0.06 | 0.03 | 11.02 |
| 1997 | 1.83 | 0.07 | 0.02 | 0.01 | 8.30 |
| 1998 | 2.66 | 0.07 | 0.04 | 0.01 | 12.96 |
| 1999 | 2.06 | 0.10 | 0.03 | 0.02 | 9.66 |
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Centre for Inland Waters, Organochlorine Contaminant Concentrations in Herring Gull Eggs from Great Lakes Colonies, unpublished, Burlington, ON, 2000.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.
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