| Year | DDE | Dieldrin | Mirex | HCB | PCBs |
| parts per million in whole egg samples, wet weight | |||||
| 1974 | 17.40 | 0.50 | 1.34 | 0.38 | 71.01 |
| 1975 | 14.03 | 0.36 | 0.51 | 0.21 | 42.67 |
| 1976 | na | na | na | na | na |
| 1977 | 16.17 | 0.54 | 0.44 | 0.36 | 70.28 |
| 1978 | 6.53 | 0.22 | 0.21 | 0.11 | 32.38 |
| 1979 | 2.30 | 0.30 | 0.19 | 0.10 | 28.66 |
| 1980 | 2.71 | 0.24 | 0.11 | 0.07 | 20.41 |
| 1981 | 3.82 | 0.24 | 0.26 | 0.07 | 25.39 |
| 1982 | 4.43 | 0.28 | 0.48 | 0.08 | 34.29 |
| 1983 | 2.74 | 0.22 | 0.15 | 0.05 | 18.28 |
| 1984 | 2.56 | 0.22 | 0.34 | 0.07 | 19.95 |
| 1985 | 2.77 | 0.30 | 0.22 | 0.06 | 16.90 |
| 1986 | 2.05 | 0.21 | 0.12 | 0.05 | 12.00 |
| 1987 | 1.32 | 0.22 | 0.08 | 0.02 | 8.33 |
| 1988 | 1.40 | 0.22 | 0.07 | 0.04 | 8.83 |
| 1989 | 1.57 | 0.20 | 0.09 | 0.03 | 10.19 |
| 1990 | 1.86 | 0.14 | 0.11 | 0.03 | 11.34 |
| 1991 | 1.97 | 0.16 | 0.11 | 0.03 | 10.01 |
| 1992 | 2.36 | 0.16 | 0.05 | 0.05 | 10.20 |
| 1993 | 3.17 | 0.19 | 0.06 | 0.03 | 10.99 |
| 1994 | 2.18 | 0.13 | 0.10 | 0.03 | 11.20 |
| 1995 | 1.60 | 0.10 | 0.06 | 0.03 | 8.96 |
| 1996 | 2.00 | 0.13 | 0.14 | 0.08 | 10.05 |
| 1997 | 1.26 | 0.06 | 0.03 | 0.02 | 5.53 |
| 1998 | 0.98 | 0.02 | 0.02 | 0.01 | 4.58 |
| 1999 | 1.30 | 0.07 | 0.05 | 0.02 | 5.84 |
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Centre for Inland Waters, Organochlorine Contaminant Concentrations in Herring Gull Eggs from Great Lakes Colonies, unpublished, Burlington, ON, 2000.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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