| Year | DDE | Dieldrin | Mirex | HCB | PCBs |
| parts per million in whole egg samples, wet weight | |||||
| 1974 | 22.30 | 0.47 | 6.99 | 0.58 | 152.37 |
| 1975 | 22.80 | 0.29 | 4.70 | 0.33 | 143.11 |
| 1976 | na | na | na | na | na |
| 1977 | 14.88 | 0.39 | 2.48 | 0.80 | 102.50 |
| 1978 | 10.65 | 0.26 | 1.59 | 0.32 | 72.43 |
| 1979 | 8.94 | 0.21 | 1.89 | 0.21 | 69.60 |
| 1980 | 7.62 | 0.19 | 1.65 | 0.17 | 56.43 |
| 1981 | 11.00 | 0.28 | 2.67 | 0.24 | 78.90 |
| 1982 | 10.04 | 0.28 | 3.05 | 0.16 | 62.89 |
| 1983 | 4.78 | 0.18 | 1.43 | 0.08 | 42.59 |
| 1984 | 6.26 | 0.21 | 1.87 | 0.12 | 51.11 |
| 1985 | 6.02 | 0.15 | 1.47 | 0.07 | 35.58 |
| 1986 | 4.41 | 0.16 | 1.10 | 0.07 | 27.86 |
| 1987 | 2.60 | 0.13 | 0.68 | 0.04 | 16.48 |
| 1988 | 4.25 | 0.15 | 0.82 | 0.07 | 23.53 |
| 1989 | 5.28 | 0.22 | 1.15 | 0.07 | 32.45 |
| 1990 | 3.36 | 0.10 | 0.64 | 0.03 | 18.44 |
| 1991 | 3.53 | 0.14 | 0.58 | 0.03 | 17.06 |
| 1992 | 5.01 | 0.13 | 0.77 | 0.05 | 21.18 |
| 1993 | 5.27 | 0.13 | 0.82 | 0.04 | 21.06 |
| 1994 | 3.83 | 0.13 | 0.80 | 0.04 | 19.73 |
| 1995 | 2.22 | 0.05 | 0.57 | 0.02 | 13.56 |
| 1996 | 3.03 | 0.1 | 0.68 | 0.04 | 16.12 |
| 1997 | 2.39 | 0.05 | 0.46 | 0.02 | 12.83 |
| 1998 | 2.01 | 0.03 | 0.39 | 0.01 | 13.29 |
| 1999 | 2.20 | 0.05 | 0.45 | 0.02 | 11.91 |
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Centre for Inland Waters, Organochlorine Contaminant Concentrations in Herring Gull Eggs from Great Lakes Colonies, unpublished, Burlington, ON, 2000.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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