| Year | DDE | Dieldrin | Mirex | HCB | PCBs |
| parts per million in whole egg samples, wet weight | |||||
| 1974 | na | na | na | na | na |
| 1975 | na | na | na | na | na |
| 1976 | 33.40 | 0.82 | 0.36 | 0.14 | 118.42 |
| 1977 | 29.25 | 0.68 | 0.14 | 0.24 | 107.79 |
| 1978 | 22.36 | 0.87 | 0.21 | 0.12 | 90.74 |
| 1979 | na | na | na | na | na |
| 1980 | 12.17 | 0.70 | 0.10 | 0.09 | 57.83 |
| 1981 | na | na | na | na | na |
| 1982 | 15.86 | 0.81 | 0.09 | 0.09 | 65.41 |
| 1983 | 6.46 | 0.61 | 0.05 | 0.05 | 30.27 |
| 1984 | 7.85 | 0.53 | 0.09 | 0.06 | 31.47 |
| 1985 | 6.98 | 0.47 | 0.12 | 0.05 | 31.94 |
| 1986 | 7.48 | 0.38 | 0.07 | 0.07 | 27.25 |
| 1987 | 3.95 | 0.33 | 0.06 | 0.04 | 16.58 |
| 1988 | 5.04 | 0.55 | 0.03 | 0.04 | 19.14 |
| 1989 | 4.74 | 0.54 | 0.04 | 0.04 | 21.00 |
| 1990 | 8.12 | 0.54 | 0.06 | 0.05 | 32.19 |
| 1991 | 10.22 | 0.34 | 0.12 | 0.05 | 31.27 |
| 1992 | 6.70 | 0.41 | 0.05 | 0.04 | 20.25 |
| 1993 | 9.56 | 0.32 | 0.09 | 0.06 | 33.75 |
| 1994 | 9.29 | 0.37 | 0.09 | 0.05 | 30.81 |
| 1995 | 6.38 | 0.19 | 0.05 | 0.03 | 23.28 |
| 1996 | 5.02 | 0.18 | 0.06 | 0.04 | 19.78 |
| 1997 | 7.40 | 0.18 | 0.03 | 0.02 | 33.32 |
| 1998 | 5.15 | 0.09 | 0.03 | 0.01 | 24.61 |
| 1999 | 5.04 | 0.14 | 0.02 | 0.02 | 23.42 |
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Centre for Inland Waters, Organochlorine Contaminant Concentrations in Herring Gull Eggs from Great Lakes Colonies, unpublished, Burlington, ON, 2000.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. Data for Lake Michigan for 1996 are based on only one count per sampling site.
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