Contaminant residues in the bloater (Coregonus hoyi) of Lake Michigan, 1969-1986

Residues of DDT, PCBs, and dieldrin in Lake Michigan bloaters (Coregonus hoyi) decreased between 1969 and 1986. All values for contaminant residues were measured and reported as μg/g of whole fish, wet weight; the error limits represented the 95% confidence interval half widths. Total DDT content declined 87%, from 9.9 in 1970, when its use was banned, to 1.3 in 1974, and then averaged 0.88 in 1978–1986 with a low of 0.67 in 1986. Between 1976–1986, p,p’DDD averaged 0.08 and p,p’DDT averaged 0.1; p,p’DDE reached a low of 0.48 in 1980, then averaged 0.53 in 1980–1986. Dieldrin averaged 0.25 until 1974, when it was banned, peaked at 0.55 in 1978, and decreased to 0.20 by 1986. PCBs, first analyzed in 1972, declined 64% (from 5.7 to 2.2) between 1972 and 1980 and were at 1.64 in 1986. The great decline in PCBs occurred following the 1976 ban. A 49% decrease in the lipid content of bloaters from 1980 to 1986 suggested a dietary change possibly due to changing food source makeup.