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 I?/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 avveraged 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.
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Contaminant residues in the bloater (Coregonus hoyi) of Lake Michigan, 1969-1986