Chronology of organochlorine compounds in Lake Michigan fish, 1929-66.

Museum specimens of six species of Lake Michigan fish collected from 1929 through 1966 were analyzed for dieldrin, polychlorinated biphenyls (PCB's), and DDT analogs. Dieldrin first appeared in the 1955 specimens. Residues were low and exhibited no trend with time. PCB's and DDT analogs appeared in 1949 in the same samples. Both PCBP'S and sigmaDDT increased progressively through 1965. PCB residues showed no decreasing trend. SigmaDDT peaked in 1965. PCB's and DDE were always detected together. The ratio of PCB to DDT showed no trend from 1949 to 1966.