National Pesticide Monitoring Program: Residues of organochlorine chemicals in freshwater fish, 1980-81
The U.S. Fish and Wildlife Service analyzed residues of organochlorine chemicals in 315 composite samples of whole fish collected in 1980-81 from 107 stations nationwide as part of the National Pesticide Monitoring Program. The mean concentrations of total DDT and all p,p' homologs except p,p'-DDT showed significant but small declines relative to mean concentrations before 1978-79. The mean concentration of p,p'-DDT did not change. The most persistent DDT homolog continued to constitute about 70% of total DDT residues, as it did in 1974-79. DDT contamination attributable to former DDT manufacturing facilities remained evident at sites in Alabama and Arkansas, and high concentrations at one site in Hawaii suggested that input to the environment was continuing. Conversely, the data do not support the contention of others that DDT was still being used in the Southwest, Residues of polychlorinated biphenyls (PCBs) remained widespread, but a significant downward trend in total PCBs was evident, especially in areas that the NPMP has previously shown to be the most heavily contaminated. Mean concentration of dieldrin had not changed since 1978-79, and levels remained highest in Hawaii and in the Great Lakes. Toxaphene concentrations plateaued after a period of steady increase through the 1970's, but the incidence of toxaphene continued to increase; residues were present at 88% of the stations sampled in 1980-81, including one in Alaska. Mean chlordane concentrations were slightly lower than in 1978-79, and residues were detected at fewer stations in 1980-81 than in 1978-79. Residues of other organochlorines were either found at relatively few of the stations sampled in 1980-81 or were characterized by relatively low concentrations.