Use of selected freshwater bivalves for monitoring organochlorine pesticide residues in major Mississippi stream systems, 1972-73.

Seven species of freshwater Pelecypoda, Amblema costata, Corbicula manilensis, Elliptio crassidens, lampsilis anadontoides, Lampsilis claibornensis, Megalonaias gigantea, and Plectomerus dombeyanus, were collected and monitored for pesticide content during 1972 and 1973. Thirteen collection sites, representing five major river basins in the state of Mississippi, were sampled and compared. During the 24-month study, 26 water samples and 58 claim samples from the five river basins were analyzed. Individual samples weighed from 8 g to 20 g and consisted of 1-30 clams, depending on size. Residues of toxaphene and methyl parathion were found only in 1973 water samples. The study shows that freshwater clams are effective monitors of pesticide content. The tendency of clams to concentrate pesticides and their corresponding ability to eliminate them varies with species. Significant reductions in DDT and a corresponding buildup of p,p'-TDE were noted in 1973, following the limitations on the use of DDT and large-scale flooding throughout the state.