RESIDUAL PESTICIDE CONCENTRATIONS IN BEAR-CREEK, MISSISSIPPI, 1976 TO 1979

Concentrations of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane], DDE [1,1-dichloro-2,2,-bis(p-chlorophenyl)-ethylene], DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)-ethane], and toxaphene (chlorinated camphene) were measured in surface waters, soils, storm runoff, and deposited bottom sediments along the 83-km length of Bear Creek. This creek is a Mississippi River alluvial stream, which includes six riverine lakes in an intensively cultivated 44 260-ha watershed. Low concentrations of pesticides were persistent in surface waters of the creek from the headwaters to the confluence with the Yazoo River with no significant differences in concentrations between sites on the creek or in isolated offstream lakes. Pesticide concentrations increased during periods of maximum runoff, which corresponded with the winter rainy season and minimum vegetative cover on the soil. Seven years after spraying had ceased, DDT was still available to surface waters and aquatic biota by way of eroded soil from farm fields and from deposited sediments in stream and lake bottom. No significant declines in concentrations of DDT in surface waters were found in comparisons with two earlier studies nor were any declines in surface water contamination noted during this 3-yr study.