Twenty-seven species of estuarine and marine fish and invertebrates were analyzed for chlorinated hydrocarbon residues from July to November 1970. In nonagricultural areas, mullet (Mugil) was the only organism to have DDT concentrations greater than 1.0 ppm and measurable levels
of toxaphene. DDT levels of most organisms were higher in areas bordered by cotton fields, and 53 per cent of the samples from these areas had measurable levels of toxaphene. Shrimp from all areas of the coastline had low levels of DDT. A fish kill was observed in a coastal lagoon bordered
by cotton fields. In this lagoon, moribund specimens of Dormitator latifrons had DDT residue levels 7 times those found in other areas. Mullet from this lagoon had average DDT levels as high as 36.6 ppm, and DDT concentrations in Poecilia sphenops in one month exceeded 45 ppm. The
cotton-growing season and pesticide application coincided with the utilization of the estuaries by postlarval and juvenile shrimp. Juvenile shrimp were absent from a coastal lagoon receiving agricultural runoff. Poecilia sphenops and Mugil, which comprise a substantial part
of the diet of the coastal and highland peoples, consistently had high residue concentrations of DDT and toxaphene.
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