THE FATE OF ENDOSULFAN IN AQUATIC ECOSYSTEMS

Endosulfan, one of the major pesticides used in cotton-growing, is of environmental concern because of its toxicity to fish and its apparent persistence in the environment. This study examines the distribution and degradation pathways for endosulfan in an aquatic system and the p rocesses by which it is removed. In the alkaline waters of the cotton region, hydrolysis is the dominant degradation process. By this mechan ism alone, the expected half-lives for the alpha- and beta-endosulfan isomers were found to be 3.6 days and 1.7 days, respectively. Partitio ning studies showed, however, that the major proportion of endosulfan would associate with the sediments (log Koc(alpha) 3.6 and log Koc(bet a) 4.3). Field studies confirmed the presence of high concentrations i n sediments. Microcosm experiments showed that loss of endosulfan was slower than predicted from hydrolysis rates. Models are presented to e xplain how desorption from sediment limits the loss of endosulfan from a system.