BIODEGRADATION OF THE ORGANOPHOSPHATE INSECTICIDE COUMAPHOS IN HIGHLYCONTAMINATED SOILS AND IN LIQUID WASTES

Approximately 400000 litres of cattle dip wastes containing approximat ely 1500 mg litre(-1) of the organophosphate insecticide coumaphos are generated yearly along the Mexican border from a USDA program designe d to control disease-carrying cattle ticks. Use of unlined evaporation pits for the disposal of these wastes has resulted in highly contamin ated soils underlying these sites. Previous work has shown that microb ial consortia present in selected dip wastes can be induced to mineral ize coumaphos. Our results demonstrate that similar microbial consorti a are present in coumaphos-contaminated soils from eight waste sites a nd that these organisms are capable of mineralizing coumaphos in these soils using soil slurries to less than 1 mg litre(-1) in 7-10 days at 28 degrees C. In addition, our results show that these consortia are able to colonize pea gravel in trickling gravel filters and can be use d in these filters to metabolize coumaphos from dip wastes to less tha n 0 . 1 mg litre(-1) in 7-10 days at 28 degrees C. These simple system s offer potential low cost means to detoxify coumaphos-containing wast es and to bioremediate soils contaminated with this organophosphate co mpound.