MANAGEMENT OF MICROBIAL PROCESSES IN CATTLE-DIPPING VATS CONTAINING COUMAPHOS

The organophosphate veterinary insecticide coumaphos [O-3-chloro-4-met hyl-2-oxo-2H-chromen-7-yl O,O-diethyl phosphorothioate] is used by the Animal and Plant Health Inspection Service of the United States Depar tment of Agriculture in its program designed to prevent re-entry of th e southern cattle tick (Boophilus microplus Can.) and the cattle tick (B, annulatus Say) into the United States from Mexico. Large amounts o f waste acaricide are generated annually in this program. One event th at triggers disposal of coumaphos dips is the accumulation of potasan [O,O-diethyl O-4-methyl-2-oxo-2H-chromen-7-yl phosphorothioate]. This process was shown to occur under anaerobic conditions and to be inhibi ted by mercury ions, indicating that anaerobic micro-organisms were re sponsible for a reductive dechlorination. Maintaining coumaphos suspen sions at pH < 7 prevented the reductive dechlorination of coumaphos an d left a suspension that was amenable to disposal by biodegradation. A field trial on an 11000-litre capacity coumaphos dipping vat demonstr ated the applicability of using acid to extend the life of coumaphos s olutions and of biodegradation for the disposal of spent material.