Aspects of the enhanced biodegradation and metabolism of ethoprophos in soil

Enhanced biodegradation of ethoprophos was evident in a soil from a previously treated field in Northern Greece. However, enhanced biodegradation was specific to ethoprophos and there was no cross-enhancement leading to rapid degradation for any of the other organophosphorus (cadusafos, fenamiphos, fonofos, isazofos) or carbamate (aldicarb, oxamyl) nematicides registered in Greece for the control of potato cyst nematodes. Studies with radio-labelled ethoprophos showed that the adapted microflora in the soil from the previously treated field was able to degrade [propyl-1-C-14]ethoprophos rapidly and mineralized about 60% of the initially applied nematicide. When [ethyl,1-C-14] ethoprophos was applied, the reduction in extractable radioactivity in the previously treated soil was coupled with evolution of lower amounts of [C-14] carbon dioxide and was similar to the amounts produced from the previously untreated soils. It is suggested that degradation of ethoprophos in the soil from the previously treated field proceeds via hydrolysis of the P-S bond in the -S-propyl moiety of the ethoprophos molecule, which is then further mineralized by the adapted micro-organisms. Enhanced biodegradation of ethoprophos in this specific previously treated soil in Northern Greece and under the local environmental conditions was still evident two years after the last ethoprophos field application. It appears that, once established, enhanced biodegradation of ethoprophos can be quite stable. A possible solution to this problem might be the introduction of a rotation scheme where other nematicides like fenamiphos, cadusafos, aldicarb or oxamyl are used as alternatives with ethoprophos application restricted to only once every three or four years. (C) 2000 Society of Chemical Industry.