Evidence for the enhanced biodegradation of ethoprophos and carbofuran in soils from Greece and the UK

Degradation of carbofuran in a topsoil sample from a previously untreated f ield site in the UK was characterized by a short lag period followed by rap id degradation. Carbofuran added subsequently to the same soil degraded rap idly without the lag period. In a subsoil sample from the same site, the fi rst application of carbofuran degraded only slowly but degradation rate inc reased with subsequent treatments and the third dose degraded as rapidly as in the pre-treated topsoil. In similar experiments with ethoprophos, degra dation was quite slow and enhanced degradation of subsequent additions of e thoprophos was not observed. A single application of carbofuran in the fiel d in the UK activated soils for rapid biodegradation of the insecticide for at least the subsequent four years. In contrast, in soils from Greece, enh anced degradation was evident six and 18 months after the last carbofuran t reatment in the field, but not after three years. Fifty per cent of ethopro phos applied to soils from Greece previously treated with the nematicide wa s lost within approximately four days, compared with 38 days in a similar, but previously untreated, soil. Very rapid degradation of ethoprophos and c arbofuran was observed in soil samples from Greece which had been treated a nnually with ethoprophos for the last 30 years but with no previous applica tions of carbofuran. Annual use of the thiocarbamate herbicide EPTC in the same field may have resulted in cross-activation for rapid biodegradation o f carbofuran. Very slow degradation of both carbofuran and ethoprophos was observed in soil samples with a history of combined applications of the two pesticides, probably because of their low pH. Fumigation of soil with chlo roform, or treatment with the antibacterial antibiotic chloramphenicol, inh ibited ethoprophos degradation in a soil where rapid rates of loss had prev iously been induced, but the antifungal antibiotic cycloheximide had no eff ect on degradation rate. (C) 1999 Society of Chemical Industry.