Accelerated degradation of methyl parathion, parathion and fenitrothion by suspensions from methyl parathion-and p-nitrophenol-treated soils

Abstract

Soils (an alluvial and a laterite) contained in pots were treated with methyl parathion, fenitrothion or p-nitrophenol at 15 day intervals under flooded or non-flooded (60% WHC) conditions. Suspensions (non-sterile and sterile) of these treated and untreated soils were tested for their ability to degrade methyl parathion, parathion, fenitrothion and diazinon in a mineral salts medium. Only non-sterile suspensions of methyl parathion- and p-nitrophenol-enriched soils (flooded or non-flooded) distinctly effected accelerated hydrolysis of methyl parathion, parathion and fenitrothion; in contrast, diazinon was not hydrolysed by the suspension of methyl parathion-enriched soils. p-Nitrophenol, formed from methyl parathion or parathion, was eventually metabolized to nitrite by the enrichment cultures while 3-methyl-4-nitrophenol, formed from fenitrothion, resisted further degradation. As in soil enrichment cultures, two bacterial isolates, one each from methyl parathion-enriched alluvial and laterite soils (flooded), effected rapid hydrolysis of methyl parathion, parathion and fenitrothion and then metabolized p-nitrophenol and not 3-methyl-4-nitrophenol, to nitrite. Fenitrothion-retreated soils (flooded or non-flooded) were not conditioned for accelerated hydrolysis of fenitrothion and related phosphorothioate insecticides.