Comparison of the disappearance of eight organophosphorus insecticides from soil in laboratory and in outdoor experiments

The persistence of eight granular organophosphorus insecticides in one loam‐type soil was studied in both laboratory experiments under controlled conditions and in outdoor experiments, by comparison of disappearance curves in semi‐logarithmic co‐ordinate systems. The pesticides studied were: Aphidan ( O,O ‐di‐isopropyl‐ S ‐ethyl‐sulphinyl methyl dithiophosphate), bromophos, chlorfenvinphos, dichlo‐ fenthion, dimethoate, mecarbam and trichloronate. The comparisons confirm that a strict control of several parameters (e.g. water content of the soil and temperature) is needed for the quantitative description of disappearance rates. However, a reasonably good agreement in the relative order of persistence was found in the experiments and a tentative classification of the eight insecticides according to degree of persistence in the soil is suggested. Metabolites were found to be present in the soil from two of the compounds, but the contributions to total residues and, accordingly, the influence on persistence evaluation from these were not included owing to lack of definite identifications and finalised determinations.