Effects of Soil Mixing and Flooding on the Fate and Metabolism of 14C-Fonofos and 14C Parathion in Open and Closed Agricultural Microcosms

Abstract

The effects of soil surface application and soil incorporation (“tillage”) of 14C-fonofos and 14C-parathion on the metabolic fate of the insecticides in soils and their translocation into oat leaves were investigated in the laboratory, using both open and closed microcosms. The effects of flooding of 14C insecticide-treated soils were also studied. The insecticides were least persistent after their application to the soil surface, whereas mixing the insecticides with the soil increased the persistence of fonofos and parathion by factors of 2 and 5.3. respectively. Most of the organic solvent-soluble radiocarbon in 14C insecticide-treated soils was recovered as the undegraded parent compound, more so with fonofos than with parathion. In oat leaves from fonofos-treated soils, most of the organic soluble 14C recovered (1% of less of the soil-applied radiocarbon) was associated with the non-insecticidal fonofos metabolite methyl phenyl sulfone; in leaves from parathion-treated soil, > 90% of the organic soluble 14C (0.1 % of the soil-applied dose) was associated with parathion. In experiments with closed systems, the amounts of 14CO2 produced from soil-applied 14C-parathion were 30% of the insecticide applied to the soil surface, 23% of that mixed with the soil, and only 0.9% of that mixed with the soil and kept under flooded conditions. With fonofos-treated soils, less 14CO2 was produced, but the general trend was the same as that observed with parathion. Binding of 14C compounds to soils increased after the insecticides had been mixed with the soil and, in particular, after soil flooding when 72% of the soil-applied 14C-parathion was unextractable.