Persistence and Degradation of Carbofuran in Soil

Abstract

The persistence and degradation of 14C-carbofuran and 14C-2,3-dihydro-2,2-dimethyl-7-hydroxy benzofuran were examined in several soils under laboratory conditions. The time required for 50% breakdown of the insecticide varied from 3 weeks to more than 50 weeks. Persistence was influenced by soil sterilization and soil p H. Carbofuran degraded 7–10 times faster in alkaline soil ( p H 7.9) than in acid and neutral soils ( p H 4.3–6.8). 14CO2 was rapidly expired from degraded carbonyl-labeled insecticide in both radiation-sterilized and nonirradiated soils. Degradation of ring-labeled carbofuran was associated with an accumulation of nonextractable radioactivity in the soil residue followed by a gradual evolution of 14CO2. Only minute quantities of carbofuran phenol, the expected hydrolysis product of the insecticide, were recovered from treated soils. Addition of 14C-carbofuran phenol to soil resulted in an accumulation of tightly adsorbed nonextractable radioactivity followed by slow expiration of 14CO2. Indirect evidence suggests carbofuran is hydrolyzed to its phenol which is immediately bound to soil constituents and slowly metabolized by microorganisms.