Degradation of Chlorpyrifos in Soil: Influence of Autoclaving, Soil Moisture, and Temperature1

Abstract

The decomposition of ¹⁴C-ring-labeled chlorpyrifos was followed in 2 soils for a 32-week period under laboratory conditions at 25°C. Time required for 50% loss of parent compound in Chehalis clay loam and Sultan silt loam was 4 and 12 weeks, respectively. Faster breakdown of the insecticide in the clay loam was due to microbial degradation since initial halflives of 24 weeks were observed in both autoclaved soils. Radioactivity from degraded chlorpyrifos was recovered as 3,5,6-trichloro-2-pyridinol, as expired CO₂, and as a nonextractable soil-bound residue component. After 32 weeks, 47% of the radioactivity from degraded insecticide were recovered as CO₂ in the clay loam as compared to only 8% in the silt loam. Temperature had a pronounced effect on the decay rate of chlorpyrifos in Sultan silt loam during a 24-week incubation period at 15°, 25°, and 35°C; initial half-lives were 25, 13, and 6 weeks, respectively. Soil moisture contents ranging from 3–20% did not affect insecticide degradation rates in the Sultan silt loam.