Persistence of Chlorpyrifos in Soils under Different Moisture Regimes

Chlorpyrifos is an organophosphorus insecticide used to control insect pests in soil. The fate of chlorpyrifos in soils under different moisture regimes is of interest because application directions specify soil‐surface treatments for a number of agricultural and urban pests. Chlorpyrifos was degraded rapidly in all air‐dry soils and slightly more slowly in soils at field capacity and/or under submerged conditions. Degradation rates were influenced by clay‐catalysed hydrolysis under air‐dry conditions and neutral or alkaline hydrolysis under submerged conditions. Degradation was faster in Bellary soil (chromic haplustert) and slower in Chettalli soil (ustic palehumult) under all three moisture regimes. The calculated half‐lives ranged from 1·6 to 10·0, 5·2 to 22·0 and 8·7 to 25·1 days under air‐dry, field capacity and submergence respectively at an application rate of 10 mg kg‐1. © 1997 SCI.