Environmental degradation of chlorpyrifos in soil

Dursban TC has become the most widely used insecticide for the control of termites since the banning of chlordane. Several laboratory studies have been conducted to investigate the degradation kinetics of chlorpyrifos applied to soil at termiticide rates. These have included a limited number of soil types and have utilized tightly regulated environmental conditions. A field study was established to investigate the degradation of chlorpyrifos in soil treated with a 1% solution via trench application and under natural environmental conditions. Once treated, soil samples were removed from the trench at scheduled intervals and extracted to determine the concentration chlorpyrifos remaining. In three of the soils studied, the concentration of chlorpyrifos decreased dramatically within the first three months. The remaining soils showed a steady decline in concentration over 12 months. After this initial phase of degradation, the slope of the degradation curve changed sharply. This may indicate that chlorpyrifos undergoes two phases of degradation in soil. Using both phases of the degradation curves may give a better estimate of the concentration of chlorpyrifos that may be present in a soil at any time period.