Comparative fate of chlorpyrifos insecticide in urban and agricultural environments

The fate and degradation of pesticides in both agricultural and urban environments are of interest. Chlorpyrifos insecticide is employed for both agricultural and urban pest control scenarios, and was used as a model compound to compare the environmental fate processes operating in the two environments. Agricultural use patterns examined included application to corn (soil-incorporated and foliar/soil spray) and citrus (foliar/soil spray). Urban use patterns selected for study included application to turfgrass via foliar/soil spray and soil trench treatment for termite control. Chlorpyrifos dissipated rapidly from the surface of cornfield soil, citrus grove soil, turfgrass, and fallow urban soil with observed half-lives of between 1 and 17 days. Chlorpyrifos applied as a pre-plant, soil-incorporated application displayed slightly greater persistence, with observed dissipation half-lives of 33-56 days. Application of chlorpyrifos as a termiticidal soil barrier resulted in initial residues of several hundred ppm in the soil and increased persistence versus other use patterns; nearly 70% of the initially applied chlorpyrifos remained in soil after 18 months. Subsequent laboratory investigations revealed chlorpyrifos degradation half-lives of between 116 and 1576 days in 5 soils treated at termiticidal application rates (1000 ppm). Results demonstrated that an increase in application rate from typical agricultural use (10 ppm) to that for urban termiticide application (1000 ppm) resulted in a dramatically decreased rate of dissipation. It appears that chlorpyrifos soil application for termite control achieves long residual control due to both the high application rate and retardation in degradation at the resultant elevated concentrations. Results of these studies illustrate the importance of examining pesticide environmental fate under the different conditions characteristic of both agricultural and urban environments.