Loss of chlorpyrifos in pond water: examination of results using three simple mathematical models

Four outdoor artificial pools were fortified with two formulations of chlorpyrifos (the active ingredient in Dursban insecticide), as emulsifiable concentrate, and a slow-release granular formulation. From concentration-time data collected during summer months, the half life of chlorpyrifos was found to be 5 +/- 3 h and 14 +/- 4 h for the emulsifiable concentrate and slow release formulations respectively. The concentration-time data was analyzed by three mathematical models; the power rate model, the hyperbolic rate model, and an empirical power function. Their average correlation coefficients, determined by linear regression, were respectively, 0.78 +/- 0.08, 84 +/- 0.07, 0.76 +/- 0.16.