Laboratory micro-ecosystems as physical models for predicting the fate of pesticides in aquatic systems

Abstract

Simple compartmental models can be used to predict the fate of pesticides in aquatic systems. However, often the process parameters needed in these models are lacking. The objective of this study was to see whether experiments in laboratory micro-ecosystems can provide these parameters. The fate of the insecticide chlorpyrifos was investigated in derived micro-ecosystems composed of water and sediment. Chlorpyrifos was measured in sediment and water, at exponential time intervals during an incubation period of 64 days. A two-compartmental model was used to describe the mass of chlorpyrifos in both water and sediment. The rate constants for transformation and transport were estimated. These rate constants were used to simulate the dynamics of chlorpyrifos in water and sediment of an experimental pond. The simulation results were compared with measured concentrations. The parameters obtained from the micro-ecosystems could not be used to predict the fate of chlorpyrifos under field conditions with this model. Only with adjustments for the rate constant for transformation in water, the fate of chlorpyrifos could be simulated adequately during the first 5 days after application.