Determination of the fate of pesticides in outdoor lysimeter experiments

For the assessment of a pesticides potential to contaminate soil and groundwater a stepwise testing scheme has been developed including laboratory testing, outdoor simulation experiments (e.g., fate studies with undisturbed lysimeters), model calculations and field testing. In 1990 the german authorities passed a test guideline for the performance of lysimeter studies. In this context some recent experiences are presented focussing on the following topics: comparative assessment of the fate based on laboratory test results, model calculations as well as results from lysimeter experiments. For comparison both indoor and outdoor lysimeter experiments are performed; influence of climate and water regime on the leaching behaviour of pesticides; and influence of soil properties on the leaching behaviour. On the basis of finalized studies with the pesticides atrazine, bentazon, chlorotoluron and two experimental herbicides, the integrative character of the experiments, the complexity of resu lts and the possibilities and limitations of their interpretations are discussed.