An appraisal of methods for measurement of pesticide transformation in the groundwater zone.

Laboratory and field studies show that pesticides may be transformed in the groundwater zone. Possible reaction mechanisms are chemical hydrolysis, catalytic reduction and aerobic or anaerobic microbial transformation. Transformation in the groundwater zone can be an important element in the advanced evaluation of the potential risk arising from a pesticide in the public drinking water supply. However, rate and pathway of transformation can show large differences, depending on the bio-geochemical conditions in the groundwater zone. Knowledge of the reaction mechanisms and the effect of aquifer conditions would allow vulnerable and low-vulnerable application areas for a pesticide to be delimited. An outline is given of possible approaches to quantifying these transformation processes and using the results in registration procedures, especially in the EU and its member states. Furthermore, areas where there is need for continued research and better understanding are highlighted.