Risk assessment of pesticide in rivers for single substances and for mixtures.

N. Chèvre, H. Singer, S. Müller, EAWAG, Überlandstrasse 133, 8600 Dübendorf.

In the last few years, several studies have shown that pesticides, after agricultural applications, are transported mainly during rain events into surface waters (run-off and drainage). Our own detailed measurements in different catchment areas as well as different grab samples revealed that i) pesticide concentrations can reach very high levels during rain events (up to several mg/l), that ii) these concentrations vary strongly with time in rivers and that iii) many pesticides (up to ca 10 different chemicals) are present at the same time. Therefore, we will discuss two topics: Firstly, measured dynamic concentrations of single pesticides in rivers – i.e. varying in time – will be compared with the “environmental quality standard (EQS)” adopted in the EU Water Framework directive from 2000 in order to evaluate the risk of these substances for the aquatic life. Generally, the EQSs used in this study have been determined with the method of safety factors. Secondly, the risk of the mixtures of pesticides, especially in spring when many herbicides are applied, will be also considered and discussed.