R8 PM Pesticide Mixtures
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 331-332

(AAA-1117-093838) Including mixtures in the determination of acute and chronic water-quality criteria for pesticides.

Chèvre, N¹, Loepfe, C¹, Fenner, K¹, Singer, H¹, Stamm, C¹, Escher, B, ¹ EAWAG, Duebendorf, Switzerland

ABSTRACT- Monitoring programs throughout America and Europe have demonstrated the widespread presence of pesticides in surface water and public concern is focused on the possible environmental impact of such pollution. The comparison of acute and chronic Water Quality Criteria (AQC, CQC) with environmental concentrations gives an indication of the pressure that each pesticide puts on the aquatic system and allows identification of those that present a risk for aquatic life. However, in the environment, aquatic organisms are not only exposed to single pesticides but typically to mixtures of these substances. It is therefore of particular importance to take mixtures into account when defining AQC/CQC. We recently developed a method to define consistent and comparable AQC/CQC for pesticides having similar mode of action. The AQC/CQC of the single compounds can be combined to define acute and chronic risk quotientsfor mixture of pesticides with similar mode of action. Following the concentration addition model, which typically applies for compounds with similar mode of action, the risk quotient of the mixture can be expressed as the sum of the ratios between the measured environmental concentration and the AQC/CQC for each pesticide. This risk should stay below 1 to ensure low risk for the aquatic life. The proposed approach has the advantage of being easy to calculate and communicate, and will be proposed to replace the present limit value of 0.1 g/l for pesticides in Switzerland. The AQC/CQC have been defined for more than 20 pesticides (herbicides, insecticides and fungicides) grouped to various mode of action classes and will be presented here.

Key words: pesticide, mixture, Water Quality Criteria