PARENT SESSION

2A - Mixture Toxicity
Hall 6
8:30 AM - 12:30 PM, Monday, 28 April 2003
Chair: Hermens, J.¹, ¹
Co-chair: Toy, R.², Backhaus, T.³, ^{2 3}

(MO6/4) Predictive hazard assessment of chemical mixtures in an agricultural exposure scenario.

Junghans, Marion¹, Backhaus, Thomas^{1, 2}, Faust, Michael², Scholze, Martin¹, Vighi, Marco³, ¹ University of Bremen, Bremen, Germany² Faust und Backhaus Environmental Consulting, Bremen, Germany³ University of Milano Bicocca, Milano, Italy

ABSTRACT- In freshwater systems, organisms are exposed to a multitude of toxicologically and structurally different substances. For regulatory purposes it is of major importance, whether the combined hazard of these substances can be assessed predictively on the basis of the single substance toxicity. For reference mixtures it has been shown so far, that the mixture toxicity is predictable by using the concept of Concentration Addition for mixtures of similarly acting and the concept of Independent Action for mixtures of dissimilarly acting substances. This study aims to analyse whether these concepts are also applicable to environmentally realistic mixtures. For this purpose an exposure scenario was modelled, which shall reflect the exposure situation in spring in a typical central-European agricultural area. 25 pesticides were finally included in the scenario and their predicted environmental concentrations were modelled. The corresponding mixture was studied for its effects on the reproduction of the freshwater green alga Scenedesmus vacuolatus. For 23 of the 25 substances complete concentration-response curves were determined. Two substances showed no significant effects within the tested concentration ranges. At a mixture concentration that equals the sum of all individual PECs a severe mixture toxicity was observed: the reproduction was inhibited by approximately 40%. The toxicities of the tested mixtures showed a good predictability by the concept of Concentration Addition. More than 90% of the observed mixture toxicity were explainable by the concentration-additive toxicity of only 6 out of 25 mixture components.

Key words: realistic mixtures, predictability, predicted environmental concentrations, concentration addition