PARENT SESSION

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

(MOP/65) Mixture toxicity of three antifouling agents on photosynthesis of microalgal communities and on algal reproduction (Scenedesmus).

Arrhenius, Åsa¹, Backhaus, Thomas², Blanck, Hans¹, Grönvall, Frederick¹, Junghans, Marion², Scholze, Martin², ¹ Botanical Institute, Göteborg University, Göteborg, Göteborg, Sweden² Dept. of Biology and Chemistry, University of Bremen, Bremen, Bremen, Germany

ABSTRACT- Mixture toxicity is generally examined according to the concepts of Concentration Addition or Independent Action, which are based on pharmacological principles suggesting that similarly acting compounds should apply to the former concept and dissimilarly acting compounds to the latter. The three antifouling agents TBT, Irgarol and Sea-Nine were tested for their individual and mixture toxicity on the photosynthesis of marine periphyton communities. TBT affects ATP formation, Irgarol inhibits photosynthetic electron transport and Sea-Nine is claimed to be an inhibitor of Krebs cycle enzymes. At the physiological level, effects on photosynthesis can be observed, but it is not known whether other effect indicators would show a different sensitivity. Hence, toxicities were also analysed in a reproduction inhibition test with the green algal Scenedesmus vacuolatus which is able to integrate over all significant physiological effects. All tested antifoulants were highly toxic in both assays, with EC50-values ranging from 4 (Irgarol) to 550 nM (Sea-Nine). No systematic differences between both assays could be observed, indicating, that photosynthesis is a primarily affected process of the tested chemicals. Nevertheless, the shapes of the concentration-response curves were quite different in both assays. The resulting mixtures gave EC50s of 200 to 500 nM, depending on bioassay and mixture ratio. Independent Action as well as Concentration Addition lead to small but clear overestimations of the observed mixture toxicity. Additionally, the shape of the predictions were clearly different from the experimental concentration-response curves, which might be due to interactions in the mixture. This was further analysed by testing binary mixtures of the three antifouling agents.

Key words: predictability, mixture toxicity, antifouling, periphyton