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(13-02) Mixture studies with natural algal communities: predictive power and limitations of Concentration Addition and Independent Action. Backhaus, Thomas*,1, Arrhenius, ABSTRACT- The presented studies analysed the predictability of mixture toxicities on a community level of biological complexity. Main emphasis was laid on mixtures of dissimilarly acting substances, as this type of mixture can be considered to be of major environmental importance. The concept of Independent Action was employed for the prediction in the first place, because it has been proven to be valid for predicting the toxicities of mixtures of dissimilarly acting chemicals to single species. It has been frequently observed, that there are only marginal differences to the prediction made by the competing concept of Concentration Addition (which is based on the assumption of a similar mechanism of action of all mixture components). To see, whether this holds true also on a community level, predictions based on Concentration Addition were also calculated. Experiments were conducted in a short-term bioassay with natural marine epipsammic (sandliving) algal communities, using the uptake of radiolabelled carbonate as the experimental endpoint. Six chemicals, each inhibiting the photosynthetic energy conversion by a unique mechanism of action, were selected as mixture components. Results indicated a good predictive power of Independent Action, but also the predictions made by Concentration Addition differed only negligibly from the experimental observations. These findings are similar to the results typically observed in single species studies. It is therefore concluded, that the validity of both concepts as tools for the predictive assessment of mixture toxicities is not limited to the single species level. But the presented studies also revealed limitations of the applicability of both concepts for multi-species analyses of mixture toxicities, which will be highlighted and discussed. Key words: mixture toxicity, independent action, concentration addition, marine epipsammic algal communities |
sa2, Blanck, Hans2, 1 Institute of Cellbiology, Biochemistry and Biotechnology, Bremen, Germany2 Department of Plant Physiology, Göteborg, Sweden