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(74-05) A demographic interpretation of mixture toxicity. Jonker, Martijs*,1, Kammenga, Jan1, 1 Wageningen University, Binnenhaven 5, Wageningen, The Netherlands ABSTRACT- The toxicity of chemical mixtures is usually examined by means of experiments that are truncated after a predefined exposure time. Subsequently the observed effects are compared with an additive or independent model, to evaluate the toxicity of the mixture in relation to the toxicity of the individual compounds. Yet, this approach makes it difficult to reveal the ecological implications of possible interactions. The understanding of the potential ecological risks of chemical mixtures can be improved by assessing the consequences of combined toxicity at the population level. This presentation concentrates on the question how effects of toxic metal mixtures on individual demographically important parameters can be translated to population effects. The consequences of synergistic or antagonistic interactions in relation to trade off relationships are discussed. The presentation will be accompanied by results from detailed experiments, addressing the effect of metal mixtures on the vital rates of Caenorhabditis elegans, a free-living nematode. Preliminary outcomes indicate a synergistic effect for Cu and Cd with respect to population growth rate (p < 0.05). The mixture caused a serious decrease in survival during the reproductive period, compared to the control. However, decomposition of the interaction parameter revealed that mortality hardly accounts for the synergistic effect. The synergistic effect was mainly induced by changes in fertility rates. Surprisingly, when the average reproduction per day was evaluated for interaction effects, no synergism is found. The data even tended to antagonism. Apparently, toxic interactions at the individual level do not translate directly to toxic interactions at the population level. Key words: mixture toxicity, population level, toxic interactions, demographic analysis |
