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(T/MF166) Variation in slope of concentration-effect relationships: consequences for environmental risk assessment. Smit, Mathijs1, Karman, Chris1, 1 ABSTRACT- Implementing the variation within populations in ecological modelling, could contribute to a more sophisticated way of modelling and derivation of safety factors. To give insight in the magnitude and spread in sensitivity within test populations the variation in sensitivity expressed as the slope of a concentration-effect curve (Sm) within over 300 test populations from toxicity tests with 36 species and 116 substances is analysed. The overall average variation from this study is 0.65 (Sm) and corresponds with an EC50/EC5 ratio of 2.9. The mode of action is often suggested as an explanation for the different slopes of concentration-effect curves. For metals and organic substances indeed significant different median slope values are observed. However, within the group of organic substances no distinction between the slope values of narcotic substances and substances with a specific mode of action could be made. Between species groups significant differences in the amount of variation could be demonstrated. The median slope for all toxicants within the data set of 96 hours tests specified for fishes and molluscs is significantly steeper (median slope of 0.38 and 0.37 respectively) than for algae and crustaceans (1.2 and 0.72 respectively). Factors that might explain these differences are discussed. Possibilities for the use of these results in risk assessment are related to the translation of effect concentrations (ECx) to threshold values. Key words: aquatic toxicity, slope, concentration-response, risk assessment |
