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Probabilistic Risk Assessment - Theory and Reality (MO4/4) SSDs - help or hindrance in ecological risk assessments? Calow, Peter1, Forbes, V.2, 1 The University of Sheffield, Sheffield S10 2TN, United Kingdom2 Roskilde University, Roskilde, Denmark ABSTRACT- In response to the perceived inadequacy of fixed extrapolation factors to address uncertainties in ecotoxicological effects, species sensitivity distributions (SSDs) are being used increasingly in ecological risk assessment. In evaluating the extent to which SSDs provide an improved method for effects assessment most focus has been placed on statistical issues related to the form of the resulting distributions (e.g., What distribution(s) provide(s) the best fit to toxicity data? How many input values are necessary to obtain a good fit? Which percentile should be used as the effects endpoint? With what level of statistical confidence?). Although these issues are no doubt important, we believe that much more attention has to be given to 1) the selection of appropriate endpoints in appropriate species and 2) rigorous interpretation of the resulting model outputs. The increased sophistication of SSDs, compared to dividing by a multiple of 10, should, in principle, result in better effects assessments, but may not if the data on which they are based are inappropriate and/or if the resulting outputs are not interpreted with great care. Key words: risk assessment, probabilistic, extrapolation, statistics |
