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(065) Estimation of HC5 taking into account uncertainties of individual points in Species Sensitivity Distribution. Jaworska, Joanna1, Aldenberg, Tom 2, 1 2 ABSTRACT- Species Sensitivity Distributions (SSD) are traditionally based on NOECs from chronic toxicity tests. Currently, NOEC values use has been under critique because of its poor statistical properties, including lack of confidence interval (CI). For this reason uncertainty of SSD itself (primary uncertainty) has only been evaluated while the points used to build it (the NOECs) were treated as without error (for Bayesian approach see Aldenberg&Jaworska Ecotox.Env.Saf. 2000) Current tendency expressed by academics and regulatory agencies is to shift from NOEC to EC10-25 (Effective Concentration) in evaluation of chemical effects on individual species. This development should be followed in construction of SSD and eventually to calculate Hazardous Concentration that affects 5% of species (HC5) and its CI . This paper discusses a novel method that takes into account uncertainties of individual ECx values to construct SSD. The ECx uncertainty distributions are sampled using Monte Carlo to build family of SSDs (form of secondary uncertainty) each of them being uncertain due to limited number of species used to construct it (primary uncertainty). Accounting for the uncertainty of the points (ECx) leads to a nonsymetric shift towards lower numbers of the HC5 and its CI due to gradient in sensitivities of the points, with smallest points the most influential. We will also address how this changes influence the uncertainty of the Fraction (of species) Affected. Key words: SSD, uncertainty, effects estimation |
