Considering Data Uncertainty in Species Sensitivity Distribution for Ecological Risk Assessment of Chemicals

Ecological risk assessment for chemical management favors multi-species as the protective object. Since different species respond differently, species sensitivity distribution (SSD) is applied to delineate the impact and to infer criterion concentration of a chemical. A SSD is usually established with ecotoxicity test data of different species, usually No-Observed-Effect-Concentrations (NOECs) derived from chronic bioassays. Based on the SSD, the concentration that begets impairment in 5% of the total species in the ecosystem, denoted as HC₅, together with its 95% lower limit value, is used for regulation. The dependence of SSD on NOECs entails that the uncertainties in NOEC values will skew the shape of SSD and consequently the HC₅, as is of much importance since NOEC value is generally prone to errors. This study demonstrated the bias in HC₅ with Monte Carlo simulations by assuming different uncertainty levels in NOECs. With increasing NOEC uncertainty, the HC₅ and its lower limit were found to shift downwards substantially, implying underestimation of the ecological risk if NOEC uncertainty is disregarded. By incorporating the NOEC variances during the HC₅ inference procedure, the bias could be adequately corrected. However, simulating SSD through Monte Carlo approach is probably indispensable in the case of irregular NOECs uncertainties.