Abstract
Running laboratory toxicity tests is costly and time consuming, and therefore extrapolations based on the limited toxicological information are necessary in performing the ecological risk assessment/management of chemical substances. Two widely-used extrapolation methods are the use of assessment factors（AF）as adopted in, for example, the Japanese chemical substances control law, and the other is the application of species sensitivity distribution（SSD）. In this study, we theoretically investigated the performance of two extrapolation methods by comparing predicted no effect concentrations（PNECs）derived by the methods. For the comparison, two criteria were adopted. One criterion considers that an extrapolation method which derives a PNEC smaller than the hazardous concentration for 5% of species（HC5）with higher possibility is better. Another criterion considers that an extrapolation method which sets a PNEC closer to the HC5 is better. The AF method adopted by the chemical substances control law was superior under the first criterion but was inferior under the second criterion. Our results show that there is no unique assessment method that always defeat the others, and thereby suggests that a better strategy may be required to compile the merits of existing extrapolation methods depending on data and goal of protection in risk assessments.
