Mean extinction time of populations under toxicant stress and ecological risk assessment

Population-level effects of chemical pollutants are evaluated in terms of d ecrements of mean extinction time of populations. Analytical solutions of t he mean extinction time based on the diffusion approximation were applied t o published chronic ecotoxicological data provided from life table experime nts or population growth experiments. Assuming a fairly large population (a million) with environmental fluctuation of an observed magnitude, chemical exposure with a concentration of 10% of LC50 is expected to cause, on aver age, an extinction risk of 16% reduction in the mean extinction time, which is equivalent to that induced by a 1.2% reduction of the population size ( or habitat area). Although the ecological risk assessment based on mean ext inction time has many limitations, it may present a possibility for interpr eting the ecological risk of chemical pollutants in the context of populati on vulnerability.