Abstract |
Results of the laboratory tests are used in assessing the environmental risk of exposure to industrial chemicals. The combined effects of dose-level exposure and time-duration exposure are tested in the laboratory, but only a single endpoint reflecting the dose-level exposure at the end of the test period is routinely reported and used. At times, this might be sufficient, or the data otherwise inappropriate for calculation of more than a single endpoint. Nevertheless, an approach that makes a more complete use of existing sufficient test information is needed. One method is presented in the paper, the focus of which is the evaluation of an LC50 endpoint at a calculated exposure time. This calculation determines a condition for the toxicity curve to become established along the time axis. The authors refer to this condition of the dose-response curve as an asymptotic state and the LC50 calculated from it as the asymptotic LC50. An analysis of 152 toxicity tests using fathead minnows show that the 96-hr LC50 is 25% more conservative than the asymptotic LC50. The calculation of LC50 under asymptotic conditions better enables comparing toxicities of different chemicals on the basis of comparable dose-level and time-duration exposures. (Copyright (c) 1988 Springer-Verlag New York Inc.) |