Predicting single-species toxicity in natural water systems



A methodology is proposed to predict single-species toxicity in natural waters by using laboratory bioassay data which relate effect to a tissue concentration of toxicant or to injury accumulation. Such relationships should be independent of test conditions and therefore be transferable from lab to field. Data for endrin and copper are presented which illustrate relationships between tissue concentrations and mortality. A mathematical model of uptake and elimination of toxicants by fish is used to relate exposure concentration to tissue concentration and then to effect. Prediction of toxicity in a laboratory test in which the exposure concentration varies in time is presented as a first step in testing the methodology. Using a dose-response relationship determined from published data for zinc toxicity to rainbow trout in a constant exposure toxicity test, the survival time under time-varying exposure is calculated and compared to observed data. The model predicted survival times that were consistent with the observed times. Whole-body residue is used as the estimate of dose.

A methodology for considering chemicals for which tissue concentration is not a useful estimate of dose is also presented. Diazinon-induced acetylcholinesterase inhibition data are used to demonstrate this methodology.