A physiologically based biotic ligand model for predicting the acute toxicity of waterborne silver to rainbow trout in freshwaters

James C. Mcgeer, CANMET Energy Technology Center
Richard C. Playle, Wilfrid Laurier University
Chris M. Wood, McMaster University
Fernando Galvez, McMaster University

Abstract

An early silver-gill binding model using conditional equilibrium binding constants (K) was fitted to actual toxicity data for rainbow trout (Oncorhynchus mykiss) and subsequently modified to produce a mechanistically based acute toxicity model for predicting silver toxicity. The model used an 'off the shelf' aquatic geochemistry software program (MINEQL+) and physiologically based log K values to predict the acute effects of waterborne silver in rainbow trout. The final version of the model does not predict total gill-silver loading, as the early model did, but rather predicts the binding of Ag+ to key toxic sites on the gill and incorporates the effects of cation competition at these sites. The acute toxicity model for Ag+ provided the best fit to toxicity data when a log K value for the affinity of these sites was 7.6 with cationic competition log K values for Na+ and Ca2+ of 2.9 and 2.3, respectively. A log K for Ag-DOM of 9.0 was used representing strong Ag+ binding to dissolved organic matter. The model we present is easy to use and provides a good match with previously published acute AgNO3 toxicity data for rainbow trout from 31 data sets in 10 studies. The modified model is now ready for full verification with a greater range of laboratory and natural waters.