Testing an application of a biotic ligand model to predict acute toxicity of metal mixtures to rainbow trout

The authors tested the applicability of a previously developed biotic ligand model (BLM) to predict acute toxicity of single metals and metal mixtures (cadmium, lead, and zinc) to rainbow trout fry (Oncorhynchus mykiss) from a single available dataset. The BLM used in the present study hypothesizes that metals inhibit an essential cation (calcium) and organisms die as a result of its deficiency, leading to an assumption that the proportion of metal‐binding ligand (f) is responsible for the toxic effects of metals on the survival of rainbow trout. The f value is a function of free‐ion concentrations of metals computed by a chemical speciation model, and the function has affinity constants as model parameters. First, the survival effects of single metals were statistically modeled separately (i.e., f‐survival relationship) by using the generalized linear mixed model with binomial distribution. The modeled responses of survival rates to f overlapped reasonably irrespective of metals tested, supporting the theoretical prediction from the BLM that f‐survival relationships are comparable regardless of metal species. The authors thus developed the generalized linear mixed model based on all data pooled across the single‐metal tests. The best‐fitted model well predicted the survival responses observed in mixture tests (r = 0.97), providing support for the applicability of the BLM to predict effects of metal mixtures. Environ Toxicol Chem 2015;34:754–760. © 2014 SETAC