Toxicity of cobalt and copper to rainbow trout: application of a mechanistic model for predicting survival

Abstract

We conducted 14-day laboratory toxicity tests with rainbow trout to evaluate, (1) the acute toxicity of Co and Cu, and (2) the effects of selected Co concentrations on the toxicity of Cu in Co/Cu mixtures. A one-compartment, uptake-depuration model was used to estimate incipient lethal levels (ILLs) and quantify differences in lethality responses among the Co-only, Cu-only and Co/Cu exposures. Additionally, we compared mortality percentages observed in Co/Cu mixtures to those predicted from two models of joint toxicity. Co was a slower-acting and less potent toxicant than was Cu. For Co, the ILL for 50% mortality was 346 μg l −1; for Cu, the ILL for 50% mortality was 14 μg l −1. Moreover, in Co/Cu mixtures, Co acted as an antagonist during the first 48–96 h, but later acted as an additive or slightly synergistic toxicant—making it difficult to predict short-term mortality of fish in Co/Cu mixtures. Lethality thresholds for Cu were reduced by 11–26% and 37–45%, respectively, in the presence of 50 and 250 μg l −1 Co, although those differences were not statistically significant. The ordering of ILLs for the metal exposures tested was: 250 μg l −1 Co+Cu>50 μg l −1 Co+Cu>Cu-only>Co-only.