John Wiley & Sons, Ltd.

Application of generalized linear mixed model to analyze mixture toxicity: Survival of brown trout affected by copper and zinc

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Increased concerns about the toxicity of chemical mixtures have led to greater emphasis on analyzing the interactions among the mixture components based on observed effects. The authors applied a generalized linear mixed model (GLMM) to analyze survival of brown trout (Salmo trutta) acutely exposed to metal mixtures that contained copper and zinc. Compared to dominant conventional approaches based on an assumption of “concentration addition” and ECx (the concentration of a chemical that causes x% effect), the GLMM approach has two major advantages: 1) binary response variables such as survival can be modeled without any transformations and thus it can take sample size into consideration, and 2) the importance of the chemical interaction can be tested in a simple statistical manner. Through this application, we investigated whether the estimated concentration of the two metals binding to humic acid, which is assumed to be a proxy of non‐specific biotic ligand sites, provided a better prediction of survival effects than dissolved and free‐ion concentrations of metals. Our results suggest that the estimated concentration of metals binding to humic acid is a better predictor of survival effects, and thus the metal competition at the ligands could be an important mechanism responsible for effects of metal mixtures. Application of the GLMM (and generalized linear model (GLM)) presents an alternative or complementary approach to analyze mixture toxicity. This article is protected by copyright. All rights reserved

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