Zinc and nickel binary mixtures act additively on the tropical mysid Mysidopsis juniae

Heavy metals may appear in the environment as a result of different anthropogenic activities, such as agriculture practices, industry and mining. They can reach aquatic environments as complex mixtures, and single chemical toxicity as a baseline for risk assessment can underestimate the impairment of ecosystems. The aim of the present study was to evaluate combined toxicity of binary mixtures of zinc and nickel to the tropical mysid Mysidopsis juniae. Acute toxicity was assessed and mixture toxicity was modelled using the conceptual models for concentration addition and independent action to predict whether both metals act additively or whether they interact with each other inside the organism. For that, the observed mortality data were compared with the modelled data. For the single toxicity assessment, results showed that nickel induced higher toxicity than did zinc, with lethal concentrations to 50% of the organisms of 180 +/- 30 mu gL(-1) and 260 +/- 40 mu g zinc L-1 respectively. In binary mixtures, both metals acted additively and no interactions were predicted by using the conceptual models. The present study has highlighted the need to fill the gaps in toxicity studies using marine species and approaches that can help improve the assessment of accurate risk in the environment. (AU)