Toxicity of exposure to binary mixtures of four anti-neoplastic drugs in Daphnia magna and Ceriodaphnia dubia

•Binary mixtures of four anti-neoplastic drugs were tested on two crustaceans.•Combined toxicities were predicted applying Bliss independence and Loewe additivity.•Generally, mixtures showed a Bliss independent action.•Imatinib diverged from Bliss action interfering with toxicity of other anticancer drugs. Anticancer drugs, interfering with DNA in every living organism, may pose a threat to aquatic environment, even more when they occur as complex mixtures. We investigated the combined long term toxic potential of four anti-neoplastic drugs (5-fluorouracil [5-FU], cisplatin [CDDP], etoposide [ET] and imatinib mesylate [IM]) testing their binary mixtures on two primary consumers of the freshwater aquatic chain with close phylogenetic relationship: Daphnia magna and Ceriodaphnia dubia. The combined toxicities were assessed using two distinct effect sizes that should be observed if Bliss independence holds. Direct statistical comparison by analysis of variance of single and combined toxicities under the assumption of Bliss independence allowed to accept or reject the independency hypothesis. Independency was confirmed for all mixtures both in D. magna and in C. dubia, except for IM+ ET and IM+CDDP in D. magna and for ET+CDDP and ET+5-FU in C. dubia which at the highest concentrations showed an antagonistic interaction. A synergic tendency was found testing IM+CDDP on C. dubia at the lowest concentration selected. Thus, the chronic ecotoxicological data evaluated in this study show not only a potential environmental risk of anticancer drugs, especially considering their potential synergistic effects, but also the necessity to integrate statistical models with experimental data to establish the real environmental impact of such compounds.