Genotoxic effects induced by the exposure to an environmental mixture of illicit drugs to the zebra mussel

•The toxicity of illicit drug mixtures to aquatic organism is largely unknown.•We measured genetic damage induced by an illicit drug mixture to the zebra mussel.•The exposure to the realistic mixture caused fragmentation of hemocyte DNA.•An induction of fixed genetic damage was noticed.•The toxicity of the mixture was higher than those of the single drugs.

Despite the growing interest on the presence of illicit drugs in freshwater ecosystems, just recently the attention has been focused on their potential toxicity towards non-target aquatic species. However, these studies largely neglected the effects induced by exposure to complex mixtures of illicit drugs, which could be different compared to those caused by single psychoactive molecules. This study was aimed at investigating the genetic damage induced by a 14-day exposure to a realistic mixture of the most common illicit drugs found in surface waters worldwide (cocaine, benzoylecgonine, amphetamine, morphine and 3,4-methylenedioxymethamphetamine) on the zebra mussel (Dreissena polymorpha). The mixture caused a significant increase of DNA fragmentation and triggered the apoptotic process and micronuclei formation in zebra mussel hemocytes, pointing out its potential genotoxicity towards this bivalve species.