Realistic mixture of illicit drugs impaired the oxidative status of the zebra mussel (Dreissena polymorpha)

•The toxicity of illicit drug mixtures to aquatic organism is utterly unknown.•We measured oxidative alterations induced by an illicit drug mixture to the zebra mussel.•The exposure to the realistic mixture imbalanced the activity of defense enzymes.•Remarkable increases of oxidative damage were noticed.

Illicit drugs are considered to be emerging aquatic pollutants since they are commonly found in freshwater ecosystems in the high ng L−1 to low μg L−1 range concentrations. Although the environmental occurrence of the most common psychoactive compounds is well known, recently some investigations showed their potential toxicity toward non-target aquatic organisms. However, to date, these studies completely neglected that organisms in the real environment are exposed to a complex mixture, which could lead to dissimilar adverse effects. The present study investigated the oxidative alterations of the freshwater bivalve Dreissena polymorpha induced by a 14-d exposure to an environmentally relevant mixture of the most common illicit drugs found in the aquatic environment, namely cocaine (50 ng L−1), benzoylecgonine (300 ng L−1), amphetamine (300 ng L−1), morphine (100 ng L−1) and 3,4-methylenedioxymethamphetamine (50 ng L−1). The total oxidant status (TOS) was measured to investigate the increase in the reactive oxygen species’ levels, while the activity of antioxidant enzymes and glutathione S-transferase were measured to note the eventual imbalances between pro-oxidant and antioxidant molecules. In addition, oxidative damage was assessed by measuring the levels of lipid peroxidation and protein carbonylation. Significant time-dependent increases of all the antioxidant activities were induced by the mixture. Moreover, the illicit drug mixture significantly increased the levels of carbonylated proteins and caused a slight variation in lipid peroxidation. Our results showed that a mixture of illicit drugs at realistic environmental concentrations can impair the oxidative status of the zebra mussel, posing a serious hazard to the health status of this bivalve species.