Single and combined acute and subchronic toxic effects of microplastics and copper in zebrafish (Danio rerio) early life stages

The evaluation of the interaction between microplastics (MPs) and heavy metals is of special importance for risk assessment. In this study, zebrafish (Danio rerio) were exposed to MPs (2 mg/L), two sub-lethal concentrations of copper (Cu, 60 and 125 μg/L) and their mixtures (Cu60 + MPs, Cu125 + MPs), from 2-h post-fertilization (hpf) until 14-days post-fertilization (dpf). Lethal and sublethal endpoints were evaluated, along with a set of biochemical and genetic biomarkers between 2 and 14 dpf. Exposure to MPs and Cu, single or combined, induced high mortality and oxidative stress in zebrafish larvae, with data showing that the antioxidant enzymes were inhibited at 6 dpf, increasing thereafter until 14 dpf, due to the accumulation of reactive oxygen species. MPs and Cu, single or combined, caused neurotoxicity in larvae by inhibiting acetylcholinesterase activity. There was an increased and significant effect of Cu + MPs groups on the evaluated biomarkers, concerning the corresponding Cu groups, suggesting that MPs may have a synergistic effect in relation to Cu. The Integrated Biomarker Response (IBR) evidenced that a higher degree of stress occurred at the larval period. Our findings highlight that MPs can act as a vector for heavy metals, therefore, influencing their bioavailability and toxicity in the organisms.