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Although microplastics’ (MPs) toxicity has been reported in several aquatic and terrestrial organisms, the knowledge about how these pollutants can affect insects at the early developmental stage remains incipient. Thus, the aim of this study was to use Culex quinquefasciatus larvae as a model system to test the hypothesis that, besides accumulating in animals, polyethylene microplastics (PE MPs) lead to biochemical changes predictive of nutritional impacts, as well as induce oxidative stress, redox state imbalance, and neurotoxicity in them. Our results have indicated that short exposure to PE MPs (5 days) at the environmental concentration of 4.24 x 106 particles m-3 induced changes suggesting damage to energy metabolism such as reduced total proteins, total soluble carbohydrates, and triglycerides levels. In addition, increased hiobarbituric acid reactive species, in association with reduced total glutathione and DPPH radical scavenging activity (%) have suggested an imbalance between oxide-reducing agents and antioxidant defense system, induced by pollutant. On the other hand, increased acetylcholinesterase activity has suggested the neurotoxic effect of PE MPs. Finally, PE MPs have accumulated in the larvae, and it may have been a triggering factor for the observed changes. Thus, our study has confirmed the potential of C. quinquefasciatus larvae to act as vector of MPs in different ecosystems and helped improving the knowledge about how PE MPs can affect their development and lead to losses in different ecological functions of this species.

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One of the most impact issues in recent years refers to the COVID-19 pandemic, the consequences of which thousands of deaths recorded worldwide, are still inferior understood. Its impacts on the environment and aquatic biota constitute a fertile field of investigation. Thus, to predict the impact of the indiscriminate use of azithromycin (AZT) and hydroxychloroquine (HCQ) in this pandemic context, we aim to assess their toxicological risks when isolated or in combination, using zebrafish ( Danio rerio ) as a model system. In summary, we observed that 72 h of exposure to AZT and HCQ (alone or in binary combination, both at 2.5 μg/L) induced the reduction of total protein levels, accompanied by increased levels of thiobarbituric acid reactive substances, hydrogen peroxide, reactive oxygen species and nitrite, suggesting a REDOX imbalance and possible oxidative stress. Molecular docking analysis further supported this data by demonstrating a strong affinity of AZT and HCQ with their potential antioxidant targets (catalase and superoxide dismutase). In the protein-protein interaction network analysis, AZT showed a putative interaction with different cytochrome P450 molecules, while HCQ demonstrated interaction with caspase-3. The functional enrichment analysis also demonstrated diverse biological processes and molecular mechanisms related to the maintenance of REDOX homeostasis. Moreover, we also demonstrated an increase in the AChE activity followed by a reduction in the neuromasts of the head when zebrafish were exposed to the mixture AZT+HCQ. These data suggest a neurotoxic effect of the drugs. Altogether, our study demonstrated that short exposure to AZT, HCQ or their mixture induced physiological alterations in adult zebrafish. These effects can compromise the health of these animals, suggesting that the increase of AZT and HCQ due to COVID-19 pandemic can negatively impact freshwater ecosystems.