Toxic effects of polystyrene microplastics on atrazine in zebrafish: Exogenous toxicity and endogenous mechanism.

The ubiquitous presence of microplastics and other contaminants in the environment poses a potential threat to organisms, yet the mode of action and mechanisms of toxicity when they are co-exposed remain underexplored. In this work, we investigated the combined effects of environmental concentrations of polystyrene (PS) and dry heat-UV-bioaged polystyrene microplastics (CPS) with the triazine herbicide atrazine on zebrafish. Acute toxicity experiments demonstrated that combined exposure of PS/CPS and atrazine enhanced the 96-h LC50 of atrazine. Long-term exposure experiments showed that combined exposures were more likely to result in tissue damage and oxidative stress disorders in the zebrafish gut and liver. Interestingly, our experiments show that co-exposure also affects exogenous water quality by decreasing dissolved oxygen and increasing NH3+-N, NO3- and NO2- in the water column, and that NO2- and NH3+-N can cause damage to zebrafish. Moreover, the combined exposure was more likely to cause changes in gut flora at the level of phylum. In terms of hepatic gene transcription, combined exposure not only led to a significant enrichment of pathways for amino acid metabolism, fat digestion and absorption, and fatty acid degradation, but also affected several disease-associated signaling pathways. These findings provide novel perspectives and evidence on the mechanisms of toxicity induced by combined exposure to new contaminants and provide guidance for ecological risk assessment.