Combined thermal stress and nanoplastic exposure induce oxidative-mediated neurodevelopmental toxicity and behavioral alterations in zebrafish.

Environmental nanoplastic pollution is an emerging concern for neurodevelopmental health; however, little is known about how subtle environmental modifiers influence its neurotoxic potential. In this study, we investigated whether a modest but environmentally relevant thermal elevation (0.5 °C) modulates the neurotoxic effects of 20 nm polystyrene nanoplastics (PNPs) in developing zebrafish. Embryonic exposure to PNPs induced significant anxiety-related behavioral alterations, as evidenced by changes in thigmotaxis. These behavioral disturbances were accompanied by increased oxidative stress, reflected by altered expression of antioxidant defense genes (SOD, CAT, GPx), and elevated markers of DNA damage, including γH2A.X and 8-OHdG in brain tissue. Immunofluorescence analyses further revealed disruptions in neurotrophic and neuromodulatory signaling, as indicated by altered BDNF, 5-HT4 receptor, and nNOS protein levels. Notably, even a 0.5 °C temperature increase markedly amplified these molecular and behavioral alterations. Metabolomic profiling supported these findings, demonstrating perturbations in amino acid and purine metabolism pathways associated with redox balance and neurotransmission. Together, our results indicate that subtle thermal stress enhances nanoplastic-induced neurodevelopmental toxicity through oxidative and DNA damage-mediated mechanisms, ultimately leading to functional behavioral impairment. These findings underscore the vulnerability of the developing nervous system to interacting environmental stressors.