Polystyrene microplastics facilitating reproductive toxicity and transgenerational transfer of ZnO nanoparticles in daphnia under chronic dietary exposure

Microplastics (MPs) act as vectors for co-existing pollutants, altering their environmental behavior and ecological risks. Yet the impact of MPs on the chronic effects of co-existing pollutants remains poorly understood. Herein, we explored the role of polystyrene (PS) MPs in facilitating the transgenerational transfer (F₀-F₄) and reproductive toxicity of zinc oxide nanoparticles (ZnO NPs) in Daphnia magna (D. magna) under chronic dietary exposure. Results showed that PS MPs facilitated the transgenerational transfer of ZnO NPs, resulting in prolonged transport of ZnO NPs by one generation. This was attributed to that PS MPs impaired Zn excretion of D. magna via significantly inhibiting the molting rates by 40% (p < 0.05), promoting the transfer of Zn to offspring. Besides, confocal microscopy confirmed Zn enrichment in the ovum and umbilical cords. Molecular docking simulation revealed stable Zn^{2 +} binding to vitellogenin (VTG) protein via hydrogen bonds (-1200 kJ/mol), indicating VTG-mediated maternal transfer of Zn. Furthermore, PS MPs facilitated the multi-generational reproductive impact of ZnO NPs to extend to the fourth generation (F₃). Transcriptomic analysis identified significant inhibition of prolactin signaling pathways, with the key genes Signal Transducer and Activator of Transcription (STAT) and VTG decreasing by 80.4% and 7.8% in the female generation (F₀), respectively, inhibiting oocyte development. Overall, these findings confirmed that MPs facilitated the reproductive toxicity and transgenerational transfer of co-existing pollutants, providing critical insights for long-term ecological risk assessment of MPs and co-existing pollutants combined exposure in aquatic systems.