Impact of virgin and weathered microplastics on zebrafish: Bioaccumulation, developmental toxicity and molecular pathway disruptions.

Microplastics (MPs) are ubiquitous environmental pollutants with significant ecological risks, particularly due to their potential for bioaccumulation and toxicity. This study examines the effects of virgin spherical MPs and environmentally weathered MPs, specifically polystyrene (PS) and polyethylene (PE), on zebrafish larvae to enhance the environmental relevance of the findings. MP concentrations used were 10-10 particles/L for the virgin MP group and 10 particles/L for the weathered MP group, reflecting levels commonly observed in natural environments. Weathered MPs were produced through mechanical grinding followed by one month of exposure to water and sunlight to simulate environmental aging. MP characterization was performed using advanced microscopy techniques, including Scanning Electron Microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The results indicated significantly higher mortality in the weathered MP group (80%) compared to the virgin MP group (20%). Zebrafish larvae ingested MPs and exhibited disruptions in key molecular pathways, including those involved in oxidative stress response, apoptosis, and DNA damage repair. Notably, this study is among the first to evaluate the impact of MPs on the complete homologous recombination (HR) and non-homologous end joining (NHEJ) DNA repair pathways. Our findings highlight the enhanced toxicity of weathered MPs and emphasize the importance of considering MP aging in toxicological assessments. These results contribute to a deeper understanding of MP pollution and provide valuable insights for the development of regulatory measures to protect aquatic ecosystems.