Aged polystyrene microplastics cause reproductive impairment via DNA-damage induced apoptosis in Caenorhabditis elegans.

Although polystyrene microplastics (PS-MPs) could induce toxic effects on environmental organisms, the toxicity of aged PS-MPs with HO on soil organisms remains unclear. Our study utilized Caenorhabditis elegans as model organism to examine the reproductive toxicity of pristine PS-MPs (pPS-MPs) and aged PS-MPs (aPS-MPs) at environmentally relevant concentrations (0.1-100 μg/L). Acute exposure to aPS-MPs could induce greater reproductive impairment compared to pPS-MPs, as evidenced by changes in brood size and egg release. Assessment of gonad development using the number of mitotic cells, length of gonad arm, and relative area of gonad arm as parameters revealed a high reproductive toxicity caused by aPS-MPs exposure. Furthermore, aPS-MPs exposure promoted substantial germline apoptosis. Additionally, exposure to aPS-MPs (100 μg/L) markedly altered the expression of DNA damage-induced apoptosis-related genes (e.g., egl-1, cep-1, clk-2, ced-3, -4, and -9). Alterations in germline apoptosis caused by aPS-MPs were observed in mutants of cep-1, hus-1, egl-1, ced-3, -4, and -9. Consequently, the augmentation of reproductive toxicity resulting from aPS-MPs exposure was attributed to DNA damage-triggered cellular apoptosis. Additionally, the EGL-1-CEP-1-HUS-1-CED-3-CED-4-CED-9 signaling pathway was identified as a key regulator of germline apoptosis in nematodes. Our study provides insights into potential environmental risk of aPS-MPs with HO on environmental organisms.