Genotoxicity effects of polylactic acid microplastic present with antibiotic sulfamethoxazole on the Pacific oyster, Crassostrea gigas (Thunberg, 1793)

In this study, we assessed the genotoxicity induced by the exposure to polylactic acid microplastics (PLA-MPs) and/or antibiotic sulfamethoxazole (SMX) in the marine bivalve species, Pacific oyster Crassostrea gigas. Oysters were exposed for 14 days to three experimental conditions: PLA-MPs alone, SMX alone and mixing PLA-MPs + SMX at concentrations of five mg/L for PLA-MPs and 64 ng/L for SMX. To achieve this goal, the mediated genotoxicity was assessed by analyzing biomarker such as micronucleus frequency, the degree of DNA damage and changes in gene expressions in gill tissues of exposed oysters, while PLA-MPs accumulation were analyzed in gill tissues. Results show that PLA-MPs were the primary driver of microplastic accumulation in oyster gill tissues, whereas co-exposure PLA-MPs + SMX resulted in significant but reduced accumulation compared with PLA-MPs. Exposure to PLA-MPs or in combination with antibiotic SMX induced additional transmission pathways which lead to DNA damage and micronucleus formation. However, oysters co-exposed to PLA-MPs + SMX exhibited increased susceptibility to micronucleus in gill tissues, whereas the extent of DNA damage in oysters exposed to PLA-MPs alone was comparable to that observed under combined PLA-MPs + SMX exposure. Notably, combination of PLA-MPs and SMX amplified oxidative stress and detoxification responses in oysters through SMX modulating PLA-induced antioxidant signaling. This combination exacerbated suppression of key detoxification pathways, thereby potentially increasing susceptibility to genotoxic effects in contaminated aquatic environments. The research findings of this study provide relevant insights for toxicology related to bio-based microplastics.