Effects of aged microplastics on the abundance of antibiotic resistance genes in oysters and their excreta

The widespread use of plastics in global aquaculture raises concerns about their environmental impact, particularly due to their degradation into microplastics (MPs). These MPs not only pose risks to aquatic organisms and ecosystems but also serve as carriers for emerging pollutants such as antibiotic resistance genes (ARGs). By facilitating the enrichment and transport of ARGs in aquatic environments, MPs may exacerbate the spread of antibiotic resistance, particularly in filter-feeding organisms. The underlying effects of MPs on ARGs in oysters and the further risks have not been clearly elucidated. Here, we explored the effects of aged polyethylene (PE) and polyethylene terephthalate (PET) MPs on ARGs abundance in oysters (Magallana angulata). Our results showed that MPs significantly enriched ARGs after three months of aging in the aquaculture environment with variations depending on polymer type. After two weeks of MPs exposure, the absolute abundance of ARGs in oyster tissues fluctuated, with tetA (PE MPs exposure), tetG (PET MPs exposure), and oqxB significantly increasing, while fexA was suppressed. However, despite being 1.16 to 5.46 × 10 times higher than in oyster tissues (excluding tetC), ARGs in excreta showed no significant trend. Additionally, significant positive correlations were observed between intI1 and sul2/tetG in tissues and between intI1 and sul1 in excreta, suggesting potential ARGs transmission through the food chain or excretion. This study advances our understanding of the complex interactions between MPs and ARGs, underscoring the need for effective management strategies to mitigate their ecological and public health risks.