Evaluation of ecological risks of antibiotics in Danjiangkou Reservoir basing on toxicity potency and antibiotic resistance genes transfer

This study investigated the spatiotemporal distribution of antibiotics in Danjiangkou Reservoir, and further assessed their potential risks to aquatic organisms based on toxicity potency as well as their relationships with antibiotic resistance genes (ARGs) host microbial communities. Sulfonamides, particularly sulfamethoxazole and sulfamonomethoxine were the most frequently detected antibiotics. Among macrolides, azithromycin showed the highest prevalence and concentrations, likely linked to therapeutic usage in COVID-19. Seasonal variations revealed higher antibiotic concentrations in the dry season (5.95–136.33 ng/L) compared to the wet season (3.35–43.99 ng/L), with tributaries being primary sources of contamination, particularly during the dry season. Risk quotient (RQ) indicated medium-to-high ecological risks for sulfamethoxazole and azithromycin, especially in tributaries. Network analysis was performed to reveal the co-occurrence patterns between ARGs and microbial communities. The results showed that Actinobacteria was positively correlated with the fluoroquinolone resistance gene patA, but negatively with evgS (fluoroquinolone/macrolide resistance), while Armatimonadetes were linked to the fluoroquinolone resistance gene Paer_ParC_FLO, which negatively correlated with the macrolide resistance gene amrA. Furthermore, environmental factors (e.g., temperature, COD, and total nitrogen) and antibiotic concentrations (e.g., sulfamonomethoxine, sulfamethoxazole and azithromycin) were significantly associated with microbial community composition, with Proteobacteria positively correlated with temperature and COD but negatively with sulfamonomethoxine and sulfamethoxazole. In summary, while the current risk level of antibiotic pollution in Danjiangkou Reservoir is relatively low, these findings highlight the persistent presence of antibiotics, emphasizing the need for targeted monitoring and management measures to mitigate potential risks to the ecosystem and human health.