Co-exposure to dimethoate and tetracycline induces synergistic ecological risks to Brachionus calyciflorus

Dimethoate, a widely used organophosphorus pesticide in agriculture and animal farming, poses significant risks to aquatic ecosystems and human health upon environmental release. Tetracycline, one of the most widely used antibiotics, is frequently detected in surface water and groundwater. In agricultural or urban watersheds, where pesticide runoff and antibiotic-laden wastewater frequently co-occur. The coexistence of tetracycline and dimethoate in nature is common, and this coexistence might impose environmental stress, affecting other organisms. This study investigated the interactive effects of tetracycline (0, 0.085, and 0.85 mg/L) and dimethoate (0, 1.6, and 16 mg/L) on the freshwater rotifer Brachionus calyciflorus , focusing on life cycle parameters, oxidative stress responses, and microbial-mediated dimethoate degradation. Key findings revealed that the co-exposure to tetracycline and dimethoate exerted a synergistic effect, significantly reducing rotifer population density and growth rate compared to exposure to either contaminant alone. Additionally, tetracycline inhibited bacterial growth, which in turn prolonged the environmental persistence of dimethoate in aquatic systems by impeding its natural biodegradation. Collectively, these results highlight the non-additive interactive risks associated with the coexistence of tetracycline and dimethoate, emphasizing the necessity of considering such contaminant interactions in environmental risk assessment to more accurately evaluate the ecological hazards of combined pollution in aquatic systems.