Risk Quotient Assessment of Mixture Toxicity of Pharmaceuticals Detected in Treated Wastewater Effluents

Abstract

The presence of pharmaceutical residues in treated wastewater effluents has emerged as a significant environmental concern due to their persistence, bioactivity, and potential adverse effects on aquatic ecosystems. This study investigates the risk quotient assessment of mixture toxicity associated with pharmaceuticals detected in treated wastewater effluents under environmental exposure conditions. The research focuses on evaluating the combined ecological risks of multiple pharmaceutical compounds and understanding their cumulative toxicological impact on aquatic organisms. Wastewater effluent samples were analyzed to identify and quantify commonly occurring pharmaceuticals, including antibiotics, analgesics, anti-inflammatory drugs, and endocrine-active compounds. Risk quotient calculations were performed using measured environmental concentrations and predicted no-effect concentrations to assess individual and mixture toxicity risks across different trophic levels. Results demonstrated that several pharmaceutical compounds exhibited moderate to high ecological risk potential, particularly when combined within complex contaminant mixtures. The mixture toxicity assessment revealed additive and synergistic interactions that increased overall environmental risk beyond the impact of individual compounds alone. Sensitivity analysis indicated that chronic exposure and continuous discharge of pharmaceutical residues significantly contribute to long-term ecological stress in receiving water bodies. Comparative evaluation confirmed that conventional wastewater treatment processes are insufficient for complete removal of certain persistent pharmaceutical contaminants. The study further highlighted the importance of incorporating mixture toxicity approaches into environmental monitoring and regulatory frameworks for more accurate ecological risk characterization.