Evaluating the Combined Toxicity of Chlorhexidine and Dibutyl Phthalate on Daphnia magna: Implications for Aquatic Ecosystem Safety and Environmental Risk Management

Introduction: Pollutant accumulation in aquatic ecosystems has become a growing environmental concern, posing serious risks to aquatic organisms. While the toxic effects of individual chemicals are well-studied, limited research has explored their combined effects. This study investigates the synergistic and antagonistic toxicity of chlorhexidine (CHX) and dibutyl phthalate (DBP) on Daphnia magna, a commonly used ecotoxicological model. The objective was to assess toxicity levels of CHX and DBP at varying concentrations and evaluate their combined effects using the Bliss Independence Model through an immobilization assay. Methodology: Different concentrations of CHX and DBP were tested both individually and in combination (ratios of 2:1 and 3:1) over a 48-hour period. Immobilization rates were recorded at 24 and 48 hours. A total of 50 organisms per concentration were assessed. The Bliss Independence Model was applied to evaluate synergistic, additive, or antagonistic interactions. Results: The individual toxicity thresholds for CHX were IC30 = 22.85 mg/L, IC50 = 47.93 mg/L, and IC70 = 1.90 mg/L. For DBP, the respective values were IC30 = 8.31 mg/L, IC50 = 14.86 mg/L, and IC70 = 2.52 mg/L. At a 2:1 ratio, the combination demonstrated synergistic effects with combination indices (CI) of 0.718 (IC30), 0.734 (IC50), and 0.758 (IC70). The 3:1 ratio exhibited antagonism at IC30 (CI = 1.42) and IC50 (CI = 1.48), but showed synergism at IC70 (CI = 0.85). Conclusion: The findings demonstrate that chemical interactions vary with concentration and combination ratios. The observed synergistic effects at the 2:1 ratio highlight potential ecological risks, while the 3:1 ratio shows complex interaction patterns. These results underscore the need for comprehensive assessments of chemical mixtures to guide environmental risk management and improved water treatment strategies.