Evaluation of the combined effects of binary mixtures of sodium hypochlorite and surfactants against Daphnia magna Straus
Detergents and disinfectants have been identified as the most probable products that are responsible for the ecotoxicity of hospital effluents. This study was carried out to evaluate the acute toxicity and the combined effects of binary mixtures of sodium hypochlorite (NaOCl) and three detergents (CTAB, SDS, TX-100) used in hospital medium, on Daphnia magna. Each binary mixture was prepared in predefined ratios of 4:1, 3:2, 1:1, 2:3 and 1:4 (w/w), according to the data found in the literature, and tested through laboratory acute bioassay on daphnids. The isobolographic and the Toxicity Index (TI) models were used to evaluate the combined effects of the various test proportions of the mixtures. Interactions between the constituents of the binary mixtures were, in most cases, in conformity with the model of antagonism, except for the mixture 2:3 of NaOCl:CTAB, which emphasises a light synergism. These results contribute to improve the knowledge on the mechanisms on pollutants actions towards aquatic organisms and strengthen the idea that combined effects of mixtures have to be taken into account to ecological risk assessment.
Keywords: additivity, antagonism, binary mixtures, combined effects, CTAB, Daphnia magna Straus, SDS, sodium hypochlorite, synergism, TX-100, surfactants, detergents, disinfectants, ecotoxicity, hospital effluents, acute toxicity, aquatic organisms, ecological risk assessment, pollution