A comparative study on toxicity identification of industrial effluents using daphnia magna

In this study, acute toxicity monitoring and toxicity identification evaluation procedures were applied to identify causative toxicants in industrial effluents. Effluents from a metal plating factory and a rubber products factory were acutely toxic toward Daphnia magna and the toxicity varied over different sampling events (2.9-5.9 and 1.7-7.6 TU, respectively). For the rubber products effluent, it was confirmed that zinc (5.65-13.18 mg L ^-1) was found to be a major cause of toxicity, which is likely originated from zinc 2-mercaptobenzothiazole and zinc diethyldithiocarbamate used as vulcanization accelerators. For the metal plating effluent, it appeared that the presence of high concentrations of Cl ^- and SO ₄ ^2- (8,539-11,400 and 3,588-4,850 mg L ^-1, respectively) caused the observed toxicity. These toxicants likely originated from sodium bisulfate (NaHSO ₃) and sodium hypochlorite (NaOCl) used as reducing and oxidizing agents. Though copper was found to be present in levels much higher than the EC ₅₀ (50% effective concentration) value, this was not attributable to the toxicity of metal plating effluent likely due to complexation with dissolved organic matter.