The Acute and Chronic Toxicity of Five Heavy Metals on the Daphnia Magna

The acute and chronic toxicity experiments were conducted towards D. magna for five heavy metals, namely Hg, Cd, Cu, Pb and Cr, existing in single or mixture. The single results suggested that Hg was the most toxic, and then Cd, Cu, Pb and Cr in turn. The joint experiments indicated that toxicity for all mixtures were synergistic to D. magna using toxic units (TU_s) and additional index (At). For more toxic Hg-Cd-Cu-Pb-Cr mixture and Hg-Cd mixture, toxicity enhancement index (TEI), a measurement index of the degree of joint toxicity enhancement compared to single toxicity, were 10.4 and 13.7, respectively. In addition, the copper ion strongly reduced the combined toxicity of Hg-Cd mixture, and lead ion affect slightly on the toxicity of Hg-Cd-Cu mixture, and chromium ion was lowest toxic to D. magna, but its exist made the joint toxicity of Hg-Cd-Cu-Pb mixture increased more than six times. Chronic test showed that the reproduction of D. magna was significantly inhibited compared to the ones of control group when concentration was designed at the level of water quality for fisheries in China (GB1160-89). It was proved in this research that it´s unreasonable to draft the environmental standard only based on the results of single toxicological test.