The Toxicological Effects of Cr~(6+) on Chlorella Vulgaris,Scenedesmus Obliquus and Microcystis Aeruginosa at Different pH Values

At present,the study of the water quality ecological criteria in China is scattered.The purpose of this study is to provide the reference to the establishing of the ecological criteria and the related study.According to the OECD guidelines for the testing of chemicals,freshwater alga and cyanobacteria growth inhibiton test have been carried out.The toxicological effects of hexavalent chromium(Cr6+)on the growth of Chlorella vulgaris,Scenedesmus obliquus and Microcystis aeruginosa have been studied at different pH levels.When the value of pH is 7.0,8.0 and 9.0,taking the 72h algal biomass as the endpoint,the specific growth rates,NOEC,LOEC,EC10 and EC20 have been calculated,respectively.The results show the pH levels significantly effect the growth of alga.The optical growth pH of Chlorella vulgaris is 7.0,while that of Scenedesmus obliquus and Microcystis aeruginosa is pH=9.0;When the value of pH is 7.0,the toxicity of Cr6+ was minimum for Chlorella vulgaris.For Scenedesmus obliquus and Microcystis aeruginosa,the toxicities were minimum at pH=9.0.At the optimal growth pH value of the algae,the toxicity of Cr6+ could reach the minimum;Microcystis aeruginosa was much more sensitive to Cr6+ than Chlorella vulgari and Scenedesmus obliquus.