Toxic effects of chromium(Cr~(6+)) on Chlorella vulgaris and Scenedesmus obliquus at different pH

Objective:The toxicological effects of hexavalent chromium(Cr6+) on the growth of freshwater green algae,Chlorella vulgaris(C.vulgaris) and Scenedesmus obliquus(S.obliquus) were investigated at different pH levels in order to provide references to the scientific establishment of water quality criteria and standard in China.Methods:According to the OECD guidelines for the testing of chemicals,freshwater alga and cyanobacteria growth inhibition test(OECD-201),taking 72 h biomass as the endpoint,the algal inhibition tests were conducted.Results:The alga grew differently at different initial pH levels,and the optimal growth pH of C.vulgaris was pH = 7.0,while the optimal pH =9.0 for S.obliquus.At different initial pH levels,Cr6 + had the stimulating effects on both C.vulgaris and S.obliquus when the concentrations were lower than 0.1 mg·L-1,and the inhibition effects were observed when the concentrations of Cr6 + were higher than 0.5 mg·L-1.The inhibition effects grew stronger with the increasing of the Cr6 + concentrations.For C.vulgaris,the toxicity of Cr6 + was minimum at pH =7.0,and maximum at pH =8.0.For S.obliquus,the toxicity of Cr6 + was minimum at pH = 9.0,and maximum at pH = 7.0.Conclusion:The toxicity of Cr6 + is minimum at the optimal pH of the algae.