Effects Of Heavy Trace Metals On The Cell Multiplication And Fluorescence Of Scenedesmus Obliquus

Algae play an important role in monitoring and assessing the water quality of natural water bodies. Chlorophyll fluorescence technology is a new technique developed recently to study the biological effects of heavy metals to algae. It is helpful to biological monitoring and bioremediation of heavy metal pollution in water environment. It would be a promising biological monitoring index, and could reveal the toxic mechanisms of heavy metals to the algae. In this study, the effects of different concentrations of heavy metal ions (Cd2+,Mn2+,Zn2+) on the absorbance (OD680),chlorophyll a (Chi a) concentration,no observed effect concentration (NOEC),growth inhibition rate and maximal photochemical efficiency (Fv/Fm)of Scenedesmns obliquus were investigated, and the main results are as follows:1. One-Way ANOVA analysis of variance showed that different concentrations of Cd2+,Mn2+ and Zn2+ had significant effects on the absorbance (OD680),chl a concentration and Fv/Fm value of Scenedesmus obliquus (P<0.05).2. It was found that the no observed effect concentration (NOEC) of Cd2+ Mn2+,Zn2+ on Scenedesmus obliquus could be ordered as Mn2+>Zn2+> Cd2+ Consequently, the toxicity of Cd2+,Mn2+,Zn2+ was ordered as Cd2+>Zn2+> Mn2+Heavy metal ions Cd2+was the most toxic to Scenedesmus obliquus. The no observed effect concentration (NOEC) on maximal photochemical efficiency (Fv/Fm) was 0.001 mg/L, which suggested that low doses of Cd2+could lead significant changes to Fv/Fm. Trace elements zinc (Zn) and manganese (Mn) were necessary to the algae growth. The experimental results demonstrated that the suitable ranges of Mn and Zn concentrations were 0.5-10 mg/L and 1-10 mg/L for Scenedesmus obliquus, respectively. However, the growth of Scenedesmus obliquus would be inhibited, when the concentrations of Mn and Zn exceeded the suitable ranges.3. Maximal photochemical efficiency (Fv/Fm) was sensitive to the concentration change of cadmium (Cd) and zinc (Zn) before 48 hour, Fv/Fm may be used for evaluating the Scenedesmus obliquus adaptations to cadmium (Cd) and zinc (Zn). Compared with Fv/Fm, concentration of manganese, the absorbance (OD680) and chl a concentration were more sensitive to the concentration of manganese (Mn). A significant change was found when the concentration of manganese (Mn) was 100 mg/L. Fv/Fm value was not suitable for evaluating the Scenedesmus obliquus adaptations to manganese (Mn).There still needs further study to determine the reliability and flexibility and whether maximal photochemical efficiency (Fv/Fm) can directly be used as heavy metals evaluation index.