Study On The Toxic Effect Of Cd²⁺ To Five Common Freshwater Phytoplankton

Heavy metal pollution has become a global environmental problem, after it into the water can cause serious threat to the aquatic ecosystems, and algae is more sensitive to heavy metal stress than other aquatic creatures, they can faster response to changes in the environment, at the same time algae itself can adsorption and transport of heavy metals, it has become the ideal and important creatures for environmental monitoring of water and heavy metal pollution prevention. In this paper, Microcystis aeruginosa?Scenedesmus quadricauda?Chlorella pyrenoidosa?Cyclotella hebeiana?Nitzschia palea as the research object, from algae growth conditions, changes in protein content, enzyme activity, chlorophyll fluorescence characteristics, studied the five kinds of algal physiological and biochemical response to heavy metals Cd²⁺ stress. The main research conclusions were as follows:?1? A certain concentration of Cd²⁺ would inhibit the growth of algae, by the methods of Alga growth inhibition test, measured the 96 h-EC₅₀ of Microcystis aeruginosa?Scenedesmus quadricauda?Chlorella pyrenoidosa?Cyclotella hebeiana?Nitzschia palea were 0.302 mg·L^-1?1.80 mg·L^-1?5.60 mg·L^-1?0.120 mg·L^-1?0.030 mg·L^-1, compare the 96h-EC₅₀, could draw on the strength of heavy metal Cd²⁺ toxicity of different algae species: Nitzschia palea > Cyclotella hebeiana >Microcystis aeruginosa > Scenedesmus quadricauda > Chlorella pyrenoidosa. This indicated that, the Nitzschia palea of Bacillariophyta was most sensitive to heavy metals Cd²⁺.?2? In 0.025 1.60 mg·L^-1 concentration range, heavy metals Cd²⁺ could significantly inhibit the growth of Microcystis aeruginosa, and with the increase of concentration, the inhibition degree increased. At 96 h-EC₅₀ concentration, Cd²⁺ on Scenedesmus quadricauda and Chlorella pyrenoidosa showed significant growth inhibition, and with the continuation of the action time, this inhibition was more obvious, its later period?after 72 h? biomass showed a downward trend. And when Cyclotella hebeiana?Nitzschia palea were stressed by Cd²⁺, throughout the culture process with respect to the control group basically showing inhibition state, but the biomass showed a trend of growth. This difference might be due to different binding sites of Cd²⁺ on Chlorophyta and Bacillariophyta.?3? When it stressed by the Cd²⁺ of 96 h-EC₅₀,by analyzing the TP of algae, can also preliminarily concluded that Nitzschia palea was most sensitive to heavy metals Cd²⁺, the EC₅₀ concentration of Cd²⁺ treatment might lead to cell damage and changed its permeability of cell membranes.?4? When the Chlorella pyrenoidosa and Scenedesmus quadricauda stressed by the Cd²⁺ of EC₅₀, the two algal responsing to oxidative stress made the stress response, SOD changed obviously, so the SOD activities could be taken as the sensitive and efficient indicators when evaluating the toxicity of heavy metals.?5? Under Cd²⁺ stress of 0.025?0.100?0.400?0.800?1.60 mg·L^-1, photosynthetic physiological characteristics of Microcystis aeruginosa were subject to different degrees of impact, chlorophyll fluorescence characteristics Fv/Fm, Y[II], ETR, qP had almost the same change trend, all showed a trend of decline. At the same time, under the stress of the Cd²⁺(EC₅₀), the photosynthesis of other four algae was affected by different degree. For two kinds of chlorophyta algae, the fluorescence parameters Fv/Fm, Y [II], ETR trended consistently and reduced compared with the control group; For the other two Bacillariophyta, Fv / Fm, Y [II], ETR, qP trended basically the same, but the Nitzschia palea Stressed by the Cd²⁺, its Fv / Fm, ETR within a certain period of 48 h nearby, were slightly higher than the value of control group.In this study, the stress effect of Cd²⁺ on the five different algae were clearly discussed, and these results could provide a theoretical basis for the exploitation of algae biomarkers and the treatment for heavy metals pollution.