Study On The Joint Toxicity Of Cd²⁺ And Cu²⁺ To Fluorescence Law Of Algal

Common heavy metal Cd²⁺ and Cu²⁺ were selected as target pollutants in this work,and microcystis aeruginosa as testing plant.The effect of the single toxicity and joint toxicity to the microcystis aeruginosa fluorescent indexes（chlorophyll fluorescence intensity,chlorophyll a concentration of fluorescence intensity）,cell index（algal density,content of chlorophyll a,cell morphology）and molecular index（SOD activity,algal blue protein）under the constant temperature,humidity and photoperiod,and the relationship among the three aspects were investigated.The toxicity of water quality detected by the algae fluorescent is of theoretical and practical significance.The results were listed as follows:1)The single toxicity experiment of heavy metal showed that different heavy metals generate different toxicity effects to microcystis aeruginosa with the order of Cd²⁺ < Cu²⁺.2)Joint toxicity of heavy metals on the algae density and chlorophyll a content of microcystis aeruginosa showed a dose-effect relationship.Algal density and chlorophyll a content in the exposed group were less than the control group,and the inhibition effect was enhanced with the increasing exposure concentration;The algal cell morphology changed after exposure of heavy metal.Cells were broken,dissolved and accumulated,resulting in the change of other indicators.3)Because the chlorophyll a content changed with the different concentrations of heavy metals,the fluorescence intensity of the extracted chlorophyll a changed.The research indicated that the fluorescence intensity of the extracted chlorophyll a matched well with the chlorophyll a content determined by the spectrophotometer.As the change of different exposure concentration of heavy metals,the photosynthesis of microcystis aeruginosa was subjected to different inhibition,which affected the fluorescence intensity of the microcystis aeruginosa.In the composite exposure experiment,lower concentrations of Cd²⁺(<0.2 mg·L^-1)induced fluorescence intensity raised at first and declined later,and higher concentrations(≥0.2 mg·L^-1)made fluorescence intensity decreased with time.4)In the compound exposure experiment,lower concentrations of heavy metals increased the SOD activity.However,SOD activity decreased with the increasing exposure concentration.Joint toxicity of heavy metals inhibited the synthesis of algal blue protein,and the inhibitory effect got more obvious with the increasing exposureconcentration.The heavy metal cadmium(Cd²⁺)and copper(Cu²⁺)showed synergetic stress to microcystis aeruginosa.The algae density,content of chlorophyll a,chlorophyll a fluorescence intensity and algal blue protein content of microcystis aeruginosa showed a negative correlation relationship with concentration of heavy metal compound.Fluorescence intensity was positively correlated with the above parameters when it wasn’t damaged but had a certain influence on microcystis aeruginosa.When heavy metal had certain influence on microcystis aeruginosa,it showed positive correlation first and negative correlation later with the above parameters as time changes with cellular structure damaged.The inhibition level of fluorescence intensity was positively related to superoxide dismutase（SOD）activity and damage extent of the cellular structure,thus heavy metal stress on the microcystis aeruginosa can be reflected by the change of the fluorescence properties.