Toxic Effects And Mechanism Of Typical Cationic Surfactants On Chlorella Pyrenoidosa And Scenedesmus Quadricauda

The acute toxicity of 12 typical cationic surfactants to Chlorella pyrenoidosa and Scenedesmus quadricauda was investigated in the present study. Significant inhibition on algae biomass was observed and 96h EC50-value of surfactants was tested. The growth rate, contents of protein and chlorophyll in algae were monitored to determine toxicity from surfactant exposure. And the toxic mechanisms of algae were analyzed by the activities of SOD enzymes and the MDA contents of algae. The effects and possible physiological mechanisms of the surfactants on the growth of two algae were investigated in this research, by the determination of biomass, structure and enzyme activities. The acute toxicity effects of surfactants on the membrane integrality and esterase activity of algae were examined using flow cytometry (FCM). Physicochemical and quantum chemical parameters of the surfactants were calculated and the multiple linear regression (MLR) was employed to derive the quantitative structure-activity relationship (QSAR) models, by which the calculated parameters were correlated to the toxicity of surfactant(s-lgEC50) on the two green algaes. The results may offer a theoretic illustration for the various effects of surfactants on algae and give a possible evaluation of the toxicity effect to aquatic biota by surfactants.The results were summarized as follows:1)The surfactants could inhibit the growth of algae including the growth rate and the protein and chlorophyll contents significantly by time-response and dose-response. Low concentration of surfactants stimulated the growth of algae; high concentration of surfactants did the converse greatly.2)Surfactants caused more sever stress to Chlorella pyrenoidosa than Scenedesmus quadricauda, although a decrease in growth rate of algae was observed in both treatments,. The toxicity of surfactants on algae was neither linear increase by concentrations nor decrease in the order of reduced.3)With increasing the concentration of surfactants, SOD activity started to rise and then dropped. SOD had usually been implicated as the first line of defense against the potential toxicity of reactive oxygen species. The response of SOD might be coupled with the ability to protect damage from free radicals insult. Under the stress of surfactants, increasing the amounts of SOD might be a strategy to protect cells from oxidative damage, but the protection would be exhausted when exposure amount was increased to a critical value. The contents of proteins and chlorophyll and SOD activities in algae were gradually decreased while the contents of MDA in algae showed a completely increasing response. The electron microscopy and flow cytometry analyses results suggested that the surfactant first hurt in algae is damaging membrane by converting membrane lipid molecules soluble. And primary toxicity mechanism on algae cells may be related to the oxidation damage of lipid and other DNA biological large molecules caused by surfactants.4)The 16 physicochemical and quantum chemical parameters of the surfactants were calculated and the multiple linear regression (MLR) was employed to derive the quantitative structure-activity relationship (QSAR) models, by which the calculated parameters were correlated to the toxicity of surfactants pEC50 on the two green algaes. Results showed that the alkyl chain lengths (CL), principal moment of inertia X (σxx) and total connectivity (Tcon ) were the main descriptors in governing the (-lgEC₅₀) values of the QACs in the two QSAR models. The two models had high predictive ability and stability.5)The mode of the toxic mechansim of the surfactants lies in their interaction with the cytoplasmic membrane of a cell. The first step of membrane destruction is damaging by converting membrane lipid molecules soluble and then surfactants molecules adsorbe the proteins and nucleic acids. And consequently the generation of proteins and nucleic acids of algae are reduced. Finally, the cell internal structure is destroyed.