Photosynthetic Toxicity And Its Mechanism Of Nano-ZnO,CTAC And Their Combined Pollution System On Chlorella Vulgaris

As the most important primary producer in the aquatic ecosystem,algae are sensitive to external environmental stress,so algae are often regarded as model organisms in evaluating the biological effects of pollutants.Nanomaterials are new materials with special functions and versatility,so their biological effects have been widely concerned by researchers.After nanoparticles being discharged into aquatic environment,they can form a composite pollution system with pollutants widely distributed in water environments,such as surfactants,however at present,the phototoxicity and its mechanism of nanoparticle and its composite pollution system are not clear.Therefore,it is necessary to investgate the biological effects of nanoparticle and its composite pollution system of algae in evaluating the biological effects of nanoparticles.In this paper,Chlorella vulgaris?C.vulgaris?,a common single-cell alga in aquatic biota,was selected as the tested organism,and ZnO nanoparticle?Nano-ZnO?was employed as the representative of the nanoparticles,and cetyltrimethyl-ammonium chloride?CTAC?was used as a representative of surfactants.The effects of Nano-ZnO,CTAC single pollution system and the composite pollution system of Nano-ZnO and CTAC on the photosynthetic toxicity effects of C.vulgaris were studied.On this basis,the biomass,oxygen evolution,oxidative damage and chlorophyll fluorescence parameters of the algae cells under the stress of single pollutant and compound pollutant were determined,and the photosynthetic toxicity and its mechanism of the pollutants to C.vulgaris were explored.This paper has obtained the following research conclusions:?1?Photosynthetic toxicity effects of Nano-ZnO on C.vulgaris as follows:when the concentration of Nano-ZnO was 0.12 mM,the growth inhibition rate of C.vulgaris was 58.8%compared with the control group?without Nano-ZnO?;the ratio of chlorophyll a to chlorophyll b and chlorophyll a to carotenoid ratio were 62.5%and44.8%of the control group,respectively.The relative electron transport rate?rETR?decreased by 46.7%and 45.4%at 96 h and 168 h,respectively.The amount of oxygen released from photosynthesis was 544.3 was reduced to 310?mol O₂/?mg·chl·h?with a reduction rate of 43%.The photosensitivity of Nano-ZnO to C.vulgaris is mainly due to its large specific surface area,which can produce strong adsorption performance in the water environment,which causes adsorption and agglomeration on the surface of algal cells,forming a shadowing effect on the algal cells.The absorption and conversion efficiency of C.vulgaris by light energy,and thus the photosynthesis process,such as photosynthetic electron transport,is weakened.?2?Photosynthetic toxicity effects of CTAC on C.vulgaris as follows:when CTAC concentration was 0.6 mg/L,the growth inhibition rate reached 79.5%compared with the control group?without CTAC?;The ratio of chlorophyll a to chlorophyll b and Chlorophyll a to carotenoid inhibition rate were 67.7%and 45.7%in the control group;rETR decreased by 55.9%and 43.7%in 96 h and 168 h,respectively;the amount of oxygen released from photosynthesis was 510.5 was reduced to 250.8?mol O₂/?mg·chl·h?,and the reduction rate is 50.9%.The reduced oxygen is converted into reactive oxygen species?ROS?in the cells,which caused the chloroplast to undergo oxidative damage,thereby affecting the photosynthesis in the chloroplast.?3?The photosynthetic toxicity effects of the composite system of Nano-ZnO and CTAC?Nano-ZnO/CTAC?has been alleviated compared with the single system,.The main performance was:in the experimental concentration range,compared with Nano-ZnO or CTAC,nano-ZnO/CTAC has reduced growth inhibition rate of C.vulgaris,which is reduced by 9%and 29%,respectively;The light energy absorption and transformation was reduced by 29%and 34%,respectively;The inhibition rate of electron transfer was reduced by 8%and 12%,respectively;The oxygen release was reduced by 5%and 12%,respectively.Combined with the influence of physicochemical properties of Nano-ZnO and CTAC in the composite system,it is known that CTAC combines with Nano-ZnO in the composite system and forms a hydrophobic layer on the surface,which reduced the aggregation of nanoparticles on the surface of C.vulgaris and reduced the physiological toxicity of Nano-ZnO and CTAC to C.vulgaris,and reduced the masking of chlorite chloroplasts by nanoparticles,which alleviated the inhibition of photosynthesis process.