Study The Response Of Freshwater Microalgae To Micro (Nano) Plastics In Water Stress

Micro?Nano?plasticsare widely distributed in freshwater environments,their impact on aquatic ecosystems and has been paid more ana more attention.We were used Microcystis flos-aquae and Chlorella pyrenoidosa as experimental objects,inquiring into the mechanism of freshwater algae in response to the stress of single microplastics?polyvinyl chloride,PVC;polypropylene,PP?,nano-plastics?nano-PVC,NPVC;nano-PP,NPP?and the above four kinds of mixed microplastics?MIX?by analyzing the response to physiological and biochemical indexes,photosynthetic activity,cell cycle and apoptosis of microalgae.The results are as follows:?1?High concentration of PVC and P P could induce the increase of ROS level in two microalgae cells,but microalgae could avoid oxidative damage by regulating the activity of antioxidant enzymes in the cells and eliminating redundant ROS.Low concentration of nano-plastics and mixed plastics had little effect on antioxidant enzyme activity,MDA content and ROS level in microalgae cells.However,under high concentration stress,the activity of CAT,SOD activity,the content of MDA and the level of ROS increased significantly,indicating that microalgae cells were damaged by oxidation.?2?Under the stress of microplastic,nanoplastic and mixed plastic,chlorophyll a content of microalgae were significantly inhibited.Under the exposure of microplastic and nanoplastic,the photosynthetic activity of the microalgae were inhibited,but can be adjusted to normal level by the self-regulation of the microalgae.However,in that proces of the mixed plastic,in the high-concentration treatment groups,the F_v/F_m,F_v/F₀,rETR,?,ETR_max,and I_k of M.flos-aquae were always inhibited,and did not return to the normal level in the later stage of the experiment.?3?Low concentration of microplastics had little effect on the cell cycle of microalgae.Under the high concentration of PVC stress,the number of microalgae cells in G₀/G₁ phase decreased,the number of microalgae cells in S phase and G₂/M phase increased.High concentration of PP treatment,the number of M.flos-aquae cells significant increased in G₂/M phase,the number of C.pyrenoidosa cells significant decreased in S phase.Under low concentration of NPVC,the cells of M.flos-aquae were mainly blocked in G₀/G₁ phase and had no effect on C.pyrenoidosa.However,the number of cells in G₀/G₁ phase,S phase and G₂/M phase decreased under high concentration of NPVC stress.At high concentration of NPP treatment,C.pyrenoidosa cells were blocked in G₀/G₁ phase.Under mixed plastic stress,the G₀/G₁phase of microalgae decreased,the S phase and G₂/M phase changed differently.When the concentration were more than 50 mg/L,it could induce the apoptosis of microalgae cells.And the higher the concentration,the higher the apoptosis rate.In addition,the apoptosis rate of microalgae cells was the highest in NPVC treatment.