The Distribution Characteristics Of Microplastics In River Water Bodies Of Shanghai And The Toxicological Study Of Plastic Microbeads On Microcystis Aeruginosa

As an emerging pollutant in the environment,microplastics(MPs)have attracted great attention from the whole society.The degradation resistance of the plastic cause the MPs to accumulate in the natural environment.At present,the pollution distribution of MPs in the water environment,and the biological effects have become research hotspots.Studies on the effects of MPs on phytoplankton have been carried out.The phytoplankton used in the experiment has various types,including marine and freshwater phytoplankton,and the toxic effects of MPs on phytoplankton are also diverse.This study is divided into two parts: in-situ investigation and indoor simulation experiment.It explores the pollution level of MPs in river systems and the toxicity of polystyrene plastic microbeads on the common cyanobacteria Microcystis aeruginosa.The research content and results are as follows:(1)We set up 65 sampling sites to investigate the distribution characteristics of MPs in the river system of Shanghai.Combined the quantitative analysis of land-use types in the buffer zone,which is a circular buffer with a radius of 500 m,the water quality and river width of the each sampling sites.The results show that MPs pollution was widespread in the river water bodies of Shanghai river system,and the abundance of MPs range from 0.7-24.3 iterms/L.Affected by the input of point-sources,the abundance of MPs at individual sites are extremely high.Overall,the spatial difference of MPs abundance in the river water bodies is small except for a limited sampling sites.Fiber are dominate MPs shape,72.7% MPs are <3mm.Fourier infrared spectroscopy(μ-FTIR)was used to detect the composition of MPs,and a total of ten types of polymers were detected,polypropylene(PP)and polyethylene terephthalate(PET)were the main components,accounting for 12.91%,37.17%,respectively.In addition,in these"MPs",non-plastic components also account for a considerable proportion,of which cotton is main type.Redundancy analysis(RDA)between the characteristic of MPs and the environmental factors found that the abundance of phytoplankton(characterized by chlorophyll a)is closely related to the shape(fragments)of the MPs,while the width of the river is closely linked to the MPs size distribution.(2)Select polystyrene plastic microbeads of different particle sizes as experimental materials,and the common cyanobacteria M.aeruginosa in freshwater environment as the experimental object.Explored the conditions of plastic microbeads of different particle sizes and concentrations,physiological and ecological response of M.aeruginosa.The plastic microbeads inhibited the growth of M.aeruginosa in the early stage of exposure,while in the late stage of the experiment,it promoted the growth of M.aeruginosa,and significantly different from the control group(P<0.01),the average maximum growth promotion rate of the plastic microbead streatment group was 80 nm,50mg/L treatment group,which reached 26.91%.During the experimental period,when M.aeruginosa were exposed to plastic microbeads,the photosynthetic activity showed an unstable and fluctuating state,but the photosynthetic activity was promoted as a whole.The content of MDA and the activity of antioxidant enzymes(SOD and CAT)showed obvious duality during the experiment cycle.At the end of the experiment,the difference between the experimental group and the control groupde were increased.The activity of SOD was higher than all experimental groups in the 80 nm,100 mg/L treatment group(P<0.05).(3)Exposed of MPs,the extracellular polysaccharide content of each plastic microbead treatment group was in a downward trend.At the end of the experiment,the CPS content of each plastic microbead treatment group was different from that of the control group(P<0.05).80 nm particle size treatment group,compared with the control group,the secreted RPS content of each concentration of plastic microbead treatment group were significantly different(P<0.01).Exposed in the environment of plastic microbead,the number of populations formed in each plastic microbead treatment group was significantly higher(P<0.05).At the end of the experiment,there were populations,over 100 algal cells,in each concentration treatment group of 80 nm plastic microbead.The determination of the content of M.aeruginosa showed that exposure to plastic microbeads increased the level of microcystin secreted by M.aeruginosa cells.From the field environment to laboratory simulation experiments,this research explores the field distribution pattern of MPs and the toxicity of polystyrene plastic microbeads on M.aeruginosa,in order to provide a basis and reference for the ecological risk assessment and pollution prevention and control of MPs pollution.