The Distribution Characteristics Of Microplastics In The Sediments Of The Chongqing Section Of The Fujiang River And Their Adsorption Behaviors For Typical Antibiotics

At present,the research on pollution in microplastics mainly focuses on the marine environment,but the fresh water system is an important source of marine plastics,but it has not been paid enough attention.Sediments are an important gathering place for microplastics,and it is of great significance to investigate microplastics in sediments in freshwater environments.China is a big country in the production and consumption of antibiotics.microplastics and antibiotics are ubiquitous in the water environment,The physical and chemical properties of microplastics,such as large specific surface area and strong hydrophobicity,make it adsorb antibiotics.Studying the adsorption behavior and mechanism of antibiotics in microplastics can deeply understand the environmental risks in microplastics,and has important scientific significance for clarifying the compound pollution of microplastics and antibiotics.Therefore,this thesis investigated the distribution of microplastics in the sediments of the Chongqing section of the Fujiang River.Analyzes the shape and color characteristics of microplastics in the sediments of Chongqing section of Fujiang River,compares the abundance difference of microplastics among sampling points,and points out the distribution characteristics of microplastics in the sediments of this section of Fujiang River.And selected polyethylene(PE),polystyrene(PS),polyvinyl chloride(PVC)three microplastics and tylosin(TYL),tetracycline(TC)two antibiotics as indoor control experimental research materials.With different microplastics concentration and salinity as influencing factors,microplastics was characterized by scanning electron microscope and Fourier transform infrared spectrometer.Through kinetic adsorption experiment and isothermal adsorption experiment,the adsorption model was used to fit the experimental results,and the possible adsorption mechanism was analyzed.The main research results are as follows:(1)The abundance of microplastics in the sediments of Chongqing section of Fujiang River ranges from 11 to 221 n/kg,with an average abundance of 75 n/kg.There are differences in spatial distribution.Generally speaking,the more densely populated and active people are,the more microplastics content is in regional sediments.The shape ratio of detected microplastics is:fiber>film>fragment>foam>microbeads,and the color ratio is:white>black>transparent>red>green>orange.Results show low levels of microplastic pollution in sediments in the region.(2)The surface morphology of the microplastics used in the adsorption experiment was observed by scanning electron microscopy.The specific surface areas of the three microplastics were:PE>PS>PVC,where the specific surface area of PE was 2.25 m~2/g,the specific surface area of PS was 1.40 m~2/g,and the PVC The specific surface area is1.34 m~2/g.The crystallinity of the microplastics was analyzed by X-ray diffractometer,and the crystallinity of the three microplastics was PE>PS>PVC.The potential of microplastics at different p H values was measured by a Zeta potential analyzer,and the Zeta potential zero-charge points(p Hpzc)on the surfaces of PE,PS,and PVC were obtained,which were 6.63,6.69,and 6.65,respectively.(3)The adsorption capacity of microplastics for TYL is PVC>PE>PS,and the adsorption capacity for TC is PVC>PS>PE.By fitting the kinetic adsorption results,it is found that the pseudo-second-order kinetic model has the highest fitting degree.The adsorption of antibiotics on microplastics has both chemical adsorption and physical adsorption.The adsorption behavior is influenced by many factors.By fitting the isothermal adsorption results,it is found that Freundlich model has the best fitting effect.The adsorption sites distributed on the surfaces of three microplastics are uneven,and the adsorption process is nonlinear.Besides hydrophobic partition,there are other functions in the whole adsorption process.Fourier transform infrared spectroscopy(FTIR)was used to analyze the microplastics before and after adsorption,and no new functional groups were found,which indicated that the adsorption was mainly physical adsorption.It is speculated that the main mechanisms of microplastics’s adsorption of antibiotics are hydrophobic partition,micropore filling and Van der Waals force,and there may also be surface complexation andπ-πinteraction.(4)Increasing the dosage of microplastics will reduce the adsorption of antibiotics per unit mass of microplastics,but the total amount of adsorption will increase.And,with the increase of microplastics concentration,the reaction is more likely to occur.Increasing salinity slightly inhibited the adsorption of TYL on microplastics,but had little effect on the adsorption of TC.