Study On The Characteristics Of Microplastics In Different Environments And Their Degradation Behaviors

Microplastics?<5 mm?as an emerging pollutant have received more attention.Researches on the microplastics pollution in the marine environments have been widely carried out,while little attention was paid on the atmospheric and freshwater lake environments.Thus,the characteristics of microplastics in different environments and their degradation behaviors have been studied.In the atmospheric fallout from Dongguan city,four kinds of polymers,i.e.,polyethylene?PE?,polypropylene?PP?,polystyrene?PS?and cellulose were identified,which accounted for 73%,14%,9%and 4%,respectively.The concentration of non-fibrous microplastics and fibers in the atmospheric fallout is 213±51,189±26 and 173±23particles/m²/day from sites S1?Dongcheng?,site S2?Guancheng?and site S3?Nancheng?,respectively.According to the rate of identified samples by?-FTIR,the concentration of microplastics is 33±8,32±5 and 28±5 particles/m²/day from sites S1,S2 and S3,respectively.The average concentration of microplastics in the three sites is 31±7 particles/m²/day.Adhering particles,grooves,pits,fractures and flakes were the common patterns of degradation,indicating that microplastics have experienced different levels of chemical weathering in the atmospheric environment.In the surface water and the lakeshore sediments of Songshan Lake,microplastics have been identified and could be classified into films,fragments,fibers and foams,and mainly are the secondary microplastics.Five kinds of microplastics,i.e.,polyethylene?PE?,polypropylene?PP?,copolymer?PP-PE copolymer?,polystyrene?PS?and polyvinyl chloride?PVC?were identified,which accounted for 47%,36%,6%,9%and 2%,respectively.The concentration of microplastics from the surface water of Songshan Lake is 1.58±0.16 to3.72±0.68 items/m³ and the average concentration is 2.29±0.98 items/m³,while the concentration of microplastics from the lakeshore sediments of Songshan Lake is 139±42 to461±84 items/kg and the average concentration is 244±121 items/kg.SEM images illustrated that flakes,linear fractures,granular oxidation,adhering particles,mechanical pits and solution pits were the common patterns of degradation,and FTIR spectra showed that new absorption peaks were found in the microplastics,indicating that microplastics have experienced different levels of chemical weathering in the Songshan Lake.The concentration of Hg,Ti,Cr,Ni,Cu,Cd and Pb is 0.05-0.15 ng/g,331-2936 ng/g,8.6-122.0ng/g,7.3-25.1 ng/g,21.4-314.3 ng/g,0.14-0.86 ng/g and 19.0-66.9 ng/g,respectively.The FTIR spectra showed that new absorption peaks appeared at approximately 3300cm^-1 and 1712 cm^-1 in the weathered plastic pellets under air and ultrapure water environmental conditions after 3 months of UV irradiation,while only one set of new absorption peaks appeared at approximately 1712 cm^-1 for plastic pellets in the simulated seawater environment,indicating that hydroxyl groups(OH,³300 cm^-1)and carbonyl groups(C=O,¹700 cm^-1)developed,and plastic pellets experienced different levels of chemical weathering after UV irradiation.The Raman spectra showed that no significant changes in the weathered plastic pellets in three different environments compared with the virgin plastic pellets,but different intensities in the characteristic peaks after exposure to UV irradiation.Thus,whether the plastic pellets experienced chemical weathering in the environment could be easily identified using the FTIR spectra,but not the Raman spectra.The SEM illustrated that granular oxidation,cracks and flakes were common degradation patterns in the chemical weathering of plastics.Observations of the degradation of identical plastic pellets in three different environments revealed that the level of chemical weathering of plastic pellets was in the following order:air environment>ultrapure water environment>simulated seawater environment.The level of chemical weathering of the plastic pellets increased with the exposure time in all three environments,indicating that the UV exposure time and the environmental differences were the important factors that affected the degradation degree of plastic pellets.This study enriches the data of microplastics pollution in the atmospheric and freshwater lake environments in China,and provides references for the monitoring and control of microplastics pollution in the atmospheric and freshwater lake environments.