Research On The Release Characteristics Of PVC And PS Microplastics Leachate Under Different Aging Conditions And Their Adsorption Performance On Pollutants

Microplastics are plastic particles with particle size less than 5 mm,which are susceptible to weathering,mechanical wear,photooxidation,thermal oxidation and a series of effects in the environment,resulting in aging,resulting in more serious harm to the environment,has become a hot issue at home and abroad.At present,the surface morphology and structural characteristics of microplastics(MPs)and their effects on ecosystems have been extensively studied,but the release characteristics of water-soluble organic matter(DOC)and nano-plastics(NPs)during the aging process of microplastics are rarely studied.In addition,as an important carrier of environmental pollutants,microplastics may increase their influence on the migration,transformation and toxicology of pollutants after various aging effects in the environment.Thus,in this paper,commercial PVC and PS were selected as the probe microplastics for aging experiment,and the aging experiment lasted for 130 days under different aging conditions(60℃/dark,25℃/dark,ultraviolet irradiation/25℃).To explore the fragmentation and morphological changes of MPs,the characteristics of MPs-DOC and the NPs produced under UV and high temperature.Finally,taking Se4+ as the target pollutant,the adsorption mechanism of Se4+ on microplastics before and after aging was studied.It provides more information about the behavior and risks of microplastics in water environment.The main results of this paper are as follows:(1)After ageing,the total abundance of the PVC and PS microplastics decreased and the microplastic surfaces were both rougher,with visible cracks,wrinkles and pits.According to FTIR analysis,the microplastic cracking is due to the destruction of the C-O and C-Cl groups in PVC and the C-H and C-O groups in PS.Smaller plastics were formed with the extent of ageing time,especially PVC-aged treatments.Compared with the UV,high temperature was beneficial for the generation of the smaller plastics ranging from 2-100μm as a result of stronger oxidation ability.According to 2D-COS analysis of microplastics,the cracking sequence of functional groups of microplastics is different under different aging conditions.(2)The DOC releasing characteristics were related to the MP type and aging condition.However,compared with ageing conditions,the type of MPs characterized with various structure and additives was served as the dominant contributor to different trends of DOC derived from PVC and PS.The details were that DOC gradually increased in PVC aged while fluctuated as a result of adsorption-desorption equilibrium occurred on PS during ageing process.At the same time,MPs were mainly prone to release protein-like and hydrophilic substances except for 60℃ aging of PS MPs.While the high temperature and UV irradiation promoted DOC adsorption and decomposition.Additionally,8.77×1098.87×1010 and 4.06×109-3.94×1010NPs/L were detected in leachates from PVC and PS MPsaged treatments,respectively.High temperature and UV promoted the NPs release,especially UV irradiation.Meanwhile,more small sizes and rough NPs were observed in UV-aged treatments,implying higher ecological risks of leachates from MPs under UV aging.(3)Compared to the initial microplastics,Aging enhanced the adsorption of Se4+ by microplastics,especially after ultraviolet irradiation(ps adsorption:1.25 mg·g-1;pvc adsorption:1.29 mg·g-1).The sorption kinetics of the pollutant selenium on the microplastics was well described by the proposed secondary kinetic model and the sorption isotherms were more in line with the Freundlich model.With the increase of temperature,the adsorption capacity of Se4+is also enhanced,indicating that the adsorption process of these two kinds of microplastics is endothermic reaction.In summary,the surface properties and particle size changes of microplastics are affected regardless of the ageing conditions,especially in UV ageing.Moreover,this study reveals for the first time the DOC characteristics of microplastic leaching under different ageing conditions,the characterisation of nanoplastic components for identification and quantitative analysis,which helps to bridge the knowledge gap between microplastic ageing and the assessment of its potential ecological threat.Furthermore,ageing can enhance the sorption of the pollutant selenium(Ⅳ)by microplastics.Therefore,focusing on the ageing of microplastics in the environment is important for improving environmental quality and reducing secondary microplastic pollution.