Interaction Behaviors And Mechanism Between Microplastics And Arsenic

Microplastics（MPs,plastic particulates with size less than 5 mm）are pervasive in various environmental media.Owing to hydrophobicity and large specific surface area,MPs could be regarded as carriers for transferring large amounts of contained plastics additives and contaminants into the surrounding environment,causing potential ecological risks,threatening human health and survival of animals.A large number of studies on risk of combined pollution and interaction behaviors between MPs and pollutants have shown that MPs are the wind vane of migration of environmental pollutants.However,few researches are relevant to the interaction between MPs and metallic pollutants.Arsenic（As）is a metalloid element that is extensively distributed in several physicochemical forms in different environmental substrates,posing serious ecological toxicity and risk.Thus,the comprehensive researches of interfacial sorption behaviors between three types of PE MPs and arsenic in four forms in water matrix was investigated in order to explore the mechanisms of the interaction behaviors between contaminants and MPs.On this basis,the soil pollution of MPs and inorganic arsenic was further investigated.The results will provide a solid theoretical basis to comprehensively assess the environmental risk of MPs.The main contents and conclusions are as follows:（1）Interfacial behaviors between PE MPs and arsenic in four forms in water matrix.Three different kinds of PE MPs and arsenic in four forms（As（III）,As（V）,ROX and p-ASA）were selected,including black PE film fragments,white PE film fragments and pure LDPE MPs.Impacts of physicochemical characteristics and environmental conditions on sorption/leaching properties were explored by conducting the sorption/leaching experiments of inorganic/organic arsenic on three types of PE MPs in water environment.The results revealed that fragments of black PE film have the highest sorption for binding inorganic arsenic and organic arsenic due to the high point of zero charge,the high accessibility of amorphous domain and the presence of additives（Ca CO₃ and Ti O₂）.No significant difference was found in sorption of arsenic on LDPE and fragments of white PE film,demonstrating that all physicochemical properties of MPs contributed to the sorption behaviors between arsenic and MPs in water.In addition,the adsorbed arsenic could be continuously desorbed at low doses into the surrounding environmental media.And the change of external environmental conditions would will directly affect the interaction between MPs and arsenic,including p H,salinity,coexisting contaminants and the different water bodies.Therefore,plastic particles can serve as transportation vectors for arsenic,resulting in potential risks to the ecological environment.（2）Interfacial behaviors between MPs and inorganic arsenic in soil.In order to comprehensively evaluate the potential ecological risks of MPs as carriers for toxic chemicals within soil environment,sorption and desorption behaviors between arsenic and four types of MPs were investigated.Aiming to explore the impact of environmental aging on physicochemical properties and environmental behaviors of MPs,virgin fragments of black PE film and PLA were exposed to artificial aging conditions.Thus,four different kinds of MPs and inorganic arsenic in two forms（As（III）and As（V））were selected,including PLA,aged PLA,black PE film fragments and aged black PE film fragments.The results demonstrated that the specific surface area,surface hydrophobicity,point of zero charge and crystallinity of PLA MPs were changed by artificial aging,but only the point of zero charge of black PE film fragments were changed by aging.Furthermore,the sorption capacity of inorganic arsenic on soil-MPs system was enhanced by the addition of PLA,aged PLA and aged PE MPs,while obviously deteriorative arsenic sorption capacity on soil-MPs system was observed.The interaction between inorganic arsenic and soil-MPs mixed system would be influenced by the variation of environmental conditions including p H,salinity and co-existing organic matter.Besides,adsorbed inorganic arsenic desorbed persistently in the aqueous environment and simulated body fluid environment,so the potential risk of MPs cannot be ignored.The interaction between MPs and arsenic substances in different environmental media was explored,aiming to provide theoretical basis for environmental risk prediction of MPs and supply data for the management of plastic production in the future.