| Microplastics(MPs)are the source of pollutants and the carrier of pollutants,which could affect the migration of organic pollutants in the aquatic environment.At present,MPs have become the study focus for many scholars.The spatial-temporal distribution and ecotoxicity of MPs have been studied.However,information of the effect of MPs on organic pollution migration is limited,especially for the desorption of organic pollutants from MPs.A sampling campaign was conducted in the Pearl River basin.The shape,size,color,and type of MPs were determined through qualitative and quantitative analysis,indicating the pollution level and distribution characteristic of MPs.The concentration of typical organic pollutants,polycyclic aromatic hydrocarbons(PAHs),in the water phase and that affiliated with MPs were also analyzed.Lastly,polyvinyl chloride microplastics(PVC-MPs)and PAHs(naphthalene,phenanthrene,anthracene and pyrene)and their hydroxy derivatives(hydroxyphenanthrene and hydroxyanthracene)were selected as the research objects.The adsorption and desorption behaviors of PAHs and their hydroxy derivatives on MPs were investigated through batch experiments and model fitting analysis,further demonstrating the interaction mechanism between MPs and target organic pollutants.Our study helps to better understand the influence of MPs on hydrophobic organic pollutants in the aquatic environment and to systematically evaluate the ecological risk of MPs.The main results of this thesis are shown as follows:(1)The average abundance of MPs in the surface water of the Pearl River basin was 0.26-0.65 items m-3.In terms of the morphology of MPs,debris was the most with the proportion of 40.4%,followed by thin films(13.7%).White MPs accounted for 29.8%of the MPs,and black MPs were the second-largest MPs(21.2%).Most of the particle sizes of MPs were less than 2 mm(94.8%).Polyethylene(42.11%),artificial fiber(28.22%),and polypropylene(21.95%)were the main polymer types.PAHs with less than five rings were the main pollutants affiliated with riverine microplastics.The concentrations of MPs-affiliated PAHs ranged from 171.6-476 ng L-1,while those of PAHs in surface water were 127.25-272.2 ng L-1.Therefore,higher concentrations of PAHs were found in MPs,revealing the role of MPs in organic pollutant migration.(2)In order to study the effect of aromatic ring number on the adsorption and desorption of pollutants on PVC-MPs,naphthalene(NAP),phenanthrene(PHE),anthracene(ANT),and pyrene(PYR)were selected as the target pollutants.The adsorption mechanism of PVC-MPs for NAP,PHE,ANT,and PYR was clarified by.traditional adsorption experiments,characterization techniques,and theoretical calculation.The results showed that hydrophobicity was responsible for the adsorption process.The adsorption of NAP,PHE,ANT and PYR on PVC-MPs conformed to the pseudo-second-order kinetic and Freundlich isotherm models and was spontaneously exothermic.The adsorption efficiency and adsorption amount of NAP,PHE,ANT and PYR on PVC-MPs increased with the increasing aromatic ring number.Under the condition of pH=1.5,the desorption efficiency of NAP from PVC-MPs in the simulated gastric juice environment was the highest among target PAHs.(3)The adsorption of phenanthrene(PHE)and its monohydroxy derivatives,including 1-hy droxylphenanthrene(1-OHP),2-hydroxylphenanthrene(2-OHP),4-hydroxylphenanthrene(4-OHP)and 9-hydroxylphenanthrene(9-OHP),on PVC-MPs were studied in aqueous solution.The results showed that the adsorption efficiency of PHE was higher than that of OHPs.A better fit for pseudo-second-order kinetic and Freundlich isothermal models was obtained,suggesting different binding sites on the surface of PVC-MPs.The adsorption process of PHE and OHPs on PVC-MPs was exothermic and spontaneous.Combined with FT-IR analysis,theoretical calculation and comparative adsorption experiments,hydrophobicity was shown to be the primary mechanism in the adsorption process.On the contrary,electrostatic repulsion,CH-? interaction and halogen bonding had fewer effects on the adsorption of PHE/OHPs on PVC-MPs.(4)In order to study the effect of hydroxyl group content on the adsorption and desorption of pollutants on PVC-MPs,anthracene and its hydroxyl derivatives(OHAs),including 2-hydroxyanthracene(MOHA),2,6-dihydroxyanthracene(DOHA)and 1,8,9-trihydroxyanthracene(TOHA)were selected as the target pollutants.Batch adsorption experiments were used to clarify the adsorption and desorption behaviors of ANT and OHAs on PVC-MPs and characterization techniques and theoretical calculation were applied to explore the interaction mechanism.The results showed that the adsorption of ANT and OHAs on PVC-MPs conformed to the pseudo-second-order kinetic model and was spontaneously exothermic.The adsorption efficiency of PVC-MPs followed the order of ANT>MOHA>DOHA>TOHA,indicating that increase in hydroxyl substitution degree will inhibit pollutant adsorption on PVC-MPs.Conversely,the release amounts of MOHA from PVC-MPs into simulated gastric fluids were higher than those of ANT.Experimental and computational results suggested that the affinity of ANT/OHAs to PVC microplastics was the most likely outcome in hydrophobic effect,electrostatic repulsion and CH-?interaction forces.Our results show evidence for the toxic chemicals affiliated with MPs in the aquatic environment,help evaluate the ecological risk of MPs and provide a reference for the pollution control of MPs by the local government.These findings clarify the influence of pollutant characteristics,including aromatic ring number and hydroxyl group content,on the adsorption and desorption of MPs,providing crucial scientific guidance for the investigation of interface behavior of MPs. |
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