Spectroscopic Properties Of DOM In The Wei River And The Interaction Between DOM And Polystyrene Microplastics

Dissolved organic matter（DOM）are a kind of organic compounds with large molecular weight and complex structure,which widely exist in the environment.DOM can produce reactive oxygen species（ROS）under ultraviolet or sunlight irradiation.As an organic pollutant,photodegradation microplastics also widely exist in the water environment.Its special surface properties（high specific surface area porosity amorphous structure,etc.）make microplastics easy to migrate and enrich in the environment and release and transport toxic pollutants,which will cause toxic effects after being ingested by organisms.When microplastics enter the water environment,they will inevitably come into contact with DOM and interact with it,which will affect its migration and transformation or environmental toxicity in the environment.It is of great significance to study the interaction and mechanism of microplastics and DOM for understanding the migration and transformation of microplastics and DOM in the environment.In this paper,DOM pollution in the Wei River was investigated,and the source and photochemical transformation of DOM in surface water and sediment of the Wei River were studied by using three-dimensional fluorescence technology combined with parallel factor analysis.DOM from four different sources was selected to study the interaction between DOM and polystyrene microplastics（PSMPs）,and various characterization methods were used to reveal its mechanism of action.The mechanism of action,and choosing fulvic acid（FA）as a representative,studied its effect on the aging of PSMPs.The main conclusions are as follows:（1）First,we investigated the source of DOM and its photochemical transformation in the Wei River.By measuring the content of DOM in surface water and sediments,it is found that the DOC content and UV₂₅₄ value of surface water are lower than sediments.The reason is that DOM is easily adsorbed on solid particles and deposited in the sediments.Using EEM-PARAFAC technology to divide DOM into three main components and determine their sources,it was found that the DOM components in surface water were terrestrial humus（W-C1）,microbial humus（W-C2）and tryptophan-like protein（W-C3）,the DOM components in the sediment were mainly fulvic-like and humic acid.The results of simulated natural light show that the DOM in the surface water had higher photodegradation potential compared with the sediment.（2）Adsorption kinetics shows that compared with the three types of HAs,PSMPs had stronger adsorption capacity for FA.The adsorption capacity of PSMPs to DOMs followed the order as FA>SHA>JHA>FHA and adsorption data conforms to pseudo-second-order model.The adsorption isotherm shows that Freundlich model fit the observed data well for the adsorption of DOMs on PSMPs,with a high coefficient of determination.Combining FTIR spectra and 2D-COS analysis shows that PSMPs initially contact with the aromatic structure of DOMs viaÏ€-Ï€conjugation,and then are entrapped in the DOMs polymers by the carboxyl groups and C=O bonds,constituting a highly conjugated co-polymer with an increased electron density.The present work clearly shows that the PSMPs-DOMs interaction affects the surface morphology and the surface chemistry of PSMPs.（3）The effect of ROS generated by DOM with or without light on the aging effect of PSMPs was studied,combined with the carbonyl index to reflect the aging degree of PSMPs.FA generates more·OH radicals than three types of HA,which makes PSMPs more aging.Ultraviolet light will promote the generation of·OH radicals in the reaction process,leading to indirect photoaging of PSMPs,resulting in increased oxygen-containing functional groups on the surface of PSMPs.The coexistence of FA and UV light makes the aging intensity of PSMPs higher than FA alone and UV light alone.Inhibition of the generation of·OH will reduce the aging effect of FA on PSMPs.