Adsorption Behavior Of Nitroaromatic Compounds By Microplastics In Freshwater And QSAR Prediction Study

Recently,researchers in the world have paid more attention to the problem of microplastics pollution.Due to the physical properties of microplastics,they will adsorb other environmental pollutants,which will affect the environmental fate and toxic effects of organic pollutants.Polyethylene?PE?and chlorinated polyethylene?CPE?are two important microplastics and they can pose risks to the water environment,especially to freshwater because of their wide range of application.However,the related reports on PE and CPE microplastics in freshwater were still very limited.Therefore,two commercial microplastics,PE and CPE,were chosen as the absorbing materials to absorb 5 nitroaromatic compounds?1,3-dinitrobenzene,2,4-dinitrochlorobenzene,p-nitrotoluene,o-nitrotoluene and nitrobenzene?and the thermodynamic process of adsorption was studied by linear and Freundlich adsorption isotherm models to investigate the adsorption mechanism of microplastics on nitroaromatic compounds.At the same time,a total of 29 equilibrium partition coefficients?K_d?of organic pollutants between microplastics and freshwater were obtained by absorption experiment and literature collection.A QSAR model for predicting the K_d values of organic pollutants on PE microplastics was constructed according to the theory and method of QSAR.The main factors affecting the adsorption were explored from the perspective of compounds structure.The detailed results are as follows:1.The adsorptions of nitroaromatic compounds on PE and CPE microplastics can be fitted very well using linear and Freundlich isotherm models.The n values of Freundlich isotherm model are approaching to 1,indicating that the adsorption of nitroaromatic compounds on PE and CPE microplastics are linear.The adsorption is mainly decided by the partition in two phases.2.The trends and the ability of adsorption by PE and CPE microplastics are similar.The reason is that PE and CPE microplastics are non-polar materials and hydrophobic.However the nitroaromatic compounds are polar compounds.The interaction between nitroaromatic compounds and PE or CPE microplastics is weak and difference between them is not significant.3.Five K_d values of nitroaromatic compounds between PE microplastics and freshwater were obtained through experiments.At the same time,some K_d values of organic compounds between PE microplastics and freshwater were collected from literatures.A total of 29 K_d values were used to develop the QSAR model based on the QSAR guidelines.The model was:lgK_d=-2.315+0.663 logK_ow+7.241 E1v.According to the statistical parameters of the model,the model has good fitness?R²=0.968?,high robustness(Q²_Loo=0.955,Q²_Boot=0.793)and prediction ability(R²_ext=0.970).From the model descriptors,it can be concluded as follows:the positive coefficients of descriptors in the model indicate that the adsorption capacity is closely related to the molecular hydrophobicity and volume.The greater hydrophobicity and the larger van der Waals volume for a compound suggest the stronger adsorption capacity on PE microplastics,leading to greater the potential harm to the environment and human health for the compound.