Study On The Adsorption Behavior Of TCAs On Microplastics

In recent years,microplastics,pharmaceutical and personal care products（PPCPs）have been become a new type of pollutant in which pollution problems they result a global concern as they are frequently detected in the environment.Particles smaller than 5 mm in size are usually defined as microplastics.In addition to their own environmental health risks,microplastics can also act as carriers of PPCPs-like organic pollutants in water,which not only affects the migration and dispersion of pollutants in the environment,but also causes the problem of compound pollution.Antidepressants belong to a class of PPCPs,and about 300 million people worldwide had deep depressive symptoms in 2015.Especially for the past few years,the more challenges from the new COVID-19 have been a serious threat to people’s mental health,thus leading to an increase in the potential use of antidepressant drugs.Therefore,studying the adsorption behavior of microplastics on PPCPs is important to assess and reveal the environmental risk,and elucidate the potential toxicity mechanisms of microplastics.In this paper,we first carried out a survey and analysis of microplastic pollution in South Lake,which has been influenced by people’s daily life.Based on the results of the survey,polystyrene（PS）microplastics and tricyclic antidepressants（TCA）were selected as the research objects to investigate the adsorption behaviors and mechanisms of microplastics on different types of TCA drugs such as amitriptyline hydrochloride（AMI）,clomipramine hydrochloride（CLO）and nortriptyline hydrochloride（NOR）.To further investigate the interaction between microplastics and organic pollutants in real environment,microplastics were in different processes of aged,and the adsorption mechanism of microplastics and AMI in the environment was simulated by changing the background solution conditions.The main research contents and conclusions of this paper are as follows.（1）The type,morphology and quantity of microplastics in sediments were analyzed by distributing sampling in the coastal zone of South Lake.The results showed that the morphology of microplastics in the sediments of South Lake was mainly in the form of shape,film and fiber,and the concentration of microplastics was higher in the area near the living and dining area（QY3）,ranging from 76-5853 n·kg^-1.The types of microplastics in the sediment were identified by Fourier transform attenuated total reflection infrared spectroscopy（ATR-FTIR）,which mainly included polyvinyl chloride,polypropylene,polycarbonate,polystyrene,and polyethylene.（2）To investigate the interaction between PS and TCA drugs,the physicochemical properties of PS were characterized and analyzed by Zete potential,SEM and contact angle tests,and the adsorption behaviors between PS and AMI,CLO,NOR were analyzed kinetically and thermodynamically.The results showed that the isoelectric point of PS was p H=3.81,the contact angle was 84.3°,and the surface was smooth with certain hydrophobic properties.The kinetic process was dominated by intraparticle diffusion,and the adsorption isotherms of PS on AMI,CLO,and NOR were more consistent with the Freundlich model,with the fitted parameter n values ranging from 0.5 to 0.9,indicating that the adsorption process was nonlinear.The adsorption of AMI by PS was significantly greater than that of NOR and CLO,at least 2.28 times greater than theirs,which was mainly due to the lower p Ka value relative to the other two drugs,AMI was easy adsorbed on PS surface when the p H kept at 6.5,and more prone to brittle cracking at the tail of the tricyclic.（3）To explore the mechanism of the adsorption about microplastics and organic pollutants in the real environment,PS was aged by UV irradiation and high temperature.The morphology of PS before and after aging was characterized and analyzed by SEM,nitrogen adsorption and desorption,contact angle test and infrared spectroscopy.The results showed that every aging methods resulted in smaller particle size,pits,folds and pores on the surface,increased specific surface area and the amount of oxygen-containing functional groups of PS,but the UV-aged PS was more obvious.One more step to acquire the adsorption characteristics of aged PS on AMI,we conducted experiments on adsorption kinetics,isothermal adsorption and the effect of salinity（natural seawater,simulated seawater and pure water）.The results showed that the adsorption rate of AMI by PS after aging was increased compared with the original PS,and the kinetic process was in accordance with the quasi-secondary kinetic and intraparticle diffusion models,and the adsorption process was controlled by intraparticle diffusion and surface adsorption.The adsorption rate of AMI by PS increased after high temperature and UV aging,which were 1.24 and 1.33 times of the original PS.In different background solutions,the adsorption capacity of aged PS in AMI was pure water>simulated seawater>natural seawater,indicating that PS has a stronger loading capacity for AMI in low-salt environments and more likely to cause migration and diffusion of contaminants.