Sorption Behavior And Mechanism Of Typical Pesticides On Microplastics

Microplastics(MPs)have been becoming a new global challenge,and increasing evidence shows that MPs can adsorb organic pollutants which may affect their distribution and bioavailability.Investigating the sorption mechanism of between microplastics and organic pollutants provides a theoretical basis for the assessment of biological toxicity.However,the majority of sorption studies focus on conventional nondegradable microplastics,the difference in sorption mechanism of pesticides on biodegradable microplastics are largely unknown.In this study,two types of biodegradable[polylactic acid(PLA),polybutylene succinate(PBS)]and four types of nondegradable[polyethylene(PE),polystyrene(PS),polyvinyl chloride(PVC),polypropylene(PP)]microplastics were selected to investigate the sorption behaviors of fipronil.In this study,two types of biodegradable[polylactic acid(PLA),polybutylene succinate(PBS)]and four types of nondegradable[polyethylene(PE),polystyrene(PS),polyvinyl chloride(PVC),polypropylene(PP)]microplastics were selected to investigate the sorption of fipronil.In order to verify the reliability of sorption mechanism,the target peticides were expanded to four fungicides onto microplastics.Three microplastics and two fungicides were selected to further investigate the effects of environmental factors in the sorption process Considering the hydrophobicity of microplastics and the variety of environmental pollutants,sorption capacity of microplastics and enrichment level of organic contaminants on microplastics were systematically evaluated through the integration and analysis.The main results are as follows:(1)Investigating sorption of fipronil on six microplastics,the resutls showed that sorption rates of biodegradable microplastics were higher than 1.42-6.18 times nondegradable microplastics,and soprtion capacities followed the order of PBS>PLA>PS>PE>PP>PVC.Sorption kinetics of fipronil onto microplastics followed the pseudo-second-order kinetic model(R2=0.953-0.998).Sorption process is controlled by three stages,and external mass transfer and intraparticle diffusion are the main rate controlling steps of the sorption of fipronil on microplastics.The isotherm results showed that Langmuir model(R2=0.997-0.999)is best suited to describe sorption isotherms of fipronil on PE,PP,PS,and PVC,while Freundlich model(R2=0.998-0.999)is the best model on PLA and PBS.The presence of surface oxygen-containing functional groups and spatial arrangement of rubberry domains may affect the sorption process.(2)Sorption of typical fungicides on microplastics showed that biodegradable microplastics PBS had the strongest sorption capacities for four fungicides,and their sorption capacity was 104.21 ?g/g for triadimefon,80.39?g/g for triadimenol,104.83 ?g/g for myclobutanil,and 188.35 ?g/g for difenconazole,respectively.Sorption kinetics fitted the pseudo-second-order kinetic model.The influence of environmental factors on the sorption of triadimefon and difenoconazole on PE,PVC and PBS showed that salinity had no significant influence on the sorption of difenoconazole on microplastics,but increased triadimenfon sorption on microplastics,which might be the salting-out effect of organic contaminants.pH had no effect on the sorption of the two fungicides on microplastics,indicating that the sorption process is not affected by electrostatic effects.The presence of humic acid and fulic acid reduced the sorption capacity of fungicides on microplastics,which may be caused by pore blockage and pore filling.(3)Statistical analysis and meta analysis showed that the sorption amounts of PE and PS varied greatly.The Qe range was(3.74×10-6)-46.15 mg/g and(3.46×10-6)-18.43 mg/g,and the Qmax ranges are(1.82×10-5)-6800 mg/g and(6.11×10-6)-5200 mg/g,respectively.The median sorption capacities of PE,PS,PVC,PP and PA had insignigicantly changed,and the average values differed greatly,indicating that the mean values cannot explain the sorption level well.The sorption capacity of PP was the lowest(0.56 mg/g),and PP and PA had not was not selective(p>0.05).Meta analysis indicated that sorption capacities of rubberry microplastics on organic pollutants were higher than those of glassy microplastics.The effect size of different microplastics was as follows:PE?PVC?PS>PP>PA.Sorption of microplastics is closely related to the hydrophilic and hydrophobic properties of organic pollutants,and follows the following order:High(logP>3)>Medium(3>logP>1)>Low(1>logP).