Typical Heavy Metals Adsorption On Microplastics And Their Desorption In Gastrointestinal Environment

Microplastic（MP）as a new type of pollutants has gained great attention.It is mainly because of that MPs can adsorb toxic pollutants such as heavy metals from environment.The microplastics can enter the organism bodies through food chain,and then desorbed in organisms’gastrointestinal.It thus causes potentially harmful effect on organisms’body.This study mainly discussed the effects of different aging microplastics on adsorption of Cu²⁺and Pb²⁺by typical MPs（polypropylene PP,polyethylene PE,polyamide PA）;and discussed the influencing factors of desorption in simulated gastrointestinal environment preliminary.Three aging methods including ultraviolet aging,heat aging,and natural aging were chosen to age MPs.The observation of the MPs before and after aging showed that the surface of the microplastics appeared peeling and dents after aging.The specific surface area of the MPs after UV aging was 31.1%higher tha n that of the new MPs,the pore volume of the MPs after thermal aging was 2 times higher than the new.After aging,the types of surface elements and chemical bond in MPs did not change compared with the new MPs.The results of static adsorption tests of heavy metals on MPs showed that the adsorption capacity of MPs for heavy metals did not change after 5 days of adsorption.The adsorption capacities of the natural aging PP for Cu²⁺and Pb²⁺were0.20 mg/g and 0.16 mg/g,respectively,which were 2.5 times and 2 times of the new MPs.When the p H increased from 3 to 11,the adsorption capacity of the new PA for Cu²⁺increased from 0.012 mg/g to 0.078 mg/g,and the adsorption capacity for Pb²⁺first increased and then decreased,reaching the maximum value 0.105 mg/g at p H=5.The adsorption of heavy metals by MPs increases with the decrease of particle size and the increase of concentration.The adsorption kinetics of heavy metals by MPs conformed to pseudo-second-order equation,and the adsorption thermodynamics conformed to Freundlich model.Changes in the concentration of Cu²⁺in solution had a greater impact on the adsorption capacity of MPs,while changes in the concentration of Pb²⁺had less impact.The results of desorption heavy metals in gastrointestinal environments showed that with the p H changed from 1 to 5,the desorption efficiency of Cu²⁺in the new PE decreased from 29.5%to 11.6%,and the desorption efficiency of Pb²⁺decreased from 67.1%to 16.2%.The desorption efficiency of Cu²⁺and Pb²⁺first decreased and then increased with the increase of salinity,increased with the increase of temperature and the quality of carbohydrate and protein in gastrointestinal environment,and decreased with the increase of cellulose quality.The desorption efficiency of aging MPs was greater than that of newly made.Among them,the desorption efficiency of natural aging MPs was the largest.Naturally aging MPs will cause greater harm than newly made MPs and ultraviolet and thermally aging MPs.