Release behavior of Zn(Ⅱ)-containing additives in expanded polystyrene microplastics
In order to explore the release rules and influencing factors of heavy metal-containing additives in microplastics to the environment,the release behaviors of Zn(Ⅱ)-containing additives from fresh and ultraviolet(UV)-aged expanded polystyrene(EPS)microplastics were studied.The release kinetics,cumulative release and orthogonal experiments were carried out under three simulated environments,including freshwater,seawater and gastric fluids.The results showed that the release capacity of Zn(Ⅱ)from UV-aged EPS microplastics was greater than that from fresh EPS microplastics.The equilibrium release amount of Zn(Ⅱ)from UV-aged EPS microplastics were(29.45±4.38),(87.41±5.18)and(109.94±3.18)μg/g in freshwater,seawater and gastric fluids,respectively,while the equilibrium release amount of Zn(Ⅱ)from fresh EPS microplastics were(20.90±0.46),(85.89±0.51)and(108.92±1.17)μg/g,respectively,suggesting that UV aging could promote the release of Zn(Ⅱ)from the additives.The gastric fluids and seawater environment were more favorable for the release of Zn(Ⅱ).The release of Zn(Ⅱ)from EPS microplastics is fitted to a pseudo-second-order kinetic model,indicating that the release of Zn(Ⅱ)from the plastics is controlled by the interfacial reaction and the diffusion on the plastic surface.The Zn(Ⅱ)in the EPS microplastics can be almost completely released by repeatedly replacing the extract.The pH value,particle size and aging time are the main factors affecting the release of Zn(Ⅱ)from EPS microplastic.
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