Cu(II) adsorption on Poly(Lactic Acid) Microplastics: Significance of microbial colonization and degradation

The current trend towards the use of biodegradable polymers is considered as a sustainable solution to plastic pollution. However, microplastics (MPs) generation due to harsh degradation conditions may impose higher environmental risks on organisms in the aquatic environment, especially when coexisted with various complicated pollutants. This study aimed at investigating the significance of microbial colonization and degradation in the Cu(II) adsorption by poly(lactic acid) (PLA) MPs. The PLA MPs covered with biofilms showed higher monolayer Cu(II) adsorption capacity than the pristine PLA (151.802 ug.g(-1) versus 1045.670 ug.g(-1)), which was attributed to the surface complexation between Cu(II) and functional groups contained in biofilms. The adsorption kinetics of the sewage-incubated PLA was limited by film diffusion and intraparticle diffusion, whereas film diffusion dominated the Cu(II) adsorption by the pristine PLA. Degradation of PLA MPs was detected by Fourier transform infrared spectroscopy (FTIR) with the breakdown of ester bonds, and the biofilm-mediated alterations were further enhanced with the extension of incubation. In addition, removal of biofilms increased the Cu(II) adsorption on PLA MPs by 32.36% due to the higher surface area with more adsorption sites and the pore-filling mechanism. Cu(II) adsorption capacity of PLA MPs was pH-dependent and the biofilm-removed PLA exhibited the lowest adsorption ability at the pH ranging from 4.5 to 6.0. Fulvic acid (FA) inhibited the Cu(II) adsorption due to the complexation of Cu(II) with FA. Our results filled the knowledge gap concerning the influence of microbial colonization and degradation on the adsorption behavior of biodegradable PLA MPs, which can further serve as the cornerstone to understand the environmental interaction between poly (alpha-hydroxy acid)-type polyesters and heavy metal pollutants.

Automated summary

The study found that biofilms can enhance the adsorption capacity of poly(lactic acid) microplastics (PLA MPs) for Cu(II), with degradation process being enhanced with longer incubation. Removal of biofilms can increase the adsorption of Cu(II) on PLA MPs, and the adsorption capacity of PLA MPs is pH-dependent.