Insights Into the Adsorption Behavior of Polyethylene Microplastics Towards Lead(II) Ions

Abstract

Microplastics and metals represent widespread contaminants which can cause significant damage to aquatic ecosystems and organisms. However, the complex interactions between microplastics and various metals in water environments remains to be understood. This study aims to investigate the interaction dynamics between lead(II) ions and polyethylene in freshwater environments. Adsorption trials were conducted systematically by adjusting operational parameters such as initial Pb(II) concentration, equilibrium pH value, and residence times. An in-depth characterization study using scanning electron microscopy (SEM), x-ray diffraction and Fourier transform infrared (FTIR) analysis was conducted to explain the adsorption mechanism of polyethylene microplastics (PEM). The data indicated the porous surface of PEM, highlighting the presence of diverse functional groups. According to the Langmuir model, the PEM exhibited maximum Pb(II) uptake of 3.69 mg/g at pH 4.5. The pseudo-first-order model demonstrated superior fitting to Pb(II)-PEM kinetics. Desorption trials were performed to assess the release of Pb(II) from Pb(II)-bounded PEM using various chemical agents. It was observed that 0.01 M HNO₃ desorbed Pb(II) ions optimally, achieving a desorption efficiency exceeding 99.9%. Consequently, desorption trials provided evidence that Pb(II)-bounded PEM may release Pb(II) ions in acidic environments, facilitating the transfer of Pb(II) to the digestive tracts of aquatic organisms.