Effect of aging on the properties of microplastics and their adsorption behavior of norfloxacin

Four different aging methods - UV irradiation, heat exposure, seawater and lake water immersion - were employed to age the microplastics (MPs) of biodegradable polylactic acid (PLA) and conventional polyvinyl chloride (PVC), and their adsorption behaviors for norfloxacin (NOR) were explored. To investigate the impacts of different aging processes on MPs, systematic characterization analyses were carried out. Results show that after 90 days of aging, PLA displayed more voids and cracks than PVC and had a higher adsorption capacity (qm) for NOR, which is 3.1-4.4 times greater than that of PVCs, indicating that PLA is more susceptible to loading NOR and forming composite pollution. Among the four aging methods, UV aging had the greatest effect on the MP performance, resulting in a 41.4 % and 80.0 % increase in the qm for NOR on PLA and PVC, respectively. The Pearson correlation coefficient was used to parameterize the characterization of MPs and establish a correlation with qm. For PLA, the coefficients of Zeta potential and specific surface area to qm were 0.99 and 0.91, respectively, showing a strong correlation. This indicates that the adsorption mechanism of aged MPs to NOR mainly depends on the increase of adsorption sites and the electrostatic attraction.