Surface Structure Changes of Biodegraded Microplastics and the Interaction Behavior with Antibiotics

Abstract

The environmental behavior of biodegradable microplastics (BMPs) is influenced by their surface characteristics during degradation, but the impact of molecular structures of emerging contaminants like antibiotics on aged BMPs is unknown. Herein, BMPs were naturally aged in wastewater over 60 days to evaluate the changes in the physicochemical characteristics, aiming to elucidate the interactional with structurally distinct antibiotics. Systematic aging of BMPs from 0 to 60 days in wastewater changes their surface area from 8.8 to 14.3 m2/g and pore size from 7.5 nm to 5.0 nm, while enhanced functionalization (-C=O, -OH, -NH2) led to improved hydrophilicity and oxygen-to-carbon (O/C) ratio from 0.75 to 1.17. The interaction dynamics between BMPs and antibiotics (tetracycline(TCL), ciprofloxacin(CPL), and norfloxacin(NOR)) vary significantly with aging. TCL demonstrates the strongest interaction with aged BMPs, featuring high adsorption rates and low desorption due to its many reactive groups. This is supported by DFT, highlighting optimal spatial configuration, significant orbital overlap, and stable TCL complexes with BMPs. The competitive evaluation confirms that the surface characteristics of aged BMPs are not the primary determinants of their interactive behavior, while the molecular structure and interactive properties of the antibiotics play a crucial role in an environment rich in antibiotics.

Keywords: Biodegradable polylactic acid, Wastewater, Antibiotics, Emerging Pollutants, Pharmaceuticals