The role of microplastics as vectors of antibiotic contaminants via a molecular simulation approach.

Microplastics (MPs) and nanoplastics (NPs) have emerged as major environmental pollutants due to their persistence, widespread distribution, and ability to interact with organic contaminants, including antibiotics. This study employs molecular dynamics (MD) simulations to investigate the adsorption mechanisms of three commonly used antibiotics-ciprofloxacin, amoxicillin, and tetracycline-on two types of non-biodegradable microplastics: polypropylene (PP) and polystyrene (PS). Furthermore, the impact of microplastic aging, simulated by introducing oxidized and hydrophilic functional groups, on adsorption efficiency and interaction mechanisms has been explored. The total interaction energy of ciprofloxacin on polystyrene increased from - 121.57 kJ/mol (pristine) to -242.04 kJ/mol (aged), while the number of adsorbed molecules doubled from 5 to 10. Similarly, amoxicillin adsorption on aged polypropylene increased from 4 to 6 molecules, with total adsorption energy increasing from - 52.14 kJ/mol to -93.43 kJ/mol. Polystyrene microplastics demonstrated stronger adsorption than polypropylene, particularly for aromatic antibiotics like ciprofloxacin, where π-π interactions dominate. The Root Mean Square Deviation (RMSD), Radial Distribution Function (RDF), and Mean Squared Displacement (MSD) analyses further confirm the stability and persistence of these interactions. Additionally, the hydrogen bond analysis highlights the role of microplastic aging in facilitating stronger antibiotic binding. These findings suggest that aged microplastics act as potent carriers of antibiotics, potentially prolonging their environmental persistence and influencing microbial resistance patterns. The results reveal that, aged microplastics exhibit significantly higher antibiotic adsorption due to increased surface roughness and enhanced electrostatic interactions. By providing molecular-level insights into MP-antibiotic interactions, this study contributes to the broader understanding of emerging pollutants.