From Foodborne Pollutant Carrier to Gastrointestinal Trojan Horse: Simulating the Bioaccessibility of Antibiotics Loaded on Aged Polylactic Acid Microplastics in Human Digestive System

Foodborne microplastics (MPs) are suspected carriers of co-ingested food contaminants, yet their digestive fate remains poorly characterized. This study simulates the role of environmentally aged polylactic acid (PLA) MPs-a common food-contact material-in transporting the antibiotic tetracycline (TC) through the human gastrointestinal tract. K₂S₂O₈-induced aging significantly increased PLA surface porosity, oxygen-containing groups, and hydrophilicity, elevating TC adsorption capacity from 0.54 to 0.95 mg/g. While adsorption kinetics were consistent with pseudo-second-order behavior, mechanistic analysis indicates that aging promotes interactions dominated by hydrogen bonding and electrostatic forces, rather than purely physical deposition. Critically, in vitro digestion models revealed that simulated intestinal fluid significantly enhances TC release (up to 62.7% of adsorbed load) compared to gastric conditions. Sequential gastrointestinal simulation yielded a bioaccessibility of 32.6%, indicating substantial digestive mobilization of MP-bound antibiotics. These findings underscore the potential of aged PLA MPs to act as digestive-stage "Trojan horses" for foodborne antibiotics. Our integrated approach-combining controlled aging, adsorption thermodynamics, and physiologically relevant digestion models-provides a mechanistic screening framework for assessing the bioaccessibility and exposure potential of microplastic-vectored contaminants in food safety contexts.