Digestive enzyme-driven desorption of phenanthrene from microplastics in a simulated human gut

Microplastics (MPs) are ubiquitous in aquatic environments and readily adsorb surrounding pollutants during transport. Upon ingestion, these pollutant-laden MPs may release their adsorbed contaminants in the human gastrointestinal tract, posing potential health risks. This study investigates the interactions between phenanthrene (Phe) and MPs in simulated digestive fluids using batch adsorption/desorption experiments and molecular dynamics simulations. Results showed that Phe undergoes rapid desorption in the early stages of digestion, strongly influenced by enzyme type and concentration. Among the tested enzymes, mucin exhibited the highest desorption efficiency, followed by trypsin, lipase, and pepsin, attributable to differences in molecular structure, surface activity, and binding affinity. Maximum desorption efficiencies reached 39.1 % for polyethylene (PE) and 55.4 % for polystyrene (PS) in mucin-containing gastric fluid. The enzymes facilitated Phe desorption by competing for adsorption sites, enhancing solubility, and weakening Phe-MPs interactions. PS showed higher than PE due to its lower sorptive affinity and distinct surface properties. Risk assessment indicated that the carcinogenic risk of desorbed Phe was below safety thresholds but could increase notably in highly contaminated real-world settings. These findings highlight the critical but underappreciated role of digestive enzymes in mediating pollutant release from MPs and underscore the need to reevaluate their health risks in biological systems. • Enzymes strongly accelerate the early Phe desorption, depending on type and level. • Phe desorption was most efficient with mucin, then trypsin, lipase, and pepsin. • Enzyme structure and surface activity govern the desorption efficiency of Phe. • Molecular dynamics simulations reveal enzyme-Phe interaction at the molecular level. • The Phe load on MPs in real environments most strongly drives ingestion risk.