Chemical and biological cargo on microplastics: current evidence for the Trojan-horse pathway to human exposure

Microplastics (MPs) are increasingly recognised not as inert litter, but as chemically and biologically active interfaces that interact dynamically with environmental contaminants and microbial communities. Environmental weathering processes, including photochemical oxidation and mechanical abrasion, increase MP surface roughness and oxygen-containing functional groups by 2-10-fold, enhancing sorption capacity and eco-corona formation. These eco-coronas, composed of natural organic matter, biomolecules, and extracellular polymers, alter MP physicochemical properties and promote microbial colonisation. The resulting "plastisphere" facilitates microbial succession and antibiotic resistance gene (ARG) enrichment by 10-100-fold relative to surrounding environments through enhanced horizontal gene transfer. MPs also act as vectors for co-contaminants through the "Trojan-horse" effect, accumulating PFAS, PAHs, and heavy metals and amplifying oxidative stress and genotoxicity. Key findings indicate that: (1) weathered MPs exhibit enhanced contaminant adsorption and transport potential; (2) eco-corona formation governs pollutant binding and microbial attachment; (3) nanoplastics (<100 nm) show increased cellular uptake and bioavailability; (4) co-exposure to MPs and contaminants increases reactive oxygen species generation by 30-300% in biological models; and (5) MPs have been detected in human tissues, including lungs (∼7.1 μg g^-1), blood (∼77% detection frequency), placenta (up to 790 μg g^-1), and feces (10-20 particles g^-1). Despite rapid advances, methodological and regulatory gaps continue to limit accurate risk assessment. Collectively, these findings establish MPs as dynamic ecological interfaces requiring integrated mitigation and regulatory strategies.