Iron minerals facilitate eco-corona formation and organic contaminants adsorption on microplastics

Interactions between microplastics and dissolved organic matter (DOM) form an eco-corona, governing the environmental fate of microplastics and the coexisting contaminants. Iron minerals, ubiquitous in soil, inevitably participate in this process. However, the effect of iron minerals on the interfacial adsorption behaviour of DOM and organic contaminants on microplastics is not well elucidated. Here, we demonstrated that iron minerals (ferrihydrite and goethite) attach to the surface of polyethylene (PE) microplastics, forming heteroaggregates. These attached iron minerals promote the adsorption capacity of DOM on PE microplastics, increasing it by 1.76-3.48 times compared to that on pristine PE microplastics. Meanwhile, lignin-like, tannin-like, and condensed aromatic compounds within DOM are preferentially adsorbed onto the surface of the heteroaggregates via ligand exchange and hydrophobic interactions, thereby forming a component-stable and degradation-resistant eco-corona on heteroaggregates. The eco‑corona inhibits organic contaminants (e.g. dibutyl phthalate and acetochlor) adsorption on heteroaggregates by adsorbing the high-oxygen (O > 10) DOM components and occupying available adsorption sites. Nevertheless, the attached iron minerals invariably enhanced organic contaminants adsorption on PE microplastics by 4.94-11.75%. This enhancement is attributed to an increased specific surface area and provision of additional adsorption sites. Collectively, these findings highlight the critical role of iron minerals in mediating the interfacial behaviour of microplastics, thereby influencing their environmental risks and the fate of coexisting contaminants in soils.