Dissolved organic matter leached from microplastic (MPs-DOM) divergently alters pyrene adsorption in soil

Microplastics (MPs) are emerging soil contaminants that significantly affect the adsorption of co-existing pollutants in soil. This study systematically investigates the distinct roles of conventional polyethylene (PE), biodegradable polylactic acid (PLA), and their derived dissolved organic matter (MPs-DOM) in regulating pyrene adsorption in soil. The results demonstrate that both MPs enhanced pyrene adsorption, with PE exhibiting higher capacity (Q_e = 4.09 mg g^-1) and faster rate (K₁ = 0.09 min^-1) than PLA (Q_e = 2.26 mg g^-1). Aging further diverged their behaviors: PE increased its adsorption partition coefficient (K_d) by 58.80 % through developing a polar-hydrophobic interface with oxygen-containing groups, while PLA decreased K_d by 39.45 % due to enhanced hydrophilicity from ester bond cleavage. Crucially, MPs-DOM, characterized as predominantly low-molecular-weight proteins (>95 %), demonstrated a dual regulatory effect: at 5 mg C L^-1, it enhanced ultimate adsorption capacity through micelle formation but concurrently retarded the adsorption rate by introducing hydrogen-bonding sites that modified soil microstructure and interaction pathways. These findings reveal that MPs-DOM operates through fundamentally different mechanisms compared to particulate MPs, predominantly involving protein-like component mediation rather than simple hydrophobic interactions. The study highlights the necessity of considering both particulate MPs and their persistent DOM derivatives in environmental risk assessments, particularly noting the contrasting long-term impacts of conventional versus biodegradable MPs on contaminant behavior in soil ecosystems.