Sequential interfacial contributions of microplastics to microbial adhesion and metal adsorption

Microplastics (MPs) are increasingly recognized as interfacial substrates for microbial adhesion and metal adsorption in aquatic environments. However, the temporal sequence and causality of MPs-microbial-metal interactions remain poorly understood. This study uncovers the mechanistic sequence and interfacial contributions of MPs in mediating B. subtilis adhesion, Cr (VI) adsorption and subsequent bio-reduction. Pristine and UV-1000 h degraded polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET) and polystyrene (PS) MPs were investigated using a combination of experiments and machine learning based mechanistic modelling. Sequential pathway analysis revealed that B. subtilis adhesion consistently precedes metal sorption across all MPs, with high model fit (r² = 0.747-0.994 for pristine MPs, 0.858-0.995 for aged MPs). Interfacial contributions analysis further confirmed that MPs surface-mediated microbial colonization was a key determinant for Cr(VI) adsorption and subsequent biotransformation. Notably, PA, PET and PS showed high contributions to microbial adhesion of 85 %, 77 % and 86 %, respectively, highlighting their distinct influence in initiating Cr(VI) bio-reduction. These findings reveal that MPs serve as active enablers rather than passive carriers of microbial and metals interfacial interactions, provide critical insights into interfacial mechanisms underlying contaminant transformation, thereby providing essential information for risk assessment and targeted strategies for the mitigation of MP-mediated pollution in aquatic environments.