BIOFILM-MEDIATED INTERACTIONS BETWEEN MICROPLASTICS AND TRACE METALS IN AQUATIC ENVIRONMENTS: FROM SORPTION AND REMOBILIZATION TO ECOLOGICAL RISK

Abstract

Microplastics (MPs) are widespread contaminants in aquatic environments and can interact with trace metals through physicochemical processes occurring at their surfaces. Following environmental exposure, MPs are rapidly colonized by microorganisms and covered by biofilms, which substantially modify their surface properties and consequently influence their interactions with metals. This review critically synthesizes current knowledge on biofilm-mediated interactions between MPs and trace metals, with particular emphasis on sorption mechanisms, environmental controls, desorption and remobilization, bioavailability, and ecological consequences. Biofilm development and environmental aging can increase surface roughness, alter surface charge, and introduce extracellular polymeric substances and functional groups capable of binding metal ions through electrostatic attraction, ion exchange, and surface complexation. However, biofilm-coated MPs should not be regarded solely as sinks for trace metals. Changes in environmental conditions, biofilm degradation or detachment, and gastrointestinal conditions following ingestion may promote metal desorption and remobilization, potentially altering metal bioaccessibility and exposure. Available evidence further indicates that co-exposure to MPs and metals can produce synergistic, additive, or antagonistic biological effects rather than a universally enhanced toxic response. Major knowledge gaps remain regarding environmentally aged particles, complex contaminant mixtures, long-term field conditions, biofilm dynamics, metal remobilization, and trophic transfer. Future studies should therefore move beyond pristine MPs and single-metal laboratory systems toward environmentally realistic approaches integrating surface chemistry, biofilm processes, metal speciation, bioavailability, and biological responses. Such an integrated perspective is necessary to better evaluate the role of biofilm-coated MPs in the transport and ecological risk of trace metals in aquatic ecosystems.