Microplastic-heavy metal ions interactions in aquatic environments: Sources, biofilm-driven adsorption mechanisms, ecological risks, and remediation frontiers

Microplastics (MPs) have recently attracted a lot of attention due to their widespread distribution in aquatic environments. MPs can act as vectors or carriers for heavy metal ions in aquatic environments, posing a potential threat to aquatic organisms and human health. In this review, the sources and interaction mechanisms of MPs and heavy metal ions in aquatic environment were summarized. This review particularly focuses on the role of MPs surface biofilms (plastisphere) in influencing the adsorption behavior of heavy metal ions. It systematically reviews the adsorption mechanisms driven by biofilms, the combined toxic effects, and the progress in removal technologies. Adsorption-analytical mechanism, adsorption kinetics and isotherms model were used to explain the interaction mechanism of heavy metal adsorption by MPs. The adsorption process was affected by many factors, including the morphological characteristics, adsorption capacity and environmental conditions of MPs. The potential risks to aquatic organisms, aquatic plants and animals from co-exposure of MPs and heavy metal ions to water were then assessed. Research progress of chemical, biological and physical methods for removal of heavy metal complex pollutants adsorbed by MPs. The aim is to provide a theoretical basis for the precise risk assessment of MPs-heavy metal composite pollution in real water bodies.