Co-adsorption of heavy metals and antibiotic pollutants by microplastic in aquatic environments and its mechanisms: A review

Microplastics (MPs), antibiotics, and heavy metals are significant pollutants that pose considerable risks to human health due to their widespread presence in aquatic ecosystems. Recent research has investigated the co-adsorption processes of heavy metals and antibiotics by MPs. However, the characteristics of co-adsorption remain inadequately understood, particularly concerning the factors that influence the process and the mechanisms involved. In this review, we synthesize and analyze the literature on co-adsorption of heavy metals and antibiotics by MPs, considering environmental conditions, physicochemical properties of MPs and pollutants, and the underlying mechanisms. Results indicate that MPs can effectively sequester both contaminant classes, with reported adsorption capacities spanning wide ranges, approximately 8.46–5550.0 μg/g for heavy metals and 53.52–7390.31 μg/g for antibiotics. Evidence points to predominantly antagonistic interactions for heavy metals and synergistic interactions for antibiotics during co-adsorption. Furthermore, our results suggest that variations in MPs properties (e.g., aging) and most environmental factors, apart from solution pH and dissolved organic matter, may exert minimal influence on co-adsorption efficiency. In contrast, the concentration ratios of heavy metals and antibiotics significantly impact co-adsorption outcomes. Mechanistically, bridging and competition effects emerge as principal drivers of the observed synergistic and antagonistic effects, respectively. Overall, this review therefore addresses key knowledge gaps in the interactions among MPs, heavy metals, and antibiotics, offering insights to inform strategies for managing coexisting MPs and pollutants in aquatic systems.