Microplastics and antibiotic resistance genes in landfills: interaction mechanisms, environmental risks, and composite pollution implications.

Microplastics (MPs) and antibiotic resistance genes (ARGs) widely coexist and interact in landfills, forming novel composite pollution. This review reveals their occurrence characteristics, migration mechanisms, interaction risks, and ecological threats in landfills. Landfills accumulate MPs, primarily composed of polyethylene, polypropylene, and polystyrene, with abundance and fragmentation increasing with depth. They migrate via leachate while undergoing continuous aging, and their dispersion is further exacerbated by reduced particle size and enhanced surface hydrophilicity. Meanwhile, aged MPs can provide attachment surfaces for plastisphere-like biofilms and may serve as carriers for pathogens and bacteria because of their large specific surface area and oxygen-containing functional groups. MP-associated biofilms may facilitate horizontal gene transfer (HGT) by increasing microbial contact opportunities and, under some experimental conditions, by promoting oxidative stress responses and membrane permeability changes. ARGs spread across species via HGT and show a significant association with heavy metals. Concomitantly, heavy metal resistance genes may modulate ARG expression, while ARG abundance is also influenced by landfill age, seasonal variations, and pH. Coexistence of MPs, ARGs, and heavy metals triggers co-selection pressure, amplifying composite pollution. Composite pollutants may migrate through soil-water systems and potentially enter food webs, with possible accumulation in organisms; however, evidence directly linking landfill-derived pollutants to human tissue exposure remains limited. The concealed and complex pollution hinders remediation, necessitating coordinated solutions. The lack of detailed policies, standardized methodologies, and inconsistent research strategies hinder cross-study comparisons. This article is aimed at summarizing the occurrence, migration, and interaction patterns of emerging pollutants in landfills and at providing a basis for systematic management and future risk warning.