Microplastics as genetic vectors for environmental DNA: A review on adsorption mechanisms, plastisphere genetics, and...

Environmental DNA (eDNA) has emerged as a highly sensitive, non-invasive biomonitoring tool for biological community profiling and ecotoxicological assessment in aquatic systems affected by microplastics. In natural environments, it predominantly exists as extracellular DNA (free or particle-associated genetic fragments), and its physicochemical behavior governs its fate. Despite rapid advances in both eDNA-based monitoring and microplastic research, the combined influence of these factors on the environmental fate, transport, and interpretation of molecular signals remains poorly understood. Failure to account for these interactions risks systematic bias in exposure assessment and community composition inference. Here, we critically review and analyze existing evidence on eDNA-microplastic interactions and highlight their implications for spatial and temporal bias in molecular ecological analysis. The physicochemical and biological mechanisms governing DNA adsorption and environmental fate are evaluated, demonstrating that eDNA-microplastic interactions are modulated by polymer chemistry, surface aging, ionic strength, microbial colonization, and hydrodynamic transport. Plastisphere biofilms further act as genetic hotspots that concentrate and redistribute extracellular DNA, antibiotic resistance genes, and mobile genetic elements under co-contaminant exposure. This review applies structured genetic-information scoring and hierarchical synthesis to link microplastic traits with molecular-level risk. The synthesis indicates that small (<200 μm) aromatic, hydrophobic microplastic fragments, films and fibers exhibit the highest genetic risk scores, accompanied by a shift from descriptive 16S profiling toward functional antibiotic resistance genes and eDNA-mediated horizontal gene transfer signals. Based on the synthesized evidence, we identify environmental variability, ambiguity in origin and persistence of eDNA on the microplastic surfaces, limited quantitative resolution, and insufficient standardization as key methodological constraints. Accordingly, targeted solutions are proposed to close technical gaps and outline priority directions for future research.