Biodegradable Plastics and Microbial Gene Dynamics: Risks of Particle Formation, Leachates and Gene Dissemination

Biodegradable plastics are increasingly adopted as alternatives to conventional polymers, yet their environmental behavior and indirect risks remain insufficiently characterized. This review synthesizes polymer chemistry, environmental fate studies and microbial ecology to evaluate how common biodegradable materials including Polylactic Acid (PLA), poly(Butylene Adipate co Terephthalate) (PBAT), Polyhydroxyalkanoates (PHAs) and starch blends undergo hydrolysis, photooxidation, enzymatic cleavage and mechanical abrasion that generate persistent microplastics and nanoplastics together with diverse chemical leachates. Reported leachate classes including monomers, oligomers, plasticizers, metal pro oxidants and UV stabilizers, detection methods and environmental concentrations are summarized, along with evidence for ecological effects on microbial communities and macrofauna. Weathering and particle formation modify surface chemistry, enhance sorption of contaminants such as antibiotics and metals and create microsites of elevated chemical stress. A central focus is the plastisphere that forms on biodegradable microplastic surfaces. Across studies, biofilms show reproducible taxonomic and functional shifts including enrichment of hydrolases, stress response pathways and biofilm associated taxa relative to surrounding matrices. Available data indicate that biodegradable microplastics concentrate antibiotic resistance genes and mobile genetic elements and that seasonal aging and surface oxidation amplify these patterns. Experimental research identifies three pathways by which biodegradable microplastics may elevate horizontal gene transfer including increased cell proximity in biofilms that promotes conjugation, oxidative and chemical stress from aged leachates that enhances transformation competence and physical transport of plasmids and mobile genetic elements across environments. Quantitative microcosm studies illustrate the magnitude and context dependence of these effects. To support risk assessment, methodological best practices are recommended including harmonized sampling, realistic aging protocols, standardized particle characterization, plasmid resolved metagenomics and stable isotope probing. A tiered monitoring framework and focused research agenda are proposed to guide responsible deployment and governance of biodegradable plastics.