<![CDATA[Background: Biodegradable plastics are widely promoted as environmentally friendly alternatives to conventional plastics, yet their real-world environmental benefits are often overstated relative to performance under standard certification conditions. This narrative review examines the gap between biodegradability certification standards and degradation under real-world conditions, the formation of microplastics and nanoplastics from biodegradable polymers, their toxicological effects, and the implications for sustainability policy. Methods: Literature was retrieved from PubMed, Scopus, Web of Science, and Google Scholar and synthesised narratively across four themes: polymer chemistry and certification, micro- and nanoplastic generation, ecotoxicological evidence, and policy implications. Findings: Common bioplastics, including polylactic acid, polyhydroxyalkanoates, and starch-based polymers, frequently degrade slowly in natural environments and can fragment into persistent microplastics and nanoplastics; these particles have been associated with oxidative stress, inflammation, endocrine disruption, and ecological harm across multiple biological levels of organisation. Conclusion: Biodegradable plastics can contribute to reducing plastic pollution, but their benefits are conditional on effective waste management, stronger regulatory oversight, and informed use; a systems-based approach combining material certification, infrastructure, and governance is required for genuine environmental sustainability. Novelty/Originality of this article: This review integrates evidence from polymer chemistry, environmental toxicology, and sustainability policy into a three-layer systems framework (material certification, waste infrastructure, and governance) for evaluating the genuine environmental benefit of biodegradable plastics, an integrative perspective that is largely absent from single-discipline treatments of the topic.]]>
