The Biodegradability Paradox: Hidden Toxicological and Additive-Driven Risks of Mismanaged Bioplastics

The global surge in plastic pollution, particularly from microplastics (MPs), has raised concerns about long-term implications for terrestrial and aquatic ecosystems. In response, biodegradable plastics are widely considered promising replacements for conventional plastics and are often marketed under labels such as “bio-based,” “biodegradable,” “compostable,” and “eco-friendly.” However, growing evidence suggests that the mismanagement of these materials contributes to the formation of microplastics derived from biodegradable plastics, which may pose ecological hazards depending on material composition and exposure conditions. This review integrates evidence on environmental fate and ecotoxicological effects with bioplastic formulation chemistry, including intentionally added substances, non-intentionally added substances and polymer degradation products. It links material composition and chemical release to biological responses, and highlights uncertainties in distinguishing particle-associated effects from chemical-mixture toxicity. The synthesis examines effects on soil properties, microbial and mesofaunal communities, and aquatic organisms, considering the limitations of extrapolating experimental findings to environmental exposure. This review identifies key knowledge gaps and emerging risks, challenging the perception that all biodegradable plastics are inherently environmentally benign. It highlights the need for regulatory oversight, standardized definitions, and transparent labelling to ensure that biodegradability claims align with real-world degradation conditions. Without sustainable end-of-life strategies, bioplastics may shift rather than solve the microplastic crisis. This work underscores the need for a precautionary approach to biopolymer development, grounded in life cycle thinking and ecological safety.