Degradation of biodegradable plastics in waste management systems and the open environment: A critical review

Decades of extensive and exponentially growing production and use of conventional plastics have led to the accumulation of plastic waste in the environment, contributing to the anthropocene pressure on ecosystems. Bioplastics (defined as bio-based and/or biodegradable plastics) have been promoted as a more sustainable alternative and substitute for conventional plastics. Nonetheless, the literature contains numerous conflicting conclusions regarding their suitability and environmental implications. One central point of contention concerns their biodegradability and the conditions necessary for proper degradation. In real-world settings, like anaerobic digestion plants or marine environments, biodegradable plastics may not degrade as rapidly or efficiently as suggested by laboratory tests. A systematic literature review was conducted to explore the current level of knowledge regarding the environmental fate and consequences of biodegradable plastics, thereby substantiating discussions on their future role in society. The review covered the degradation of biodegradable plastics in waste management environments (e.g., compost, sludge, or landfill) and the open environment (e.g., seawater, freshwater, or soil). As clearly highlighted by this review, comparisons and quantitative analysis of data on plastic degradation are challenged by significant methodological variations, encompassing differences in testing methods, test materials, and quantification strategies. Moreover, the review revealed several research gaps, highlighting, in particular, the need to i) intensify the research on polyhydroxyalkanoates (PHAs), polybutylene adipate terephthalate (PBAT), and polybutylene succinate (PBS) to match the level of polylactic acid (PLA) and starch-based plastics, ii) develop standard test methods in field conditions, and iii) couple degradation testing with ecotoxicological tests. The overview established in this review is essential for a more thorough evaluation of the environmental performance of biodegradable plastics. Furthermore, the findings of this study contribute to supporting the responsible future production and use of biodegradable plastics in various products, including assessing their role as alternatives to conventional plastics.