Fate and effects of bioplastics in waste management systems and the environment

Plastic pollution is a growing environmental concern driven by the widespread use and persistence of fossil-based, non-biodegradable plastics – commonly referred to as conventional plastics. In response, bioplastics – defined as biobased, biodegradable, or both – are increasingly promoted as sustainable alternatives. However, as bioplastics differ widely in polymer composition, degradability, and end-of-life (EoL) treatment potential, so will their environmental impact. Thus, there is a risk of introducing regrettable substitutions, where one problematic material is replaced by another with similar or new environmental harms.

This PhD thesis investigated the fate and effects of bioplastics in waste management systems and natural environments. The research addresses critical knowledge gaps in degradation behavior, microplastic (MP) formation, chemical release, and ecotoxicological effects. Combining a systematic review with empirical studies, the thesis evaluates the environmental performance of bioplastics and contributes to a more informed and context-sensitive implementation. A review of 900 experimental degradation studies on five common biodegradable plastics revealed significant methodological inconsistencies and limited application of standardized test protocols. Most studies focused on pure polymers, particularly polylactic acid (PLA) and starch blends. In contrast, commercial products and other biodegradable plastics – such as polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), and polyhydroxyalkanoates (PHAs) – were significantly underrepresented. Composting consistently emerged as the most effective treatment for promoting degradation, whereas degradation under anaerobic digestion (AD), landfilling, and aquatic conditions was limited. These findings were corroborated by experimental tests conducted during this PhD project, which demonstrated that commercial biodegradable plastic products underwent greater disintegration than conventional plastics under composting conditions, achieving degradation degrees between 75 % and 100 %. When degradation was assessed in freshwater, seawater, or aerobic digestion environments, biodegradable plastics exhibited degradation degrees ranging from 1.7 % to 13 %, which, although low, were still higher than the < 1 % degradation observed for conventional plastics across all test environments. These results underscore the variability in degradation performance across different products and environmental conditions.

Crucially, the thesis demonstrated that MPs can be generated from biodegradable plastics (bio-MPs) during degradation. Bio-MPs were detected in compost after 90 days (55 ± 10 particles per gram of compost), even under standardized industrial composting conditions. In contrast, conventional plastics showed negligible degradation and did not release detectable MPs under the same conditions. Results further demonstrated that bio-MPs degraded during standard MP extraction processes, compromising their detection. To address this, a novel oleo-extraction method was developed using low concentrations of hydrogen peroxide (H₂O₂), at room temperature, and rapeseed oil to isolate bio - MPs from compost matrices while preserving polymer integrity. This method enabled the reliable detection and quantification of bio-MPs down to < 100 μm, demonstrating high recovery rates for both bio-MPs (88 % ± 6.2 %) and conventional MPs (83 % ± 3.3 %), and offering broader applicability to other complex matrices.

Beyond physical degradation, chemical release and associated toxicity were assessed. Chemical analyses showed that biodegradable plastics released a broader range of chemical features, as detected through non-targeted analysis. Additionally, targeted elemental analysis revealed higher concentrations of metals in some cases compared to conventional and non-biodegradable plastics. Leachate ecotoxicity tests showed that bioplastics induced effects equal to or greater than conventional plastics, especially in aquatic species such as freshwater algae (up to 80 % growth inhibition). The chemical composition and environmental effects of bioplastics varied widely between commercial products, even among those based on the same polymer type, likely due to differences in additives and formulation, which are often undisclosed.

Novel findings of this PhD project challenged the assumption that bioplastics are inherently more sustainable than conventional plastics. Their fate and effects are strongly dependent on context, shaped by factors such as polymer chemistry, product formulation, and environmental or waste treatment conditions. To achieve evidence-based sustainability of bioplastics, it is essential to address these complexities through a more robust framework.

To ensure the sustainable implementation of bioplastics, their environmental safety must be carefully demonstrated through comprehensive, context -specific evaluations. These evaluations should encompass key factors such as degradation, MP formation, chemical leaching, and ecotoxicity. Without this scrutiny, bioplastics risk contributing to the very forms of pollution they aim to reduce. Their environmental benefits cannot be assumed. Therefore, this thesis provided several targeted recommendations, including, but not limited to, the following:

• Researchers should apply harmonized degradation test protocols, assess MP formation and ecotoxicity, and reflect real-world conditions, including diverse waste treatments and aquatic environments.

• Industry must disclose full polymer and additive compositions to enable robust environmental evaluations.

• Policymakers should implement clear regulatory frameworks and labeling requirements tailored to bioplastics, while investing in appropriate waste treatment infrastructure.

The environmental sustainability of bioplastics cannot be assumed based on material labels alone. It must be earned through evidence-based evaluation of environmental performance across the entire product life cycle.