Biodegradable Does Not Mean Biodegradable Everywhere: Understanding Bioplastics in Real-World System
Spotlight on Sevil Vafadar Afshar
Bioplastics are increasingly discussed as potential alternatives to conventional plastics. But what happens to these materials once they enter waste management systems or the environment?
At the InPlasTwin Summer School 2026, Sevil Vafadar Afshar from the Department of Environmental and Resource Engineering at the Technical University of Denmark (DTU Sustain) addressed this question in her presentation, “Degradation of Bioplastics in Real-World Systems: Pathways, Transformation, and Environmental Relevance.”
Her presentation highlighted an important point: understanding whether a material is described as “bioplastic” or “biodegradable” is only the beginning. What matters is where, how, and under which conditions degradation actually takes place.
What exactly is a bioplastic?
The term bioplastic can easily lead to misconceptions. A bioplastic can be bio-based but not biodegradable, biodegradable but fossil-based, or both bio-based and biodegradable. Examples of bio-based and biodegradable polymers include polylactic acid (PLA), starch blends and polyhydroxyalkanoates (PHA), while polybutylene adipate terephthalate (PBAT) and polybutylene succinate (PBS) are examples of fossil-based biodegradable polymers. Bio-based polyethylene (bio-PE), meanwhile, is bio-based but not biodegradable. This distinction is important because the origin of the raw material does not automatically determine what will happen to a plastic at the end of its life.nMost importantly, biodegradable does not mean biodegradable everywhere. Biodegradable plastics are generally designed to degrade under specific conditions, and during this process microplastic formation can occur as an intermediate step.
What does plastic degradation actually mean?
Plastic degradation is an irreversible process in which the material gradually loses its structural integrity through biotic or abiotic mechanisms. Abiotic degradation (disintegration) involves factors such as UV radiation, heat, and mechanical stress, that can cause physical fragmentation, while biotic degradation (biodegradation) occurs when microorganisms break down the plastic. Under aerobic conditions, biodegradation can ultimately produce carbon dioxide, water and biomass, while under anaerobic conditions methane can also be generated. This distinction is particularly important when evaluating biodegradable materials because simply observing that a plastic product has fragmented or disappeared visually does not necessarily demonstrate complete biodegradation. Incomplete degradation may leave smaller plastic particles behind, while degradation processes may also involve the release of chemicals. These factors need to be considered when assessing the environmental performance of biodegradable plastics.
What does the scientific literature tell us?
A critical review presented during the Summer School examined 152 scientific articles covering experimental degradation studies of PLA, starch-based plastics, PBAT, PBS and PHAs in both waste management environments, such as composting and anaerobic digestion, and open environments, including soil and freshwater. The review revealed substantial gaps. PLA and starch-based plastics have received considerably more research attention than PBS, PBAT and PHAs. Many studies investigate polymers rather than actual final products, and differences in experimental setups make direct comparisons between degradation studies difficult. Another important challenge is the lack of harmonisation in standard test methods for plastic degradation. Some environments have multiple standardised methods, others have none, and many studies simply do not use standardised methods. Consequently, reported degradation degrees can vary considerably depending on how an experiment is designed, further complicating comparisons across studies.
The environment makes a difference
Temperature, moisture, oxygen availability, microorganisms, time and the characteristics of the plastic itself can all influence degradation. This helps explain why a material that performs well under one set of conditions may behave very differently somewhere else. For example, industrial composting provides relatively controlled conditions, typically involving temperatures of 50-70 °C, moisture levels of 50-60 % and aerobic conditions. These systems are designed to promote rapid biodegradation. Home composting is much less predictable. Temperatures are generally lower and can fluctuate significantly, moisture content varies and conditions may, therefore, be considerably less favourable for biodegradation.
From controlled tests to real-world conditions
The experimental work presented by Afshar et al., 2025, illustrates why this difference matters. In one industrial composting experiment, 10 commercial biodegradable plastic products certified as compostable, including products made from PLA, PBAT/starch and PHA, were tested according to ISO 20200. Samples were incubated for 90 days at 58 °C and 55 % moisture under regular aeration and moisture control. Under these controlled and optimal composting conditions, the tested biodegradable plastic products achieved degradation degrees ranging between 75 – 100 %.
But what happens when conditions are less controlled?
A citizen-science experiment involving 33 participants tested biodegradable plastic spoons under Danish home-composting conditions. During the eight-month experiment, temperatures ranged from -1.5 °C to 65 °C and pH from 4.5 to 8. The result was striking: no measurable degradation was observed after eight months under those conditions. This provides a clear example of why a biodegradability claim needs to be interpreted in relation to the conditions for which the material was designed and tested.
What happens in aquatic environments?
The same question applies when biodegradable plastics reach freshwater or marine environments. Experiments presented during the Summer School tested biodegradable waste bags, shopping bags and mulching films made from PBAT/starch, PBAT/PLA and PHA, alongside conventional low-density polyethylene (LDPE) and a positive control. Tests were conducted in freshwater and seawater under aerobic conditions, with biodegradation assessed through oxygen consumption.
These experiments reinforce the broader message that biodegradation is environment-specific. A material designed for degradation under composting conditions should not automatically be expected to behave in the same way in soil, freshwater, seawater or wastewater-treatment systems.
Why real-world testing matters?
Biodegradable plastics may have an important role in future approaches to plastic use and waste management, but their environmental performance cannot be assessed from a label alone. Testing needs to consider the actual product, its intended use, its likely end-of-life pathway and the conditions it may encounter if it reaches the environment. This is particularly relevant for agricultural plastics, where materials can interact directly with soil and where incomplete degradation may contribute to the formation of smaller plastic particles.
Sevil highlights important messages:
- Not all bioplastics are biodegradable.
- Biodegradable plastics do not necessarily degrade in every environment.
- Degradation under realistic conditions can be lower than under controlled laboratory conditions.
- Experimental design strongly influences measured degradation and our ability to compare studies.
Understanding these differences is essential for developing better testing approaches, interpreting biodegradability claims correctly and ensuring that new materials provide genuine environmental benefits rather than simply shifting the plastic pollution problem from one form or environment to another.
About the expert
Sevil Vafadar Afshar is a postdoctoral researcher at DTU Sustain, working on the environmental fate and effects of bioplastics. Within the InPlasTwin project, her research has focused on comparing the performance of biodegradable and conventional plastic mulching films, including their degradation, microplastic formation, and ecotoxicological effects. Her work combines experimental and analytical approaches to contribute to more robust assessment frameworks and informed decision-making on the use and end-of-life management of plastic materials.