Biodegradable plastics
Biodegradable plastics are materials that can only be degraded under specific, optimal conditions. However, such conditions are rarely present in the natural environment. If not properly managed, biodegradable plastics can harm ecosystems as plastic litter or microplastics, in the same way as conventional plastics.
The term biodegradable needs to be supported by scientific data on the environmental conditions under which degradation can occur. For example, the term compostable, which is used for some plastic products, often refers to plastics that can biodegrade in an industrial composting facility but not necessarily in a home composting context, and even less so in the natural environment. The term may also give the impression that the plastic is harmless to dispose of in nature.
Biodegradable plastics can be made from either bio-based or fossil-based feedstock, and bio-based plastics are not necessarily biodegradable. Plastic materials that are waste-sorted in the Nordic countries are directed to material recycling or energy recovery and do not undergo biodegradation. For both bio-based and fossil-based plastics that are not part of circular reuse systems, the greatest environmental benefit is achieved through mechanical recycling into new plastic products.
The European Strategy for Plastics in a Circular Economy states that biodegradable plastics can create problems for the mechanical recycling of conventional plastics. These specific polymers are not part of current mechanical recycling systems, and consumers may not know how to sort biodegradable plastics. Consequently, in the Nordic countries, the preferred waste stream for biodegradable plastics is incineration with energy recovery, which represents a lower level in the waste hierarchy. While this may change in the future, biodegradable plastics do not currently offer an environmental advantage within Nordic resource streams.
Even with regard to reducing microplastics in the ocean, the characteristic of being biodegradable is not a solution. Like conventional plastics, biodegradable plastics can break down into microplastics if they are not degraded under optimal conditions, which rarely occur. See also the final section on test methods for composting and biodegradation. The most effective solution is to ensure that no plastic ends up in nature – and this applies to all types of plastic.
In line with the way requirements are set for the Nordic Swan Ecolabel, the European Environment Agency states:
“In a circular economy, all plastics should be recycled into new plastics in the first instance. Compostable plastics that can be treated with bio-waste offer environmental benefits for specific applications and situations, provided their use is aligned with the bio-waste treatment infrastructure.”
How does the Nordic Ecolabelling set requirements?
At present, Nordic Ecolabelling generally sets requirements that prioritise recyclable plastics over biodegradable plastics. An exception is water-soluble plastic films used for dishwasher or laundry detergents that enter the wastewater system and therefore need to be readily biodegradable and water-soluble. The Nordic Swan Ecolabel requirements for plastics are generally adapted to specific product groups.
Environmental background – test for biodegradability
In Directive (EU) 2019/904, the term biodegradable plastic is defined as “[…] a plastic capable of undergoing physical and biological decomposition, such that it ultimately decomposes into carbon dioxide (CO₂), biomass, and water, and is, in accordance with European standards for packaging, recoverable through composting and anaerobic digestion.”
Examples of conditions for which specific test standards for the biodegradability of plastics exist include the following.
Composting of plastics often requires the presence of specific environmental conditions, including elevated temperatures, pressure, and nutrient concentrations, as well as specific chemical conditions. These requirements can generally only be met in industrial composting facilities and can be verified using, for example, standards such as EN 13432 or EN 14995. These standards do not test for biodegradation in the natural environment. Composting typically takes place under aerobic conditions, in contrast to anaerobic biodegradation, for example in seawater and sediments.
Further challenges arise in more uncontrolled, open environments. Currently, some methods exist for determining the biodegradation of plastics in certain marine and aqueous environments, for example ISO 23977-1, ISO 14851, and ISO 14852. Standards for biodegradation in soil also exist, for example ISO 17556. However, these tests are only indicative and are conducted under optimal laboratory conditions designed to maximise degradation. Natural environments can vary significantly in factors that influence degradation, such as temperature, organic content, pH, salinity, and chemical composition.