The headlines in recent years on plastic pollution have played a major role in raising public awareness about the need for an effective strategy to tackle the problem. Waste management is under heavy scrutiny for prevention, value extraction and the proper handling of waste. Products offering biodegradability and compostability are now increasingly being presented as alternative options. Polly Wong and Michael Thompson of impact solutions, currently the only UK UKAS approved laboratory capable of testing for ultimate biodegradability of material explain more about how to assess true biodegradability.
The pressure on the plastics industry to take action continues to rise, especially with the recent entry into force of a new piece of European legislation known as Single-Use Plastic Directive (SUPD). Put forward in May 2018 by the European Commission as a proposal to address the issue of marine litter from plastics, the directive, targeted at ‘the reduction of the impact of certain plastic products on the environment', came into effect on 3 July of this year.
While the SUPD includes bio-based and biodegradable plastics in its ban on single-use plastics, impact solutions have nonetheless noted an increase in the number of products offering ‘biodegradable’ or ‘compostable’ end-of-life options, developed with the aim of reducing the pressure on landfills.
The question which then arises is: how do we classify what is ‘biodegradable’ and what is ‘compostable’? The answer is standardisation, which provides internationally agreeable definitions for both biodegradability and compostability. To achieve these agreeable definitions, we need standards that involve efforts from industry subject matter experts that:
- Standardise test methods with clear guidance and testing procedures; and
- Specify criteria for a product or material to be categorised into a pass or fail acting as a regulative function.
Deciding on the biodegradability of a polymer is the utmost for the evaluation of the ecological behaviour of materials. As biodegradability is a key parameter, it ensures that the degradable substance decomposing within the surroundings will not cause long-term risk to plants, vegetation, and or marine environments.
Biodegradation is not a one-size-fits-all process as the process can take place via different mechanisms, such as aerobic and anaerobic. Aerobic degradation takes place in the presence of oxygen, while anaerobic degradation occurs in an oxygen-deprived environment. Nevertheless, both mechanisms require microorganisms to ease the breakdown of the materials. The process of biodegradation will differ depending on the surrounding conditions, i.e., temperature, pH, level of oxygen, moisture etc.
According to ISO 1485, the degree of aerobic biodegradability of plastic materials, including those containing formulation additives, can be determined by measuring the amount of carbon dioxide that has evolved during the process. The standard defines ultimate aerobic biodegradation as ‘the breakdown of an organic compound by micro-organisms in the presence of oxygen into carbon dioxide, water, and mineral salts of any other elements present (mineralization) plus new biomass’.
Currently, however, there are no EU laws to comprehensively regulate bio-based, biodegradable, and compostable plastics. Frameworks such as the EN 13432 and certifying bodies such as TUV Austria or Din Certco have been put in place to supply guidelines and benchmarks with which products must comply in order to qualify as ‘biodegradable’ or ‘compostable’. At present, adherence to existing standards and certification schemes is voluntary for individual market participants, which unfortunately means we will see misleading claims regarding products' biodegradable/compostable credentials on the market.
One such standard that has been developed in the battle against misleading information is the ASTM D6691, a test method developed to assess the biodegradation of polymeric materials, and more particularly, plastics in a marine environment.
How do we assess the biodegradability of plastics in marine environments?
We currently live in a world where plastic waste has become a major problem, especially in the form of marine debris. Finding solutions for the end-of-life disposal of this waste is crucial. If biodegradability is being weighed as an option for a particular material, the biodegradability of that material in a marine environment must also be considered.
Plastic waste that is littered on land is inevitably transported - by many mechanisms - into the marine environment. It is therefore essential to consider the biodegradation mechanisms of a material within a marine environment as well.
To determine the mechanism, a test sample is assessed for the characterisation of carbon content and molecular weight before any biodegradation testing is started. Within ASTM D6691, the preparation of the marine environment for testing is a critical step, as it must be ensured that the correct microorganisms are present in the required quantities. Then and only then can the polymer sample be submerged in the inoculum (marine solution). A biochemical oxygen demand (BOD) system is used to measure the pressure difference between the evolved carbon dioxide (CO2) given off and oxygen (O2) consumed. The BOD system includes a set of receptacles and CO2 sensors which together create a closed system. The microorganisms within the marine solution slowly consume the polymer sample, developing carbon dioxide as a by-product, the result of which is a pressure drop within the BOD system.
To determine the ultimate degree of biodegradation using ASTM D6691, the biodegradability of the material is validated by the release of biogas i.e., CO2 and is compared to the reference sample being run in conjunction with the test sample.
A typical test can be active for between 10-90 days. If, however, the specimens are extremely biodegradable, it is acceptable to end the experiment when the cumulative biogas production plateaus; conversely, the experiment can be extended if limited biodegradation has occurred within the specified timeframe.
How to certify your products
To accredit a product as ‘biodegradable’ or ‘compostable’, businesses must go to an independent accredited laboratory with the capability of testing products to the required standards, such as ISO EN 13432 or ISO EN 14855. In the UK, the most appropriate route is to search the database of UKAS (United Kingdom Accreditation Services) for an accredited laboratory. In Europe, the EA, the European co-operation for Accreditation offers a list of the various national accreditation services. Typically, the relevant testing method can be searched for on the accreditation services website, yielding a list of accredited laboratories that can perform the tests. These laboratories typically begin by first characterising the material, then testing the biodegradability potential, analysing the disintegration of the product and finally checking the ecotoxicity of the material to ensure that it will have no adverse effect on the environment it is disposed of in.
The requirement of these accredited laboratories is to supply impartial accredited data so that a certifying body can assess the data for certification through schemes such as OK Compost and others. As previously mentioned, there is no legal obligation to certify products as ‘biodegradable’ or ‘compostable’ and self-labelling is possible, with EN ISO 14021 giving guidance on this. For consumers, however, the certification schemes add an extra layer of confidence, whereas for an accountable business, these provide assurances in preventing potential disputes, if the product imposes a risk to the environment due to negligent disposal