Reflections on biodegradability

How do we assess biodegradability? Why is it important to separate between bio-based and biodegradable? And how does biodegradability fit into the concept of sustainability? Three experts share their thoughts.

Karin Hennung

Product HSE Manager, Nynas

Over twenty years’ experience of working with issues relating to HSE. Master of Science in Chemical Engineering from Chalmers University of Technology (Sweden).

“Our starting point is always to minimise the risk of a spillage”

"OECD screening tests are used to determine whether a substance or a product is readily biodegradable. For oil products, we usually use methods with the designation OECD 301F/301B. These are conservative methods. This means that if you achieve the pass level, which represents 60% within 28 days, the product is considered to be readily biodegradable. A lower result does not necessarily mean that the substance or product is not biodegradable in the environment. But it is still important to keep to the limits for a pass level that are specified in these methods. Nor is it advisable to use other, unverified, criteria for the OECD tests, as this results in a lack of clarity.

Many oil products do not meet the requirements for being readily biodegradable in accordance with the OECD criteria. The question then is: how does this affect their handling and when it is important to use a product that is readily biodegradable?

Regardless of product, our starting point is always to minimise the risk of a spillage. But if an accident does happen and there is a spillage, it is my firm conviction that remediation is required, whether or not the product is readily biodegradable. It is of course an advantage to have a readily biodegradable product in sensitive environments, so that the impact of any spillage is reduced. In such cases a product like Nynas NYTRO® BIO 300X could be an option.

It must also be borne in mind that a product’s degradability is only one aspect under the sustainability umbrella that needs to be considered. Other aspects like raw material, production process, durability and recyclability also need to be evaluated."

Chris Hughes

Principal Regulatory Consultant, Ricardo (NCEC)

Over ten years’ experience working on biodegradability assessments and the implementation of REACH for multinational chemical companies. Master’s degree in Chemistry.

“Biodegradability assessments may need to be adapted”

"Products containing hydrocarbons are usually very complex mixtures of constituents, with varying structures and properties. Also, the composition can vary from one batch to another. This makes assessing the biodegradability of these products very challenging.

The screening methods used to test biodegradability employ high test substance concentrations in water. As biodegradation generally occurs in the dissolved phase, many hydrocarbons are at a massive disadvantage due to their very poor water solubility. Many are also quite volatile, making them even harder to test. They get lost from the system, never actually getting the chance to degrade.

There are ways of modifying test methods and equipment to account for these challenging properties, leading to improved test results. Because of how they are devised, the standard methods do not always reflect what might happen in a natural environment.

The standard testing methods provide a bulk result for a set amount of the product based on the production of CO2 or the amount of oxygen used. Such bulk results provide limited information about complex hydrocarbon products, and biodegradability assessments may need to be adapted to provide greater information on a constituent level rather than a bulk level.

For example, there are computational tools that can be used to help predict the biodegradability of constituents of certain products that might be particularly hard to assess."

Nicole Grobert

Associate Head of Department (Research), Professor of Nanomaterials, Department of Materials, University of Oxford

Chief Scientific Advisor, European Commission; Committee Member, The Royal Society; Fellow of Materials, Corpus Christi College, Oxford.

“Confusion often exists among end users”

"Whether or not a biodegradable plastic item biodegrades depends not only on the properties of the material itself, but also on the environment in which biodegradation takes place. In our 2020 Scientific Opinion on “Biodegradability of Plastics in the Open Environment” as the European Commission’s independent Group of Chief Scientific Advisors, we recommended a definition of biodegradability as a “system property.”

This includes the interplay of the specific material properties of the plastic and the conditions of the specific receiving environment where biodegradation takes place. In the same way that food stored in a fridge lasts longer than food stored at higher temperatures, for example, on a kitchen counter, many biodegradable plastics biodegrade slower at colder temperatures.

Confusion often exists among end users between bio-based and biodegradable plastics. Bio-based polymers (or biopolymers) such as cellulose, starch, and lignin are composed of carbon derived from renewable biological sources such as plants, in contrast to fossil-based polymers. The fact that these plastics are bio-based, however, does not necessarily mean they are biodegradable, and both bio-based and fossil-based polymers can be either biodegradable or non-biodegradable.

Clear information about the difference between bio-based, biodegradable and compostable plastics, needs to be conveyed to end users both through labelling and information campaigns."


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