Oxo-(bio)degradables: the who, what, and why of breaking down fossil-based plastics

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The EU’s ban on oxo-degradable plastics has triggered a years-long legal and scientific tug-of-war. This report unpacks the contentious claims, court decisions, and industry stakes surrounding oxo-biodegradable packaging, revealing a deep divide between environmental caution and technological advocacy.

• The EU ban stands firm: The European General Court upheld the 2019 directive banning oxo-degradable plastics, citing microplastic risks, unproven biodegradability, and threats to recycling streams.
• Symphony Environmental’s legal challenge failed: The company claimed reputational and financial damage, arguing its additives promote biodegradation, not fragmentation – but the court found no breach of proportionality or fair treatment.
• Scientific consensus remains fractured: Critics argue oxo-plastics break into persistent microplastics under most conditions; proponents cite lab evidence of full biodegradation into CO2, water, and biomass.
• Environmental conditions are key: Studies show oxo-biodegradation depends heavily on heat, light, and oxygen – conditions rarely met in nature, landfill, or ocean environments.
• Terminology drives confusion: Stakeholders disagree on whether to label these plastics ‘oxo-biodegradable’, ‘oxo-fragmentable’, or ‘pro-oxidant additive-containing’, with implications for both regulation and consumer trust.
• Circular economy goals are at odds: Because oxo-plastics degrade over time, they can’t be reused or reliably recycled, clashing with industry efforts to design packaging for long-term circularity.

The battle over oxo-degradable plastics is far from over, but the EU’s stance is clear: uncertain claims and inconsistent degradation timelines don’t meet the bar for environmental safety. While some companies continue to defend the technology, momentum is shifting toward proven, standards-backed solutions. Going forward, regulatory clarity, scientific rigor, and transparency will be critical for any material claiming to be part of the solution, not the problem.

The legal battle surrounding ‘oxo-degradable plastics’ has extended as far as the European General Court, which recently doubled down on its decision to ban such materials on the EU market. But what are they and why are they so controversial? In this edition of the Brief, we dig deeper into their turbulent history and the claims made on both sides of the fence.

Technically speaking, any material that enters the natural environment will eventually break down. It is the speed at which this happens, influenced by various environmental factors, that differentiates certain materials as harmful to the planet – such is why fossil-based plastics are considered pollutive, with some taking up to one thousand years to fully degrade.

In this context, so-called ‘oxo-degradable’ or ‘oxo-biodegradable’ plastics have arisen in the packaging space. Unlike compostable or biodegradable plastics, they are not separate, bio-based materials, but conventional plastics infused with an inorganic additive. These are differentiated from ‘enzyme-mediated degradable’ additives, which are organic.

In theory, these additives accelerate the breakdown of a fossil-based plastic until its pieces are small enough that naturally occurring microorganisms like bacteria and fungi can initiate an organic recycling process.

The development of oxo-degradable plastics has been controversial from the start and, in the Directive (EU) 2019/904, the European Parliament and Council prohibited the placement of such materials on the European market, “as that type of plastic does not properly biodegrade and thus contributes to microplastic pollution in the environment, is not compostable, negatively affects the recycling of conventional plastic and fails to deliver a proven environmental benefit.”

In response, Symphony Environmental filed a lawsuit in 2021. It sought an estimated compensation claim of up to £82 million in reputational damage, loss in profits, and a general decline in the company’s value – alleging that the ban is not backed by evidence from the European Chemicals Agency and ignores the safeguards against arbitrary legislation provided by Arts. 69-73 of REACH.

At the manufacturing stage, Symphony Environmental adds a masterbatch to its plastic films, which are then extruded and turned into bin bags, food bags, refuse sacks, and water-soluble laundry bags. The company asserts that its packaging is recyclable but, if it ends up in the natural environment, it will biodegrade into carbon dioxide, water, and biomass under heat and light in the space of 12-18 months. Cold and dark conditions are thought to slow the process down, but not stop it completely.

Reportedly, this technology quickly reduces a plastic’s molecular weight and results in a ‘waxy substance’ to be consumed by microorganisms in the natural environment. As such, it is not considered by its creators to be a source of microplastics.

“The degradation process is not only a fragmentation, but is an entire change of the material,” Professor Ignacy Jakubowicz, senior researcher at the Research Institutes of Sweden (RISE), explains on the Symphony Environmental website. “The material changes from a high molecular weight polymer to monomeric and oligomeric fragments, and from hydrocarbon molecules to oxygen-containing molecules which can be bioassimilated.”

Conflicting parameters

Despite these claims, the Court of Justice of the European Union (CURIA) dismissed the lawsuit in February 2024. The General Court reiterates that the Directive in question is intended to protect both human health and the natural environment, meaning it is not an infringement on the principle of proportionality. Furthermore, since plastics treated with pro-oxidant additives are ‘not in a situation comparable with products made from conventional plastics’, according to CURIA, the ban does not violate the principle of equal treatment.

In its written pleadings, the European Parliament did not refer to Symphony Environmental’s masterbatch as distinctly ‘oxo-biodegradable’, believing that the term ‘may imply a view has been taken on the biodegradability of that type of plastic’. The Council preferred the term ‘pro-oxidant additive containing plastic’, while the Commission was similarly skeptical in its use of ‘oxo-(bio)degradable’.

Symphony Environmental frequently emphasizes its differentiation between oxo-degradation, in which a material degrades abiotically through oxidation but breaks down into microplastics and is neither compostable nor biodegradable; and oxo-biodegradation, in which oxidation lowers a plastic’s molecular weight to the point that it can be recycled in the natural environment. Not every industry player agrees with this distinction, however, and European Bioplastics raises ‘oxo-fragmentation’ as a more accurate term.

Green Dot Bioplastics aligns with this terminology in its own stance on the matter. It argues that the breakdown of oxo-biodegradable plastics does not occur at a molecular or polymer level, instead forming microplastics that remain in the natural environment for years to come. Indeed, the European Parliament and Council have pointed to a study by Eunomia indicating that, unless these plastics were initially exposed to ultraviolet radiation and heat, they biodegraded very slowly, if at all. This was because they had not fragmented enough for microorganisms to handle them, the researchers explained, which contradicts the unique selling point of oxo-biodegradable products.

Given the differences in light and temperature between global regions, a caveat like this would make it difficult to estimate how much plastic must fragment within a certain time frame for biodegradation to take place. Therefore, advertising oxo-biodegradable materials with a specific breakdown period could be misleading – and to avoid this, Green Dot Bioplastics suggests the definition of standard conditions and a timeframe in which a product advertised as ‘biodegradable’ completely degrades.

Yet, another European Commission report raises questions as to how a ‘reasonable’ time frame is even determined. A HSAC review indicates that a complete breakdown can take anywhere between ‘several’ to ‘hundreds of years’ – and that, where studies exist, ‘it is common for researchers to simply demonstrate some level of biodegradation has happened rather than it being complete.’

On that point, Eunomia’s study took place under laboratory conditions, with the shortest observed period of near-complete degradation taking two years. As the written pleadings pointed out, this does not necessarily reflect the materials’ performance in nature, and no studies have yet been conducted with oxo-biodegradable materials in an ordinary climate.

Despite pro-oxidant additives potentially breaking down a fossil-based plastic more quickly than the elements and microorganisms would, it is possible that more harm could be caused during the degradation process. Eunomia’s study suggests that aerobic biodegradation, or the degradation that takes place during exposure to oxygen, may take place for the upper layers of landfill, but will become slow to non-existent in the deeper layers. Anaerobic biodegradation is possible there, yet this process produces methane – one ton of which immediately traps at least 100 times more heat in the atmosphere than the same amount of CO2, according to the Massachusetts Institute of Technology.

Data as to whether plastics containing a pro-oxidant additive sufficiently break down in the ocean is also lacking, says the report. Some of its experiments are thought to indicate quicker fragmentation in a marine environment, but slower biodegradation compared to open environments on land. If this is the case, smaller pieces could remain underwater for a longer period of time – reinforcing the ‘oxo-fragmentation’ label.

Pre-existing pushback

Resistance against oxo-degradable plastics is not new, however, and predates the Symphony Environmental trial. The plastics themselves date back to the 1970s as a response to the increasing threat of polyethylene and polypropylene waste.

In 2009, Fred Pearce wrote in The Guardian that “priming plastic bags for destruction is itself an ecological crime”. His article raised the point that plastics require high levels of energy and oil to produce, which some consider a waste if the bags they produce are ultimately designed to break down. Also, it was thought that consumers would be less likely to make the effort to recycle if they were told their bags would biodegrade in the environment anyway – and it was around this time that the New York Times declined to wrap its newspapers in oxo-biodegradable plastics, believing its claims to 100% biodegradability to be false.

Professor Gerald Scott of the Oxo-Biodegradable Plastics Association explained to NS Packaging that small compounds of cobalt, iron, nickel, or manganese are added to conventional polymers during extrusion to unlock oxo-biodegradation, reporting that the results are tested against ASTM D6954-04 and D6400 standards. Yet Pearce cited a study arguing that manganese additives actually prevented polyethylene breaking down in compost, likely due to the presence of ammonia or other gases generated in the composting process.

Much like the European Parliament and Council now, OWS was suggesting alternate terms for an oxo-degradable plastic back in 2013 – in this case, ‘thermo-fragmentable’ or ‘photo-fragmentable’. It cited ‘the oxo-degradable industry’ itself in its argument that, although oxo-biodegradable plastics will eventually degrade in full, this would not happen ‘in the foreseen timeframe as set forth in the different standards on (industrial and home) composting’.

Notably, it distinguished between a standard, which specifies a timescale and criteria that must be met to define a material as biodegradable, and a guideline, which is ‘comparable with test methods and merely prescribe[s] how the different tests need to be performed’. A material cannot conform to a guideline, it added, and must therefore adhere to a standard to earn its status as biodegradable.

Whether industrially or home composted, though, OWS stated that oxo-biodegradables fell short of existing standards. Apparently, the results of biodegradation tests could not be repeated under the same conditions more than once, whether by initial testers or by others replicating the experiment.

It added that, assuming a linear correlation between molecular weight and temperature applies across a broad range of temperatures, an oxo-biodegradable plastic’s molecular weight would only continue to decrease under specific conditions. Namely, these involve temperatures of between 55°C and 70°C lasting from 44 to 80 days, depending on the heat. This exceeds the hottest temperature ever recorded on Earth (56.7°C at Furnace Creek, California in July 1913), as well as the mere handful of times temperatures above 54.4°C have been recorded on the planet.

According to OWS, oxo-degradable plastics were most likely to enter recycling streams, become litter, be used in mulching films, or end up in landfill. With the exception of especially hot days in Death Valley, most natural environments will not reach the extreme temperatures required to break oxo-degradable plastics down quickly.

A statement from the Ellen MacArthur Foundation was also signed by 143 businesses, industry organizations, and NGOs – alongside twelve scientists and ten Members of the European Parliament – in 2017. As well as reiterating the unknown duration of its full biodegradation and the shortage of research surrounding oxo-degradables, it pointed out that a fragmenting material cannot be reused – going against the Foundation’s circular economy principles.

Furthermore, when it comes to sorting technology, recyclers and converters have reported that oxo-(bio)degradable plastic packaging is not currently detectable at scale. As such, they remain mixed in with conventional plastics – and the necessary amount of stabilizers needed to slow the degradation process, as well as the extent to which the material has already degraded, are difficult figures to estimate. It only becomes harder to do so with every recycling loop the plastic in question undergoes.

The Foundation continues that these plastics fall short of such standards as ISO 18606 for organic recycling, EN 13432 for compostability and anaerobic treatability, ASTM D6400 for home and industrially compostable plastics, and AS 4736 for compostable and biodegradable plastics. Because they are slow to break down and can leave plastic fragments in the compost, they can contaminate composting streams and cause plastics to leach into the environment.

This ‘oxo statement’ was temporarily removed in June 2018 after Symphony Environmental challenged its claims. “It seems that EMF do not understand the difference between oxo-degradable and oxobiodegradable plastics,” the company argued, criticizing the Foundation’s call for further evidence as “nobody makes degradation claims in respect of oxo-degradable plastic”. If the signatories are referring to oxo-biodegradable plastics specifically, the company continued, manufacturing them to degrade too soon would render them useless as a packaging material.

Rather, it underlined research from Queen Mary University of London suggesting that oxo-biodegradable plastic degraded 90 times faster than fossil-based alternatives and argued that the Ellen MacArthur Foundation’s “precautionary principle” was instead a “ban first and ask questions later” mentality – quoting English jurist Lord Sumption to describe this view as “essentially a principle for making decisions radically affecting people’s lives without adequate evidence.”

As legal challenges have now reached the General Court, the controversy is clearly ongoing. So far, the majority of the packaging industry is not showing signs of backing down, and Symphony Environmental remains one of few industry players in favour of oxo-biodegradable plastics. With a European ban remaining in place, it is certain that there will be no legal distribution of these materials amidst EU Member States, but time will tell what the future holds for these materials and their place in the sustainability conversation.

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