Oxo-degradation

OXO-degradable is a term used by the EU and others which has caused confusion.  The specific definitions are found in CEN (European Committee for Standardisation) Technical report CEN/TR 15351 "Oxo-degradation" is degradation identified as resulting from oxidative cleavage of macromolecules". This describes ordinary plastics which abiotically degrade by oxidation in the open environment and create microplastics, but do not become biodegradable except over a very long period of time. Additives are not used to make plastic oxo-degradable and plastic is not marketed as oxo-degradable.  

By contrast "oxo-biodegradation" is "degradation resulting from oxidative and cell-mediated phenomena either simultaneously or successively". this means that the plastic degrades by oxidation until its molecular weight is low enough to be accessible to bacteria and fungi, who then recycle it back into nature by cell-mediated phenomena.  These plastics are marketing as oxo-biodegradable."

Background

"Biodegradable plastic" is a term which causes confusion and should not be used, because it could apply to two completely different type of plastic.

• Vegetable-based plastics, which are also loosely known as "bioplastics" or "compostable plastics", are tested in accordance with ASTM D6400 or EN13432 as to their ability to biodegrade under conditions found in industrial composting or biogas facilities.

• Oxo-biodegradable plastics—which are made from polymers such as polyethylene (PE), polypropylene (PP), contain a prodegradant catalyst—usually a salt of manganese or iron, and are tested in accordance with ASTM D6954 or BS8472, or AFNOR Accord T51-808, as to their ability to degrade and then biodegrade in the open environment. The prodegradant catalyzes the abiotic degradation process so that Oxo-biodegradable plastic will degrade in the presence of oxygen much more quickly than ordinary plastic. The plastic material has then been converted into small-chain organic chemicals, such as ketones, alcohols, carboxylic acids, and low molecular mass hydrocarbon waxes. The remaining chemicals are no longer plastic and are biodegradable by bacteria, which are ubiquitous in the terrestrial and marine environments. The timescale for complete biodegradation at any time or place in the open environment is much shorter than for "conventional" plastics, which in normal environments are very slow to biodegrade and cause large scale harm.

Degradation is initially prevented by the presence of polymer stabilizers in the plastic, which ensure a useful service-life for the article. Once the stabilisers have been exhausted OXO-biodegradation will begin. The chemical mechanism is that of autoxidation but it is greatly accelerated by the presence of metal-catalysts, which promote the homolysis of hydroperoxides into free radicals which drive the degradation process. Access to oxygen is essential and OXO-degradable plastics will not degrade if buried deep in landfill.

Conventional polyethylene (PE) and polypropylene (PP) plastics will typically fragment quite quickly, but will then take decades to become biodegradable. OXO-biodegradable plastic, if discarded in the environment, will degrade to oxygenated low-molecular-weight chains (typically MW 5–10,000 amu) within 12–18 months, depending on the material (resin, resin thickness, anti-oxidants, etc.), temperature, and other factors in the environment.

Biodegradation of up to 92.74% has been observed in a soil environment within 180 days, when tested in accordance with ASTM D6954. OXO-degradation has been studied at the Eurofins laboratory in Spain, where on 25 July 2017 they noted 88.9% biodegradation in 121 days.

The statements about biodegradation of oxo-degradable plastics were considered in the 2016 Eunomia Report for the EU Commission.

Standards applicability

Oxo-biodegradable plastic degrades in the presence of oxygen. Heat and UV light will accelerate the process, but neither they nor moisture are necessary. Such plastic is not designed to be compostable in open industrial composting facilities, according to ASTM D6400 or EN13432; but it can be satisfactorily composted in an in-vessel process, and has been proved to be compostable according to ISO 14855 [Eurofins Laboratories 6.11.16].

The standards for industrial composting, ASTM D6400 and EN13432, require the plastic to convert to carbon dioxide (CO₂) gas within 180 days by industrial composting. Indeed materials which do comply with ASTMD6400, EN13432, Australian 4746, and ISO 17088 cannot properly be described as 'compostable' because those standards require them to convert substantially to CO2 gas within 180 days. you cannot therefore make them into compost - only into CO2 gas.  This contributes to Climate Change, but does nothing for the soil. A leaf is generally considered to be biodegradable, but it will not pass the ASTM composting standards, due to the 180-day limit.

OXO-biodegradable plastic conforms to the American Standard (ASTM D6954) and a British Standard (BS8472), which specify procedures to test degradability, biodegradability, and non-toxicity, and with which a properly designed and manufactured OXO product must comply. These standards contain pass/fail criteria.

There is no need to refer to a standard specification unless a specific disposal route (e.g., composting), is envisaged. ASTM D6400, EN13432, and  Australian 4736 are standard specifications appropriate only for the special conditions found in industrial composting.

According to an EU report the oxo-degradable plastics do not biodegrade on a landfill neither should they be regarded as compostable.

Environmental issues

Oxo-biodegradable plastic, including plastic carrier bags, will biodegrade much more quickly in the open environment than conventional plastic. Nobody has given any reason why biodegradation once commenced should stop before it is complete, even if it did not fully biodegrade it would be better than conventional plastic., which would not have biodegraded at all in that timescale.  It is not intended to biodegrade in landfill, because anything (e.g. compostable plastic) which biodegrades in anaerobic conditions will generate methane, another Greenhouse Gas.  As to the marine environment see the Oxomar Study.

As to microplastics, these are caused by the fragmentation of ordinary plastic under the influence of weathering, but they do not become biodegradable except over a long period of time. Oxo-biodegradable plastics disintegrate because the molecular weight of the polymer has reduced to the point where it has no physical strength and has become biodegradable. In December 2017 the European Chemicals Agency (ECHA) were asked to study oxo-biodegradable plastic and on 30th October 2018 ECHA informed the BPA (Biodegradable Plastics Association) that they were not convinced that microplastics were formed.

EN13432 does not require testing of compostable plastic in a compost heap and ASTM D6954 does not require oxo-biodegradable plastic to be tested in a field or in the ocean.  In both cases they are tested according to standards designed by scientists to replicate the conditions in the environment where they are intended to biodegrade, The standard for oxo-biodegradable plastics require eco-toxicity testing to ensure that they material will be safe in the environment.

Controversy

On 6 November 2017, the Ellen MacArthur Foundation issued a report which they had to revise in 2019 after complaints had been received regarding its accuracy.  See https://www.biodeg.org/wp-content/uploads/2019/11/emf-report-1.pdf

The Biodegradable Plastics Association (BPA) claimed that the report was inaccurate, and pointed out that many of the organisations shown as endorsing the report aggressively promoted a rival bio-plastic technology, while many of the others whose logos appeared in the document were themselves producers of the very plastic items that get into the open environment as litter. The paper's conclusions were rejected by professor Ignacy Jacubowicz, who said the degradation process was not merely a fragmentation, but a change from a high molecular weight polymer to a material that can be bio-assimilated.

The evidence for and against oxo-biodegradable plastic was also reviewed in November 2018 by Peter Susman QC, a deputy judge of the High Court on England, who had over 25 years experience of adjudicating cases in the technology and construction branch of the high court, involving the evaluation of expert evidence. He declared the scientific case in favour of oxo-biodegradable plastic to be "clear and compelling". Susman examined the processes of abiotic and biotic degradation of plastics, and then looked specifically at degradation in air and degradation in seawater. He concluded, in a 15-page written opinion that

"It is no longer tenable to conclude that there is 'no firm evidence either way' whether oxo-biodegradable is effective. I consider that recent research provides clear and compelling evidence that oxo-biodegradable plastic is indeed effective in facilitating very significantly speedier degradation than is the case when that technology is not used.... [I] cannot imagine that such significantly speedier final degradation occurs later than 'within a reasonable time', however that the expression might be defined.... [I regard the idea that biodegradable plastics might encourage littering as] "fanciful and unreasonable".

European strategy for plastics in a circular economy

On 16 January 2018, the European Commission published its report on the use of oxo-degradable plastic. The document forms part of the European strategy for plastics in a circular economy, which was released the same day.

The Commission focused on three key issues relating to oxo-degradables: the biodegradability of oxo-degradable plastics in various environments; the environmental impacts in relation to littering; and recycling.

The Commission found there was no conclusive evidence that, in the open environment, oxo-degradables fragmented to a sufficiently low enough molecular weight to enable biodegradation. There was no conclusive evidence about the time needed for oxo-degradable plastics to fragment in marine environments, nor about the degree of fragmentation. It said there was a considerable risk that fragmented plastics would not fully biodegrade, leading to subsequent risk of an accelerated and accumulating amount of microplastics, especially in the marine environment. Rapid fragmentation was found to increase the risk of microplastic ingestion by marine animals.

In relation to littering, the report found that, although it appeared the oxo-degradable plastics industry could create products with minimal toxic impact on flora and fauna, it had not been conclusively proven that there were no negative effects. Marketing oxo-degradables as a solution for plastic waste in the environment may make it more likely that items are discarded inappropriately and in marine environments; the fragmentation process made oxo-degradable plastic less likely to be recovered during clean-up exercises.

The report was criticised by the Biodegradable Plastics Association (formerly the Oxo-biodegradable Plastics Association)  (BPA), which said the European Commission had failed to understand the difference between oxo-degradable and oxo-biodegradable plastics. The BPA accused the Commission of not listening to evidence relating to the breakdown of oxo-plastics, which it maintained showed the plastic broke down to a molecular level that could be bioassimilated. In relation to timescales for biodegradation, the OPA said it was not useful to examine how long it took for particular specimens to breakdown in particular conditions, due to the variability of environmental conditions. It said the key point was that oxo-biodegradable plastics would breakdown faster than conventional plastics under the same conditions. Regarding recycling, it said its members had been successfully recycling oxo-biodegradable plastics for more than ten years, with no adverse reports. It rejected the Commission's view on littering and said that, as oxo-degradable plastics were indistinguishable from other plastic products, they were unlikely to cause any additional levels of littering. It criticised the Commission's use of external reports, including that of the Ellen MacArthur Foundation, the findings of which it previously disputed.

A more recent report, of October 2018, is in line with the previous one. It states that micro-plastics need to be restricted, including oxo-degradable plastics.

The EU directive 2019/904 of the European Parliament and of the Council (5 June 2019) prohibits the introduction in the market of products made from oxo-degradable plastic (Article 5)

Response of the Oxo-biodegradable Plastics Association to the EU

In its Proposal (2018/0172(COD)) for a Directive on "Reduction of the impact of certain plastic products on the environment", the EU Commission proposed various measures for reducing the quantity of plastic goods being produced, and measures for encouraging collection for recycling. Most people would support those measures, but plastic will still escape into the open environment in unacceptable quantities until such time as plastic waste has been eliminated. This is not likely to happen any time soon.

According to the Biodegradable Plastics Association (formerly the Oxo-biodegradable Plastics Association) oxo-biodegradable technology is the only way to prevent the accumulation of plastic waste in the environment; and if oxo-biodegradable technology were severely restricted in the EU, there would be unintended consequences. There would be a distortion of markets, if European companies were effectively prevented from manufacturing for countries where oxo-biodegradable plastic is mandatory. Alternatively, some countries could follow Europe's lead with disastrous consequences, and much of their accumulated plastic waste would eventually find its way to the shores of Europe.

Recital (3) to the draft Directive says "Marine litter is of a transboundary nature and is recognized as a global problem." The Reis report to the European Parliament (11 October 2018) says "Every year in Europe, 150,000 tonnes of plastic are dumped into the sea. The situation is even more alarming at [the] global level, with 8 million tonnes ending up in the sea each year." Recital (5) to the draft Directive says "In the Union, 80 to 85 % of marine litter, measured as beach litter counts, is plastic, with single-use plastic items representing 50%." This is why the plastic needs to be urgently upgraded so that it will convert into biodegradable materials much sooner than ordinary plastic, if it does escape into the open environment, especially the oceans.

Microplastics being recovered from the oceans are from "oxo-degradable" plastics, which degrade and fragment but do not biodegrade except over a very long period of time. These are conventional plastics which undoubtedly create persistent microplastics, and this is why they have been banned for a wide range of products in Saudi Arabia and 11 other countries, where oxo-biodegradable technology for making these products is now mandatory. The products have to comply with strict standards, based on ASTM D6954.

External links

• Oxo Biodegradable Plastics Federation