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.
By contrast oxo-degradation 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 marketed as "oxo-(bio)degradable."
Oxo-degradable plastics are intended to fragment if they get into the open environment as litter and should not be confused with plastics intended to biodegrade in the special conditions found in an industrial composting unit. These compostable plastics use an entirely different technology, but confusion is caused by the fact that they are so often referred to in discussions of oxo-degradable plastic.
"Biodegradable plastic" is a term that causes confusion and should not be used, because it could apply to two completely different types of plastic.
Degradation is initially prevented by the presence of polymer stabilizers in the plastic, which ensures a useful service-life for the article. Once the stabilisers have been exhausted Oxo-degradation 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.[5] 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-degradable 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.[6] 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.
Oxo-degradable 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 that 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-degradable 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.
The Oxomar project(9) was a four-year interdisciplinary study, sponsored by the French Government. The scientists reported that “The goal was to evaluate the biodegradation of oxo-bio in marine waters.
They concluded that “We have obtained congruent results from our multidisciplinary approach that clearly shows that [oxo-degradable] plastics biodegrade in seawater and do so with a significantly higher efficiency than conventional plastics. The oxidation level obtained due to the d2w degradant catalyst was found to be of crucial importance in the degradation process.”
See also the report from Queen Mary University London by Rose et. al 11th February 2020(10). Para 2.6 says “Before testing, samples of LDPE and oxo‐LDPE were surface‐weathered in seawater for 82 days, undergoing natural variations in sunlight and UV intensity.
Landfill: Oxo-degradable plastic is not designed to be able to degrade in a landfill. If the plastic has been taken to a landfill, it has been responsibly disposed of and there is no need for it to degrade. Also, if anything biodegrades in anaerobic conditions it will generate methane, which is undesirable unless the landfill has been designed to collect the gas. Oxo-degradable plastic will not become biodegradable in the absence of oxygen.[7] Recycling:(11)
Many of the microplastics in the environment are caused by the fragmentation of ordinary plastic when exposed to sunlight. These fragments are very persistent in the environment because their molecular weight is too high for microbes to consume them, and can remain so for decades. This is why oxo-degradable plastic was invented, for single-use plastics The plastic falls apart because the molecular chains have been dismantled and it is no longer a plastic.
The European Chemicals Agency (ECHA) was asked to study oxo-degradable plastic in December 2017.[8] They made a Call for Evidence, and they informed the BPA on 30th October 2018 after 10 months of study, that they had not been convinced that it creates microplastics. ECHA has never provided a dossier to support any ban on oxo-degradable plastic, and there is no evidence that microplastics from oxo-degradable plastic have ever been found in the environment. It has been used for bread bags for more than ten years by the largest bread producer in the world (Bimbo bakeries) and there have been no problems with microplastics or recycling.[9]
The Biodegradable Plastics Association (BPA) claimed that the EMF report was inaccurate and pointed out that many of the organizations shown as endorsing the report aggressively promoted a rival bio-plastic technology. In contrast, many of the others whose logos appeared in the document produced the same plastic items that get into the open environment as litter(13). 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(14). [10]
The evidence for and against oxo-degradable plastic was also reviewed in November 2018 by Peter Susman QC, a deputy judge of the High Court of England, who had over 25 years of experience in adjudicating cases in the technology and construction branch of the High Court, involving the evaluation of expert evidence. He declared the scientific case favouring oxo-degradable plastic "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 report(15) that
It is no longer tenable to conclude that there is 'no firm evidence either way' whether oxo-degradable is effective. I consider that recent research provides clear and compelling evidence that oxo-degradable 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, the expression might be defined... [I regard the idea that biodegradable plastics might encourage littering as] "fanciful and unreasonable".[11]
On 16 January 2018, the European Commission published its report on using oxo-degradable plastic. The document forms part of the European strategy for plastics in a circular economy, which was released the same day.[12]
The Commission focused on three key issues relating to oxo-degradable: the biodegradability of oxo-degradable plastics in various environments, the environmental impacts of littering, and recycling.
This report was critically reviewed by the Biodegradable Plastics Association (formerly the Oxo-biodegradable Plastics Association) (BPA)(16) 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 number of plastic goods being produced and standards for encouraging collection for recycling. Most people would support those measures, but plastic will still escape into the open environment in unacceptable quantities until the plastic waste has been eliminated. This is not likely to happen any time soon.[13] Notably, the Commission’s proposal did NOT include a ban on oxo-degradable plastics. This was inserted into the draft in the Environment Committee of the Parliament. The BPA says that oxo-degradable technology is the ONLY way to prevent the accumulation of plastic waste that has escaped into the environment. If oxo-degradable technology were severely restricted in the EU, unintended consequences would exist. Some countries outside the EU could follow the EU’s lead with disastrous results, 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 transboundary 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 plastic needs to be urgently upgraded to convert it into biodegradable materials much sooner than ordinary plastic if it does escape into the open environment, especially the oceans.The Directive was based on the Prodi, Reis, and Demesmaeker Reports to the European Parliament, none of which provided any scientific justification for a ban.
The BPA says that it has never been able to understand how it was possible to impose a ban on “oxo-degradable plastic” (by Art. 5 of the Single-use Plastics Directive 2019/904) without any dossier from the European Chemicals Agency (ECHA) showing any justification for any such ban. To make matters worse, the Commission had asked ECHA (under Art 69 of the REACH Regulation) to study whether these products created microplastics. ECHA received hundreds of pages of evidence but informed the BPA on 30 October 2018 that they were not convinced that microplastics were formed. They were instructed to terminate the study.
The Parliament and Council then proceeded to legislate, circumventing all the safeguards against arbitrary legislation provided by the Arts. 69-73 of REACH. Could it be that there was some improper influence?
According to the BPA, “The loser here is the environment because ordinary plastic is still being used to make products that get into the open environment every day, where they will lie or float around for decades. They should urgently be made with oxo-degradable technology, at little or no extra cost, so that they will biodegrade much more quickly and will not leave harmful residues.”