Oxo-biodegradation

Oxo-degradation is a process of plastic degradation utilizing oxidation to reduce the molecular weight of plastic, rendering the material accessible to bacterial and fungal decomposition. To change the Molecular structure in order to break down under sunlight, the plastic can be broken down and eaten by micro-organisms. Oxo-degradable plastics- composed of polymers such as polyethylene (PE) or polypropylene (PP) -contain a prodegradant catalyst, typically a salt of manganese or iron.

Background, Characteristics, and Performance

Oxo-degradable plastic was invented in the 1970s by professor of chemistry Gerald Scott and colleagues to confront the environmental liabilities of polyethylene and polypropylene plastics. Abiotic degradation was catalyzed in the presence of oxygen, the polymers converted into small-chain organic chemicals, such as ketones, alcohols, carboxylic acids, and low molecular mass hydrocarbon waxes, by way of homolysis of hydroperoxides into free radicals; these chemicals, in turn, are biodegraded by bacteria ubiquitous to terrestrial and marine environments. The addition of a catalyst shortens decomposition by orders of magnitude.

While not required, light and heat will accelerate the transformation; the presence of moisture neither accelerates nor impedes this process. However, oxygen is essential: if buried deep in landfill, for example, significant catalyzation will halt.

Degradation is initially prevented by the presence of polymer stabilizers in the plastic, ensuring a useful storage and service life; once stabilizers have been exhausted, oxo-biodegradation commences.

Conventional polyethylene and polypropylene typically fragment relatively quickly, but take decades to chemically decompose to the point of susceptibility to biodegradation; by contrast, oxo-biodegradable plastic 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 by Interek within 180 days when tested by ASTM D6954(4). Oxo-biodegradation has also been studied at the Eurofins laboratory in Spain, where on July 25th 2017 they observed 88.9% biodegradation in 121 days.

Standards applicability

EN13432 for "compostable" plastic requires biodegradation to be tested in a laboratory (not in a compost heap) but it is sometimes suggested that oxo-biodegradable plastic should be tested in outdoor conditions. See however the statement(6) of De Graham Swift (Vice-chairman of the Technical Committee at ASTM) who says "It has been my experience that results from laboratory testing are very likely to be reproduced in the real world. I can see no cause for concern that they would not, and have seen no evidence that they have not.

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

A standard specification unless a specific disposal route (e.g. composting), is envisaged. ASTM D6400, EN13432, and Australian 4736 are standard specifications designed for the special conditions found in industrial composting.

In the marine environment

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-biodegradable 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-biodegradable 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-biodegradable plastic will not become biodegradable in the absence of oxygen. Recycling:(11)

• Recyclers have to assess the level of degradation of any plastic sent for recycling whether it is oxo-biodegradable or not. They cannot recycle ordinary plastic which has started to degrade after exposure to sunlight.
• If the recyclate is to be used to make short-life products (eg food packaging) it does not matter whether it contains oxo-biodegradable plastic, because biodegradation is desirable.
• Stabilization is, therefore, necessary only for long-life products, and the producer of long-life products would stabilize them in the same way whether the recyclate contains oxo-biodegradable plastic or not. He does not need to know the proportion of oxo-biodegradable plastic in the feedstock. This normal stabilization would neutralize any oxo-biodegradable residue.
• It is not necessary to separate oxo-biodegradable PE or PP from conventional PE or PP before recycling, but if so desired oxo-biodegradable masterbatch could be made visible to automatic sorting equipment by including a marker.
• Oxo-biodegradable masterbatch is used in PE and PP, but NOT in PET.

Microplastics

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-biodegradable 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-biodegradable plastic in December 2017. 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-biodegradable plastic, and there is no evidence that microplastics from oxo-biodegradable 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.

Controversy

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).

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 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 favoring oxo-biodegradable 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-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, 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 using 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-degradable: the biodegradability of oxo-biodegradable 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.

Notably, the Commission’s proposal did NOT include a ban on oxo-degradable or oxo-biodegradable plastics. This was inserted into the draft in the Environment Committee of the Parliament.

The BPA says that oxo-biodegradable technology is the ONLY way to prevent the accumulation of plastic waste that has escaped into the environment. If oxo-biodegradable 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-biodegradable technology, at little or no extra cost, so that they will biodegrade much more quickly and will not leave harmful residues.”

References

• 1 Scott, Gerald “Degradable Polymers, Principles and Applications” ISBN 1-4020-0790-6
• 2 ibid
• 3 ibid
• 4 Intertek 2.12.21
• 5 https://www.biodeg.org/subjects-of-interest/composting/
• 6 https://www.biodeg.org/wp-content/uploads/2021/02/Swift-evidence-to-BEIS.pdf
• 7 https://www.biodeg.org/wp-content/uploads/2021/07/Final-report-OXOMAR-10032021.pdf
• 8 https://www.biodeg.org/wp-content/uploads/2022/10/QM-published-report-11.2.20-1.pdf
• 9 Ibid fn 7
• 10 Ibid fn8
• 11 See https://www.biodeg.org/subjects-of-interest/recycling-2/
• 12 See https://www.biodeg.org/wp-content/uploads/2019/11/emf-report-1.pdf
• 13 https://www.biodeg.org/wp-content/uploads/2019/11/emf-report-1.pdf
• 14 https://www.biodeg.org/wp-content/uploads/2020/05/Reply-to-Ellen-MacArthur-Foundation-from-Prof-Ignacy-Jakubowicz-21-8-17.pdf
• 15 https://www.biodeg.org/uk-judge-find-the-case-for-oxo-biodegradable-plastic-proven/
• 16 https://www.symphonyenvironmental.com/wp-content/uploads/2022/09/bpa-responds-to-european-commission-2.pdf

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• Chiellini, Emo; Cortia, Andrea; Swift, Graham (2003). "Biodegradation of thermally-oxidized, fragmented low-density polyethylenes". Polymer Degradation and Stability. 81 (2): 341–351. doi:10.1016/s0141-3910(03)00105-8.

• Report from CIPET (India) test on Renatura OxoDegraded PE Film using ASTM D5338 demonstrates 38,5% Bio-mineralization of PE in 180 days 1991; 57(3): 678–685.

• Jakubowicz, Ignacy (2003). "Evaluation of degradability of biodegradable polyethylene (PE)". Polymer Degradation and Stability. 80: 39–43. doi:10.1016/s0141-3910(02)00380-4.

• Jakubowicz, Ignacy; et al. (2011). "Kinetics of abiotic and degradability of low-density polyethylene containing prodegradant additives and its effect on the growth of microbial communities". Polymer Degradation & Stability. 96 (5): 919–928. doi:10.1016/j.polymdegradstab.2011.01.031.

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• Koutny, Marek; Sancelme, Martine; Dabin, Catherine; Pichon, Nicolas; Delort, Anne-Marie; Lemaire, Jacques (2006). "Acquired biodegradability of polyethylenes containing pro-oxidant additives" (PDF). Polymer Degradation and Stability. 91 (7): 1495–1503. doi:10.1016/j.polymdegradstab.2005.10.007.

• Seneviratne, Gamini; Tennakoon, N. S.; Weerasekara, M. L. M. A. W.; Nandasena, K. A. (2006). "Polyethylene biodegradation by a developed Penicillium–Bacillus Biofilm". Current Science. 90: 1.

• Sipinen, Alan J.; Rutherford, Denise R. (1993). "A Study of the Oxidative Degradation of Polyolefins". Journal of Environmental Polymer Degradation. 1 (3): 193–202. Bibcode:1993JEPD....1..193S. doi:10.1007/bf01458027.

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• Taylor, Lynn J.; Tobias, John W. (1981). "Accelerated Photo-Oxidation of Polyethylene (II). Further Evaluation of Selected Additives". Journal of Applied Polymer Science. 26 (9): 2917–2926. doi:10.1002/app.1981.070260908.

• Ungtae Lee, Anthony L. Polmetto III; Fratzke, Alfred; Bailey Jr, Theodore B. (1991). "Biodegradation of Degradable Plastic Polyethylene by Phanerochaete and Streptomyces Species". Applied and Environmental Microbiology. 57 (3): 678–685. Bibcode:1991ApEnM..57..678L. doi:10.1128/AEM.57.3.678-685.1991. PMC 182779. PMID 16348434.

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External links

• Oxo Biodegradable Plastics Federation