Are “compostable” plastics biodegradable?
Peer-reviewed research from the University of California San Diego says “Referring to compostable plastics as biodegradable plastics is misleading as it may convey the perception of a material that degrades in the environment.”
The research, published in Plos One says “To undergo rapid biodegradation, most compostable plastics require specific conditions that are achieved only in industrial settings……. Our results show that polylactic acid, a so-called biodegradable plastic, does not degrade in the marine environment for over 428 days. The results on PLA stress that compostability does not imply environmental degradation.”
Literature Review from UCL
In April 2023 three researchers from University College London published “The performance and environmental impact of prooxidant additive containing plastics in the open unmanaged environment” Their paper has been reviewed by the BPA at BPA Response to UCL Report
The BPA says: “This is yet another literature review of the science relating to oxo-biodegradable plastic. The UCL paper says “Globally, 22% of the annual plastic production enters terrestrial and aquatic environments where they can remain for decades.”
Measures such as deposit-return schemes and ocean and beach clean-ups can help, but the open environment is so vast that the only practical way to deal with this problem is to make the plastic oxo-biodegradable.
Studies and literature reviews have been going on now for more than 40 years, but it seems unlikely that all scientists will ever agree with each other on this subject, (nor on most other subjects). This is a classic example of the best being the enemy of the good, and in the meantime thousands of tonnes of ordinary plastic are getting into the open environment every week.
Oxo-biodegradable plastics have a serious practical application. They are intended to perform in the same way as normal plastic, but to biodegrade if waste-management fails and they end up in the environment as litter. They are not therefore intended as part of any waste-management strategy. Reduce, re-use and recycle are all very well but a large quantity of plastic does get into the open environment, and there is no other way to prevent it accumulating.
The most recent and important piece of scientific research on this subject is Oxomar – a four-year project sponsored by the French government, which says “We have obtained congruent results from our multidisciplinary approach that clearly shows that oxo-biodegradable plastics biodegrade in seawater and do so with significantly higher efficiency than conventional plastics. The oxidation level obtained due to the d2w prodegradant catalyst was found to be of crucial importance in the degradation process.”
The authors of the UCL paper have devoted a lot of time to show that as conditions in the open environment are variable it is not possible to predict the precise rate of biodegradation. However, this was already well understood, and this is why only an approximate timescale is given by the manufacturers.
There is no point therefore in doing further work in trying to establish precise timescales. Instead, attention needs to be focussed on the fact that an oxo-biodegradable plastic would oxidise and become biodegradable in the environment significantly more quickly than ordinary plastic at the same time and place.
The UCL authors point out that testing according to climatic conditions in South Florida would not show a degradation timescale applicable to conditions in the UK or Northern Europe. This is correct. Abiotic degradation may proceed more quickly in a hot, sunny, country than in a cold, dark country, but that is not a difference in principle.
The industry standards for oxo-biodegradable plastic are ASTM D6954 and BS8472. They contain six pass/fail tests, including tests for gel-formation/ cross-linking, and eco-toxicity.
The UCL authors say that they cannot be sure that the plastic will fully biodegrade, but Symphony has a report from Eurofins laboratories showing 88.9% biodegradation, and another from Intertek showing 92.74% (only 90% is required by EN13432 or ASTM D6400 for plastic marketed as compostable). Also, the UCL authors cite testing done by Prof. Jakubowicz in Sweden showing 91%. Testing will never find 100% carbon-evolution, because some of the material converts into water and biomass.
Even if it did not fully biodegrade it would still be better than ordinary plastic, which would have fragmented quite quickly under the influence of sunlight but would not have biodegraded at all.
Microplastic formation is highly unlikely in the case of oxo-biodegradable plastics, given their oxygen reactivity and degradation into low molecular weight oxygenated hydrophilic materials.
The European Chemicals Agency (ECHA) made a Call for Evidence in 2017, and informed the BPA after 10 months study that they had not been convinced that microplastics were formed.
Oxo-biodegradable masterbatches do not contain heavy-metals. They do not contain lead, and do not contain any substances in excess of the limits permitted by Art. 11 of the EU Packaging Waste Directive 94/62/EC. Symphony has tested products made with its d2w masterbatch according to the OECD eco-toxicity tests 201, 202, 203, 207, and 208 and they were all found to be non-toxic.
Oxo-biodegradability is the only way to remove enough plastic litter from the open environment, and if it had been widely adopted when it was invented, there would be no ocean garbage patches. There is now an urgent need for wide adoption of this technology before the problem gets even worse. This paper by UCL is an interesting survey of the literature, but provides no reason why oxo-biodegradable technology should not be made compulsory for a wide range of plastic products, as it already is in the Middle East.
I have just read an interview with Professor Marinella Levi, in DesignWanted.com. She says “We cannot live without plastic, and promoting the use of bioplastic as an alternative can be misleading.”
She says that “plastic haters” are a cohort that – as the Materials Science and Technology professor “Giulio Natta” at the Politecnico di Milano says – “is larger than ever, sadly blinding the public at large to the real issue when it comes to plastic and sustainability”.
“We should use plastic with respect, dispose of it properly, clean it up where the damage is already done, and design things differently.
Can we live without plastic? “No, we cannot”, says Professor Levi. “Without plastic and rubber, we would go back a century. We wouldn’t be able to use planes, drive cars, run hospitals, have computers or smartphone. And this is a material that – during the Covid outbreak – saved lives”.
“Yet plastic is the enemy number one when people talk about sustainability.” According to Levi, this is a global scam.
She claims that “Plastic is highly necessary to do almost everything that’s why it’s everywhere. Yet its production accounts for only 5% of all the oil used world-wide. The global crusade against plastic is not due to the fact that it uses a lot of oil, or that it pollutes by emitting CO2 during manufacture (transportation + heating and cooling have a far higher impact). It’s related to the fact that plastic is visible, abandoned on beaches, sucked in by oceans, cluttering cities, spoiling landscapes.”
“Surely some of you will now be turning up their noses,” she said. “Plastic is a super controversial issue especially in the design world. If you ask most people, especially Gen Z, they are convinced that we should get rid of all plastic and replace it with bioplastic options, but most people don’t know how bioplastics are manufactured, nor understand that their mechanical qualities are not always comparable to those of traditional plastic.”
“Furthermore, the suffix bio is very alluring and confusing, especially when coupled with adjectives such as degradable, biodegradable and compostable. It makes people think that they are more natural than plastic and that they dissolve.”
Are bioplastics natural? “They are just as normal plastic is. Both are created using natural resources (biomasses and microorganisms or fossils, hence mineral waste) but both require an equally complex chemical process (hence energy) to come to life.
“Research has shown that the use of fertilizers and pesticides in crop production and the chemical processes required to turn them into plastic generated a greater number of pollutants and damaged the ozone layer more than traditional plastic, while also requiring extensive land use (land that could be used for producing food for people).”
“Even if bioplastics, typically made from starch, cellulose, and lactic acid are biodegradable, …. they require composting facilities, and most cities in the world are not equipped with one. So waste management is the biggest issue with bioplastics as it is with traditional plastic. In some ways, it could be worse.”
“If bioplastic ends in the landfill ….when deprived of oxygen it degrades under other trash and releases methane. This is 23 times worse as a greenhouse gas than carbon dioxide. Also, if bioplastic is discarded with normal plastic, its non-fossil nature contaminates the rest of the plastic which cannot then undergo the normal recycling process. The result is that the yield of the recycling process can be greatly worsened.”
Michael Stephen is a lawyer and was a member of the United Kingdom Parliament, where he served on the Environment Select Committee. When he left Parliament Symphony Environmental Technologies Plc. attracted his attention because of his interest in the environment. He is now Deputy Chairman of Symphony, which is listed on the AIM market of the London Stock Exchange, and is the founder and Chairman of the Biodegradable Plastics Association.
Earlier Postings in this Column
Interview with Michael Stephen
The opinions expressed here by Michael Stephen and other columnists are their own, not those of Bioplasticsnews.com