As we reported recently, a study conducted by researchers at the University of Plymouth, designed to provide insights into the environmental deterioration of plastic bags made from different polymer types, has been the subject of some dispute.

In brief, the five bags chosen for the study comprised two oxo-degradable bags, one fossil non-biodegradable polyethylene bag, one bag marked as biodegradable, and one bag certified compostable according to the European Norm 13432.

Its main conclusions, according to the official press release, were that: “After nine months in the open air, all the materials had completely disintegrated into fragments. However, the biodegradable, oxo-biodegradable and conventional plastic formulations remained functional as carrier bags after being in the soil or the marine environment for over three years. The compostable bag completely disappeared from the experimental test rig in the marine environment within three months but, while showing some signs of deterioration, was still present in soil after 27 months.”

While the researchers point out that the study was peer-reviewed and achieved the purpose for which it was designed, some organisations, notably European Bioplastics, have argued that the conclusions it makes are misleading. They emphasise, for example, that only the compostable bag was actually certified biodegradable in the first place – and only under the scenario of industrial composting, for which it was not tested.

We were interested in how this study, and reactions to it, highlight the continued confusion surrounding the use of plastics and terms such as ‘compostability’ and ‘biodegradability’. It has also put a spotlight on the sometimes negative role certain sections of the media can play in sensationalising a complex and important issue that should perhaps be treated with a little more nuance.

With this in mind, Victoria Hattersley invited François de Bie from European Bioplastics, and Professor Richard Thompson from the team at the University of Plymouth, to give their respective takes on the study and its conclusions. The resulting discussion makes for interesting reading.

VH: It seems to me that one of the main issues European Bioplastics had with the study is that the results obtained on what it refers to as ‘fake and non-biodegradable oxo-bags’ were presented as results obtained on ‘biodegradable and compostable bags’. Would this be a fair summation?

FdB: Yes, the authors ‘purchased’ four different types of plastic bags and it was very clear, at the start of the study, that the PE bag with a false biodegradation claim, the oxo-degradable bag and the traditional PE bag would not degrade/decompose in the natural environment due to biological activity [n.b., we should point out here that oxo-degradability has already been widely discredited from an environmental standpoint - VH]. We have no issues with a university investigating ‘biodegradation’ of falsely labelled bags, but when reporting on the results these fake bags should be called out as greenwashing! Mixing the results obtained on those bags, together with ‘correctly EN13432 certified and labeled’ compostable and biodegradable bags is misleading.

The research actually confirms (here we quote from the university’s publication): “In the marine environment, the compostable bag completely disappeared within three months … the same compostable bag type was still present in the soil environment after 27 months but could no longer hold weight without tearing...”.

Bags which are certified compostable according to EN13432 have been checked and verified to meet ALL of the below conditions:

• Fragment into pieces < 2 mm in less than 12 weeks in an industrial composting facility

• Biodegrade into CO2, water, and biomass within 6 months due to biological activity

• Leave behind NO harmful substances in the environment after degradation and biodegradation.

RT: Our research sought to establish whether bags that are ‘labelled’ as degradable, biodegradable, or compostable do in fact deteriorate readily across a range of natural environments – and to look at how they compare with conventional plastic.

No other institution that we are aware of has previously conducted a test of this nature, over three years using multiple bag types and in different environments. The results revealed that over a three-year period, none of the materials examined could be relied upon to deteriorate sufficiently to reduce the negative effects of littering on biota or aesthetics across all three environments.

The European Bioplastics Association have since asserted that some bags labelled as biodegradable are fake and that they have been aware of this for some time. If that is the case, then this is an issue that they should address with the manufacturers concerned. Consumers will be guided by the labelling on the bag, as we were in our study, and they are unlikely to be able to distinguish whether a bag is fake or not.

FdB: The University of Plymouth is now, for the first time, mentioning the objective of the study was to check how bags ‘labelled’ as biodegradable would perform in the real-world environment. In the official press release this objective was less visible and also the conclusions were not at all directed to expose or ‘name & shame’ the ‘fake’ labelled bags.

If the objective was to establish how different bags would ‘deteriorate’, why was actual fragmentation and biodegradation of certified biodegradable and compostable bags not investigated in a scientific way? The way the results and conclusions were drawn left this very open; it was even written in such a way that the casual reader could also just as well conclude that “even the certified biodegradable bags do not biodegrade in CO2, water and harmless substances”. We invite the University of Plymouth for a further round of research to scientifically detail what happens with EN13432 certified bags if they end up in the environment.

Actually, we consider that the study is already out of date at the time of its publication, since:

  • Oxo-degradable plastics have been extensively researched by the European Commission and were recently banned in the context of the EU directive on single-use plastic products.
  • Biodegradability of plastics has been clearly defined in said directive and linked to the standard EN 13432 for industrial composting.
  • Additionally, the EU Plastics Strategy 2018 also acknowledges that industrial compostable products have value for separate collection of bio-waste and facilitate organic recycling (composting). Consequently, they shall be treated in a corresponding facility and shall produce high quality compost / soil improvers according to circular economy principles.

RT: A press release is not a summary of the entire study. The paper itself is very clear on what the rationale was and what it was not, as the following extract makes clear:

“The present study describes the deterioration in different natural environments of bags, which were stated to have biodegradable, oxo-biodegradable or compostable properties. We do not specifically attempt to quantify biodegradation performance in relation to any specific standard such as degradability in a commercial composting facility. Rather we assess whether or not there has been any meaningful deterioration in the context of reducing marine litter; for example, had the bag remained intact or deteriorated into visible fragments? A conventional polyethylene plastic carrier

bag was also examined for comparison. All bags were available at the point of sale in UK high-street retailers.”

A scientific evaluation is not approached from the perspective of ‘name and shame’ – it is conducted to obtain objective outcomes to hypotheses. If you have funding for further research we would be happy to consider your requirements.

FdB: Again, our problem is not the fact that you tested the deterioration of different bags in different natural environments over a period of three years - this may, indeed, be something new.

As stated, the main issue we have is with the fact that the bags in your study labelled to be allegedly biodegradable were in fact not biodegradable - a fact obviously known to you (see table 1 in your study, where you refer to the website of the Exo-Plastics masterbatch, specifically citing that it did not claim biodegradability). This was not (sufficiently) made clear.

Given that the average journalist - let alone reader - cannot distinguish between biodegradable and compostable (i.e. biodegradable in industrial composting facilities), the impression was given that biodegradable bags will not deteriorate in any environment.

On the other hand, the compostable bag showed strong signs of deterioration in the different natural environments, as your study’s findings correctly pointed out. However, if a bag, intended and certified to biodegrade / compost in only the most aggressive of all environments (i.e. industrial composting facilities), actually deteriorates in far less aggressive environments, it is only logical that truly biodegradable bags would be prone to deteriorate even faster than the compostable ones. I am well aware that this kind of deduction would have been beyond the scope of your study. However, it is one thing to omit this rationale (for scientific reasons) and yet another to more or less state the opposite.

For the average consumer, the takeaway of your study is that biodegradable bags are no different from conventional PE bags when it comes to deterioration in natural environments, and this is clearly not the case, as your study shows for compostable bags.

These findings are a blow to our industry, something that, with sound communication, could and should have been avoided.

RT: With regard to the Exo-Plastics masterbatch, the bag itself clearly said on it: ‘Biodegradable bag ([Exo-Plastics logo], sustainable bioplastic; biodegradable ISO 14855)’ A lack of claim on a website does not alter in any way the claims made directly on the product itself. Neither will it alter the assumptions a consumer might make about the product.

Following the publication of our research paper, we have received numerous messages from the public and industry thanking us for making this issue more transparent. Indeed, the study has been cited in the UK’s House of Lords, when The Lord Bishop of St Albans called on the government to “produce clear standards and guidelines so we can be sure that these are biodegradable and improve the environment, and that we are not misled.”

For more than 20 years, scientists at the University of Plymouth have been working to understand the scale and drivers of plastic pollution in the environment. We were the first to describe the presence of microplastics in the ocean back in 2004, which is now a globally recognised term. We pride ourselves on engaging with industry, policy and scientific partners, because these issues cannot be tackled in isolation – they require a coordinated approach, from consumers, manufacturers, and governments.

VH: I think from the above, it seems that something we can all agree on is that there is a fundamental misunderstanding among the general public (and even certain sections of the media) about what terms such as ‘biobased’, ‘biodegradable’ and ‘compostable’ really mean in the real-world context, which needs to be addressed through clear communication. Such confusion could indeed be argued to have played its part in holding back the wider adoption of bioplastics. Perhaps another common thread is the need for more transparency when it comes to labelling of bags?

RT: We entirely agree that our study indicates the need for consistent standards on degradation and labelling and this is exactly what we state in the paper. Policy and industry need to move forward so that such labelling cites the relevant standards and is transparent as to the conditions and timescales behind them. Since degradable and compostable materials are in many locations not compatible with available recycling infrastructure, it is also important that the users are informed of the appropriate disposal route, which in many circumstances will be disposal to the residual waste stream. It is only by providing accurate, unambiguous, and complete guidance to the user regarding disposal that the potential benefits of these novel materials can be realised.

This research into degradable plastic bags has prompted debate and public interest, and that is a good thing, especially if it leads to much needed improvements in labelling.

FdB: Regarding labelling, European Bioplastics strongly recommends having the conformity to a standard verified by an independent body that issues according certificates and corresponding labels. Biodegradability as a sole claim without a standard specification is misleading. If a material or product is advertised as biodegradable, further information on the timeframe, the level of biodegradation and the surrounding conditions should be provided. Moreover, data should be made available to interested parties for verification. This means that a plastic bag needs a clear label to claim biodegradability.

In the case of the fake biodegradable plastic bag, the researcher should have checked before initiating the study if it was certified as biodegradable in any of the environments tested.

RT:  We examined five types of material with multiple replicates of each. These were examined in three environments over three years. The study shows the outcomes for those bags. The details of each bag type are given in the paper. We are not able to comment (nor do we) about bags that we did not examine.

Again, if you have concerns about the labelling used by any of the bag manufacturers in the study please can I suggest you discuss these with them (and or any relevant trading standards organisations) directly. Perhaps consider using the outcomes of our research to support your points?

VH: Thank you both for all your very clear and considered points. Are there any concluding remarks you would like to give?

FdB: The approach to labelling of biodegradable and compostable plastics already is transparent and uniform. There are already several trustworthy third-party certification bodies responsible for testing and awarding corresponding certification to products for both compostability and biodegradability in different environments. For instance, a properly certified compostable product by an independent certifier according to the standard EN 13432 can be labelled with the Seedling Logo and include the registration number.

The fact that some producers out there in the world deliberately print a label on their PE bag and claim it to be biodegradable is bad enough as it is, and, unfortunately, there is little that we can do about it.

RT: I have been working on the topic of plastic pollution for over 20 years. Never before has there been such a global level of interest to address this issue. The public, policy and industry are all seeking for solutions and in my view this is an environmental challenge that can be solved. Plastics have the potential to bring immense societal benefit and the majority of those benefits can be achieved without the accumulation of waste and litter.

Broadly speaking the solutions lie in more responsible use of plastics. In order to make appropriate and informed choices it is essential for novel products, such as degradable and biodegradable plastics, to be clearly, accurately and consistently labelled; indicating the receiving environments and timescales for degradation and the waste streams that should be used for their disposal.