Environmental persistence – why chemical biodegradability is taking centre-stage in a greener Europe

Environmental persistence – why chemical biodegradability is taking centre-stage in a greener Europe
03 September 2020

With the advent of the European Green Deal, tectonic shifts are once again taking place in the European policy landscape. In particular, in the sphere of chemicals policy, the strategy under development is being described as a ‘game-changer’ – unparalleled since the development of the Registration, Evaluation and Authorisation of Chemicals (REACH) Regulation nearly two decades ago. Top of the list of priorities for this strategy is action on ‘very persistent chemicals’. This reflects a new perspective on an old issue, and one that is seeing chemical persistence and biodegradability rocket up the sustainability and regulatory agenda. 

But what does this change really mean for chemical businesses and how should they respond to these new developments? 


What is persistence?

Persistence describes the time it takes for chemicals to degrade (i.e. break down) in the environment. This property is important as it controls how long a chemical may reside in environmental compartments such as air, water and soil before it is converted into less harmful metabolites, such as carbon dioxide and water. The times these chemicals reside in the environment indicates the levels to which humans and other organisms are unintentionally exposed to chemicals via the environment and affects the extent to which this exposure can be reduced by discontinuing the use of a particular chemical. Persistent chemicals are those that resist degradation processes in the environment, resulting in their potential for widespread distribution and exposure that may pose a risk to human health and the environment. 

The issue of chemical persistence goes back as far as the 1950s. At that time, poorly degradable detergents were found in water bodies leading to foaming events and Rachel Carson was studying the effects of chlorinated pesticides on wildlife, later to be published in the 1962 book Silent Spring. This led to standardised methods for testing chemical biodegradability to be developed and to frameworks being established to identify and regulate substances that have persistent, bioaccumulative and toxic (PBT) properties. These substances are also known as persistent organic pollutants (POPs), based on the view that they pose a particular threat to society and the planet. Today, there are various international regulations containing provisions for such chemicals. However, more recent events and scientific developments have led to a change in the way we look at persistence and, as such, the types of chemicals we now wish to examine more closely. 

Free on-demand webinar

We hosted a free webinar on environmental persistence where our ecotoxicology experts focused on the implications that potential new requirements surrounding environmental persistence may create for businesses, as well as best practices for assessing and managing issues related to chemical persistence.

View the webinar on-demand

What is changing?

Recent events highlighting the problem of persistent chemicals have helped to reinvigorate the discussion and action on this issue in Europe. Perhaps one of the biggest and most well-known examples is per- and polyfluoroalkyl substances (PFAS).

These chemicals are widely used – from non-stick and waterproof coatings in households to foams used by firefighters. Due to their extreme persistence they are known as ‘forever chemicals’, and there is a growing body of evidence about their adverse effects on humans. They are also very mobile in water due to their highly polar nature. This allows them to be transported long distances where they can contaminate remote regions. Contamination of drinking water sources has also been reported due to the ability of PFAS to evade sorption-based water treatment processes. The European Chemicals Agency (ECHA) has recently announced its intention to take broad action on PFAS chemicals. This will include:

  • Assessing PFAS in groups to quicken the regulatory progress.
  • Restricting the use and production of some PFAS.
  • Requesting evidence – regarding a recent proposal by five countries – for a broad PFAS restriction. 

In a landmark regulatory decision in June 2019, the properties of mobility and persistence associated with PFAS were used to identify GenX-related chemicals as substances of very high concern (SVHCs), as an ‘equivalent level of concern’ to PBT; very persistent, very bioaccumulative and toxic (vPvB); and carcinogenic, mutagenic or toxic to reproduction (CMR) substances.

The 2019 film ‘Dark Waters’ depicted the legal battle against the chemical manufacturer DuPont for releasing the PFAS chemical perfluorooctanoic acid (PFOA) into the environment. The lawyer against DuPont, Robert Bilott, publicly wrote to the ECHA in early 2020 calling for urgent action on PFAS, saying that ‘PFAS are a global disaster, and the true extent of the damage done to us and our environment will only be known and felt by people living beyond our lifetimes’.

The impact of PFAS chemicals is a primary driver of recent interest in establishing regulatory criteria for so-called persistent, mobile and toxic (PMT) chemicals. This has been championed by the German competent authorities and some scientists, and reported to be part of the proposed updates to REACH in the new EU chemicals strategy. Some scientists have gone further and argued for a ‘P-sufficient’ approach, arguing that persistence alone is sufficient to warrant regulatory action because of the uncertainty surrounding possible future issues that cannot be foreseen or predicted. 

However, what appears to have been lost in discussions is the difference between no degradation, and slow degradation. As forever chemicals, PFAS are generally regarded to be effectively non-degradable. However, many chemicals classified as persistent under the current PBT frameworks have comparatively modest half-lives (e.g. 40 to 100 days in water). Distinction between a forever chemical and P/vP chemical is important as it has significant implications for a chemical’s potential to build up and pose a long-term environmental burden that is difficult to reverse. Also, somewhat unfortunately, under REACH a ‘very persistent’ (vP) classification already exists, and its half-life criterion of 60 days in water is only marginally longer than that of the P classification (40 days). As a result, current discussions on ‘very persistent chemicals’ have become synonymous with the vP classification under REACH, whereas the concern may in fact be for chemicals with much greater persistence. Arguably, revisiting the existing P/vP criteria of classical PBT/POP regulation is warranted to assess their fitness for purpose to address these newly identified concerns.

The public interest and regulatory activity concerning persistence has been catalysed further through the issue of plastic pollution. The BBC documentary series, Blue Planet II (2017), showed images of how oceans and marine creatures are being affected by plastic waste. This provided unambiguous visual evidence of the impact that discarding materials resistant to degradation can have on the environment. The programme has sparked a groundswell of public support and acceleration of measures to reduce the environmental burden of plastic pollution. One of these measures was to introduce a REACH restriction on intentionally added microplastics, which includes a proposed derogation for (bio)degradable microplastics. This has highlighted that the current methods and scientific understanding are insufficient to satisfactorily address the question of (micro)plastic persistence, and that the standard frameworks and criteria for assessing chemical persistence may also be inadequate to address these materials.

With the explosion of public interest in chemical persistence and significant activity in the regulatory sphere, industry has started to take note. For example, Unilever, a giant multinational fast-moving consumer goods (FMCG) producer, that produces about 70,000 products and is used by 2.5 billion people each day, has recently committed to making all of its 1product formulations biodegradable by 2030. This initiative includes reformulating or replacing ingredients that have no viable biodegradable alternatives. Combined with last year’s commitment to 2reduce plastic packaging, this initiative by Unilever to reduce persistent product formulations and packaging is a welcome voluntary action. It is likely to have far-reaching implications for the chemical supply chain and broader chemicals industry.


The renewed focus on persistence means that the importance of product biodegradability has increased in the mind of the customer, and that chemical persistence presents a new regulatory risk that must be understood and managed. Ultimately, it means that addressing the issue of chemical persistence is now an essential part of running a sustainable business. It is vitally important for chemical manufacturers to have good quality biodegradation data to support their products, and for companies that procure chemicals to know and understand the potential business risks associated with the biodegradability and persistence of these chemicals. 

It is very likely that there will be significantly more regulatory activity around persistence in the future. Therefore, at this point, It is worthwhile considering the current persistence assessment frameworks and some of the challenges that are faced in conducting these assessments.

Challenges with current persistence and biodegradability assessments

Although persistence assessment frameworks and criteria have been established for decades, there remain challenges that affect the robustness and consistency of chemical assessments. Foremost among these is the sheer variety of environmental conditions under which chemicals occur, and the extent to which this affects their degradation. Typically, persistence is assessed by comparing degradation half-lives in water, sediments and soil to set criteria. However, degradation half-lives for a chemical can often vary by orders of magnitude depending on factors such as bioavailability and the presence of oxygen, nutrients and degrading organisms. To overcome some of this variability in regulatory assessments, standard test methods are often applied. However, these tests come with their own challenges. 

An example of a framework for persistence assessment is the one applied under the EU REACH Regulation. Under REACH, persistence is assessed chiefly based on biodegradation tests performed to the Organisation for Economic Co-operation and Development (OECD) guidelines. Biodegradation is the micro-organism-mediated breakdown of chemicals that, in most cases, accounts for the bulk of environmental degradation. Biodegradation tests range from stringent ready biodegradability tests (RBTs) that are designed to screen for chemicals that degrade rapidly in the environment, to more environmentally realistic simulation tests in soil, sediment and water that are designed to yield representative half-lives for comparison to persistence criteria. Being biological tests with live microbial inocula, standardised biodegradation tests can never eliminate all possible variability in chemical biodegradation measurements. RBTs, in particular, are prone to false negative results, which means readily biodegradable chemicals do not pass the stringent test criteria. This is particularly the case for chemicals with certain physical-chemical properties that render them difficult to test. It is important to ensure that RBTs are conducted properly and with an appropriate method to have the best chance of achieving a positive result. Thankfully, the stringency of RBTs is widely recognised, and it is normally the case that positive results take precedence over negative results. 

If a chemical fails the RBT, it is flagged as ‘potentially persistent’ and may be prioritised for further regulatory evaluation. Typically, this would involve biodegradation simulation testing. Simulation tests are significantly more expensive and complex than RBTs, and pose a number of challenges, such as issues with their applicability to certain chemical types (e.g. complex and difficult-to-test substances). This can raise significant issues with conducting and interpreting of these tests. Furthermore, new REACH guidance around test temperatures and interpretation of non-extractable residues (NERs) has increased the stringency of these assessments, meaning that what was interpreted to be not persistent (not P/vP) before may now be considered persistent (P) or even very persistent (vP). 

Recommendations for businesses carrying out biodegradability and persistence assessments

  • Expertise is key

It is imperative that companies use appropriate expertise when performing persistence and biodegradability assessments of their chemical products to ensure they are conducted and interpreted properly. This can often make the difference between positive and negative results. If working with contract research organisations (CROs), it is important to have the support of an expert who understands the unique challenges posed by your substance and can work on your behalf to ensure that the CRO study is appropriately managed and delivered to a high standard. Finally, in reviewing and interpreting the results of your study, it is essential that expertise is available to you to engage with the regulatory authorities and ensure that appropriate decisions are subsequently taken. 

  • Establish ready biodegradability 

It is critical to establish with certainty whether or not a chemical is readily biodegradable, as this has important implications for further testing under REACH. This includes endpoints not related to persistence, such as bioaccumulation and ecotoxicity. Due to the stringent nature for RBTs and high rate of false negatives, it is advisable to consider what RBT data is available on a chemical and assess whether it is likely that this can be improved upon. This is particularly the case for chemicals with certain properties that render them problematic in these tests. A positive result in an RBT can lead to significant cost savings and limit further potential regulatory action on a chemical. The RBT result is also important for the environmental hazard classification under the classification, labelling and packaging of substances and mixtures (CLP) Regulation), and for marketing claims and other potential accreditations (e.g. ecolabels) for the product.  

  • Exercise care with simulation testing

If simulation testing on a chemical is necessary, then it is essential to have appropriate expertise available to ensure that tests are carried out and interpreted properly. Aside from the intrinsic biodegradability of a chemical, there are many other factors that can affect study performance, and a lot that can ‘go wrong’ with these complex and expensive tests. Negative results in simulation tests can have far-reaching implications for the ongoing viability of a product. Therefore, the importance of getting the testing right cannot be overstated. 

How NCEC can help you 

NCEC has extensive first-hand experience in supporting clients to properly assess the biodegradability and persistence of their chemical products. Our services include designing the most appropriate ready biodegradability test, overseeing simulation tests, addressing difficult test properties, and engaging with regulatory authorities in the subsequent evaluation and interpretation of assessments. 

We can help you achieve optimum and scientifically robust regulatory outcomes for your chemical products. This is irrespective of whether you are conducting proactive biodegradability testing to improve marketability and risk-proof your portfolio or responding to a regulatory evaluation on your substance. 

Our deep technical knowledge of persistence and bioavailability assessment is also recognised by industry. We are working on a project with the European Chemical Industry Council (Cefic) as part of its Long-range Research Initiative (LRI) programme (Cefic-LRI). The project is entitled ‘ECO52: Expanding the conceptual principles and applicability domain of persistence screening and prioritization frameworks, including single constituents, polymers, and UVCBs’ and will investigate improvements to the EU persistence assessment framework. We are leading experts in evaluating substances of unknown or variable composition, complex reaction products or of biological materials (UVCBs), assessing difficult-to-test chemicals and in understanding the limitations of standard biodegradation tests.

For information on how we can help you, please read more about our expertise and services here. If you have any questions related to persistence assessment of chemicals, biodegradability assessments or any other regulatory queries, please speak to us through the contact form on the side or email us at [email protected]


  1. https://www.unilever.co.uk/news/press-releases/2020/unilever-sets-out-new-actions-to-fight-climate-change-and-protect-and-regenerate-nature-to-preserve-resources-for-future-generations.html
  2. https://www.unilever.com/news/press-releases/2019/unilever-announces-ambitious-new-commitments-for-a-waste-free-world.html#:~:text=Unilever%20has%20confirmed%20that%20by,plastic%20packaging%20than%20it%20sells