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01 / Introduction

Per- and polyfluoroalkyl substances (PFAS) have been drawing growing concern and attention from the public, media and regulators for many years as their persistence and mobility in the environment have resulted in widespread diffuse contamination as well as affecting sensitive drinking water supplies across the globe. The scale and potential impacts are huge and still emerging, with some commentators describing PFAS as the new asbestos.

PFAS have been used in a huge range of industrial and consumer applications since the 1940s because of their valuable properties of oil, water and stain repellency, stability and low friction. Many PFAS are also surfactants and their use within firefighting foams, in particular, has been associated with significant environmental contamination.

Several PFAS compounds have been associated with a range of serious health conditions. There is a clear trend globally towards restricting a greater range of PFAS compounds to ever more stringent levels, which in turn is driving contamination management at source sites. Alongside this are growing liabilities and lawsuits associated with PFAS, including several high-profile class action lawsuits from exposed communities in the US, Australia and Sweden. Last year, for example, a major PFAS manufacturer announced a $10.3bn settlement to multiple US public water supply companies to test and treat PFAS.

So, while certain sectors have been assessing PFAS for many years, attention is now widening to focus more on PFAS discharges and historic land contamination. As a result, mainstream development sites are now experiencing significant challenges. A recent article in the Ends Report environmental bulletin described PFAS as 鈥渂rownfield鈥檚 bubonic plague鈥�, with examples of developers being told to re-run site investigations as well as insurers shying away from insuring projects, potentially leaving sellers with stranded assets and retained liability.

The brownfield site problem reflects growing UK regulatory pressure from several angles, including revised drinking water guidelines, larger datasets on PFAS prevalence, a range of potential restrictions under the UK REACH chemical regulations, and a growing awareness of the range of sites where PFAS many be present. There are calls for more guidance, and development of suitable screening criteria. Furthermore, there has been criticism of the current regulations when compared with other countries 鈥� in particular, a Royal Society of Chemistry (RSC) campaign calling for stricter drinking water thresholds, the development of a PFAS inventory and a national chemicals regulator with a strong role.

In time, there will be significant changes to the UK鈥檚 PFAS landscape, but at the moment there is an urgent need to robustly, pragmatically and cost-effectively address today鈥檚 challenges. The UK brownfield sector is well placed to lead this response, being mature, innovative and benefiting from a strong track record in dealing with novel contaminants.

This article explores what PFAS are, the current regulatory drivers and how PFAS can be assessed and remediated at brownfield sites 鈥� in particular, how an informed, risk-based approach can enable early-stage consideration of PFAS and a proportionate response. While the challenges are real, armed with the right tools and approach, developers will continue to be able to safely bring forward brownfield land for much-needed housing and other development.

02 / What are PFAS?

PFAS are a large and diverse class of human-made chemicals comprising thousands and potentially millions of individual compounds. Several hundred are registered and in active use. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are the two most well-studied and commonly regulated members of the PFAS family, but an expanding range of PFAS are now being regulated in many regions.

PFAS have been termed 鈥渇orever chemicals鈥� in the media. Their combination of extreme persistence and high mobility has led to widespread detections in plants, animals and the wider environment. Some PFAS are bioaccumulative and are associated with a range of serious health conditions, including cancers, even as the understanding of their toxicity continues to evolve. Unfortunately, low background levels of PFAS in soil, groundwater and surface water are present at many brownfield sites.

It is useful to understand the basic chemical properties of PFAS to understand why they are such a problem.

• All PFAS contain a fully fluorinated carbon chain somewhere in their chemical structure. The high strength of the carbon-fluorine bond means this chain is in effect armour-plated and is not biodegraded in the environment.
• All PFAS have a 鈥渉eadgroup鈥� structure on the end of the fluorinated chain. This can have a very diverse functionality for different industries. More complex headgroups can be partially broken down in the environment, with these PFAS known as 鈥減recursors鈥�. This will always leave the fully fluorinated chain behind as persistent daughter products. This process is termed 鈥渂iotransformation鈥�. The amount of precursor PFAS can be significant and present a long-term source of contamination but remain hidden unless advanced analysis is employed.
• The length of the perfluorinated carbon chain is another important consideration. Increasingly, long-chain PFAS such as PFOS and PFOA have been replaced by short-chain PFAS and other novel PFAS chemistries. There is concern that these new compounds are also persistent and potentially toxic. This is known as 鈥渞egrettable substitution鈥�. In order to restrict this trend, there are moves in the EU and the UK towards the restriction of PFAS as a class, rather than as individual compounds.

However, the properties that make PFAS so useful are often the same properties that make them so widespread and hard to manage. Their persistence means that there can be shallow soil contamination present decades after original use, and their mobility means there can be extensive groundwater contamination, extending out to significant distances from the actual site.

Brownfield sites frequently associated with PFAS contamination include:

• Sites where fluorosurfactant firefighting foams may have been used for training, incident response, spray testing and so on, such as airports, military bases and petrochemical and industrial sites that store bulk flammable liquids.
• Sites that may have manufactured or used PFAS. PFAS have been used in nearly every industrial sector so should be considered across a wide range of sites. High-risk sites include fluoropolymer manufacturing, non-stick coatings for textiles, carpets and paper products as well as metal plating, electronics and many more manufacturing applications. While the UK has fewer PFAS and fluoropolymer manufacturing sites than the US, the brownfield site challenge is becoming much more widespread.
• PFAS are also prevalent in wastes and so end up in landfills and landfill leachates as well as at wastewater treatment works (WWTWs) where, in many cases, they are poorly removed. As a result, PFAS have been identified in WWTW discharges and biosolids, which may be applied to land as fertiliser.

03 / PFAS regulations

Regulations and guideline values for PFAS continue to evolve globally, with a trend towards regulating a larger range of PFAS compounds and groups of compounds to ever lower acceptable limits. In the UK, regulatory drivers affecting brownfield redevelopment typically come from the drinking water guidelines and surface water standards that are used to inform compliance criteria for site assessment and remediation. Soil screening levels (SSLs) are currently available for PFOS and PFOA but do not reflect risks to human health or water resources. More detailed category 4 screening levels (C4SLs) for PFAS are currently under development.

Different countries assess risks in different ways and at different times, and there is increasing divergence between the UK and the EU following Brexit. This is particularly the case for drinking water standards and the chemical regulations, REACH. Similarly, the US PFAS regulations are more advanced than the UK鈥檚 in many respects. There has been concern that UK drinking water standards are less stringent than those in both the EU and the US.

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The clear implication is that as guidelines are reassessed over time, any future changes could have major impacts both on the drinking water sector and at sensitive brownfield sites.

In March 2023, the UK Environment Agency (EA) and the Health and Safety Executive (HSE) produced a regulatory management options analysis (RMOA) report, which summarised available information and set out a range of potential regulatory and management approaches for PFAS. Restrictions of PFAS within firefighting foams and consumer products via UK REACH and changes to the Environmental Permitting Regulations (EPR), suggested by the RMOA, are included within the Department for Food and Rural Affairs鈥� (DEFRA) Plan for Water policy paper, from April 2023.

It is noted that the Construction Industry Research and Information Association (CIRIA) is expected to publish guidance on PFAS in soil and water in the coming months.

04 / PFAS assessment and management approaches

In many ways, PFAS can be effectively managed through existing framework guidance for managing risks from contaminated land in the UK. This includes the 2023 guidance Land Contamination Risk Management (LCRM), as well as industry codes of practice for reusing materials during redevelopment. These approaches support risk-based and sustainable management solutions based on the suitability of the land for end use and so should be proportionate to site-specific risks and constraints.

The brownfield redevelopment industry has previously encountered novel and emerging contaminants, including ether oxygenates, pharmaceuticals and chlorinated solvents, and will continue to do so as new risks are identified.

It is important to incorporate the latest understanding, tools and guidance on PFAS within our existing approaches to make sure we robustly conceptualise sites and take a risk-based, pragmatic approach to the implementation of management. This involves looking outside the site boundary to establish background levels in order to place any PFAS detections in context. It is important to understand how PFAS might have been used previously and where the source areas might be located. Every site is unique, with its own history. The PFAS problem goes well beyond airports and fire training areas.

The industry also needs to get out of the mindset of only looking for individual PFAS compounds. The problem is similar to petrol or diesel contamination, where we are dealing with complex mixtures. PFAS mixtures typically contain precursor PFAS that are not detected by typical analysis methods, but which can biotransform over time into toxic and regulated PFAS. This hidden and unregulated PFAS mass can be greater than the amount of individual and regulated PFAS, so it is crucial to understand the true magnitude and longevity of the source.

Fortunately, there are a number of advanced analytical techniques now available to more robustly characterise PFAS, although they are more expensive. Furthermore, sampling for PFAS requires additional procedures and QA/QC tests to confirm there is no cross-contamination from background PFAS in products or sampling equipment.

Further challenges that the risk-based PFAS management approaches must address include:

• The sheer volume of potential PFAS sources and widespread detections in the environment, particularly as these detections may be above quality standards. The objectives for site remediation should be set within the wider context of the site, including relevant background concentrations, to ensure they are achievable and pragmatic.
• The concentration requirements set out in PFAS standards and guidance are often very low and, as PFAS do not biodegrade, even more detailed site-specific assessment of PFAS鈥檚 fate and transport still result in very low thresholds to remediate or manage.
• Data on the physical and chemical properties of certain PFAS is either limited or absent. Further studies to assess PFAS toxicity, which underpins current standards, are needed.
• PFAS are present within construction materials which also need to be assessed and managed to support appropriate reuse, waste circularity and disposal.

There is so much research and innovation in this area that it is important to look at regulatory and technology trends globally to inform the potential direction of travel in the UK and try to manage future liabilities. This can sometimes mean that projects have to go a little above and beyond minimum regulatory requirements. For example, permitted discharges to surface water, including trade effluents and stormwater, are now coming under increased scrutiny with a current Environment Agency focus on airports requiring site surveys and extended monitoring programmes. This approach is likely to be expanded to cover other sectors.

05 / PFAS remediation

Remediation of PFAS in soils and waters can be more challenging for several reasons. However, cost-effective and sustainable technologies are available and are being increasingly deployed and optimised for PFAS. Widespread impacts and low treatment criteria require approaches that target source areas and first concentrate then destroy PFAS, often employing multiple technologies in 鈥渢reatment trains鈥� to address the range of PFAS that are likely to be present.

Treatments have to address a number of challenges:

• PFAS do not biodegrade, and so bioremediation approaches that are used widely for other organic contaminants are not suitable.
• PFAS require high temperatures to volatilise or destroy the contamination. This makes thermal approaches very costly. Incineration is seen as unsustainable for both soils and water, with limited capacity in the UK.
• More sustainable options, such as soil washing and stabilisation/solidification (S/S) are increasing being seen as robust, pragmatic technologies with multiple solutions deployed at full scale globally.
• The range of PFAS and diverse properties present unique challenges. For example, shorter-chain PFAS are less readily removed by granular activated carbon (GAC) or other approaches relying on hydrophobic sorption. Precursor PFAS are often less well studied.
• Novel destructive techniques, such as super-critical water oxidation (SCWO) and sonolysis, are less established but are being deployed and optimised at field scale.

The diagram below summarises the range of technologies that are being used and developed for PFAS remediation of soils and waters.

Whatever techniques are used, holistic lifecycle assessment and management of any PFAS residuals is critical. A key effort at the moment is to share best practice and demonstrate what is achievable with PFAS remediation so that regulators have the confidence to support these remediation strategies and thus mitigate further emissions of PFAS into the environment.

Further regulatory action regarding waste management sites would be welcome, as PFAS impacted materials can potentially be disposed of cheaply and legally at facilities that do not necessarily have robust requirements to test for, or treat, PFAS in their discharges. This can undermine sustainable materials management and remediation.

07 / Conclusion

Increasing awareness and regulatory requirements around PFAS across the brownfield sector can cause additional costs and delays if not foreseen. While PFAS can be effectively managed through the UK鈥檚 existing contaminated land management frameworks, the approach taken needs to reflect the complex challenges that PFAS bring 鈥� in particular, the need to work within a context of widespread background levels of PFAS in the environment. Already we need to consider PFAS at a greater range of sites and during initial stages of a project, ensuring robust characterisation of the types of PFAS that are potentially present.

The UK鈥檚 regulatory landscape is changing rapidly, and there is a need to learn from global best practice to anticipate and manage potential future liabilities. There is a clamour for more guidance and suitable screening levels to provide confidence to stakeholders managing and insuring brownfield sites.

However, while the challenges of PFAS to the sector are real and many projects are facing hurdles, the UK brownfield sector is adaptive and has a track record in managing complex novel contaminants. There are already site assessment approaches and remediation techniques that are suitable for PFAS, and a huge amount of innovation is taking place. Responding to the PFAS challenge at brownfield sites is a journey requiring collaboration between industry, regulators and all stakeholders so we can manage PFAS effectively but also target our efforts pragmatically alongside wider restrictions on the use of PFAS.