Industrial Fire Journal - Fire & Rescue - Hemming Group Ltd
Methods for evaluating poly- and perfluoroalkyl substances (PFASs) released to the environment from firefighting foam use
Published:  06 March, 2018

Ian Ross PhD, Erika Houtz PhD, Erica Kalve, Jeff McDonough, Jake Hurst, Jonathan A. L. Miles PhD.


Class B firefighting foams that contain fluorosurfactants or poly- and perfluoroalkyl substances (PFASs) have been available since 1964. The term PFASs refers to a class of approximately 3,000 individual compounds that include both long and short carbon chain compounds known as C8, C6, C4 etc. [1]. Many PFASs present in firefighting foams were largely undetectable until introduction of a new analytical tool, the total oxidiseable precursor (TOP) assay.

PFASs have historically been (and continue to be) used extensively to suppress fuel-based fires during fire training and emergency response, to protect fuel storage facilities with above ground storage tanks (ASTs), in sprinkler systems in some warehouses, aircraft hangars, etc., and for use in fire suppression systems in shipping.

These foams that contain PFASs include the following, with alcohol resistant (AR) versions of each also available.

  • Aqueous film forming foam (AFFF)
  • Film forming fluoroprotein foams (FFFP)
  • Fluoroprotein (FP) foams

Over the past decade, an increasing number of PFASs have become chemicals of potential concern. Their presence in the environment at relatively high concentrations is frequently linked to the use of Class B firefighting foams containing PFASs. These foams were used historically without awareness of the potential environmental and human health impacts of the PFASs they contain, as some PFASs are now been discovered in drinking water supplies. Considering other industrial applications of PFASs, use of these foams for fire training and in emergency response is one of the most dispersive activities. They have been applied repeatedly or in large quantities to the ground surface in many locations creating potential legacy contamination issues.

Owners and operators of high-hazard facilities that require the use of PFAS-containing Class B foam products may need to consider the environmental liabilities associated with the continued or historical use of these foams. Additionally, training and use of some PFAS-containing Class B foams may still be an ongoing activity at high-hazard sites.

It may be wise to consider the future potential environmental liabilities of the historical and continued use of all PFAS-containing foams. This may be particularly important if the high-hazard site is situated on an aquifer used as a drinking water supply or for crop spray irrigation. Over the last 2 years, there has been a rise in the number of firefighting foam related sites that are being investigated to evaluate environmental and human health impacts thus requiring potential future clean up via remediation.

This article aims to explain how environmental regulators risk assess chemicals that may potentially cause harm. It provides useful information regarding the environmental characterization of known release points of PFASs to the owners and operators of high-hazard facilities so that site managers are equipped with the knowledge needed to manage their liabilities appropriately. The implications of the recent developments in analysis of PFASs, following introduction of the TOP assay and the rationale behind its use is explained in terms of potential latent environmental liabilities.

Environmental properties of PFASs

The most well-known PFASs are perfluorooctane sulphonic acid (PFOS) and perfluorooctanoic acid (PFOA) – also referred to as C8-compounds because of the 8 carbons in the molecule (“octo” being latin for 8). Both PFOS and PFOA were historically present in AFFF, and PFOS was a primary ingredient of some AFFF formulations for decades.

When assessing the environmental or human health impact of chemicals, the following terms are often used to describe how they behave:

  • Persistence (P): Compounds that do not break down in the environment over long periods of time (i.e., they do not readily biodegrade).
  • Bioaccumulative (B): Compounds that build up and are retained in organisms at a faster rate than they can be removed or expelled.
  • Mobility (M): Compounds that can travel long distances in groundwater or surface waters from their point of release.
  • Toxicity (T): Compounds impart an adverse health effect to an organism at a relatively low concentration of exposure.
  • Biopersistence: Compounds that tend to remain inside an organism, rather than being expelled or broken down.
  • Biomagnification: The increased concentration of a compound, such as a toxic chemical, in the tissues of organisms at successively higher levels in the food chain.

 The use of these terms in relation to environmental risk assessment of differing PFASs is described below.

PFOS was restricted for most uses in 2009 by an internationally ratified treaty called the Stockholm Convention on Persistent Organic Pollutants that aims to eliminate or restrict the production and use of persistent organic pollutants (POPs). The methods to classify chemicals of concern for evaluation under the Stockholm Convention include some of those listed above such as persistence, bioaccumulation, and toxicity; termed PBT. PFOA, and the six carbon (C6) analog of PFOS, perfluorohexane sulphonic acid (PFHxS), are also currently under consideration to be restricted under the Stockholm Convention.

There are additional emerging methods to evaluate environmental hazards posed by PFASs. These include assessing persistence, mobility, and toxicity (PMT) and the assessment of very bioaccumulative and very persistent (vPvB) compounds [2] [3]. The use of these additional criteria to assess environmental effects of PFASs will potentially lead to the identification of a far wider range of PFASs to be restricted under future environmental regulations.

Most owners of high-hazard sites are involved in the storage of liquid hydrocarbons, such as petroleum products and fuel oxygenates such as ethanol or methyl tertiary butyl ether (MTBE). Therefore, owners likely understand the potential risks to the environment and human health posed by these liquid hydrocarbon compounds. Fortunately, liquid hydrocarbon compounds and MTBE can eventually biodegrade to carbon dioxide and water, which diminishes the environmental harm they potential could cause. When compared to liquid hydrocarbon compounds, PFASs can exhibit a significantly different set of potential risks.

The fluorinated carbon chain in all PFAS molecules defines them, and is termed the perfluoroalkyl group. It enables unique partitioning behaviour (i.e., both hydrophobic [repels water] and oleophobic [repels oil] properties) and thermal stability, which are desirable commercial properties. However, this also imparts extreme persistence in the environment, a property which is irrespective of the length of the chain length. One major difference between PFASs and liquid hydrocarbon compounds and MTBE is that no PFASs biodegrade, regardless of chain length (C8, C6, C4, etc.). The total lack of observed biodegradation is somewhat extreme for PFASs, such that they have recently been termed “forever chemicals” [4]. Some PFASs (termed precursors) do biotransform in the environment but do so to create compounds such as PFOS and PFOA and their C6 and C4 analogs, termed perfluoroalkyl acids (PFAAs), which are increasingly subject to environmental regulations.

The shorter chain PFASs are generally more mobile than the longer chain, so C4 compounds move faster and further in groundwater than C6 compounds, which move faster and further in groundwater than C8 and so on. PFASs have also been shown to be more mobile than other common chemicals of concern. For example, environmental investigation work done to monitor PFOS and MTBE migration after the fire at the Buncefield fuel terminal in 2005 demonstrated that PFOS would migrate at 29 meters per year (m/year) versus MTBE, which would migrate at 17 m/year [5]. Therefore, it can be considered that PFOS is likely to be more mobile than MTBE in some aquifers.

The bioaccumulation of PFASs varies with chain length as well, although it increases as the chain length increases. For example, long chain PFASs such as with PFOA, PFOS, and PFHxS are more bioccumulative than the short chain PFASs, such as the C4 compounds, including perfluorobutanoic acid (PFBA) and perfluorobutane sulphonic acid (PFBS). The potential toxicity of bioaccumulative compounds is greater than similarly toxic but non-bioaccumulative compounds because bioaccumulative compounds build up in human beings rather than being rapidly eliminated. This is reflected in the regulated water quality standards suggested by several locations, such as Germany, Canada, Texas, and Italy. Lower compliance concentrations of the more bioaccumulative C8 compounds are required versus the lesser bioaccumulatve short chain PFASs. However this does not mean short chain compound are not a concern, the edible portion of plants, such as fruit, have been shown to concentrate the short chain PFASs [6, 7] with some plants reported to be removed from the human food chain in Germany as a result of their short chain PFASs concentrations [3].

The long chain compounds (e.g., PFOS, PFOA, PFHxS) are considered more bioaccumulative than short chain compounds, but there is uncertainty over the extent of bioaccumulation of the short chain compounds [3]. Recently, PFASs compounds associated with the C6 compounds have been described as having suspected bioaccumulation in organisms across species [8].

Emerging regulations

C8-compounds, such as PFOS and PFOA, have been the initial focus of environmental regulations in many countries; however, many environmental regulators internationally are now focusing on some of the other chain length PFASs, such as the C6-compounds. There are environmental regulations considering the C6 compound, perfluorohexanoic acid (PFHxA), in Germany, Texas, Denmark, Switzerland, Italy, Canada, and Sweden and the C6 compound 6:2 fluorotelomer sulphonate (6:2FTS) in Germany, Australia, Denmark, Switzerland, and Sweden. The long chain PFHxS is now regulated in Australia, Germany, Texas and New Zealand.

It’s clear that regulations considering many PFASs beyond PFOS and PFOA are evolving quickly. In some jurisdictions, the use of PFAS-containing Class B foams such as AFFF has already been restricted significantly, with a recent ban on fluorosurfactant based foams announced in South Australia in February [9, 10] and similar restrictions progressing in the state of Washington in the U.S. [11].

In 2016, the U.S. Environmental Protection Agency adopted a long-term health advisory level of 70 nanograms per liter (ng/L) or parts per trillion (ppt) for the sum of PFOS and PFOA detected in drinking water. These extremely low standards are similar to concentrations considered acceptable in drinking water in other countries and individual U.S. states. In New Jersey, an enforceable maximum concentration limit (MCL) for PFOA of 14 ng/L in drinking water has been recommended with the state considering a recommended MCL of 13 ng/L for PFOS  [12] [13].

Hidden proprietary precursors

Current PFAS testing methods are geared towards relatively few compounds, primarily the PFAAs, which are currently subject to regulation. However, class B firefighting foams contain many other types of PFASs that vary by manufacturer [14]. These are often proprietary foam formulations, meaning their exact chemical content is not public knowledge due to its commercial value. Therefore, most of the chemical identifications and structures of PFASs in these foams are unknown. The proprietary PFASs are generally termed PFAA precursors because as briefly indicated above they ultimately biotransform in the environment and in higher organisms to make the persistent PFAAs [15, 16]. Several hundred proprietary PFASs have been identified either as components of Class B foams or as their environmental breakdown products in soil and water [17]. The concentration of the majority of these proprietary PFASs cannot be determined, in samples of soil, groundwater or firefighting foams using conventional analytical methods (i.e., techniques that currently measure PFAAs) so they remain hidden.

From an environmental risk assessment perspective, knowing the exact chemical structure of these precursors is important as it allows testing to determine toxicity, whether they bioaccumulate or biotransform, and how mobile they are in an aquifer. Regulatory values that restrict chemicals to prevent human health effects are typically based on animal studies. These animal studies define a concentration below which there are no adverse health effects observed and then an extrapolation of that information informs a safe exposure value for humans. The largely unknown properties of these variable precursors adds a general uncertainty when attempting to assess risks they potentially pose to the environment and human health. Therefore, more work is needed to understand the environmental risks posed by the many precursors. However, it is known that the toxicity of some fluorotelomer compounds has been observed to be greater than that of the PFAAs they form [18].

In the face of this uncertainty, the Australian Government Department of the Environment and Energy (DoEE) has recently published a PFAS National Environmental Management Plan (NEMP) which highlights that the precautionary principle should be applied to managing uncertainties considering PFASs [19]. The precautionary principle states that when there are threats of serious or irreversible environmental damage a lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation. How the precautionary principle will be applied to the uncertainties pertaining to precursors is yet to be defined.

One powerful new tool to measure the concentration of total PFASs (both known PFAAs and proprietary PFASs) is an indirect measurement technique known as the TOP Assay, which was developed at the University of California, Berkeley. TOP Assay is designed to chemically convert all precursors in a sample into PFAAs [20, 21], as shown in Figure 1. This method removes the proprietary part of the molecule, using an oxidative conditions which struggle to attack the perfluoroalkyl group. This results in the generation of PFAAs which are used as a measure of the presence of the precursors. By measuring PFAAs in the sample before and after chemical conversion, the concentration of precursors can be indirectly measured. In this way the TOP Assay provides a true estimate of the concentration of total PFASs.

Figure 1: Diagrammatic representation of the chemical analytical challenge the TOP Assay addresses [20]

Since publication of the TOP Assay in the academic literature in 2012, TOP Assay has been made commercially available at laboratories in the U.K., Europe, North America, and Australia.

In 2016, the state of Queensland, Australia, became the first jurisdiction to codify the use of TOP Assay in the certification of firefighting foams. TOP Assay has gone from a research method to a well-established analytical method with a high reliability. Arcadis is currently assisting the state of Queensland with guidance on detailed interpretation of the TOP Assay output data and data quality objectives to ensure consistent use across multiple commercial laboratories.


As awareness of these hidden precursors is growing, approaching this issue using tools that provide insight into the total potential mass of PFASs at a site, seems likely to become more important over time for managing long term latent liabilities. It is clear that environmental regulations are progressing to consider many differing PFASs beyond PFOS and PFOA. Commercial decision-making on managing risks and liabilities associated with historical and ongoing use of Class B firefighting foams containing PFASs may need to consider future proofing their long-term management plans in light of the reality that PFASs are being described by regulators to cause permanent environmental damage. When considering long liability management of PFASs, the fast emerging environmental regulations focussed on this complex class of contaminants should be considered, so that commercial and operational planning is done with awareness of future potential environmental liabilities.


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