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Per- and Polyfluoroalkyl Substances (PFAS)

Our understanding of the presence, toxicity and potential effects of this group of emerging contaminants continues to advance.  Although PFAS have been used for decades, only recently, due to advances in laboratory techniques, has it been possible to reliably quantify their presence and potential impacts.  
ALS has vast experience in working with environmental consultants and remediation contractors throughout the world.  The assessment of PFAS presents specific and unique challenges, it is therefore essential to partner with a laboratory with experience in analysing such samples to ensure sites are properly characterised using the most advanced analytical techniques available.

ALS Leading the Industry in the Analysis of Per- and Polyfluoroalkyl Substances (PFAS) 

Our understanding of the presence, toxicity and potential effects of this group of emerging contaminants continues to advance.  Although PFAS have been used for decades, only recently, due to advances in laboratory techniques, has it been possible to reliably quantify their presence and potential impacts.  

ALS has vast experience in working with environmental consultants and remediation contractors throughout the world.  The assessment of PFAS presents specific and unique challenges, it is therefore essential to partner with a laboratory with experience in analysing such samples to ensure sites are properly characterised using the most advanced analytical techniques available.

PFAS – THE ANALYTICAL CHALLENGES

PFAS are challenging contaminants because most constituents cannot be detected by conventional analytical techniques.  The sources of PFAS in the environment, such as Aqueous Film Forming Foam (AFFF), involve complex mixtures of individual PFAS constituents.  Assessment of sites impacted by PFAS require decisions to be made on the most robust, accurate and reliable data.

PFOS (perfluorooctane sulfonic acid) and PFOA (perfluorooctanoic acid), termed long-chain PFAS, are the best known examples and have been the focus of regulatory attention. Their potential impact on human health has been recognised globally as they are extremely persistent, bioaccumulative and toxic.  More recently, concern has extended to a much wider number of the PFAS including short-chain PFAS that are generally more soluble and mobile in groundwater.

Conventional methods allow for the analysis of around 15-20 different compounds.  There are, however, many more PFAS which will be left undetermined including a significant number of polyfluoroalkyl substances.  Under specific conditions in the environment, these compounds can be converted into perfluoroalkyl acids (PFAA).  Several common PFAA precursors containing a C8-perfluoroalkyl chain, including C8 sulphonamide compounds and 8:2 fluorotelomer alcohols, have been shown to partially transform to PFOA.  The behaviour of PFAS can vary depending, not only on the composition of the mixture, but also on the presence of co-contaminants and the impact of remediation induced changes in the subsurface.  As a result, there are significant analytical challenges to overcome when considering how to assess soil and groundwater. The failure to detect this hidden mass of precursors has led to increased uncertainty leaving sites with future residual liabilities.  A new innovative approach was needed.  

TOP ASSAY – A SIGNIFICANT STEP FORWARD

Total Oxidisable Precursor (TOP) Assay is a more comprehensive analysis technique and represents a significant step forward in the assessment of PFAS.  It converts precursors in a sample which are detectable by liquid chromatography with tandem mass spectrometry (LC-MS/MS).  Results are provided both pre and post digest, at a limit of detection (LoD) of around 2 ng/l.  The method removes the proprietary part of the molecule, using oxidative conditions, this results in the generation of PFAA which are used as a measure of the presence of the precursors.  TOP Assay also provides indicative data regarding the perfluoroalkyl chain length of the precursors, which can assist with assessing the source of the PFAS contamination and their potential to bioaccumulate.

In terms of investigation and remediation of sites impacted by PFAS, the approach taken is often different to conventional contaminants in view of the large number of compounds, precursors and breakdown products as well as the complex source compositions and fate and transport characteristics.  

TOP Assay provides a pragmatic and cost-effective solution to assessment of risks from PFAS.  Increasing consideration of PFAS chemistry and precursor loading will be needed in the future to better assess PFAS impacted sites.  

PFAS TOP ASSAY ANALYTES

PFAS Pre Oxidation (standard suite)

CAS

LoDs (ng/l)

PFBA Perfluoro-n-butanoic acid

357-22-4

<2

PFPA Perfluoro-n-pentanoic acid

2706-90-3

<1

PFHxA Perfluoro-n-hexanoic acid

307-24-4

<1

PFHpA Perfluoro-n-heptanoic acid

375-85-9

<1

PFOA Perfluoro-n-octanoic acid

335-67-1

<0.65

PFNA Perfluoro-n-nonanoic acid

375-95-1

<1

PFDA Perfluoro-n-decanoic acid

335-76-2

<1

PFUnA Perfluoro-n-undecanoic acid

2058-94-8

<1

PFDoA Perfluoro-n-dodecanoic acid

307-55-1

<1

PFBS Perfluoro-1-butanesulfonate

375-73-5

<1

PFPeS Perfluoro-1-pentanesulfonate

2706-91-4

<1

PFHxS Perfluoro-1-hexanesulfonate

355-46-4

<1

PFHpS Perfluoro-1-heptanesulfonate

375-92-8

<1

Linear PFOS Perfluoro-1-octanesulfonate

1763-23-1

<0.65

Branched PFOS

N/A

<1

Total PFOS

N/A

<1

PFDS Perfluoro-1-decanesulfonate

335-73-3

<1

PFOSA Perfluoro-octanesulfonamide

754-91-6

<2

6:2 FtS

27619-97-2

<1

PFAS Post Oxidation

CAS

LoDs (ng/l)

PFBA Perfluoro-n-butanoic acid

357-22-4

<4

PFPA Perfluoro-n-pentanoic acid

2706-90-3

<2

PFHxA Perfluoro-n-hexanoic acid

307-24-4

<2

PFHpA Perfluoro-n-heptanoic acid

375-85-9

<2

PFOA Perfluoro-n-octanoic acid

335-67-1

<2

PFNA Perfluoro-n-nonanoic acid

375-95-1

<2

PFDA Perfluoro-n-decanoic acid

335-76-2

<2

PFUnA Perfluoro-n-undecanoic acid

2058-94-8

<2

PFDoA Perfluoro-n-dodecanoic acid

307-55-1

<2

PFBS Perfluoro-1-butanesulfonate

375-73-5

<2

PFPeS Perfluoro-1-pentanesulfonate

2706-91-4

<2

PFHxS Perfluoro-1-hexanesulfonate

355-46-4

<2

PFHpS Perfluoro-1-heptanesulfonate

375-92-8

<2

Linear PFOS Perfluoro-1-octanesulfonate

1763-23-1

<2

Branched PFOS

N/A

<2

Total PFOS

N/A

<2

PFDS Perfluoro-1-decanesulfonate

335-73-3

<2

PFOSA Perfluoro-octanesulfonamide

754-91-6

<4

6:2 FtS

27619-97-2

<2

Analytical challenges and solutions 

Analytical Challenges

  • Sources of PFAS in the environment, such as Aqueous Film Forming Foam (AFFF) involve complex mixtures of individual PFAS constituents. 
  • Conventional methods allow for the analysis of around 15-20 different compounds.  There are, however, many more PFAS which will be left undetermined.  Under specific conditions in the environment, these compounds can be converted into perfluoroalkyl acids (PFAA). 
  • Total oxidisable precursor (TOP) Assay is a more comprehensive analysis technique and represents a significant step forward in the assessment of PFAS.  It converts all precursors in a sample which are detectable by liquid chromatography with tandem mass spectrometry (LC-MS/MS). 
  • ALS are internationally recognised as industrial leaders and technical experts.
  • Collaborative working with consultants and contractors to manage uncertainty and inform best-value investigation and remediation strategies.

Sampling Challenges

  • We use HDPE (High-density polyethylene) or PET (polyethylene terephthalate) containers known to be free of PFAS.  We don’t use glass because of the potential for analyte sorption – PFAS adsorbs strongly to glassware. 
  • There is a high potential for cross-contamination during sampling and very careful consideration needs to be given to sources of contamination during the planning of any investigation.
  • Field sampling equipment, including oil/water interface meters, trowels and other non-dedicated equipment used at the sampling location require cleaning.  The detergents used in decontamination procedures should be reviewed to ensure fluorosurfactants are not listed in their ingredients.  Use laboratory-certified PFAS-free water for the final rinse during decontamination of sampling equipment.  Decontaminate larger equipment (for example, drilling rigs) with potable water using a high-pressure washer.  To the extent practical, rinse parts of equipment coming into direct contact with samples with PFAS-free water.  Heavy equipment is best cleaned within a decontamination facility or other means of containment. 
  • The conceptual site model (CSM) or previous phases of investigation may indicate areas of high concentrations of PFAS for which single use, disposable equipment is recommended.  If single use is not possible, take additional precautions such as implementing a greater frequency of decontamination blanks and not reusing equipment to sample potentially low PFAS contamination samples.  High concentration samples should be segregated during transport to the laboratory.
  • All AFFF samples must be considered as having high concentrations.  These samples should be segregated from other samples during sampling and transport to avoid cross-contamination.  Samples that may contain high concentrations of PFAS should be clearly identified on the Chain of Custody form within the known hazard box.

Regulatory challenges

  • Regulatory focus has previously been on a very limited number of PFAS, namely PFOS (perfluorooctane sulfonic acid), PFOA (perfluorooctanoic acid) and PFHxS (perfluorohexane sulfonic acid) but there are many more PFAS which are now regulated across the world including other countries in Europe but not in the UK. 
  • Regulatory focus has been on long-chain PFAS (C8) because they have a higher potential to bioaccumulate.  They bioaccumulate in the proteins rather than fats and lipids.  Short-chain PFAS are generally more soluble and therefore more mobile in the environment often creating extended plumes.  Short-chain PFAS are also less effectively treated by granular activated carbon.
  • The AA-EQS (Annual Average Environmental Quality Standard) which is set at 0.65 ng/l PFOS is lower than background levels in most UK surface waters.
  • The UK has a tiered approach to Drinking Water Guidance published back in 2009 - PFOS and PFOA have a first tier level of 0.3 µg/l above which consultation and monitoring must be undertaken.  However current DWI guidance only requires measures to reduce concentrations to below 1 µg/l for PFOS and 5 µg/l for PFOA.  These thresholds were based on Tolerable Daily Intakes set by the European Food Safety Agency (EFSA).  We are likely to see a reduction in drinking water standards based on more recent research by EFSA on PFOS and PFOA (2019) and PFAS (2020).

Number of PFAS in the environment

  • Our standard list of PFAS includes 19 individual components.  We can also offer 8:2 FTS (fluorotelomer sulfonate), 4:2 FTS and 5:3 FTCA (fluorotelomer carboxylic acid) as part of an extended suite.
  • There are many thousands of PFAS which cannot be detected by standard analytical methods however these can transform in the environment to regulated PFAA.  AFFF contains many hundreds of individual PFAS that will evade detection unless using an advanced analytical method for determining the total amount of oxidisable precursors.  One new tool to potentially measure the concentration of total PFAS (including known and unknown forms) is an indirect measurement technique known as TOP Assay.

Usful Documents 

PFAS Overview Flyer --> pfos-and-pfoa2020.pdf

PFAS Sampling Guidance --> pfas-sampling-guidance.pdf

Common Mistakes When Testing for PFAS --> common-mistakes-pfas.pdf

Contact US: For further information contact our Client Services Team on:

Tel: +44 (0)1244 528 777    •    Email: hawardencustomerservices@alsglobal.com

 

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