EnviroMail™ 110 – Identifying Hidden PFAS Chemicals in Environmental Samples and Firefighting Foams

EnviroMail™ 110 – Identifying Hidden PFAS Chemicals in Environmental Samples and Firefighting Foams

Posted 21 September 2016
Traditional PFAS analysis only targets the key analytes and therefore may or may not greatly underestimate the presence of PFAS in the environment and the Total Oxidisable Precursor Assay and the determination Total Organic Fluorine have been suggested as means of exposing these underling cryptic PFAS.
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Total Oxidisable Precursor Assay

The Total Oxidisable Precursor Assay (TOP assay or TOPA) is a standardised pre-treatment of water samples or sample extracts (soil and water) designed to expose underlying PFAS not amenable to standard analysis. Water samples, sample extracts (soil or water) or diluted foam products are incubated with potassium persulfate (60 mM) and sodium hydroxide (0.125 M) at 85°C for 6 hours. Samples are neutralised and then run for the full suite of PFAS compounds [3,4].

Note that this is an empirical test and comparable results can only be achieved by precisely following the conditions of the test.

Under the conditions of the assay it is expected that fluortelomer sulfonates are broken down to shorter chain carboxylates by cleavage of the non-fluorinated portion of the molecule. Perfluorinated carboxylates and sulfonates are stated to remain intact under the conditions of the assay.

Queensland Operational Policy on the Management of Firefighting Foam

The Queensland Department of Environment and Heritage Protection released its “Foam Policy” in August 2016 [5]. ALS now offers testing following application of the TOP “digest” to provide this information.

This policy is the first Australian guidance that recognises the potential contribution of cryptic PFAS to the environment. This also provides guidelines for using the TOPA for the assessment of soils, waters and foam products in QLD.

Particular guidance is given for the evaluation of the suitability of foam products for use (table 6.2.2). Foams where TOPA (C7 – C14) results are > 50mg/kg (as fluorine) must be withdrawn from use. Similarly Table 6.4.2 A specifies levels for wastewaters, with criteria for PFOS and PFOA (0.3 μg/L) and Sum of *TOPA C4-C14 plus C4-C8 sulfonates (1 μg/L).

ALS Reporting

ALS provides TOP pre-treatment and reporting of TOP sums per the Queensland foam management policy in soils, waters and foam products. ALS will perform the usual sample preparation used for waters (including low level waters), diluted foam products and soils followed by oxidation of the sample under the standard conditions for the TOP assay.

Please note that only the full analytical suite is available for this assay in order to account for the full range of products produced post-oxidation.

In addition to large compounds the following will be reported:

  • Sum of TOP for C7 to C14 compounds as fluorine – applicable to foam products (0.01 mg/kg)
  • Sum of TOP C4-C14 carboxylates plus C4-C8 sulfonates in soils (0.0002 mg/kg)
  • Sum of TOP C4-C14 carboxylates plus C4-C8 sulfonates in waters (0.002 to 0.01 µg/L, standard and low-level)

Oxidation of AFFF Products

Over the last six months, ALS has performed numerous oxidation trials in order to obtain a deeper knowledge of the Total Oxidisable Precursor Assay. This includes the impact of concentration plus the differences between first generation and modern foams. 

A number of foam products were subject to the TOP alkaline persulfate digest and analysed by LCMSMS. Three products were examined, 3M :Lightwater ™, Ansulite™ and Aer-O-Water ™ The first being the classic pre-2000 AFFF and the latter two examples of more recent short-chain foams. Note that only the Aer-O-Water product was in its original packaging whilst the other products had been supplied as subsamples of uncertain origin.  

Note that only the Aer-O-Water product was in its original packaging whilst the other products had been supplied as subsamples of uncertain origin.

Figure 1 indicates significant growth in total PFAS following oxidation for Ansulite and Aer-O-Water. Growth of perfluorocarboxylic acids in 3m Lightwater may be attributable to unspecified “fluoroalkyl amide derivatives” described in a 1996 MSDS from 3M in Australia. The outcomes of these digests are consistent with results reported in the literature on this subject [6].

In figure 2 the concentration of the AFFF can affect both qualitative and quantitative outcome of the oxidation process. Oxidation at high dilutions leads to full conversion of the material to carboxylic acids. At higher concentrations, this conversion is less than complete which indicated exhaustion of the oxidant. At a 500-fold dilution, 6:2-FTS is a large component of the composition which is consistent with the presence of fluorotelomer sulfonamido betaines in some modern-day products [2].

Discussion

The TOP assay is capable of revealing the presence of PFAS that may, given time, weather to Perfluorinated Alkyl Substances of concern but is definitely not a predictor of the endpoint of abiotic and biotic breakdown in the field.

Oxidation (and in particular, the use of activated persulfate) has been well considered as a treatment option [7].  This includes both alkaline and heat activated persulfate, both of which are used in the TOP assay.To some extent, this may explain the small loss of PFOS observed with oxidation of 3M Light Water.

In experiments performed at ALS, a 13C-labelled PFOS surrogate was added pre-oxidation and regularly recovered around 80%.  Oxidation of a full analytical standard (not under standard conditions) also yielded less than a mass balance when summed, indicating some loss to shorter chain PFAS carboxylates not normally quantified (e.g. trifluoroacetic and pentafluoropropanoic acids).

On the flip side, if the oxidant is exhausted either by competition from non-PFAS organic carbon or high concentrations of PFAS, both qualitative and quantitative conversion of AFFF PFAS precursors may be incomplete.  Referring to figure 2 and the 500-fold dilution of Aer-O-Water, we see a massive growth in 6:2-FTS which is not present at lower concentrations.  ALS has demonstrated that, in the absence of persulfate, incubation of the sample under the conditions specified in the assay (alkalinity, temperature and time) there is still a significant growth of the fluorotelomers.  This is consistent with alkaline hydrolysis of fluorotelomer sulfonamide precursors which will yield the fluorotelomer sulfonic acid and an amine.  See reference [1] discussion on National Foam (Aer-O-Water) AFFF composition

When comparing data between laboratories, it is essential that the oxidation conditions are absolutely standardised and that sample dilutions are reasonably equivalent.

In conclusion, the TOP assay is a useful tool in exposing the potential for ongoing contamination by PFAS compounds through biotic and abiotic weathering processes.  Results, however should be treated with caution, especially where a health or ecological risk assessment is required.

There may also be a case to expand analytical suites to cover other PFAS that may arise from weathering that might include some oxidation and hydrolysis and, ideally, to have better models for predicting environmental endpoints of AFFF degradation.

If you wish to discuss this further feel free to contact Marc Centner, National Technical Manager, Environmental, Australia (marc.centner@alsglobal.com)

Oxidation Field Samples

ALS has taken samples that recorded reasonably high results in normal testing and subjected these to the TOP assay.

The pre-oxidation composition of samples indicate use of both PFOS and fluortelomer containing foams in the one location (PFOS in light blue and 6:2-FTS in pale orange).

From the composition of un-oxidised samples it can be seen that contamination originates from a mixed source – both PFOS-containing and more recent fluorotelomer foams. Note that post-oxidation there is not much growth in total fluorinated compounds but that the fluorotelomers undergo oxidation to carboxylic acids. Also, in the case of samples 2 and 3 PFOS is seen to reduce which is contrary to the assumptions behind the assay.

References

  1. Place, Benjamin J.; Field, Jennifer A. (2012): Identification of Novel Fluorochemicals in Aqueous Film-Forming Foams Used by the US Military. In Environmental Science & Technology 46 (13), pp. 7120–7127. DOI: 10.1021/es301465n.
  2. Backe, Will J.; Day, Thomas C.; Field, Jennifer A. (2013): Zwitterionic, Cationic, and Anionic Fluorinated Chemicals in Aqueous Film Forming Foam Formulations and Groundwater from U.S. Military Bases by Nonaqueous Large-Volume Injection HPLC-MS/MS. In Environmental Science Technology 47 (10), pp. 5226–5234. DOI: 10.1021/es3034999.
  3. Houtz, Erika F. (2013): Oxidative Measurement of Perfluoroalkyl Acid Precursors: Implications for urban runoff management and remediation of AFFF-contaminated groundwater and soil. Doctor of Philosophy. University of California. Berkeley.
  4. Houtz, Erika F.; Sedlak, David L. (2012): Oxidative conversion as a means of detecting precursors to perfluoroalkyl acids in urban runoff. In Environmental Science & Technology 46 (17), pp. 9342–9349. DOI: 10.1021/es302274g.
  5. Queensland Government Department of Environment and Heritage Protection (2016): Operational Policy – Environmental Management of Firefighting Foam, pp. 1–16.
  6. Houtz, Erika F.; Higgins, Christopher P.; Field, Jennifer A.; Sedlak, David L. (2013): Persistence of Perfluoroalkyl Acid Precursors in AFFF-Impacted Groundwater and Soil. In Environmental Science & Technology 47 (15), pp. 8187–8195. DOI: 10.1021/es4018877.
  7. FMC Environmental Solutions: Activated Persulfate Oxidation as a Remediation Technology for PFOS PFOA. Available online: http://www.peroxychem.com/media/22910/FMC_Peroxygen_Talk_2011-12_Treatment_of_PFOS_and_PFOA.pdf, checked on 8/15/2016.
  8. Yang, Shewei; Cheng, Jianhua; Sun, Jian; Hu, Yongyou; Liang, Xiaoyan (2013): Defluorination of Aqueous Perfluorooctanesulfonate by Activated Persulfate oxidation. In PloS One 8 (10), e74877. DOI: 10.1371/journal. pone.0074877.

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