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 50mg/kg (as fluorine) must be withdrawn from use.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].
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].