ALS offers PFAS (poly- and perfluoroalkyl substances) testing in environmental matrices and the option to include TOP assay to estimate the total content of these fluorinated compounds in samples.


ALS offers the following methods, with over 30 individual compounds included. TOP assay may be performed on the listed matrices.


 Matrix Method Reporting limit
Drinking Water EPA 537 Rev 1.1 or 537.1 2 ng/l
Drinking Water EPA 533
2 ng/L
Sediment EPA 537Mod
1 µg/kg
Soil EPA 537Mod  
1 µg/kg
Soil LC/MS/MS compliant with QSM 5.1 Table B-15
1 µg/kg
Soil ASTMD 7968 25 ug/Kg - 125 ug/Kg
Tissue EPA 537Mod
1 µg/kg
Water EPA 537Mod 2 ng/l
Water LC/MS/MS compliant with QSM 5.1 Table B-15 5 ng/L
Water EPA 8327 10ng/L - 50 ng/L
Water ASTM D7979 10ng/L - 50 ng/L


Containers for Sampling

Contact ALS for sample container requirements. The use of unsuitable containers may compromise results.

About PFAS

Perfluoroalkyl Substances (PFAS) are a class of synthetic compounds widely used in industrial applications that are characterized by highly fluorinated hydrophobic linear carbon chain attached to a hydrophilic functional group. PFAS’ are of interest due to their extreme persistence in the environment, ability to bioaccumulate, toxicity potential, and adverse human health effects.

The chemical structure of PFAS’ gives them unique properties, such as thermal stability and the ability to repel water and oil, making them useful in a wide variety of industrial and consumer products (fabric stain protectors, waterproofing of fabric, non-stick cookware, food packaging, lubricants, firefighting foams).

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two of the best known and most studied PFAS’. During the manufacturing process of some PFAS, and the use of PFAS products PFOA and PFOS have been released to the air, water and soil throughout the world. PFOA and PFOS have been detected in many isolated parts of the word indicating that long-range transport of these chemicals is possible.

Other PFAS’ of environmental concern include Perfluorooctane sulfonamides, sulfonamidoethanols, Fluorotelomer sulfonates, and other forms of Perfluoro carboxylates and Perfluorosulfonates.

EPA has found that there is suggestive evidence that PFOS and PFOA may cause cancer (EPA 2016d, 2016e).

The World Health Organization’s International Agency for Research on Cancer has found that PFOA is possibly carcinogenic to humans (Group 2B) (IARC 2016).

In May 2016, EPA established drinking water health advisories of 70 parts per trillion (0.07 micrograms per liter (µg/L)) for the combined concentrations of PFOS and PFOA. Above these levels, EPA recommends that drinking water systems take steps to assess contamination, inform consumers and limit exposure. The health advisory levels are based on the RfDs (EPA 2016b, 2016c).

What is TOP Assay

Traditional PFAS analyses report only of few of the thousands of known PFAS compounds and therefore may be under reporting the presence of these compounds in environmental samples.

However, an alternative method is available for PFAS analysis using Total Oxidizable Precursor Assay (TOP Assay). TOP Assay is a standardized pre-treatment of water samples or sample extracts designed to expose underlying PFAS not amenable to standard analysis. Perfluorinated carboxylates and sulfonates are stated to remain intact under the conditions of the assay.

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 six hours. Samples are neutralized and then run for the full suite of PFAS compounds.

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.

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 has been well considered as a treatment option. This includes both alkaline and heat activated persulfate, both of which are used in the TOP assay. In experiments performed at ALS, a 13C-labeled 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, which indicated some loss to shorter chain PFAS carboxylates not normally quantified. 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.

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 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.