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
Perfluoroalkyl Substances (PFAS), formerly referred to as Perfluorochemicals (PFCs), are a class of synthetic compounds widely used in industrial applications that are characterized by a fully 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'. In their ionic form, they are water soluble and can readily migrate from soil to groundwater, where they can be transported long distances. PFOS is the predominant PFAS found in aquatic species around the world.
Other PFAS' of environmental concern include Perfluorooctane sulfonamides, sulfonamido ethanols, Fluorotelomer sulfonates, and other forms of Perfluoro carboxylates and Perfluoro sulfonates.
The EPA Science Advisory Board suggests that PFOA is likely to be carcinogenic and the American Conference of Governmental Industrial Hygienists has classified PFOA as a Group 3 carcinogen. The U.S. National Health and Nutrition Survey indicates serum PFOA and PFOS are associated with thyroid disease in the U.S. population and several PFAS' are now part of the EPA UCMR-3 list.
The ALS laboratory in Kelso, Washington utilizes three methods for the analysis of PFAS:
- In-house analytical method for water, soil, sediment, and tissues by LC/MS/MS
- EPA Method 537 selected perfluorinated alkyl acids in Drinking Water by LC/MS/MS
The Kelso facility offers PFAS analysis of water, soil, sediments, biosolids, and tissues matrices.
The standard Method Reporting Limits are:
- Water: 2 ng/L
- Soil/Sediment: 1 ug/Kg
- Tissues: 0.25 ug/Kg
Contact our laboratory in Kelso, Washington today! +1 360 577 7222
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.