Per and Poly- Fluoroalkyl Substances (PFAS) are a heavily discussed topic at present and until their impacts on human and environmental health are fully understood they must be carefully monitored and managed.
One of the most common analytical techniques in PFAS soil and water contamination investigations is Total Oxidable Precursor Assay (TOPA) which oxidises unknown precursor fluorinated compounds into detectable PFAS.. Marc Centner from ALS Environmental discussed the applications and limitations of TOPA laboratory analysis. The focus of analysis was 0.5% to 1.5% fluorosurfactant products which are used to reverse engineer substances, such as Aqueous Film-Forming Foam (AFFF) or Firefighting Foam, to identify partially fluorinated substances such as perfluoro alkyl butane which is a precursor to Perfluorooctanoic Acid (PFOA). Other precursors such as Persulfate are heat activated, have highly heat sensitive half-lives and oxidise at a high pH. If the pH decreases sufficiently, oxidation ceases to take place and sulfate radicals form due to chain shortening.
Empirical analyses and dilutions at present are the only responses available, though with dilution comes the potential to dilute beyond the guideline standards which may cause interlab inconsistency. However, as long as the oxidant and the base are consistent there is no need for empirical analysis. Limitations during analysis of a sample arise as oxidation causes a loss of the total mass of butane and there is potential for incomplete oxidation. This results in a vast variety of different chain lengths only a portion of which are able to be identified through TOPA.
With regard to reducing these limitations, the 2018 ALGA R&D Grant winner research project focused on “improving measurement reliability of the PFAS TOPA”. Annette Nolan, the lead consultant at Ramboll Australia, discussed how the grant was utilised to benefit the industry.
Currently, approximately 4700 PFAS substances have been identified and approximately 90% of precursors making the risks of PFAS contamination difficult to estimate. It was found that in waste water treatment plants, precursors are more prevalent in influent waste streams than effluent because pre-treatment converts precursors into carboxylic acid by-products. As such, TOPA should be utilised when there is a semi-quantitative risk from precursors. TOPA does not mimic the natural environment, it cannot incorporate oxidation and loses mass and precursors during its conversion. It targets and identifies the maximum chain length PFAS. Thus, the sum of PFAS post-TOPA is generally greater than the total PFAS pre-TOPA due to the precursors conversion into carboxylic acids and sulfonic acids post-TOPA. QA/QCs monitor precursors identified during oxidation and oxidise to target analytes and surrogates. The National Environmental Management Plan (NEMP) states that the performance of TOPA will be masked in aqueous samples if:
Overall, it is the consultant’s responsibility to review the QA/QC and ensure that the laboratory’s limit of reporting (LOR) is fit for purpose.
PFAS are impacting a range of primary productions, industries, waterways and wetlands. Bearing in mind that environmental harm can incorporate any adverse or potentially adverse effects (Environmental Protection Act (EPA), 1994), PFAS are considered a regulated and trackable waste requiring containment and treatment to a concentration less than the LOR. With such a broad spectrum of PFAS -- with significantly more unknown than observable PFAS -- and precursors, only a portion of them can be analysed with TOPA.
Tony Bradshaw from the Department of Environment and Science (DES) discussed why TOPA is still an important analytical technique. Fluorotelomer carboxylic acids have been identified in landfill leachate under anaerobic digestion which are a precursor though are not in the main TOPA suite. Furthermore, precursors in fish accumulate PFAS over time which convert into sulfonic acids. PFAA accumulate in plants becoming PFOS, C4, C6 and C8 through aerobic transformation. These are identifiable through TOPA. TOPA can identify up to 250 times more PFAS than standard PFAS analysis. Even dairy cows exposed to precursors can accumulate PFAS in their milk. Shorter chain length carboxylic acids absorbed in plants (such as PFHxS) and accumulated in invertebrates are unaffected under TOPA which targets more absorbable PFAS though electrochemical fluorination and telomerisation production (PFAS production). This telomerisation allows different chain lengths to become observable. Pre-TOPA provides an underestimation of PFAS present while TOPA provides the precursors and their significance. Despite some mixed reviews, Bradshaw reminds us that it is an analysis tool and to keep up with the scientific developments on PFAS and that laboratories will unlikely adapt their LORs or alter their analysis until DES guidelines change.
A point of discussion was the shift of focus from long chain PFAS (such as AFFF) to short chain PFAS potentially giving rise to Total Organic Fluorine (TOF) analysis. However, it was concluded that the science of the effects of PFAS on people will dictate the future of PFAS treatment.
||Department of Environment and Science
10 October 2019 New Zealand Branch report by Lauren Reynolds – Graduate Environmental Engineer - WSP
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