The how and why of PFAS

Initially the PFAS used in early products like fabric protectants and firefighting foam were perfluoroalkyl acids like C8 PFOS and PFOA produced by electrofluorination. Since about 2000 there had been a switch towards fluorotelomer compounds with most modern PFAS firefighting foams and other products based on a diversity of complex fluorotelomers. This has presented challenges for development of methods for disposal that are economic and effective across the very wide diversity of PFAS in wastes [1], which include mixtures of anionic, cationic and zwitterionic compounds, with some methods only effective for specific compounds or types and subject to interference from other components in the wastes.

Disposal methods therefore need to be effective across the range of all modern fluorotelomer surfactants as well as for legacy perfluoroalkyl PFAS in products, as well as the intermediates that result from the transformation of fluorotelomers in the environment.

Modern fluorotelomer PFAS manufacture starts with the mineral fluorspar, natural crystalline calcium fluoride (CaF2), being treated with concentrated sulfuric acid to produce hydrofluoric acid (HF). The HF is then combined with organic compounds to make telogen perfluoroalkyl iodides, most commonly pentafluoroethyl iodide (C2F5I) which is reacted with tetrafluoroethylene (C2F4) to produce the desired longer-chain perfluoroalkyl iodide, such as C8 heptadecafluorooctyl iodide (C8F17I); these perfluoroalkyl iodides are then used to produce fluorotelomers, as summarised in Figure 1. After the perfluoroalkyl iodide is formed, a suitable non-fluorinated functional group is added to give the desired fluorosurfactants end-product, such as a perfluoroalkyl betaine or aminoxide. The end-products are fluorotelomer chains that have diverse and complex functional groups, but all have linear perfluoroalkyl C-F chains that always contain an even number of carbon atoms (4,6,8, etc.), usually with a non-fluorinated dimethylene (-CH2-CH2-) group between the perfluoroalkyl group and the functional group. This contrasts to the PFOS related compounds produced by electrofluorination that contain both odd and even (5,6,7,8...) linear and branched fluorinated carbon chains.

Fluorotelomers are sometimes dismissively referred to as “PFAS precursors” with the misconception that they are benign. Fluorotelomers are not benign or inert, they are nonetheless PFAS as are the endpoint products. Their functional groups can confer toxicity, bioavailability and bioaccumulation characteristics greater than the more commonly referenced endpoint PFAS sulfonates and carboxylates like PFOS and PFOA. The key issue from the point of view of toxicity, persistence, disposal and destruction is that no matter what their origins and forms are, all PFAS have perfluorinated carbon moieties that are part of, or result in, persistent, bioaccumulative and toxic products highly resistant to degradation.

Figure 1. The main building blocks for fluorotelomer PFAS. The fluorotelomer perfluoroalkyl group (left) separated from the functional group (right) by the non-fluorinated -CH2-CH2- “spacer” group (circled).

PFAS destruction practicalities

Both the Stockholm Convention and the Basel Convention Guidelines [2,3] describe the co-processing of various hazardous wastes in rotary cement kilns, in the well-established and common industrial process that is characterised by extremely high kiln temperatures (~1,200-1,600°C) with long residence times of the order of minutes. These conditions far exceed temperature and residence times achieved in normal commercial domestic waste incinerators. The conditions for PFAS destruction are usually cited as temperatures of at least 1,100°C and residence times of >2 seconds [4]. Cement kilns not only exceed these conditions but also have the significant advantage of an excess of calcium in the feedstock that not only catalyses the breaking of the C-F organo-fluorine bonds at temperatures much lower than 1,100C but also progressively and permanently captures the fluorine as calcium fluoride minerals (e.g., alite, pseudoalite and fluore-spurrite).

By contrast, standard commercial incinerator temperatures are rarely high enough, with the potential for ultra-short PFAS like CF4 and C2F6 to pass through, or for other PFAS to reform in the flue gases, plus the generation of corrosive, toxic hydrogen fluoride (HF) that must be scrubbed from the flue gases at additional and considerable cost.

For the most part the stable operating conditions of cement kilns with an excess of calcium provide wide safety margins for PFAS destruction and fluorine capture, so the primary regulatory controls need to be around the process points, timing and temperatures for PFAS waste introduction.

The temperatures and residence times of material in the kiln main burner region exceed the minima that are considered to be required for PFAS to be broken down. It has now been established that the presence of calcium catalyses the breakdown of PFAS at around 800C PFAS so that wastes can also be introduced earlier into the kiln during the calciner process.

In terms of control over the timing of PFAS introduction to the kiln for destruction, this needs to be once the kiln production conditions of temperature and throughput are stable (Figure 2). For liquid PFAS wastes, introduction can be by incorporation into liquid fuel such as waste oil, rather than as a waste introduced directly into the burner flame (which can cause disturbance to the flame by the water content). Introduction with the liquid fuel also gives the ability to immediately cease waste input should kiln conditions become unstable.

Solid wastes can also be introduced into the calcining zone at some facilities for disposal of wastes such as PFAS-contaminated activated carbon and resin remediation wastes.

Figure 2. Typical temperature profile in a long rotary cement kiln.

Thermal Breakdown of Fluorochemicals
Decomposition mechanisms for the breakdown of PFAS at elevated temperatures are beginning to be better understood, as are the influences of the presence of calcium compounds that are available in excess in cement kilns. Calcium has a dual action, it catalyses the cleavage of the PFAS carbon-fluorine bonds at lower temperatures than for PFAS alone [6,7]. Calcium also progressively captures the liberated fluorine free-radicals, forming inert calcium fluoride minerals progressively throughout the process (Figure 3). The captured fluorine is very strongly bound, moving through the clinker process to finally be a harmless, trace component of the final cement product.

Co-processing of PFAS and other fluorine wastes in cement kilns does not require any modification of the process. Other significant advantages are that it does not require additional fuel and has no end-point waste for disposal, and as such it represents a sustainable, permanent disposal of PFAS as inert mineral trace components of cement.

Figure 3. Cement kiln destruction of PFAS and the capture of the fluorine

PFAS destruction trials and proof-of-concept

Disposal and destruction of hazardous wastes is subject to legislative and specific regulatory provisions to manage handling, transport, storage, treatment, and disposal of the wastes. PFAS wastes are of particular concern being permanent and dispersive pollutants that are toxic, highly mobile and do not degrade in the environment. Dedicated hazardous waste incinerators are often operating at the limits of their temperature range, stability and capacity to scrub toxic and hazardous materials from the flue gases associated with process disturbances and the possibility of carbon and fluorine reforming into ultra-short chain C1 and C2 PFAS. By comparison, trials of PFAS destruction in cement kilns have found that normal cement kiln operation has excess capacity to destroy PFAS and remove the fluorine, with wide safety margins around destruction efficiencies, temperature, and residence times, with permanent capture of fluorine plus significant fuel efficiencies.

Cement kiln PFAS destruction trials in 2016-17 in Queensland included fluorine inputs of up to 5kg/hr in PFAS plus runs with an additional 90 to 325kg/hr fluorine in wash-water and calcined ash from aluminium smelter pot line wastes. In view of research [6,7] that had shown that calcium catalysed PFAS destruction at temperatures lower than the commonly cited 1,100°C (from ~350°C), the trials also included input of PFAS wastes into the calciner where temperatures range from 800°C to 1,000°C.

For PFAS input to both the calciner and main kiln there were no PFAS detected in emissions or in cement clinker with PFAS destruction efficiencies for PFOS, PFOA and PFHxS of 99.999% or better (Figure 4). There was no change in the normal process concentration of HF in flue gases of 0.045 mg/Nm3 (1,000 times lower than the licence limit of 50 mg/Nm3) when PFAS was introduced, or even when there was an extra input of up to 325 kg of fluorine when smelter pot line waste was also introduced.

Figure 4. Cement kiln process and advantages.

Based on the PFAS destruction trial results, in 2018 the cement kiln licence was amended to allow destruction up to 5kg-F/hr of PFAS (approximately equivalent to the fluorine content of one 1,000L IBC of foam concentrate) introduced into the calciner or the main kiln, on condition that the kiln process was stable with minimum temperatures of 850°C in the calciner and 1,200°C in the main kiln.

Analyses to monitor for PFAS in flue gases are conducted annually with no detections of PFAS since then. Operationally there was no need for changes to the normal kiln processes, no extra energy input and no change to cement clinker quality with the fluorine bound up in the cement as trace amounts of insoluble, inert, non-toxic calcium fluoride minerals.

Interest in effective and safe high-temperature incineration or co-processing of fluorine-containing PFAS waste using rotary cement kilns has increased substantially since we first published a brief description of the Queensland trials in 2018 [8]. Recent work by the US EPA has identified high-temperature cement kiln co-processing as a viable and energy efficient method for disposing of PFAS waste streams [9,10,11]. The Basel Convention General technical guidelines on environmentally sound management of wastes now also reference cement kiln co-processing as a method for PFAS destruction [12]. The life cycle of any resource should be a closed loop of use and reuse or, if that is not practical, then at least have a disposal end point that is benign. The EU has defined a ‘circular economy’ as “…. a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing and recycling existing materials…” [5]. In practice, a circular economy implies reducing waste, and thus keeping environmental contamination to a minimum.

Calcium-catalysed cement kiln co-processing for destruction of PFAS waste and the capture of the fluorine can be considered as a pseudo-circular economy (Figure 5) at least resulting in the return of fluorine to an inert, non-toxic state.

Figure 5. Cement kiln destruction of PFAS achieves a quasi-circular life cycle.

References
[1] Kwiatkowski, C.F., Andrews, D.Q., Birnbaum, L.S., Bruton, T.A., DeWitt, J.C., Knappe, D.R.U., Maffini, M.V., Miller, M.F., Pelch, K.E., Reade, A., Soehl, S., Trier, X., Venier, M., Wagner, C.C., Wang, Z., and Blum, A. (2020) Scientific Basis for Managing PFAS as a Chemical Class. Environ. Sci. Technol. Lett. 7, 532−543.
[2] UN Stockholm Convention (2008) “Guidelines on best available techniques and provisional guidance on best environmental practices relevant to Article 5 and Annex C of the Stockholm Convention on Persistent Organic Pollutants- cement kilns firing hazardous waste”.
[3] UN Basel Convention (2012) “Technical guidelines on the environmentally sound co-processing of hazardous wastes in cement kilns”.
[4] Basel Convention (2012) In the case of hazardous wastes with a content of more than 1 per cent halogenated organic substances (expressed as chlorine), the temperature should be raised to 1100°C for at least two seconds. Under the United States TSCA disposal of PCBs requires a temperature of 1200°C and 2 seconds retention time (at 3 per cent excess oxygen in the stack gas).
[5] European Commission (2020) “A new Circular Economy Action Plan for a cleaner and more competitive Europe”, COM/2020/98 final, Brussels. European Parliament News Item Updated 26 April 2022.
[6] Wang, F., Xinghwen, L., Xiao Yan, L., Kaimin, S. (2015) “Effectiveness and mechanisms of defluorination of perfluorinated alkyl substances by calcium compounds during waste thermal treatment”. Environ. Sci. Technol. 49 (9) 4672-4680;
[7] Riedel, T.P., Wallace, M.A.G., Shields, E.P.; Ryan, J.V.; Lee, C.W.; Linak, W.P. (2021) “Low temperature thermal treatment of gas-phase fluorotelomer alcohols by calcium oxide”. Chemosphere 272, 129859.
[8] Klein, R.A. (2018) Recycling Bubbles. Industrial Fire Magazine Q2, 24-26.
[9] Longendyke, G.K., Katel, S., and Wang, Y. (2022) PFAS fate and destruction mechanisms during thermal treatment: a comprehensive review. Environmental Science: Processes Impacts 24, 196-208.
[10] Patterson, C., and Dastgheib, S.A. (2020) “Cement Kiln and Waste to Energy Incineration of Spent Media” presentation at a joint USEPA/ORD and DOD/SERDP/ESTCP Workshop on the Thermal Treatment of PFAS, Cincinatti, Ohio, 25 February 2020. pp.15.
[11] Gullett, B., and Gillespie, A. (2020) US Environment Protection Agency Technical Brief. “Per- and Polyfluoroalkyl Substances (PFAS): Incineration to Manage PFAS Waste Streams” February 2020.
[12] UN Basel Convention (2023) “General technical guidelines on environmentally sound management of wastes“ UNEP/CHW.16/CRP.12, Geneva CoP, May 2023.

Microplastics: tiny plastics, big problems

Microplastics – plastic particles smaller than 5 mm, are a pervasive contaminant that has been detected from the depths of oceans to the heights of Mt Everest, and even inside of our bodies. Microplastics are an emerging contaminant and researchers are just starting to uncover their effects on the environment and on human health. This means that there is a lot of potential for research, and Aotearoa New Zealand is a good setting for microplastic waterway research because it’s an island nation so there aren’t any messy geopolitical boundaries when trying to isolate point source pollution. New Zealand could be a leading example in microplastic freshwater research and while there are already several high-resolution analyses and studies, quantifying and establishing a baseline of microplastic concentrations around the country is a huge effort. This is where citizen science comes in.

Microplastics collected by students from our local river (Otepuni)

What is citizen science?

Citizen science, or participation of people in scientific processes who are not institutionally linked to that particular field of science, has been referred to as “the favoured twenty-first century model for conducting large-scale scientific research” (K. Toerpe, "The rise of citizen science," The Futurist, no. 4, 2013). Citizen science is an inclusive scientific methodology and there are innumerable social benefits ranging in scale of influence from increasing awareness in participants, to contributing to policies and national reports (e.g. the Sustainable Coastlines programme Litter Intelligence contributes to government reports about marine litter). Citizen science pushes the boundaries of research by expanding observation networks and databases in scope and availability to a larger extent or variety of spatial and temporal coverage. In the context of microplastics in waterways, citizen science could provide a nationwide snapshot of microplastic quantification, and help to identify hotspots that warrant further scientific investigation.

Micro-Investigators: microplastics citizen science

Since 2020, the Micro-Investigators programme has been implemented across schools in the Southland region in coordination with national organisation Enviroschools and various community groups. Primary school students use a plankton net to collect water samples from their local river and also try out various water quality sampling techniques (e.g. macroinvertebrate identification, clarity tube, water pH). Students from high schools are involved in the laboratory analysis and microplastics identification. Field and lab sessions are facilitated by tertiary students from the Southern Institute of Technology. Through this “Tuakana-Teina” framework the older students share their knowledge and set an example for the younger students, who can see first-hand some of the STEM pathways and further study in science that they could be getting into. At the end of the year we hold a Hui, or gathering, to celebrate the work of all the participants of the programme, and to give the students a chance to present their results and give a call to action to local council representatives and decision makers. The Hui consolidates learning and shows students that they have a voice and can make a difference.

Students from Makarewa School at a Micro-Investigators field session

Waterway microplastic concentration data

Besides the value added to education through hands-on environmental experiences, the data collected by citizen scientists is available and accessible on the Micro-Investigators website. The goal is to keep populating the microplastic concentrations map with more points on waterways, adapting long-term monitoring with the same schools returning regularly to their local river sites to measure microplastics and water quality. Ideally, after the first field session, the schools would be able to do the sampling themselves, since a good citizen science programme should ultimately be autonomous. In order to facilitate this autonomy, we put together sampling equipment and materials for 6 kits that have been placed in hubs around Southland. The kits include resources like how-to videos and manuals on how to use the equipment, in order to avoid sampling error, which is an important consideration for citizen science.

The microplastics data collected by citizen scientists is available on the Micro-Investigators website.

Success stories

We interviewed teachers whose classes were involved in the Micro-Investigators sessions and found that the programme fit well into their curriculum and that they wanted to see repeat sessions, which aligns well with our objective of ongoing environmental monitoring. One teacher told us about a student that arranged a meeting with the manager of their local supermarket to discuss alternatives to single use plastic packaging for produce. Students were sharing the ideas widely through media: a high school student even made a short documentary as part of the Keep New Zealand Beautiful Young Reporters Challenge, which won 1st prize in its category. The take home message of Micro-Investigators and one thing that makes it unique to conventional education, is that citizen science empowers the community and gives them the knowledge and resources to take environmental monitoring into their own hands.

– see Figure 1. They are of interest as refrigerants because they have zero ozone depletion potential and low global warming potential. They are considered the fourth generation of fluorinated materials used as refrigerants, blowing agents, propellants, and solvents. HFOs are designed explicitly as alternatives to hydrofluorocarbons (HFCs) and were developed to address the concerns associated with HFCs, which are potent greenhouse gases contributing to climate change. One of the critical advantages of HFOs is their significantly lower global warming potential (GWP) compared to HFCs. GWP is a measure of how much heat a greenhouse gas traps in the atmosphere relative to carbon dioxide (CO2) over a specific time period. HFOs have GWPs typically less than 1, whereas some HFCs have GWPs in the thousands, viz., HFC-23 GWP100 = 14,800 and methane’s GWP100 = 25. This means that HFOs have a much smaller impact on global warming when released into the atmosphere. It is important to note that while HFOs offer environmental benefits over HFCs in terms of climate impact, as mentioned earlier, there are ongoing discussions and studies regarding potential concerns related to their degradation products, such as trifluoroacetic acid (TFA) – see Figure 2.

Figure 1 HFO-1234yf (2,3,3,3-Tetrafluoropropene) with the formula CH2=CFCF3. Source: Wikipedia

Figure 2 Trifluoroacetic acid Source: Wikipedia

HFO-1234yf (Figure 1 & Figure 3) is a type of HFO that is used as a refrigerant in automobile air conditioners. It has a low global warming potential (GWP) of less than 1, but it also has some environmental concerns related to its breakdown products. One of these products is trifluoroacetic acid (TFA), which is a type of perfluoroalkyl substance (PFAS). PFAS are a group of synthetic chemicals that are persistent, bioaccumulative, and potentially toxic to humans and wildlife. TFA is a strong acid that can accumulate in water bodies and affect aquatic ecosystems. Another breakdown product of HFO-1234yf is HFC-23 or CHF3, which is a very potent greenhouse gas. HFC-23 can form from HFO-1234yf in the open atmosphere, adding to the secondary GWP of HFO-1234yf. The amount of HFC-23 that may form from HFO-1234yf is still uncertain and depends on various factors, such as atmospheric conditions and emissions. Therefore, the environmental impact of HFO-1234yf and its breakdown products is still being studied and evaluated by researchers and regulators.

Figure 3: Honeywell R1234YF AC Refrigerant for Mobile Systems Solstice HFO-1234YF Source: Walmart.com

One such study by Björnsdotter et. al detected the ultrashort-chain perfluoroalkyl acids (PFAAs), perfluoropropanoic acid (PFPrA), perfluorobutanoic acid (PFBA) as well as TFA in Lake Vättern that is one of Sweden’s largest lakes and is an important source for drinking water. Ultrashort-chain PFAAs are highly polar, which generally leads to a lower potential for bioaccumulation in organisms. Still, accumulation in plants has been observed, indicating some degree of uptake and retention. There is limited data available on human exposure to ultrashort-chain PFAAs, but TFA has been detected in human blood. The combination of high persistence and mobility in the environment makes ultrashort-chain PFAAs a potential threat to drinking water. Once contamination occurs, it can be challenging and costly to remove these substances from water sources, unlike their longer-chain counterparts, where conventional treatment systems are less effective.

Figure 4: from Björnsdotter et. al. https://pubs.acs.org/doi/10.1021/acs.est.1c04472

In February 2023, the European Chemical Agency (ECHA) published its proposals for bans of fluorinated substances under the REACH regulations. As proposed, fluorinated refrigerants, namely HFOs and HFCs, would be banned from manufacture and sale where suitable alternatives exist. ECHA’s scientific committees have begun their scientific evaluation of the proposal and if adopted, they will be sent to the European Commission, who, together with the EU Member States, will then decide on the potential restriction. The projected timeline is outlined below.

Figure 5: ECHA’s proposed timeline below the next steps

The analysis of these ultrashort PFAS is undertaken at Eurofins with a recent study of drinking water samples taken in Norway and Sweden showing levels of TFA ranging from 70 ng/L - 720 ng/L with trifluoromethanesulfonic acid (TFMS) being detected at seven sites where TFA concentrations were highest. The mobility and persistence of these ultrashort PFAS make them a candidate for inclusion in the EU drinking water directive (DWD) to be adopted in EU Member States whereby drinking water quality standards for a defined sum of 20 PFAS at 100 ng/L or for total PFAS at 500 ng/L.

Marc was a great friend and mentor to many at ALS and, as Technical Manager was a central figure in the growth and success of the ALS Environmental Division, not only in Australia but around the world. Anyone who met Marc will have been struck by his incredible intelligence, his technical leadership as well as his quirky personality and sense of humour.

Marc was a brilliant and passionate analytical chemist. From his very first day he looked for ways to advance processes, questioning why something was done in a particular way and whether there was a better alternative. For the next 28 years, he was responsible for the development and continuous improvement of ALS’ environmental analytical methodologies. He was instrumental in the advancement of environmental organic analytical chemistry and was a world leader in the field.

Marc was recruited to ALS in May 1995 to be the Senior Organic Chemist for the planned new laboratory in Sydney. Marc freely shared his knowledge of analytical chemistry, chromatography and the environmental business and in 1996 became the ALS Sydney Laboratory Manager, working tirelessly to improve our service to clients--even introducing his own home-made LIMS called BatchTrack to track work through the facility.

In January 1999, he was appointed to the role of Technical Manager, leading the technical development of the ALS Environmental Division as it grew into a global business with a massive expansion in technical scope and capabilities. He was involved in the development of ALS’ first true Enviro LIMS, travelling to Asia and Canada to ensure its successful deployment. In 2008, Marc developed the first commercially available analysis of PFAS compounds in Australia (and possibly the world). PFAS chemistry quickly became a passion and he became one of the world’s preeminent practitioners of PFAS analysis.

In 2017, Marc was promoted to Technical Manager–APAC and prior to COVID, relished the opportunity to travel and offer technical assistance to our laboratories in Asia.

As Marc battled cancer over the last few years, through the pandemic he predominately worked from home, but remained active in his role, continually providing advice and technical assistance. He even took his laptop with him to hospital when receiving treatment to stay connected with his team, keep his mind active and continue to ponder solutions to ever more technical conundrums.

Marc was a brilliant man, a great friend and mentor to many and will forever be part of the ALS family. He leaves behind his wife Margie, children Johnathan, Stephanie and Emily and a granddaughter, Juno.

Marc Centner
Chemist
1954–2023

Michael Heery,
General Manager Environmental, ALS

It is with great sadness that the Board informs you of the passing of Dr Sarah Richards, the President of the Australasian Land and Groundwater Association (ALGA).

Sarah has been part of the contaminated land and research industry for over 25 years and joined our association in 2015. Sarah is widely known for her active contribution as a volunteer, speaker and member. In 2019, Sarah was elected to the Board and within one year was selected to lead the organisation as President in 2020. Sarah led the association through the pandemic, supporting the team at ALGA to pivot to online/hybrid events, allowing our members to maintain access to training, information and networking throughout that period. This ensured the ongoing success of the organisation. Sarah was an inspiration to us all in what was clearly one of the most challenging times and her passing is a loss to the ALGA community.
 

Sarah has supported many clients and colleagues through her work as a Senior Principal Geoenvironmental Engineer at Tetra Tech Coffey for 20 years and will be greatly missed.
 

The Board extends their condolences to her family, colleagues and friends. Sarah is survived by her daughter Jacqueline, sons David and Will and her husband Newell.
 

We understand this message may be difficult to process. Please reach out for assistance if needed to help you deal with this loss in the coming days and weeks.
 

Australasian Land and Groundwater Association (ALGA). 
 

Notice distributed to Members and Corporate Partners by email on 26 May 2023.