PFAS environmental trends require us to look wider rather than closer.

Over the past decade, there has been a worldwide effort to understand the impact of man-made Per- and Polyfluoroalkyl Substances (PFAS) emissions on the environment and human health. Despite the phase out some types of PFAS, the emergence of short chain and novel PFAS species as replacements has become of increasing concern, yet the environmental fate and transport of many of these species remains unclear.

PFAS typically occur in the environment as mixtures of individual PFAS chemicals with their fate and transport based on each compounds chemical structure and its determination of solubility in water, sorption capacity for soils and sediments and resistance to biological and chemical degradation. Little data exists concerning precursor, short chain, and ultra short chain PFAS species fate, transport and toxicity either individually or via additive, synergistic, or antagonistic modes (Ateia et al., 2019).

Global regulation and monitoring efforts have primarily focused on PFOS, PFOA, and related compounds. Recently, attention has shifted towards PFHxS, PFNA, PFBA, and PFBS. This shift is reflected in the PFAS National Environmental Management Plan of the Heads of the EPA for Australia and New Zealand, which includes provisions for situations where PFOS, PFOA, and PFHxS are not the primary PFAS risk drivers. Similarly, the National Primary Drinking Water Regulation proposed by USEPA is a positive step towards managing six PFAS species, including PFOS and PFOA, with a significantly lower limit for PFOS (4.0 ppt). However, the current PFAS state of knowledge appears to be driving in a different direction, suggesting a greater need to align a global approach with toxicity assessment, monitoring, and regulation for a wider range of PFAS species detected in the environment.

Temporal PFAS trends in the environment are difficult to define based on low PFAS concentration, numerous environmental variables, and limited and inconsistent datasets for novel PFAS species. However, wastewater treatment plants (WWTPs) provide important conduits between consumer and industrial PFAS sources and the environment and are useful to better understand trends in PFAS mass flows to the environment. A review study by Houtz et al. (2016) found that total PFAS concentrations in wastewater in the United States have not changed significantly over time, whereas they have increased in China from 11 - 37% per year. Cookson et al. (2022) found that short-chained PFAS increased in wastewater effluent globally from 2004 to 2020.

Although, regional WWTPs in Australia have recorded an 18% decrease in background PFOS concentrations from 2010 to 2020 (Gallen et al., 2022), studies such as Szabo et al. (2023) have shown an increasing dominance of the perfluoroalkyl carboxylic acids (PFCAs) and disubstituted phosphate esters (diPAPs) groups, and noted compounds of shorter chain length are more frequently detected at higher concentrations. This is likely due to the degradation of precursors such as diPAPs to perfluoroalkyl carboxylates (PFCAs) (Lee and Madbury, 2010) or the degradation of common fluorotelomer surfactants, like 6:2 fluorotelomer sulfonamide alkylamine (FTAA) and 6:2 fluorotelomer sulfonamide alkylbetaine (FTAB) to 6:2 FTOH and short-chain PFCAs (D'Agostino and Madbury 2017). Similarly, landfill leachates provide useful information regarding PFAS species reflective of industrial and consumer usage of PFAS, with leachate frequently also discharged to WWTPs. Chen et al. (2023) found that PFCAs and PFAA-precursors formed the dominant subgroups in all leachates tested. Organic waste streams such as biosolids and commercial food waste have been demonstrated to contain PFCAs and polyfluoroalkyl phosphates (PAPs), which make their way into recycled organic products such as composts and soil amendments. Sivaram et al. (2022) found PFAS in all Australian recycled organics products (n=17) ranged from 1.26 – 11.84 µg/kg Ʃ38 PFAS and noted that short chain ƩPFCAs increased after total oxidisable precursor assay (TOPA) by a factor of approximately 2. This suggests significant PFAS precursor mass loads may have direct access to agricultural land when applied as soil amendments.

PFAS have been frequently detected in food and water, however little long term temporal data is available for novel PFAS species in tap water and food. Kaboré et al. (2018) employed a suspect-target screening approach that identified that perfluoroethyl cyclohexane sulfonate (PFECHS) and ultrashort chain (C2–C3) PFSAs, were repeatedly present in tap water samples (concentration ranges: < LOD to 4.0 ng/L). Similarly, the investigation of novel PFAS species in crops has shown shorter-chain PFCAs, especially perfluorobutanoic acid (PFBA), represented the majority of PFAS uptake in multiple crops (Liu et al., 2019). While PFOS and PFHxS have been shown to accumulate in cattle (beef and dairy), chicken and eggs, little research has been conducted to further study the prevalence and accumulation of novel PFAS in animal products (Death et al., 2021). Human exposure to PFAS extends to food packaging. APCO (2021) studied 74 fibre-based food packaging materials and found roughly a quarter of the studied materials had fluorine concentrations over 800 ppm and over 10% of samples had post TOPA total PFAS concentrations over 8000 ppb, (maximum = 31, 730 ppb) suggesting the presence of a significant precursor mass load.

Since the early 2000’s PFOS and PFOA have been decreasing in human serum in Australia (Yueng et al 2013). However, there is concern as only a few of the >4000 registered PFAS are commonly monitored, suggesting that exposure to these chemicals and associated risk may be underestimated. The toxicity of longer chain PFAS is assumed to be greater than shorter chain species because of slower excretion of long chain species results in a higher internal dose from the same administered dose. However, there is significantly less toxicological or epidemiological data available for short chain and novel PFAS species. This is important as it has been shown that there are exceptions that contradict this assumption in both toxicity and elimination half-life, and that animal analogues do not necessarily reflect the toxic mode or bioaccumulation potential of many PFAS in humans (DME, 2015). In considering all the above, it is highly likely that the risks posed by short chain PFAS, precursors, and other novel PFAS species is understated due to the significant knowledge gaps in their prevalence in the environment, fate, and transport. Further, the fact that the majority of PFAS found in commercial and consumer use, have very limited or no toxicity data, highlights that there is a critical need to prioritise, characterise, and develop solutions for the management of potential risks posed to human health and the environment by a wider range of PFAS species.

 6:2 fluorotelomer sulfonate (6:2FTS), a common second generation PFAS in firefighting foams.

Disubstituted polyfluoroalkyl phosphate (DiPAP), a Polyfluoroalkyl Phosphate increasingly found in the environment and a precursor for a number of short chain PFCAs.

Perfluorobutanoic acid (PFBA) and Perfluorohexanoic acid (PFHxA) - Two common terminal degradant short chain PFCA species.

Perfluoroethylcyclohexane sulfonate (PFECHS) is an 8-carbon cyclic PFAS and a replacement for PFOS in various formulations.

Dr Matthew Askeland
Emerging Contaminants Unit Manager, ADE Consulting Group

Matthew Askeland presently heads ADE's Consulting Groups Emerging Contaminants, Treatment Remediation and Research (ECTRR) business unit. Matthew has been focused on tackling multiple elements within the PFAS risk management practice. These include site characterisation, risk mitigation, development and implementation of new PFAS management tools (treatment technologies and analytical tools), and the deployment of effective management strategies for both legacy and ongoing PFAS impacts. Matthew has a very keen interest in the management of emerging contaminants within the circular economy.

References:

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Article Published on 21/04/2023

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