Production of perfluoroalkyl acids (PFAAs) from precursors in contaminated agricultural soils: Batch and leaching experiments

Assessment of PFAS contamination in agricultural soils: Non-target identification of precursors, fluorine mass balance and microcosm studies

Biodegradation of PFAS is examined in eight PFAS precursor-contaminated topsoil samples in order to determine generation rate constants for perfluorocarboxyl acids (PFCA) and to elucidate soil properties affecting these. PFAS were analyzed via both target (HPLC-MS/MS) and non-target (HPLC-QTOF) (semi)quantification. FTMAPs, diPAPs, and diSAmPAP were identified and accounted for > 80 % of the total PFAS burden, which ranged from ∼ 280-9700 ng g-1. These levels were confirmed by chemical oxidation of precursors (TOP assay) which allowed to close the fluorine mass balance against extractable organic fluorine (EOF). Notably, in some organic carbon rich samples, repeated oxidation was needed to achieve a complete fluorine mass balance. Batch microcosm incubations and total precursor quantification allowed to determine production rate constants of short-chain PFCA, which ranged from 0.02 to 0.50 year-1 depending on PFAS and soil physicochemical properties. Principal component analysis (PCA) indicated that both acid phosphomonoesterase and, to some extent, microbial biomass influences the production rates of short-chain PFAS in soils. This allowed to assess contamination time scales, indicating that production and thus release of PFAS from precursor decay will continue for years to decades. This bears the risk of contamination of adjacent environmental compartments such as groundwater and surface water bodies.

The quest for the perfect "total PFAS" method: how can the total oxidisable precursor (TOP) assay be made reliable?

Per- and polyfluoroalkyl substances (PFAS) make up a large and complex class of manmade chemicals. They have been widely used in numerous industrial branches and are incorporated into many consumer products. Today, there is a consensus on the fact that PFAS are present in all environmental compartments and that populations all over the world are subjected to them via internal exposure. It has been estimated that thousands of individual PFAS have been manufactured and marketed since the 1950s, to which impurities present in commercial products and intermediate environmental transformation products should be added. Since it is unrealistic to be able to individually identify, detect and quantify all the PFAS present in a sample, several analytical approaches have been developed to assess the presence of "hidden/unseen" PFAS. One of these, known as the total oxidisable precursor (TOP) assay, was first described in 2012. Basically, it converts some PFAS, hereafter referred to as precursors, into stable terminal products readily measurable by routine target methods. This review is based on more than 100 studies in which the original TOP assay was simply applied or optimised. The review found that the TOP assay was selective, sensitive, applicable to many matrices, useful within a forensic context, inexpensive, and easy to implement and has been assessed in the literature on a wide range of precursors. However, this method comprises many subtleties and has some flaws that operators should be made aware of so that they may be addressed as far as possible. Finally, this review tries to lay the foundations for better practices and quality assurance/quality control measures, in order to improve accuracy and reliability of TOP assay results.

Electrostatic and Chemical Interplay between Air-Water and Mineral-Water Interfaces during PFOS Transport in Unsaturated Porous Media

Perfluorooctanesulfonate (PFOS) migration from vadose zone sources to groundwater is determined by multiple interfacial retention processes and their dependency on hydrochemistry. This study investigates the impact of air-water and mineral-water interfacial retention on PFOS transport under different hydrochemical conditions to assess their adsorption magnitudes and feedback dynamics as a function of ionic strength. Flow-through experiments were conducted in unsaturated quartz and goethite-coated quartz sands equilibrated with different background electrolyte concentrations to distinguish between air-water and goethite-water interfacial adsorption contributions to PFOS retardation. Measurements of PFOS breakthrough curves at column outlets allowed tracking the differences in spatio-temporal evolution of the PFOS plumes between the two porous media. Process-based reactive transport simulations, incorporating a thermodynamic framework of mass-action reactions accounting for multiple interfacial retention processes, allowed the quantitative interpretation of physical and geochemical processes. Experimental and modeling results reveal that multiprocess retention causes nonideal PFOS transport, with plume retardation and spatio-temporal mass transfer between the different phases determined by the relative contribution of the individual retention processes and their electrostatic interplay driven by solution counterions. These findings illuminate the interplay between air-water and mineral-water sorption and emphasize the need for reactive transport simulators implementing interdependent interfacial retention processes, influenced by water chemistry conditions.

Implementation of Matrix-Matched Semiquantification of PFAS in AFFF-Contaminated Soil

This study presents a novel semiquantification approach for nontarget screening (NTS), combining matrix-matched calibration and ionization class-specific average calibration curves (ACCs) to address the lack of analytical reference standards for most per- and polyfluoroalkyl substances (PFAS). Ionization class-specific ACCs for carboxylic and sulfonic acids, sulfonamides, and cationic PFAS result in high accuracy, with median absolute accuracy quotients below 2.27×. The approach was applied to soil impacted by aqueous film-forming foam (AFFF) contamination. A total of 96 tentatively identified PFAS were semiquantified in addition to 28 quantified compounds based on available standards. Semiquantified concentrations exceeded those of target analytes, demonstrating the critical role of this method in capturing broader PFAS contamination. In this case, validation against extractable organofluorine (EOF) showed a 102% closed mass balance. The innovative approach not only enables comprehensive PFAS contamination assessment in complex matrices but also expands the scope of the NTS for environmental monitoring, remediation, and risk assessment of AFFF-contaminated sites.

Contamination of per- and poly-fluoroalkyl substances in agricultural soils: A review

Numerous reviews have focused on the chemistry, fate and transport, and remediation of per- and poly-fluoroalkyl substances (PFAS) across various environmental media. However, there remains a significant gap in the literature regarding a comprehensive review specifically addressing PFAS contamination within agricultural soils. Recognizing the threat PFAS pose to ecosystems and human health, this review critically examines the sources of PFAS in agricultural environments, their uptake and translocation within plant systems, and recent advancements in soil remediation techniques. PFAS ingress into agricultural soils primarily occurs through the application of biowastes, wastewater, and pesticides, necessitating a thorough examination of their pathways and impacts. Factors such as carbon chain length, salinity, temperature, and pH levels affect PFAS uptake and distribution within plants, ultimately influencing their transfer through the food web. Moreover, this review explores a range of physical, chemical, and biological strategies currently employed for the remediation of PFAS-contaminated agricultural soils.

Quantification of PFAS in soils treated with biosolids in ten northeastern US farms

This study, one of the few conducted to date on working farms in the US, examined per- and polyfluoroalkyl substances (PFAS) contamination in 10 farms treated with biosolids using a paired control-treatment approach. Biosolids are nutrient-rich and inexpensive soil amendments, however, if the biosolids contain PFAS which are known to be toxic, mobile and to bioaccumulate, they can leave lasting negative impacts on farming soil and water. Our study showed significantly higher concentrations of PFAS in biosolids-treated (treatment) soils compared to (untreated) controls. Soil depth, soil physicochemical properties (e.g., organic matter and pH), and biosolids sources affected concentrations and types of PFAS in treated soils. While PFAS precursors were present in biosolids, they were absent in treated soils, likely due to biotransformation to terminal perfluoroalkyl products. The detection of shorter-chain PFAS in surface water highlights their greater mobility, raising concerns beyond the boundaries of the biosolids-treated farms.

Examining disparities in PFAS plasma concentrations: Impact of drinking water contamination, food access, proximity to industrial facilities and superfund sites

BACKGROUND

Most of the US population is exposed to per- and polyfluorinated substances (PFAS) through various environmental media and these sources of PFAS exposure coupled with disproportionate co-localization of PFAS-polluting facilities in under-resourced communities may exacerbate disparities in PFAS-associated health risks.

METHOD

We leveraged two cohorts in Southern California with 8 PFAS concentrations measured in plasma. We obtained PFAS water testing data from the Third Unregulated Contaminant Monitoring Rule and state monitoring data, census tract-level information on food access using the Food Access Research Atlas, the location of Superfund sites on the National Priorities List, and data on facilities known to release PFAS pollutants. These data were then spatially linked to the participants' home addresses.

RESULTS

In the first cohort, we found that detections of PFOS, PFOA, and PFHxS in drinking water were associated with 1.54 ng/mL (95% CI: 0.77, 2.32), 0.47 ng/mL (0.25, 0.68), and 1.16 ng/mL (0.62, 1.71) increase in plasma PFOS, PFOA, and PFHxS. The presence of Superfund sites was associated with higher plasma concentrations of PFOS, PFHxS, PFPeS, and PFHpS (betas [95% CIs]: 0.96 [0.21, 1.71], 0.9 [0.22, 1.58], 0.04 [0.02, 0.06] and 0.05 [0.02, 0.09], respectively). Each additional PFAS-polluting facility present in the neighborhood was associated with a 0.9 ng/mL (0.03, 0.15) increase in the concentration of PFOS. In the other cohort, we found that the presence of Superfund sites was associated with higher plasma PFDA, PFHpS, PFOS (betas [95% CIs]: 0.03 [0.01, 0.06], 0.05 [0.01, 0.09], and 1.96 [0.31, 3.62]). Neighborhood low access to food was associated with a 2.51 ng/mL (0.7, 4.31) increase in plasma PFOS, 0.6 ng/mL (0.16, 1.06) increase in plasma PFOA and 0.06 (0.02, 0.1) increase in plasma PFHpS.

CONCLUSION

Reducing sources of PFAS exposure in under-resourced neighborhoods may help reduce disparities in human exposure levels.

Insight into the relationship between similarity and the degree of equilibrium of contaminant release curves through numerical simulations

The assumption of local equilibrium, especially in test standards for assessing the leaching of hazardous substances from materials, is crucial for the use of test results and the robustness of testing. However, previous studies of contact time conditions in percolation test standard have evaluated equilibrium and robustness separately. Therefore, this study tests the assumption of local equilibrium in the up-flow percolation test, standardized as ISO 21268-3 in 2019, and discusses the relationship between the similarity of test results and degree of equilibrium. Thus, we conducted approximately 6000 numerical simulations in total with varying leaching parameters to determine breakthrough curves (BTCs) for the substances investigated by the test standard. The results showed that the two BTCs for the longest and shortest contact time conditions within the standard test were identical over a wide range of parameters, supporting the robustness of the standard test. Interestingly, identical BTCs occur in equilibrium or near-equilibrium and nonequilibrium leaching. This finding indicates the need to reconsider the conventional interpretation that equilibrium is reached when test results with different contact time conditions appear identical and encourages efforts to develop procedures to verify equilibrium leaching.

Non-target screening reveals 124 PFAS at an AFFF-impacted field site in Germany specified by novel systematic terminology

The uncontrolled release of aqueous film-forming foam (AFFF) ingredients during a major fire incident in Reilingen, Germany, in 2008 led to significant soil and groundwater contamination. As the identity of fluorochemical surfactants in AFFF are often veiled due to company secrets, it is important to characterize AFFF contaminations and their impact on the environment comprehensively. In this study, we adapted a systematic approach combining a suitable extraction method with liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) for an extensive non-targeted analysis. Our analysis identified 124 per- and polyfluoroalkyl substances (PFAS) from 42 subclasses in the contaminated soil (confidence levels of identification between 1 and 3). Typical for AFFF-impacted field sites, these included anionic, cationic, and zwitterionic substances with perfluoroalkyl chains spanning from 3 to 14 carbon atoms. Furthermore, we identified 1 previously unreported substance, and detected 9 PFAS subclasses for the first time in soil. AFFFs have long been employed to extinguish large hydrocarbon fires, yet their environmental consequences remain a concern. This study sheds light on the complex composition of AFFFs at this particularly contaminated area, emphasizing the necessity for extensive contaminant characterization as sound basis for informed management strategies to mitigate their adverse effects. AFFF PFAS are often named differently in the literature, leading to inconsistency in terminology. To address this issue, we introduced partially new terminology for AFFF-related PFAS to establish consistent terminology, to facilitate communication of identified compounds, and to ensure that the chemical structure can be directly derived from acronyms.

PFAS Porewater concentrations in unsaturated soil: Field and laboratory comparisons inform on PFAS accumulation at air-water interfaces

Poly- and perfluoroalkyl substance (PFAS) leaching from unsaturated soils impacted with aqueous film-forming foams (AFFFs) is an environmental challenge that remains difficult to measure and predict. Complicating measurements and predictions of this process is a lack of understanding between the PFAS concentrations measured in a collected environmental unsaturated soil sample, and the PFAS concentrations measured in the corresponding porewater using field-deployed lysimeters. The applicability of bench-scale batch testing to assess this relationship also remains uncertain. In this study, field-deployed porous cup suction lysimeters were used to measure PFAS porewater concentrations in unsaturated soils at 5 AFFF-impacted sites. Field-measured PFAS porewater concentrations were compared to those measured in porewater extracted in the laboratory from collected unsaturated soil cores, and from PFAS concentrations measured in the laboratory using batch soil slurries. Results showed that, despite several years since the last AFFF release at most of the test sites, precursors were abundant in 3 out of the 5 sites. Comparison of field lysimeter results to laboratory testing suggested that the local equilibrium assumption was valid for at least 3 of the sites and conditions of this study. Surprisingly, PFAS accumulation at the air-water interface was orders of magnitude less than expected at two of the test sites, suggesting potential gaps in the understanding of PFAS accumulation at the air-water interface at AFFF-impacted sites. Finally, results herein suggest that bench-scale testing on unsaturated soils can in some cases be used to inform on PFAS in situ porewater concentrations.

Per- and Polyfluoroalkyl Substances in Food Packaging: Migration, Toxicity, and Management Strategies

PFASs are linked to serious health and environmental concerns. Among their widespread applications, PFASs are known to be used in food packaging and directly contribute to human exposure. However, information about PFASs in food packaging is scattered. Therefore, we systematically map the evidence on PFASs detected in migrates and extracts of food contact materials and provide an overview of available hazard and biomonitoring data. Based on the FCCmigex database, 68 PFASs have been identified in various food contact materials, including paper, plastic, and coated metal, by targeted and untargeted analyses. 87% of these PFASs belong to the perfluorocarboxylic acids and fluorotelomer-based compounds. Trends in chain length demonstrate that long-chain perfluoroalkyl acids continue to be found, despite years of global efforts to reduce the use of these substances. We utilized ToxPi to illustrate that hazard data are available for only 57% of the PFASs that have been detected in food packaging. For those PFASs for which toxicity testing has been performed, many adverse outcomes have been reported. The data and knowledge gaps presented here support international proposals to restrict PFASs as a group, including their use in food contact materials, to protect human and environmental health.

Impact of Variable Water Chemistry on PFOS-Goethite Interactions: Experimental Evidence and Surface Complexation Modeling

Perfluorooctanesulfonate (PFOS) has become a major concern due to its widespread occurrence in the environment and severe toxic effects. In this study, we investigate PFOS sorption on goethite surfaces under different water chemistry conditions to understand the impact of variable groundwater chemistry. Our investigation is based on multiple lines of evidence, including (i) a series of sorption experiments with varying pH, ionic strength, and PFOS initial concentration, (ii) IR spectroscopy analysis, and (iii) surface complexation modeling. PFOS was found to bind to goethite through a strong hydrogen-bonded (HB) complex and a weaker outer-sphere complex involving Na+ coadsorption (OS-Na+). The pH and ionic strength of the solution had a nontrivial impact on the speciation and coexistence of these surface complexes. Acidic conditions and low ionic strength promoted hydrogen bonding between the sulfonate headgroup and protonated hydroxo surface sites. Higher electrolyte concentrations and pH values hindered the formation of strong hydrogen bonds upon the formation of a ternary PFOS-Na+-goethite outer-sphere complex. The findings of this study illuminate the key control of variable solution chemistry on PFOS adsorption to mineral surfaces and the importance to develop surface complexation models integrating mechanistic insights for the accurate prediction of PFOS mobility and environmental fate.

PFΔScreen - an open-source tool for automated PFAS feature prioritization in non-target HRMS data

Per- and polyfluoroalkyl substances (PFAS) are a huge group of anthropogenic chemicals with unique properties that are used in countless products and applications. Due to the high stability of their C-F bonds, PFAS or their transformation products (TPs) are persistent in the environment, leading to ubiquitous detection in various samples worldwide. Since PFAS are industrial chemicals, the availability of authentic PFAS reference standards is limited, making non-target screening (NTS) approaches based on high-resolution mass spectrometry (HRMS) necessary for a more comprehensive characterization. NTS usually is a time-consuming process, since only a small fraction of the detected chemicals can be identified. Therefore, efficient prioritization of relevant HRMS signals is one of the most crucial steps. We developed PFΔScreen, a Python-based open-source tool with a simple graphical user interface (GUI) to perform efficient feature prioritization using several PFAS-specific techniques such as the highly promising MD/C-m/C approach, Kendrick mass defect analysis, diagnostic fragments (MS2), fragment mass differences (MS2), and suspect screening. Feature detection from vendor-independent MS raw data (mzML, data-dependent acquisition) is performed via pyOpenMS (or custom feature lists) with subsequent calculations for prioritization and identification of PFAS in both HPLC- and GC-HRMS data. The PFΔScreen workflow is presented on four PFAS-contaminated agricultural soil samples from south-western Germany. Over 15 classes of PFAS (more than 80 single compounds with several isomers) could be identified, including four novel classes, potentially TPs of the precursors fluorotelomer mercapto alkyl phosphates (FTMAPs). PFΔScreen can be used within the Python environment and is easily automatically installable and executable on Windows. Its source code is freely available on GitHub ( https://github.com/JonZwe/PFAScreen ).