Sorption Of Perfluorooctanoic Acid Research Articles

Towards elevated perfluorooctanoic acid (PFOA) enrichment in water: Sequential liquid-liquid extraction pretreatment for ion chromatography detection

The widespread detection of perfluorooctanoic acid (PFOA) in the environment has raised significant concerns. The standard PFOA analytical method relies on expensive solid-phase extraction (SPE) and liquid chromatography tandem mass spectrometry (LC-MS/MS) instruments, making routine use prohibitive. We herein proposed a cost-effective yet novel enrichment method for determining PFOA at ng L−1 level. This method entailed a two-step sample preparation process: firstly, PFOA was extracted and enriched using a forward-extraction under acidic conditions, followed by a backward-extraction and enrichment step utilizing alkaline water. The enriched samples were subsequently subjected to a common ion chromatography (IC). Results reveal that maintaining a forward-extraction pH below its pKa value (2.8) is essential, as protonated PFOA proves effective in enhancing the enrichment factor (EF). The challenge lied in driving PFOA from forward-extractant to aqueous backward-extractant due to the decreased hydrophobicity of deprotonated PFOA (log Kow2 = 1.0). In addition, we found that evaporating forward-extractant with alkaline backward-extractant (containing 5% methanol) reduced potential analytical uncertainties associated with PFOA evaporation and sorption. Under optimal conditions, the method achieved a detection limit of 9.2 ng L−1 and an impressive EF value of 719. Comparison with SPE-LC-MS/MS confirmed the proposed method as a promising alternative for PFOA determination. Although initially targeted for PFOA, the novel methodology is likely applicable to preconcentration of other poly-fluoroalkyl substances.

Transport parameters for PFOA and PFOS migration through GCL's and composite liners used in landfills

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, Kd ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

Superb green cycling strategies for microbe-Fe0 neural network-type interaction: Harnessing eight key genes encoding enzymes and mineral transformations to efficiently treat PFOA

To address time-consuming and efficiency-limited challenges in conventional zero-valent iron (ZVI, Fe0) reduction or biotransformation for perfluorooctanoic acid (PFOA) treatment, two calcium alginate-embedded amendments (biochar-immobilized PFOA-degrading bacteria (CB) and ZVI (CZ)) were developed to construct microbe-Fe0 high-rate interaction systems. Interaction mechanisms and key metabolic pathways were systematically explored using metagenomics and a multi-process coupling model for PFOA under microbe-Fe0 interaction. Compared to Fe0 (0.0076 day−1) or microbe (0.0172 day−1) systems, the PFOA removal rate (0.0426 day−1) increased by 1.5 to 4.6 folds in the batch microbe-Fe0 interaction system. Moreover, Pseudomonas accelerated the transformation of Fe0 into Fe3+, which profoundly impacted PFOA transport and fate. Model results demonstrated microbe-Fe0 interaction improved retardation effect for PFOA in columns, with decreased dispersivity a (0.48 to 0.20 cm), increased reaction rate λ (0.15 to 0.22 h−1), distribution coefficient Kd (0.22 to 0.46 cm3∙g−1), and fraction f´(52 % to 60 %) of first-order kinetic sorption of PFOA in microbe-Fe0 interaction column system. Moreover, intermediates analysis showed that microbe-Fe0 interaction diversified PFOA reaction pathways. Three key metabolic pathways (ko00362, ko00626, ko00361), eight functional genes, and corresponding enzymes for PFOA degradation were identified. These findings provide insights into microbe-Fe0 “neural network-type” interaction by unveiling biotransformation and mineral transformation mechanisms for efficient PFOA treatment.

Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon.

Sorption to activated carbon is a common approach to reducing environmental risks of waterborne perfluorooctanoic acid (PFOA), while effective and flexible approaches to PFOA sorption are needed. Variations in temperature or the use of electrokinetic phenomena (electroosmosis and electromigration) in the presence of external DC electric fields have been shown to alter the contaminant sorption of contaminants. Their role in PFOA sorption, however, remains unclear. Here, we investigated the joint effects of DC electric fields and the temperature on the sorption of PFOA on activated carbon. Temperature-dependent batch and column sorption experiments were performed in the presence and absence of DC fields, and the results were evaluated by using different kinetic sorption models. We found an emerging interplay of DC and temperature on PFOA sorption, which was linked via the liquid viscosity (η) of the electrolyte. For instance, the combined presence of a DC field and low temperature increased the PFOA loading up to 38% in 48 h relative to DC-free controls. We further developed a model that allowed us to predict temperature- and DC field strength-dependent electrokinetic benefits on the drivers of PFOA sorption kinetics (i.e., intraparticle diffusivity and the film mass transfer coefficient). Our insights may give rise to future DC- and temperature-driven applications for PFOA sorption, for instance, in response to fluctuating PFOA concentrations in contaminated water streams.

Biochar and surfactant synergistically enhanced PFAS destruction in UV/sulfite system at neutral pH

The UV/sulfite-based advanced reduction process (ARP) emerges as an effective strategy to combat per- and polyfluoroalkyl substances (PFAS) pollution in water. Yet, the UV/sulfite-ARP typically operates at highly alkaline conditions (e.g., pH > 9 or even higher) since the generated reductive radicals for PFAS degradation can be quickly sequestered by protons (H+). To overcome the associated challenges, we prototyped a biochar-surfactant-system (BSS) to synergistically enhance PFAS sorption and degradation by UV/sulfite-ARP. The degradation and defluorination efficiencies of perfluorooctanoic acid (PFOA) depended on solution pH, and concentrations of surfactant (cetyltrimethylammonium bromide; CTAB), sulfite, and biochar. At high pH (8–10), adding biochar and BSS showed no or even small inhibitory effect on PFOA degradation, since the degradation efficiencies were already high enough that cannot be differentiated. However, at acidic and neutral pH (6–7), an evident enhancement of PFOA degradation and defluorination efficiencies occurred. This is due to the synergies between biochar and CTAB that create favorable microenvironments for enhanced PFOA sorption and deeper destruction by prolonging the longevity of reductive radicals (e.g., SO3•−), which is less affected by ambient pH conditions. The performance of UV/sulfite/BSS was further optimized and used for the degradation of four PFAS. At the optimal experimental condition, the UV/sulfite/BSS system can completely degrade PFOA with >30% defluorination efficiency for up to five continuous cycles (n = 5). Overall, our BSS provides a cost-effective and sustainable technique to effectively degrade PFAS in water under environmentally relevant pH conditions. The BSS-enabled ARP technique can be easily tied into PFAS treatment train technology (e.g., advanced oxidation process) for more efficient and deeper defluorination of various PFAS in water.

Development of Poly(acrylamide)-Based Hydrogel Composites with Powdered Activated Carbon for Controlled Sorption of PFOA and PFOS in Aqueous Systems.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic compounds developed for various applications; some are connected to adverse health impacts including immunosuppression and higher susceptibility to some cancers. Current PFAS remediation treatments from aqueous sources include granular activated carbon (GAC) adsorption, membrane separation, and anion-exchange resin (AER) removal. Each has specific disadvantages, hence the need for a new and efficient technology. Herein, acrylamide-based hydrogel composites were synthesized with powdered activated carbon (PAC) and characterized to determine their affinity for PFAS. Physicochemical characterization included Fourier-Transform infrared spectroscopy (FTIR) to identify chemical composition, thermogravimetric analysis (TGA) to confirm PAC loading percentage, and aqueous swelling studies to measure the effect of crosslinking density. FTIR showed successful conversion of carbonyl and amine groups, and TGA analysis confirmed the presence of PAC within the network. Surface characterization also confirmed carbon-rich areas within composite networks, and the swelling ratio decreased with increasing crosslinking density. Finally, sorption of PFAS was detected via liquid chromatography with tandem mass spectrometry (LC-MS/MS), with removal efficiencies of up to 98% for perfluorooctanoic sulfonic acid (PFOS) and 96% for perfluorooctanoic acid (PFOA). The developed hydrogel composites exhibited great potential as advanced materials with tunable levers that can increase affinity towards specific compounds in water.

Mechanisms of heating-electrokinetic co-driven perfluorooctanoic acid (PFOA) adsorption on zeolite

Slow release of emerging contaminants limits their accessibility from soil to pore water, constraining the treatment efficiency of physio-chemical treatment sites. DC fields mobilize organic contaminants and influence their interactions with geo-matrices such as zeolites. Poor knowledge, however, exists on the joint application of heating and electrokinetic approaches on perfluorooctanoic acid (PFOA) transport in porous media. Here, we investigated electrokinetic PFOA transport in zeolite-filled percolation columns at varying temperatures. Variations of pseudo-second-order kinetic constants (kPSO) were correlated to the liquid viscosity variations (η) and elctroosmotic flow velocities (vEOF). Applying DC fields and elevated temperature significantly (>37%) decreased PFOA sorption to zeolite. A good correlation between η, vEOF, and kPSO was found and used to develop an approach interlinking the three parameters to predict the joint effects of DC fields and temperature on PFOA sorption kinetics. These findings may give rise to future applications for better tailoring PFOA transport in environmental biotechnology.

Retention and transport of PFOA and its fluorinated substitute, GenX, through water-saturated soil columns

Perfluoro-2-propoxypropanoic acid (GenX) has emerged as a substitute for perfluorooctanoic acid (PFOA) especially since PFOA was listed among the persistent organic pollutants (POPs) by the Stockholm Convention in 2019. However, limited knowledge exists regarding the behavior and mobility of GenX in natural soils hindering the prediction of its environmental fate. This study investigated the mobility and retention of GenX and PFOA in soils under batch and water-saturated flow-through conditions. Batch experiments revealed that GenX has a lower binding affinity to soil than longer-chained PFOA, potentially threatening groundwater resources. Unlike metal-oxides/minerals (ferrihydrite, gibbsite and manganese dioxide), biochar (BC) and activated carbon (AC) amendments significantly enhanced the sorption of both GenX and PFOA in soil. Sorption data on minerals and carbonaceous materials implied that for shorter-chained GenX, the predominant mode of sorption was through electrostatic (ionic) interactions, while for longer-chained PFOA, hydrophobic interactions became progressively more important with increasing chain length. The dynamic flow experiments demonstrated that these soil amendments enhanced the retention of both compounds, thereby decreasing their mobility. Simultaneous injection of both compounds into columns pre-loaded with either PFOA or GenX increased their retardation. GenX sorption was more affected by pre-sorbed PFOA compared to the minimal impact of pre-loaded GenX on PFOA sorption. A newly developed reactive transport model, which incorporates a two-site sorption model and accounts for kinetic-limited processes, accurately predicted the sorption and transport of both compounds in single and binary contamination systems. These findings have important implications for predicting and assessing the fate and mobility of per- and polyfluoroalkyl substances (PFAS) in soils and groundwaters.

Sorption and partitioning of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) onto sediments of Diep and Plankenburg river systems Western Cape, South Africa

Partitioning behaviour of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in sediments obtained from river systems were investigated in this study. The partitioning coefficient (log K OC ) and distribution coefficient (log K D ) of PFOA and PFOS between sediments and the aqueous solution were estimated from the sorption data. Levels of PFOA and PFOS in the sediment samples ranged between 30.01–191.96 ng/g dw and 0.50–248.14 ng/g dw, respectively. The kinetic study showed that the time required for equilibrium was <400 min for the compounds. Sediment samples SS-C provided the highest sorption capacities (0.11 and 0.13 mg/g) for both PFOA and PFOS. Sorption studies revealed that the removal kinetics fitted well into the Elovich rate equation (R 2 = 0 . 98 and 0.92) followed by the pseudo-second-order kinetic model (R 2 = 0 . 91 and 0.89) for PFOA and PFOS, respectively. Mean values for the partitioning coefficient (log K OC ) in the river systems were 1.04 ± 0.26 and 1.85 ± 0.65 (cm 3 /g) for PFOA and PFOS respectively. Partitioning coefficient (log K OC ) significantly (p < 0.05) increased over time. This study represents the first report on partitioning and distribution of PFOA and PFOS in sub-Sahara Africa, which provide data and a scientific base to understand the fate and sorption of PFOA and PFOS in an aquatic system. The findings showed that lower pH values and increasing ionic strength favours sorption and partitioning of perfluoroalkyl substances (PFAS) in aqueous solution onto sediments; hence, plays an important role in their availability in water. Presence of PFAS in the aquatic system sediments is a potential risk to organisms. • Maximum concentration of PFOA and PFOS in the sediments from the river systems were 191.9 and 248.1 ng/g dw, respectively. • Mean values for the log K OC in the river systems were 1.04 ± 0.2 and 1.85 ± 0.6 (cm 3 /g) for PFOA and PFOS respectively. • Sorption kinetics for PFOA and PFOS fitted well into the elovich rate equation for the investigated sediment samples. • Lower solution pH and increase in Ca 2 + concentration favours the sorption and partitioning behaviour of PFOA and PFOS.

Efficient sorption of perfluoroalkyl acids by ionic liquid-modified natural clay

Contamination caused by per- and polyfluoroalkyl substances (PFAS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), is a big concern worldwide due to their persistence in the environment. Removal of PFAS represents a special challenge for water/wastewater treatment because of their diverse structures and unique physicochemical properties such as high water solubility and high stability of the C-F bond. In this study, we primarily investigated the removal of PFOA and PFOS from water through sorption with ionic liquid (IL)-modified natural clay. A series of ILs with varied alkyl chain lengths were applied for clay modification, and the successful intercalation of ILs was verified with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), zeta potential measurement, and elemental analysis. The structure and properties of IL-modified clays were strongly affected by the IL chain lengths. Specifically, long-chain IL not only changed the surface potential of clay, but also expanded the interlayers of clay, both of which greatly facilitated PFOA and PFOS sorption. Clay modified with the long-chain IL exhibited both fast kinetics for PFOA and PFOS sorption and high PFOA and PFOS removal efficiency under various water chemistry conditions. Furthermore, long-chain IL-modified clay was very effective for the removal of a suite of perfluorinated carboxylic and sulfonic acids with various chain lengths of the perfluoroalkyl moiety. IL-modified natural clay may be potentially applied for PFAS pollution control.

Column versus batch methods for measuring PFOS and PFOA sorption to geomedia.

The objective of this study is to compare the consistency between column and batch experiment methods for measuring solid-phase sorption coefficients and isotherms for per and polyfluoroalkyl substances (PFAS). Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used as representative PFAS, and experiments are conducted with three natural porous media with differing geochemical properties. Column-derived sorption isotherms are generated by conducting multiple experiments with different input concentrations (multi-C0 method) or employing elution-front integration wherein the entire isotherm is determined from a single breakthrough curve (BTC) elution front. The isotherms generated with the multi-C0 column method compared remarkably well to the batch isotherms over an aqueous concentration range of 3-4 orders of magnitude. Specifically, the 95% confidence intervals for the individual isotherm variables overlapped, producing statistically identical regressions. The elution-front integration isotherms generally agreed with the batch isotherms, but exhibited noise and systematic deviation at lower concentrations in some cases. All data sets were well described by the Freundlich isotherm model. Freundlich N values ranged from 0.75 to 0.81 for PFOS and was 0.87 for PFOA and are consistent with values reported in the literature for different geomedia. The results of this study indicate that column and batch experiments can measure consistent sorption isotherms and sorption coefficients for PFOS and PFOA when robust experimental setup and data analysis are implemented.

Oxalic Acid in Root Exudates Enhances Accumulation of Perfluorooctanoic Acid in Lettuce

Perfluorooctanoic acid (PFOA) is bioaccumulative in crops. PFOA bioaccumulation potential varies largely among crop varieties. Root exudates are found to be associated with such variations. Concentrations of low-molecular-weight organic acids (LMWOAs) in root exudates from a PFOA-high-accumulation lettuce variety are observed significantly higher than those from PFOA-low-accumulation lettuce variety (p < 0.05). Root exudates and their LMWOAs components exert great influences on the linear sorption-desorption isotherms of PFOA in soils, thus activating PFOA and enhancing its bioavailability. Among root exudate components, oxalic acid is identified to play a key role in activating PFOA uptake, with >80% attribution. Oxalic acid at rhizospheric concentrations (0.02-0.5 mM) can effectively inhibit PFOA sorption to soils by decreasing hydrophobic force, electrostatic attraction, ligand exchange, and cation-bridge effect. Oxalic acid enhances dissolution of metallic ions, iron/aluminum oxides, and organic matters from soils and forms oxalate-metal complexes, based on nuclear magnetic resonance spectra, ultraviolet spectra, and analyses of metal ions, iron/aluminum organometallic complexes, and dissolved organic carbon. The findings not only reveal the activation process of PFOA in soils by root exudates, particularly oxalic acid at rhizospheric concentrations, but also give an insight into the mechanism of enhancing PFOA accumulation in lettuce varieties.

Sorption and desorption behavior of PFOS and PFOA onto a Gram-positive and a Gram-negative bacterial species measured using particle-induced gamma-ray emission (PIGE) spectroscopy

In this study we examined whether a Gram-positive and a Gram-negative bacterial species have the capability to remove perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) from solution through sorption reactions under two different pH conditions. We developed a novel approach for quantifying PFAS in solution using particle-induced gamma-ray emission (PIGE) spectroscopy, and we used the results to constrain the important PFAS-bacterial sorption mechanisms. A mass balance experiment measuring PFOS in the aqueous phase and solid phase confirmed that PIGE spectroscopy measurements can account for all PFOS in the system, demonstrating for the first time how PIGE spectroscopy can be used to quantify the extent of PFAS sorption in experimental systems. Significant sorption occurred under most conditions studied, with up to 40 ± 5% and 67 ± 11% sorption of PFOA and PFOS, respectively. PFOA and PFOS sorption were both rapid, with steady-state being attained within minutes. PFOS sorption was pH dependent while PFOA sorption was pH independent, and greater sorption occurred onto Bacillus subtilis biomass compared to Pseudomonas putida biomass for both PFAS types. This sorption behavior suggests that pH, the PFAS head molecule, and cell wall structure all have a significant effect on the extent and mechanisms of bacterial sorption of PFAS. The observed sorption behaviors suggest that sorption of both molecules involves electrostatic and hydrophobic components. PFOS desorption was rapid and exhibited complete reversibility for both bacterial species, indicating that sorption is likely a cell surface phenomenon with no internalization occurring on the timescale of these experiments, and that the process can be modeled as an equilibrium reaction. Our work demonstrates that different PFAS molecules react to bacteria differently, and thus likely have markedly different mobilities in the environment. PFAS sorption in geologic systems is strongly influenced by organic matter, and our results suggest that biosorption may represent an inexpensive and effective PFAS remediation technique.

Predicting partitioning of radiolabelled 14C-PFOA in a range of soils using diffuse reflectance infrared spectroscopy

The aim of this study was to establish partitioning coefficients (Kd) of perfluorooctanoic acid (PFOA) in a wide range of soils and determine if those values can be predicted from soil properties using multiple linear regression (MLR) and from infrared spectra of soils using partial least squares regression (PLSR). For 100 different soils, the Kd values of spiked radiolabelled 14C-PFOA ranged from 0.6 to 14.8 L/kg and significantly decreased with soil depth (p < 0.05) due to soil properties that change with depth. The MLR modelling revealed that PFOA sorption was significantly (p < 0.05) influenced, in decreasing order, by organic carbon (OC) content, silt-plus-clay content and soil pH. Soils were partitioned into all soils and surface soils alone. The MLR models using OC, silt-plus-clay content and pH together explained most of the variation in sorption in all soils as well as surface soils alone (0-15 cm). However, correlations between soil properties and Kd values in some soils could not be explained by the MLR model. Modelling of Kd prediction in soils with PLSR and diffuse reflectance (mid) infrared Fourier transform spectroscopy (DRIFT) showed comparable success in explaining the predictions of Kd values, including some of the outliers identified in the MLR model. The PLSR loading weights suggested that quartz, and possibly pyrophyllite minerals, were inversely correlated with the Kd values. Given that MLR requires a-priori characterisation of a range of soil properties and PLSR-DRIFT is a method based on the direct relationship between spectra and soil components, mid-infrared spectroscopy may be a more economical and rapid technique to predict the solid-liquid partitioning of PFOA in soils.

Metal-organic frameworks cavity size effect on the extraction of organic pollutants

Zirconium Metal-organic frameworks (MOFs, UiO-66 and UiO-67) have been used for the removal from aqueous solutions of persistent fluorinated pollutants, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The two isostructural materials differ in cavity size, defined by the ligand, bdc (benzene-dicarboxylic acid) or bpdc (biphenyl-dicarboxylic acid) for UiO-66 and UiO-67 respectively. Both materials enable efficient sorption of PFOA and PFOS. Sorption kinetics and isotherms have been experimentally determined, and thermodynamic parameters ΔH°, ΔS° and ΔG° have been determined. UiO-67 shows higher sorption capacities (up to 743 mg·g−1 for PFOA and 585 mg·g−1 for PFOS) compared to these of UiO-66 (388 and 160 mg·g−1 for the sorption of PFOA and PFOS respectively) with a change in the sorption mechanism.

Effects of soil organic carbon (SOC) content and accessibility in subsoils on the sorption processes of the model pollutants nonylphenol (4-n-NP) and perfluorooctanoic acid (PFOA)

Subsoils control the release of hydrophobic pollutants to groundwater systems, but the role of subsoil soil organic carbon (SOC) in sorption processes of hydrophobic organic pollutants remains unclear. Thus, this study aimed to understand the role of subsoil SOC in sorption processes of 4-n-nonylphenol (NP) and perfluorooctanoic acid (PFOA) as model pollutants. To characterize the sorption behavior of NP and PFOA, 42 sub- and 54 topsoil samples were used for batch experiments. Differences in NP and PFOA sorption between sub- and topsoil samples and its mechanisms were identified using multiple regression analysis. Generally, the sorption of NP and PFOA was linear in all samples. The sorption of NP to soil samples (logKD = 1.78–3.68) was significantly higher and less variable than that of PFOA (logKD = −0.97–1.44). In topsoils, SOC content had the highest influence on NP and PFOA sorption. For NP, hydrophobic interactions between NP and SOC were identified as the most important sorption mechanism. For PFOA, hydrophobic as well as electrostatic interactions were determined depending on soil pH. In subsoils, the relevance of SOC content for pollutant sorption decreased drastically. For NP, not SOC content but rather SOC quality was relevant in SOC poor subsoils. For PFOA, clay and iron oxide content were found to be relevant for pollutant interactions with the solid phase. Thus, especially in SOC depleted subsoils, the sorption potential for PFOA remained unpredictable.

Sorption of PFOA onto different laboratory materials: Filter membranes and centrifuge tubes

Measurement and reporting of concentrations of contaminants of emerging concern such as per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA), is an integral part of most investigations. Occurrence of sorption losses of PFAS analytes onto particular laboratory-ware (e.g. glass containers) has been suggested in the published literature but has not been investigated in detail. We examined sorption losses from aqueous PFOA solutions in contact with different commonly-used materials in filter units and centrifuge tubes (glass and plastics). Sorption of PFOA onto different filter membrane types ranged from 21–79% indicating that filtration can introduce a major source of error in PFOA analysis; pre-treatment of filter membranes with phosphate or methanol solutions did not improve PFOA recovery. Substantial adsorption of PFOA was also observed on tubes made from polypropylene (PP), polystyrene (PS), polycarbonate (PC), and glass where losses observed were between 32–45%, 27–35%, 16–31% and 14–24%, respectively. Contrary to suggestions in the literature, our results indicated that the greatest sorption losses for PFOA occurred on PP, whereas losses on glass tubes were much lower. Variations in ionic strength and pH did not greatly influence PFOA recovery. When PFOA concentrations were increased, the percent recovery of PFOA increased, indicating that binding sites on tube-walls were saturable. This study draws attention towards analytical bias that can occur due to sorption losses during routine procedures, and highlights the importance of testing the suitability of chosen laboratory-ware for specific PFAS analytes of interest prior to experimental use.

Mechanism and Implication of the Sorption of Perfluorooctanoic Acid by Varying Soil Size Fractions.

Sorption of perfluorooctanoic acid (PFOA), a toxic and persistent organic pollutant, by various size fractions of an agricultural soil at environmentally relevant concentrations was evaluated. PFOA sorption to all fractions involved both film diffusion and intraparticle diffusion with the rate-limiting step by the latter. PFOA isotherm data fitted a linear model. Organic matter (OM), cation exchange capacity, pore volume, and the Brunauer-Emmett-Teller area played key roles in PFOA sorption. The sorption capacity followed the order of humic acid > clay (0.15-4.4 mm) > fine silt (1.9-39.8 mm) > coarse silt (17.3-79.4 mm) > fine sand (45.7-316.2 mm) > coarse sand (120-724.4 mm), opposite to their contributions to overall PFOA sorption due to the influence of their percentage weight in the original soil. Percentage OM content was the dominant factor controlling the fraction contributions to overall PFOA sorption, demonstrating influence of the hydrophobic force on sorption. PFOA should be highly mobile and bioavailable in soil-crop systems due to the low log Koc values.

Physicochemical factors controlling the retention and transport of perfluorooctanoic acid (PFOA) in saturated sand and limestone porous media

Comprehensively understanding the fate and transport of perfluorooctanoic acid (PFOA) in subsurface environment is crucial to assess its environmental impacts. In this work, column experiments were conducted to investigate the effects of physicochemical factors on the retention and transport of 14C-labeled PFOA in saturated sand and limestone porous media. The retention of PFOA in limestone columns was higher than that in sand columns under the same solution chemistry conditions. This can be attributed to that the limestone had less negative zeta-potential and larger specific surface area than the sand. Changes in ionic strength (low to high) and cation type (Na+ to Ca2+) had little influences on the mobility of PFOA in sand porous media, but significantly enhanced the retention of PFOA in limestone porous media. Nearly no PFOA was retained in the sand columns, but relatively high levels of PFOA retention (28.7–48.4%) were achieved in the limestone columns. Higher input concentration resulted in lower PFOA retention in limestone porous media, reflecting the blocking effect of the sorption sites. The blocking effect was insignificant in sand porous media, probably because the experimental conditions were unfavorable for PFOA sorption on sand media. A two-site kinetic retention model effectively simulated both the breakthrough and retention behaviors of the PFOA in the sand and limestone porous media.

Sorptive remediation of perfluorooctanoic acid (PFOA) using mixed mineral and graphene/carbon-based materials

Environmental contextPer- and poly-fluoroalkyl substances (PFASs) are contaminants of emerging concern, creating a need to develop efficient multi-functional adsorbents for improved remediation performance. By exploiting the versatility of graphene technology, we demonstrate that combining mineral and carbonaceous phases greatly increases and strengthens PFAS-binding to the adsorbent. The study highlights the benefits and potential applications of mixed adsorbents in PFAS-remediation. AbstractAs the degradation of perfluorooctanoic acid (PFOA) and related per- and poly-fluoroalkyl substances (PFASs) is energy-intensive, there is a need to develop in situ remediation strategies to manage PFAS-contamination. The sorption of PFOA by graphene oxide (GO), an iron-oxide-modified reduced-GO composite (FeG) and an activated-carbon(C)/clay/alumina-based adsorbent, RemBindTM (RemB), are evaluated. Sorption by FeG and RemB (&amp;gt;90%) is much greater than GO (60%). While an increase in pH hinders PFOA-sorption by GO, owing to the increased repulsion of anionic PFOA, variations in pH and ionic strength do not significantly influence PFOA-sorption by FeG and RemB, which indicates that binding is predominantly controlled by non-electrostatic forces. Hydrophobic interactions are assumed at the graphene or C-surface for all adsorbents, with added ligand-exchange mechanisms involving the associated Fe- and Al-minerals in FeG and RemB, respectively. Desorption of adsorbed PFOA is greatest in methanol, compared to water, toluene, or hexane, which provides estimates of the binding strength and reversibility from an environmental-partitioning perspective; i.e. risk of remobilisation of bound PFOA owing to rainfall events is low, but the presence of polar organic solvents may increase leaching risk. Iron-mineral-functionalisation of GO enhances the amount of PFOA adsorbed (by 30%) as well as the binding strength, which highlights the advantage of combining mineral and C-phases. Successful sorption of a range of PFASs from a contaminated-site water sample highlights the potential of using ‘mixed’ adsorbents like FeG and RemB in situ for PFAS-remediation, as they provide avenues for enhanced sorption through multiple mechanisms.