Perfluorooctanoic Acid In Soil Research Articles

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.

Synergetic degradation of perfluorooctanoic acid (PFOA) in soil using electrical resistance heating induced persulfate activation

Due to wastes from production of fluorinated materials and use of aqueous fire-fighting foams (AFFF), soils contaminated with perfluorooctanoic acid (PFOA) is of concern. However, current PFOA-contaminated soil disposal techniques have relatively low degradation efficiencies and are not suitable for on-site remediation. In this study, an electrical resistance heating (ERH) device and a box experimental device were used to study whether ERH induced persulfate activation (ERH/PS) could degrade PFOA in the soil. The results indicated that single ERH and single PS addition could not effectively degrade PFOA (with approximately 0.3 % and 3.9 % degradation after 9 h, respectively), while the degradation efficiency of PFOA with coupled ERH/PS could reach 87.3 % after 9 h of reaction. Moreover, effects of PS content, heating temperature, and soil organic matter on the degradation of PFOA were explored. During the ERH/PS process, PFOA was gradually transformed into short chain perfluorinated compounds and finally mineralized to fluoride ions. Finally, using a box experimental device, PS was effectively transported to the target contaminated area through electrokinetic (EK)-assisted delivery. After activating PS through ERH, the degradation rate of PFOA could reach 95.5 %. This is a novel study demonstrating the feasibility of ERH induced PS activation to degrade PFOA in soil, which provides a potential on-site strategy for remediation of PFOA-contaminated soil.

Thermal assisted heterogeneous activation of peroxymonosulfate by activated carbon to degrade perfluorooctanoic acid in soil

The chemical degradation of perfluorooctanoic acid (PFOA), an –environmentally persistent contaminant, has recently attracted much attention. Still, very few reports have focused on the degradation of PFOA in soil due to the process’s non-liquid, complex system and uneasy operation. In this study, thermal treatment was applied in the remediation of PFOA contaminated soil. Complementary to thermal activation of peroxymonosulfate (PMS), fresh activated carbon (FAC) and modified activated carbon (NAC), which were used as heterogeneous catalysts, were incorporated into the system to promote the production of sulfate radicals (SO4•−) and the diminution of PFOA in soil. Two portions of soils, both homogenous but one with and the other without natural organic carbon (OC), were provided to study the impact of OC on the elimination of PFOA in soil. The degradation of PFOA was initiated using the combined methods in cohesion with heat activation. During the process, the effect of temperature, the dosing amount of catalyst and oxidant, the reaction time and the volume ratio between soil and solution on the degradation of PFOA in soil were fully studied and optimized. The results showed that over a 12 h period, a PFOA (1.0 mg/kg) removal of 76% and 70% by using FAC/PMS and NAC/PMS respectively could be achieved at 60 °C. Furthermore, density functional theory (DFT) calculations were combined with experimental data and verify that the adsorption ability of both FAC and NAC for PFOA are 3 times stronger than that of soil grain. This greater adsorption can attract PFOA molecules from within soil and provide opportunities for interactions with oxidative radicals. This work sheds light on a much over-looked aspect of advanced oxidation of PFOA in soil systems, which might provide a potential option for the in-situ remediation of PFOA contaminated soil in the future.

Comprehensive adsorption behavior and mechanism of PFOA and PFCs in various subsurface systems in China

The adsorption-desorption performance of perfluorooctanoic acid (PFOA), one of the environmentally persistent pollutants which is refractory to degrade in soil, was investigated and reported. The adsorption-desorption process of PFOA was firstly conducted using different fractions (sand, coarse silt and fine silt) of soil collected from Shanghai, China. More than 50% of PFOA (2.0 mg/L) could be adsorbed by soils while only less than 10% of which could be desorbed once contamination occurs. The kinetics and particle diffusion rates of PFOA in different fractions of soil were calculated and analyzed in detail. Apart from this, the retention of short-chained PFCs, which can be generated as degradation products of PFOA, were also measured. In single solute systems, the adsorption of pollutants in soils dramatically increased as the chain length of PFCs grew longer. Similarly, in mixed solutions, preferential adsorption of longer-chained PFCs over shorter chains in soils were sited, attributable to the stronger hydrophobicity of the pollutants. However, the desorption of them performed in reverse, where the desorption rates of longer-chained PFCs were far lower than those of shorter ones. Furthermore, influencing factors including pH, temperature and co-existing matters were studied during the adsorption process. After comprehending the adsorption behavior of PFOA in soil fractions, the situation of the adsorption of PFOA in various soils chosen from nine provinces in China was investigated and compared. There was an obvious discrepancy, whether it be from the rate or the amount of adsorption of PFOA (approximately 10%), in the nine different soils. Finally, a multiple linear regressive equation was employed to sort influencing parameters which are prone to affect the adsorption of PFOA in soils, the contribution of these are provided in order of relevance. These results demonstrate the adsorption performance and behavior of PFOA and PFCs in different soils, which can be utilized as a scientific reference for maximizing remediation of PFOA polluted sites in the future.

Thermal Assisted Heterogeneous Activation of Peroxymonosulfate by Activated Carbon to Degrade Perfluorooctanoic Acid in Soil

Thermal Assisted Heterogeneous Activation of Peroxymonosulfate by Activated Carbon to Degrade Perfluorooctanoic Acid in Soil

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.

Ecological risk assessment for perfluorooctanoic acid in soil using a species sensitivity approach

Perfluorooctanoic acid (PFOA) is one of the persistent organic pollutants that has been listed in Annex A of the Stockholm Convention and has attracted attention owing to its endocrine-disrupting properties. However, there is currently little information available regarding the soil ecotoxicity of PFOA and the associated ecological risks. Accordingly, in this study, we sought to assess the soil ecological risk of PFOA based on a probabilistic approach using data obtained from multispecies bioassays and soil toxicity assessments, from which we generated soil species sensitivity distributions and estimated soil protective concentrations for PFOA. Using the latter distributions, we also undertook a probabilistic ecological risk assessment. On the basis of acute and chronic toxicity estimates obtained from bioassays involving eight soil-associated organisms from six diverse taxonomic groups, we could deduce that PFOA poses a negligible risk to soil ecosystems. However, we also found that this chemical may be more toxic than some of the established endocrine-disrupting chemicals such as bisphenol A, nonylphenol, and methylparaben, thereby indicating that further in-depth studies would be necessary to obtain a better understanding of the toxic potential of this chemical in the soil environment.

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.

Transport and retention of perfluorooctanoic acid (PFOA) in natural soils: Importance of soil organic matter and mineral contents, and solution ionic strength

Effects of soil organic matter and mineral contents, and solution ionic strength on the transport of perfluorooctanoic acid (PFOA) in different types of soils (i.e., desert soil, black soil, and red soil) were systematically investigated with a set of laboratory column experiments. The retention of PFOA in the soils under two solution ionic strengths conditions (1.0 mM and 10.0 mM CaCl2) followed an order of red soil > black soil > desert soil (expect red soil in 10 mM CaCl2). PFOA retention in the black soil (soil organic carbon content: 2.57%) was higher than that in the desert soil (soil organic carbon content: 0.05%). In addition, PFOA also showed higher mobility in treated black soils with lower organic carbon contents. These results suggest that the hydrophobic interaction is a key mechanism governing PFOA retention and transport in soils. Besides, more PFOA retention in the red soil (zeta potential: 7.25 ± 0.10 mV and 14.80 ± 0.20 mV) than the desert soil (−15.70 ± 0.10 mV and − 9.11 ± 0.10 mV) was observed, suggesting that electrostatic interaction may be another important mechanism for PFOA retention and transport in soils. Increasing ionic strength slightly increased the retention of PFOA in negatively charged desert and black soils, but significantly decreased the retention of PFOA in the positively charged red soil. Findings of this study point to the importance of soil physiochemical properties to the fate and transport of PFOA in natural soils.

Laccase induced degradation of perfluorooctanoic acid in a soil slurry

Perfluorooctanoic acid (PFOA) can induce undesirable effects to humans and animals and has thus attracted much attention from the public and scientific communities in recent years. Extensive studies have been devoted to exploring PFOA degradation in aqueous phase, while information for that in soil is rather limited. Understanding the transformation of PFOA in soil is important in developing strategies to assess and manage its environmental fate. In this study, we have demonstrated that PFOA can be effectively degraded by enzyme catalyzed oxidative humification reactions (ECOHRs) with a natural organic material, soybean meal, as the mediator. In the presence of soybean meal and laccase, PFOA was degraded 24% in water after 36 days, 40% in soil slurry after 140 days. The water extract of soybean meal contained high concentrations of natural organic mediators and multivalent metal ions, both of which were essential to PFOA degradation by ECOHRs. The ECOHR degradation products of PFOA in soil were identified to be partially fluorinated organic compounds, and the molecular features of the products suggest that the degradation mechanism involves free radical chain reaction processes, which was initiated by direct free radical attacks on the CC bonds in perfluoroalkyl acids.

Biomarker responses of earthworms (Eisenia fetida) to soils contaminated with perfluorooctanoic acid.

Perfluorooctanoic acid (PFOA) is considered a persistent environmental pollutant. The aim of this study was to assess the potential toxicity of PFOA to earthworms (Eisenia fetida) in artificial soil. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST) as well as the contents of malondialdehyde (MDA) were measured after exposure to 0, 5, 10, 20, and 40mgkg-1 PFOA in soils for 7, 14, 21, and 28days. The results showed that SOD activity increased at 14days and decreased from 21 to 28days; MDA levels were highest in the treatment with 40mgkg-1 PFOA after 28days of exposure. In contrast, CAT and POD activities increased after 14-21days of exposure and significantly decreased with long-term exposure (28days). GST activity increased significantly from 14 to 28days. Our results indicate that PFOA has biochemical effects on E. fetida, thereby contributing to our understanding of the ecological toxicity of PFOA on soil invertebrates.

Pollution pathways and release estimation of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in central and eastern China.

China has gradually become the most important manufacturing and consumption centre for perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in the world, and inadvertently become the world's major contamination hotspots. However, a systematic analysis of pollution pathways for PFOS/PFOA into the different environmental compartments and their quantification in China has yet to be carried out. This study focused on PFOS and PFOA release into the environment in the central and eastern region of China, which accounts for the vast majority of national emission. About 80-90% of PFOS/PFOA contamination in the Chinese environment was estimated to come directly from manufacturing and industrial sites mostly via wastewater discharge from these facilities. The other major contamination sources for PFOS were identified as being linked to aqueous fire-fighting foams (AFFFs), and pesticides including sulfluramid. For PFOA, following some way behind industrial wastewater, were industrial exhaust gas, domestic wastewater and landfill leachate as contamination sources. For surface water contamination, the major pollution contributors after industrial wastewater were AFFF spill runoff for PFOS, and domestic wastewater and precipitation-runoff for PFOA. The majority of PFOS that contaminated soil was considered to be linked with infiltration of AFFF and pesticides, while most PFOA in soil was attributed to atmospheric deposition and landfill leachate. Where groundwater had become contaminated, surface water seepage was estimated to contribute about 50% of PFOS and 40% of PFOA while the remainder was mostly derived from soil leaching. A review of the available monitoring data for PFOS/PFOA in the literature supported the view that industrial wastewater, landfill leachate and AFFF application were the dominant sources. Higher concentrations of PFOA than PFOS found in precipitation also corroborated the prediction of more PFOA release into air. To reduce PFOS/PFOA contamination of the Chinese environment the focus for control should be on industrial wastewater emissions.

Removal of aqueous perfluorooctanoic acid (PFOA) using starch-stabilized magnetite nanoparticles

Fully stabilized magnetite (Fe3O4) nanoparticles were prepared with a water-soluble starch as a stabilizer and tested for removal of aqueous perfluorooctanoic acid (PFOA). The presence of starch at ≥0.2wt% can fully stabilize 0.1g/L as Fe of the Fe3O4 nanoparticles. The particle stabilization technique resulted in 2.4 times higher PFOA uptake. Fourier transform infrared spectra suggested that the main PFOA removal mechanism was inner-sphere complexation. Batch kinetic experiments revealed that the starch-stabilized nanoparticles facilitated a rapid PFOA uptake with a sorption equilibrium time of 30min, and the sorption process followed a pseudo-second-order kinetic model. The Langmuir model was able to well interpret the adsorption isotherm, with a maximum adsorption capacity of 62.5mg/g. Increasing pH from 4.7 to 9.6 led to a sharp increase (by 2.6 times) in PFOA uptake. The presence of 12mg/L humic acid inhibited PFOA uptake by 96%, while effect of ionic strength (CaCl2=0–2mmol/L) was negligible. The nanoparticles significantly reduced the biological toxicity of PFOA. The results demonstrated promise of starch-stabilized Fe3O4 nanoparticles as a “green” adsorbent for effective removal of PFOA in soil and groundwater.

Bioavailability of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in biosolids-amended soils to earthworms (Eisenia fetida)

The bioavailability of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in seven biosolids-amended soils without any additionally spiking to earthworms (Eisenia fetida) was studied. The uptake and elimination kinetics of PFOS and PFOA fit a one-compartment first-order kinetic model. PFOS displayed higher uptake and lower elimination rate coefficients, and longer time to reach steady-state (tss) than those of PFOA. The bioaccumulation factors (BAFs) of PFOS and PFOA ranged 1.54–4.12 and 0.52–1.34gsoilgworm−1, respectively. The BAFs and tss decreased with increasing concentrations of PFOS and PFOA in soils. Stepwise multiple regression analysis was used to elucidate the bioavailability of PFOS and PFOA. The results showed that the total concentrations of PFOS and PFOA, and organic matter (OM) contents in soils explained 87.2% and 91.3% of the variation in bioavailable PFOS and PFOA, respectively. PFOS and PFOA concentrations exhibited positive influence and OM contents showed the negative influence on the accumulation of PFOS and PFOA in earthworms. Soil pH and clay contents played relatively unimportant role in PFOS and PFOA bioavailability.