Influence of soil composition and environmental factors on the adsorption of per- and polyfluoroalkyl substances: A review

Ecosystem-wide PFAS characterization and environmental behavior at a heavily contaminated desert oasis in the southwestern U.S

Record-high PFAS contamination levels were recently reported in birds and small mammals from Holloman Lake, a high-salinity wastewater oasis located in southern New Mexico, USA. We expanded the PFAS screening to surface water, soils, algae, invertebrates, fish, reptiles, and a larger number of plants, birds, and mammals to examine the fate, transport, and bioaccumulation of PFAS in the ecosystem and generate contamination profiles across both the water-land interface and multiple trophic levels. C5 and C6 perfluorocarboxylic acids, both of them known degradation products of 6:2 FTS, were the dominant PFAS in surface water in the lake. In contrast, perfluorooctanesulfonic acid (PFOS) was the main PFAS found in sediments along the shoreline, with the number of fluorinated carbons in the alkyl chain and clay minerals both appearing to play a key role in soil sorption. High soil PFAS concentrations up to 900 m from the edge of the water could not be explained by air transport of contaminated dust and instead seemed related to past inundation events involving contaminated water. Higher PFAS concentrations along the main body of the lake included an extraordinary 30,000 ng/g ww of PFOS recorded for a composite saltcedar (Tamarix sp.) tissue sample. Bioaccumulation pervaded the ecosystem's food webs and trophic levels, with PFAS detection in all species and all types of animal tissue (blood, liver, muscle, and bone). Contamination involved mainly PFOS, followed by perfluorohexanesulfonic acid (PFHxS), with the observed concentrations of PFAS increasing concomitantly among tissue types but the liver bioaccumulating at a faster rate.

Interactive effects of soil dissolved organic matter (DOM) and Per- and polyfluoroalkyl substances on contaminated soil site: DOM molecular-level perspective

Dissolved organic matter (DOM), as the most active soil component, plays a crucial role in regulating the transport of contaminants. Per- and polyfluoroalkyl substances (PFAS) have been found to be widespread contaminants in the soil environment, and their migration would be also affected by DOM. Herein, the surface and subsurface soil samples collected from two PFAS manufacturing factories were studied for the variation characteristics of DOM under PFAS contamination, and the interaction between DOM and PFAS in soil was further explored. The results showed that PFAS contamination significantly reduced the richness of surface soil DOM. For the specific DOM components, the potential transformation of DOM in subsurface soil indicates that the presence of PFAS promotes the transformation of other DOM components to PA compounds. Moreover, a strong positive relationship was observed between the concentration of most perfluoroalkyl sulfonic acids (PFSAs) and the average unsaturation (DBE) and aromaticity index (AImod) of DOM, while no such relationship for perfluoroalkyl carboxylic acids (PFCAs), suggesting DBE and AImod may be a potential contributor influencing the distribution and transport of PFSAs. These findings highlight the interaction between DOM and the PFAS in the soil environment, which may enhance our understanding of the release and fate of PFAS in the soil environment.

PFAS removal via adsorption: A synergistic review on advances of experimental and computational approaches

Per- and polyfluoroalkyl substances (PFAS), commonly known as "forever chemicals", have become a major focus of current research due to their toxicity and persistence in the environment. These synthetic compounds are notoriously difficult to degrade, accumulating in water systems and posing long-term health and environmental risks. Adsorption is one of the most investigated technologies for PFAS removal. This review comprehensively reviewed the PFAS adsorption process, focusing not only on the adsorption itself, but also on the behavior of PFAS in the aquatic environment prior to adsorption because these behaviors directly affect PFAS adsorption. Significantly, this review summarized in detail the advances made in PFAS adsorption from the computational approach and emphasized the importance of integrated experimental and computational studies in gaining molecular-level understanding on the adsorption mechanisms of PFAS. Toward the end, the review identified several critical research gaps and suggested key interdisciplinary research needs for further advancing our understanding on PFAS adsorption.

Adsorption-desorption of propyrisulfuron in six typical agricultural soils of China: Kinetics, thermodynamics, influence of 38 environmental factors and its mechanisms

Propyrisulfuron, a novel sulfonylurea herbicide, effectively suppresses intracellular acetolactate synthase activity for weed control, but its adsorption behavior in the soil environment remains unclear. To assess potential agroecosystem risks, the adsorption-desorption behavior and mechanism of propyrisulfuron in six typical agricultural soils of China were investigated using a batch equilibrium method, Density Functional Theory (DFT), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy equipped with Energy Dispersive X-ray (SEM-EDX) techniques. It is indicated that the adsorption-desorption of propyrisulfuron in six soils reached equilibrium at 36 h under the optimum water-to-soil ratio (WSr) of 5:1. Adsorption kinetics followed the quasi-second-order kinetic model, while the Freundlich model best described the adsorption process at equilibrium. The adsorption and desorption were significantly and positively correlated with soil clay content, and 38 environmental factors had varying degrees of influence on its adsorption properties, especially those influenced by microplastics (MPs). Furthermore, the adsorption of propyrisulfuron in six soils was primarily a spontaneous, non-homogeneous, and non-ideal physical process, and special strong forces, such as hydrogen bonding might be involved. Consequently, due to its continuous application, potential persistent residues and pollution may occur in some soils. The investigations systematically reported the adsorption-desorption behavior of propyrisulfuron in various agricultural soils for the first time, providing scientific guidance for environmental risk assessment of groundwater pollution caused by its continuous application in agro-ecosystems.

Non-extractable residues of perfluorooctanoic acid (PFOA) in soil

PER: and polyfluoroalkyl substances have gained increased attention due to their persistence, ubiquitous presence in the environment, and toxicity. We hypothesised that the formation of non-extractable residues [NER] occurs in soils and contributes to the overall persistence of these priority pollutants, and that NER formation is controlled by temperature. To test these hypotheses, we used 14C-labelled perfluorooctanoic acid [PFOA] as target compound, added it to two arable soils (Cambisol, Luvisol), and incubated them at 10 °C and 20 °C in the dark. To support potential co-metabolic decomposition, some samples were additionally fed with glucose to enhance microbial activity. The PFOA residues were then sequentially extracted using 0.01 M CaCl2, followed by accelerated solvent extraction (ASE) with methanol or methanol/acetic acid after 0, 1, 3, 9, 30, 62, and 90 days of incubation. In addition, we monitored the release of 14C into the gas phase as well as [14C]-PFOA-NER after dry combustion and liquid scintillation counting. After 90 days, we found that the [14C]-PFOA content declined in the extraction order of CaCl2 ((bio)available fraction) > ASE (residual fraction) > NER > gas fraction), with most rapid changes occurring in the first 9 days of incubation. NER formation was different in the two soils and reached 5-9% of the applied amount in the Cambisol and Luvisol, respectively. Noteworthy the proportion of 14C-PFOA in the (bio)available fraction remained relatively stable over time at 56-62% of the applied amount, indicating the reversible transfer into this fraction from a bi-exponentially declining residual (ASE) pool. These dissipation patterns were neither influenced by temperature nor by the addition of glucose. We conclude that NER exist for PFOA, but that the majority of PFOA remains in (bio)available form, thus maintaining toxicity and mobility in soil for prolonged periods of time.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

Per- and polyfluoroalkyl substances (PFAS) pose significant health risks due to their widespread presence in various environmental and biological matrices. However, the molecular-level mechanisms underlying the interactions between PFAS and biological constituents, including proteins, carbohydrates, lipids, and DNA, remain poorly understood. Here, we investigate the interactions between a legacy PFAS, viz. perfluorooctanoic acid (PFOA), and the milk protein β-lactoglobulin (BLG) obtained using a combination of experimental and computational techniques. Circular dichroism studies reveal that PFOA perturbs the secondary structure of BLG, by driving a dose-dependent loss of α-helicity and alterations in its β-sheet content. Furthermore, exposure of the protein to PFOA attenuates the on-rate constant for the binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonic acid (ANS), suggesting potential functional impairment of BLG by PFOA. Steered molecular dynamics and umbrella sampling calculations reveal that PFOA binding leads to the formation of an energetically favorable novel binding pocket within the protein, when residues 129-142 are steered to unfold from their initial α-helical structure, wherein a host of intermolecular interactions between PFOA and BLG's residues serve to insert the PFOA into the region between the unfolded helix and beta-sheets. Together, the data provide a novel understanding of the atomic and molecular mechanism(s) by which PFAS modulates structure and function in a globular protein, leading to a beginning of our understanding of altered biological outcomes.