Calibration of organic-diffusive gradients in thin films (o-DGT) passive samplers for perfluorinated alkyl acids in water

On-site evaluation of DGT passive sampling for quantitatively measuring per- and polyfluoroalkyl substances in a river-estuary-sea water system

The passive sampling technique of diffusive gradients in thin-films (DGT) is promising for monitoring emerging contaminants such as per- and polyfluoroalkyl substances (PFAS). It is urgent to evaluate the impacts of salinity and exposure time on DGT sampling before it can be set as a standard method. Herein, DGT sampler based on the binding gel of weak anion exchanger (WAX) resin was deployed in a representative water system of the Xiaoqing river-estuary-sea for representative sampling windows (<1 day to 28 days) with high pH (8.18 ± 0.04 to 8.51 ± 0.17) and wide ranges of salinity (0.95 ± 0.07‰ to 14.37 ± 3.92‰), total dissolved solids (1.20 ± 0.09 g/L to 15.29 ± 3.91 g/L) and dissolved organic matter (2.8-32 mg/L). The results showed that the WAX-DGT sampler exhibited good performance for most target PFAS except for short-chain perfluorocarboxylates (C ≤ 5) in 14 days. When the exposure time was over 14 days, biofouling of the sampler may deflect the mass accumulation of the PFAS in the sampler. Salinity played an important role in the mass binding of PFAS by DGT. The shorter the carbon chain of the compound, the greater the influence of the salinity. PFAS with carboxyl groups had greater affinities for the biofouled membrane filter than those with sulfonic groups. In the river-estuary-sea system, where PFAS concentrations changed dynamically, the temporal resolution of the monitoring strategy has been demonstrated to be more important than spatial resolution. DGT provided a better integral of PFAS exposure than grab sampling in the dynamic water system and offered equivalent sensitivity of grab sampling with exposure time <10 d and greater sensitivity with exposure time ≥10 d. Thus, DGT has the advantage of providing high temporal resolution monitoring. This study provided support for the standardization of the DGT technique.

Utility of a modified o-DGT passive sampler for measurement of bisphenol analogues in freshwater and coastal waters

Bisphenol analogues (BPs) are commonly found in riverine and coastal waters. However, the lack of a reliable and robust passive sampling method has hindered our ability to monitor these compounds in aquatic systems. The study developed a novel organic-diffusive gradients in thin film (o-DGT) sampler based on stainless steel mesh membrane, polyacrylamide diffusive gel, and hydrophilic-lipophilic balance (HLB) binding gel. This innovative design tackled issues of filter membrane sorption in traditional o-DGT devices and potential gel damage in membrane-less o-DGT devices, showing promising application prospects. The mass accumulation of 15 target BPs was linear over 10 days in both freshwater (r2 ≥ 0.92) and seawater (r2 ≥ 0.94), with no saturation observed. The diffusion coefficients (D) through polyacrylamide diffusive gels ranged from 4.04 × 10-6 to 5.77 × 10-6 cm2 s-1 in freshwater and from 1.74 × 10-6 to 4.69 × 10-6 cm2 s-1 in seawater for the target BPs (except for bisphenol PH) at 22 °C. The D values of the target BPs in seawater were lower than those in freshwater due to the high salinity in seawater (35 ‰). The o-DGT samplers demonstrated good integrity in field applications. The total concentrations of the eight detected BPs ranged from 9.2 to 323 ng L-1, which was consistent with the measurements obtained by grab sampling. Among all BPs, bisphenol S, bisphenol F, and bisphenol A were consistently detected at all sites using both sampling methods. The concentrations of some novel BPs in coastal water measured by grab sampling were comparable to those measured in rivers, suggesting the need to strengthen pollution control of BPs in coastal areas. These results indicate that the o-DGT passive sampling method developed in the present study can be effectively used for monitoring BPs in freshwater and coastal environments.

Measurement of perfluoroalkyl substances in drinking water sources by DGT sampler with a novel fluorinated graphite binding gel

Extensive use of per- and polyfluoroalkyl substances (PFASs) has resulted in their widespread presence in natural waters. Concern for public health requires reliable measurement methods for determining their distribution and risks. Here, a sampling method based on diffusive gradients in thin films (DGT) was developed for measuring PFASs in drinking water sources. Fluorinated graphite (FG) particles were used to prepare the DGT binding gel for selective enrichment of trace PFASs in an aqueous environment. The FG-DGT method did not show sensitivity to relevant environmental parameters including pH (5.0-9.0), ionic strength (0.001-0.5 M), or DOM concentration (0-30 mg/L). The FG-DGT had enough capacity for deployment of up to four months. Six traditional and emerging PFASs including PFOS, PFOA, PFHpA, PFHxS, PFNA, and 6:2 FTSA at the ng/L level were detected in two major reservoirs serving as public drinking water sources by FG-DGT method coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS). PFOA appeared at the highest observed concentrations in the drinking water sources. The research demonstrates that FG-DGT is an effective and efficient tool for monitoring PFASs in drinking water.

Factors affecting diffusion of polar organic compounds in agarose hydrogel applied to control mass transfer in passive samplers

Diffusive hydrogel-based passive sampler (HPS) based on diffusive gradients in thin films (DGT) is designed for monitoring polar organic contaminants in the aquatic environment. DGT technique controls the compound's overall uptake rate by adding a hydrogel layer of known thickness, which minimizes the importance of the resistive water boundary layer in the compound uptake process. In this work, we investigated several factors which may influence the diffusion of a range of aquatic contaminants in 1.5% agarose hydrogel. Diffusion in hydrogel was tested using the sheet stacking method. We demonstrated that a thin nylon netting incorporated into the diffusive hydrogel for mechanical strengthening does not significantly affect the diffusion of 11 perfluoroalkyl compounds. Further, we investigated the effect of pH in the range from 3 to 11 on the diffusion of a range of 39 aromatic amines (AAs) -36 aromatic, 2 aliphatic, and azobenzene in hydrogel. AAs were chosen as representatives of compounds with pH-dependent dissociation in water. Analysis of variance showed no significant difference in mean diffusion coefficient log D value at five pH values. The demonstration that the diffusion coefficient D and thus the sampling rate Rs are independent on pH simplifies the interpretation of data from field studies because we can neglect the influence of pH on the Rs. log D values (m2 s-1) of tested AAs ranged from to - 9.77 for 3,3'-dimethylbenzidine to - 9.19 for azobenzene. A negative correlation of log D with molar mass (log M) and molecular volume (log Vm) was observed (R =  - 0.57 and - 0.56, respectively). The diffusion coefficient presents a critical parameter for the sampling rate estimation of HPS. Theoretical sampling rates Rs of AAs were calculated for a HPS using the average D values. Theoretical Rs values calculated for AAs at 22°C ranged from 29 mL day-1 for 3,3'-dimethylbenzidine to 106 mL day-1 for 2-aminopyridine. Our calculated values of Rs are in the same range as those already published for a range of low-molecular polar organic contaminants, which supports the possibility of deriving sampler performance parameters in the field from laboratory-derived diffusivity of analytes in hydrogel.

Organic diffusive gradients in thin films (o-DGT) for determining environmental behaviors of antibiotics: A review

Antibiotics are recognized as effective medicine that has been extensively used in human and veterinary. Since the rate of releasing into the environment is stronger than the rate of elimination, antibiotics are regarded as persistent or "pseudo-persistent" organic compounds that result in the development of microbial antibiotic resistance. Therefore, assessment for their ecological risks to the environment are essential. Diffusive gradients in thin films for organic compounds (o-DGT) have been adapted to investigate the environmental behaviors of antibiotics. Currently, more than 20 compounds have been tested by o-DGT in waters and soil environments. In this review, we explained the theoretical reason that o-DGT is feasible to determine the labile fraction of antibiotics in different environmental media. The most used agarose diffusive gel, and various binding agents such as resin, porous carbon and nano-scale materials have been compared to optimize the sampling of antibiotics by o-DGT. Results of deploying o-DGT devices in waters and soils from previous studies were discussed to understand the bioavailability and dynamic transport of antibiotics. Also, we provided the feasibility analysis of using o-DGT in sediments for antibiotics measurements, which is required to be carried out in future studies. To have a deep view on the development of o-DGT, its technical limitations and viable improvements were summarized in this study for further applications on antibiotics research.

Analysis of a Passive Sampling Device to Assess the Behavior of Per- and Polyfluoroalkyl Substances in Sediments

Per- and polyfluoroalkyl substances (PFAS) are an emerging class of compounds that cause health and environmental problems worldwide. In aquatic environments, PFAS may bioaccumulate in sediment organisms, which can affect the health of organisms and ecosystems. As such, it is important to develop tools to understand their bioaccumulation potential. In the present study, the uptake of perfluorooctanoic acid (PFOA) and perfluorobutane sulfonic acid (PFBS) from sediments and water was assessed using a modified polar organic chemical integrative sampler (POCIS) as a passive sampler. While POCIS has previously been used to measure time-weighted concentrations of PFAS and other compounds in water, in our study, the design was adapted for analyzing contaminant uptake and porewater concentrations in sediments. The samplers were deployed into seven different tanks containing PFAS-spiked conditions and monitored over 28 days. One tank contained only water with PFOA and PFBS, three tanks contained soil with 4% organic matter, and three tanks contained soil combusted at 550 °C to minimize the influence of labile organic carbon. The uptake of PFAS from the water was consistent with previous research using a sampling rate model or simple linear uptake. For the samplers placed in the sediment, the uptake process was explained well using a mass transport based on the external resistance from the sediment layer. Uptake of PFOS in the samplers occurred faster than that of PFOA and was more rapid in the tanks containing the combusted soil. A small degree of competition was observed between the two compounds for the resin, although these effects are unlikely to be significant at environmentally relevant concentrations. The external mass transport model provides a mechanism to extend the POCIS design for measuring porewater concentrations and sampling releases from sediments. This approach may be useful for environmental regulators and stakeholders involved in PFAS remediation. Environ Toxicol Chem 2023;42:2171-2183. © 2023 SETAC.

Sorption affinity and mechanisms of per-and polyfluoroalkyl substances (PFASs) with commercial sorbents: Implications for passive sampling

Effective monitoring tools, including passive samplers, are essential for the wide range of per- and polyfluoroalkyl substances (PFASs) in aquatic matrices. However, knowledge of the extent and mechanisms of PFASs sorption with sorbents in a passive sampling context is limited. To address this, sorption behavior of 45 anionic, neutral and zwitterionic PFASs ranging in perfluorocarbon chain length (C₃-C₁₆) and functional groups with 11 different commercial sorbents (cross-linked β-cyclodextrin polymers, activated carbon, anion exchange (AE), cation exchange, hydrophilic-lipophilic balanced (HLB) and non-polar) was investigated. A broad range of equilibrium sorbent-MilliQ water (MQ) distribution coefficients (K_d) were observed (10^-1.95 to 10^8.30 mL g^-1). Similar sorbent types (e.g., various AE and HLB sorbents) exhibited very different sorption behavior, likely due to their different polymeric structures and relative importance of sorbate/sorbent interactions other than coulombic interactions. HLB and AE with hydroxyl functionalities are most effective for sampling of the full suite of PFASs. Reduced sorptive affinity was observed in the presence of matrix co-constituents in wastewater influent for most PFASs. HLB had the smallest reduction in log K_d in wastewater suggesting that these sorbents are appropriate for applications in complex matrices. Sufficient sorbent capacity was observed for linear uptake of many target analytes which facilitates passive sampling.

A field-validated equilibrium passive sampler for the monitoring of per- and polyfluoroalkyl substances (PFAS) in sediment pore water and surface water

A simple equilibrium passive sampler, consisting of water in an inert container capped with a rate-limiting barrier, for the monitoring of per- and polyfluoroalkyl substances (PFAS) in sediment pore water and surface water was developed and tested through a series of laboratory and field experiments. The objectives of the laboratory experiments were to determine (1) the membrane type that could serve as the sampler's rate-limiting barrier, (2) the mass transfer coefficient of environmentally relevant PFAS through the selected membrane, and (3) the performance reference compounds (PRCs) that could be used to infer the kinetics of PFAS diffusing into the sampler. Of the membranes tested, the polycarbonate (PC) membrane was deemed the most suitable rate-limiting barrier, given that it did not appreciably adsorb the studied PFAS (which have ≤8 carbons), and that the migration of these compounds through this membrane could be described by Fick's law of diffusion. When employed as the PRC, the isotopically labelled PFAS M₂PFOA and M₄PFOS were able to predict the mass transfer coefficients of the studied PFAS analytes. In contrast, the mass transfer coefficients were underpredicted by Br^- and M₃PFPeA. For validation, the PC-based passive samplers consisting of these four PRCs, as well as two other PRCs (i.e., M₈PFOA and C₈H₁₇SO₃^-), were deployed in the sediment and water at a PFAS-impacted field site. The concentration-time profiles of the PRCs indicated that the samplers deployed in the sediment required at least 6 to 7 weeks to reach 90% equilibrium. If the deployment times are shorter (e.g., 2 to 4 weeks), PFAS concentrations at equilibrium could be estimated based on the concentrations of the PRCs remaining in the sampler at retrieval. All PFAS concentrations determined via this approach were within a factor of two compared to those measured in the mechanically extracted sediment pore water and surface water samples obtained adjacent to the sampler deployment locations. Neither biofouling of the rate-limiting barrier nor any physical change to it was observed on the sampler after retrieval. The passive sampler developed in this study could be a promising tool for the monitoring of PFAS in pore water and surface water.

Calibration of Perfluorinated Alkyl Acid Uptake Rates by a Tube Passive Sampler in Water

Per- and polyfluoroalkyl substances (PFAS) are a group of 4000+ man-made compounds of great concern due to their environmental ubiquity and adverse effects. Despite a general interest, few reliable detection tools for integrative passive sampling of PFAS in water are available. A microporous polyethylene tube with a hydrophilic-lipophilic balance sorbent could serve as a flow-resistant passive sampler for PFAS. The tube's sampling rate, Rs, was predicted based on either partitioning and diffusion, or solely diffusion. At 15 °C, the laboratory measured Rs for perfluorohexanoic acid of 100+/-81 mL day-1 were better predicted by a partitioning and diffusion model (48+/-1.8 mL day-1) across 10-60 cm s-1 water flow speeds (15+/-4.2 mL day-1 diffusion only). For perfluorohexane sulfonate, Rs at 15°C were similarly different (110+/-60 mL day-1 measured, 120+/- 63 versus 12+/-3.4 mL day-1 in respective models). Rs values from field deployments were in-between these estimates (46 +/-40 mL day-1 for perfluorohexanoic acid). PFAS uptake was not different for previously biofouled membranes in the laboratory, suggesting the general applicability of the sampler in environmental conditions. This research demonstrates that the polyethylene tube's sampling rates are sensitive to the parameterization of the models used here and partitioning-derived values should be used.

Evaluation and Application of a Novel Diffusive Gradients in Thin-Films Technique for In Situ Monitoring of Glucocorticoids in Natural Waters

The potential environmental risks of glucocorticoids (GCs) have attracted attention in the past few decades. In this study, a novel diffusive gradients in thin-films (DGT) device and analytical technique based on the second generation of polar enhanced phase (PEP-2), PEP-2-DGT, were developed for sampling and quantifying natural and synthetic GCs in aquatic systems. The capacity of PEP-2 gels for accumulating all target compounds was >600 μg per disc, sufficient for long-term passive sampling of selected GCs, even in wastewaters. Systematic tests were carried out to verify the application of DGT in natural waters and wastewaters. The performance of PEP-2-DGT devices was independent (C_DGT/C_soln was in the acceptable range of 0.9-1.1) of a wide range of environmental conditions: ionic strength (0.001-0.5 mol L^-1), dissolved organic matter (0-20 mg L^-1), and pH (3.06-9.02). It was tested for various diffusive layer thicknesses (0.565-2.065 mm) and different deployment times (10-168 h). Diffusion coefficients (D) of selected GCs through an agarose-based diffusive gel were determined for the first time (3.80-4.85 × 10^-6 cm^-2 s ^-1 at 25 °C). Linear correlations between D and log K_ow were established for three groups of target GCs (R² = 0.96-0.99). This could enable prediction of D values for other GCs with similar structures in the future, which will help for rapid screening and emergency monitoring. Concentrations and distribution patterns of analytes obtained by PEP-2-DGT devices in five rivers after 7- and 14-day deployments were in accordance with those measured from grab samples, with total GC concentrations ranging from 7 to 27 ng L^-1 at all sampling sites, confirming the reliability and robustness of the DGT devices for monitoring GCs in natural waters. The development of the new DGT technique will help improve understanding of the behavior and fate of these compounds in the aquatic environments.

Diffusive gradients in thin films (DGT) probe for effectively sampling of per- and polyfluoroalkyl substances in waters and sediments

The passive sampling technique, diffusive gradients in thin films (DGT) has attracted increasing interests as an in-situ sampler for organic contaminants including per- and polyfluoroalkyl substances (PFAS). However, its effectiveness has been questioned because of the small effective sampling area (3.1 cm²). In this study, we developed a DGT probe for rapid sampling of eight PFAS in waters and applied it to a water-sediment system. It has a much larger sampling area (27 cm²) and as a result lower method quantification limits (0.15 - 0.21 ng/L for one-day deployment and 0.02 - 0.03 ng/L for one-week deployment) and much higher (by > 10 factors) sampling rate (100 mL/day) compared to the standard DGT (piston configuration). The sampler could linearly accumulate PFAS from wastewater, was sensitive enough even for a 24 hr deployment with performance comparable to grab sampling (500 mL). The DGT probe provided homogeneous sampling performance along the large exposure area. The use of the probe to investigate distributions of dissolved PFAS around the sediment-water interface was demonstrated. This work, for the first time, demonstrated that the DGT probe is a promising monitoring tool for trace levels of PFAS and a research tool for studying their distribution, migration, and fate in aquatic environments including the sediment-water interface.

Field Validation of a Novel Passive Sampler for Dissolved PFAS in Surface Waters

Numerous per- and polyfluoroalkyl substances (PFAS) are of growing concern worldwide due to their ubiquitous presence, bioaccumulation and adverse effects. Surface waters in the United States have displayed elevated concentrations of PFAS, but so far discrete water sampling has been the commonly applied sampling approach. In the present study we field-tested a novel integrative passive sampler, a microporous polyethylene tube, and derived sampling rates (Rs ) for nine PFAS in surface waters. Three sampling campaigns were conducted, deploying polyethylene tube passive samplers in the effluent of two wastewater treatment plant (WWTP) effluents and across Narragansett Bay (Rhode Island, USA) for 1 month each in 2017 and 2018. Passive samplers exhibited linear uptake of PFAS in the WWTP effluents over 16-29 days, with in situ Rs for nine PFAS ranging from 10 ml day-1 (perfluoropentanoic acid) to 29 ml day-1 (perfluorooctanesulfonic acid). Similar sampling rates of 19 ± 4.8 ml day-1 were observed in estuarine field deployments. Applying these Rs values in a different WWTP effluent predicted dissolved PFAS concentrations mostly within 50% of their observations in daily composite water samples, except for perfluorobutanoic acid (where predictions from passive samplers were 3 times greater than measured values), perfluorononanoic acid (1.9 times), perfluorodecanoic acid (1.7 times), and perfluoropentanesulfonic acid (0.1 times). These results highlight the potential use of passive samplers as measurement and assessment tools of PFAS in dynamic aquatic environments. Environ Toxicol Chem 2022;41:2375-2385. © 2022 SETAC.

Development of diffusive gradients in thin film technique for seasonal monitoring of benzophenone-type UV filters in coastal waters

Benzophenone(BP)-type UV filters are continuously released into various aquatic environments via the effluent discharge of wastewater treatment plants (WWTPs) and recreational activities in coastal beaches. In this study, we developed a robust and reliable sampling approach, diffusive gradients in thin-films (DGT), for seasonal monitoring of six BP derivatives in coastal waters to investigate their occurrence and environmental risk. The binding capacities of both XAD-2 and HLB gels for test BPs were over 252 μg with no significant deterioration in marine environment, suggesting that theoretically, DGT is capable of sampling for at least 3 months effectively. The diffusion coefficients of BPs in freshwater and seawater were determined for the first time. The sampling performance showed no dependence on environmental conditions including pH (4.0-8.5), ionic strength (0.0001-0.5 M) and dissolved organic matter (0-20 mg L^-1). The developed DGT samplers were successfully applied in a river estuary linked to a WWTP and a bathing beach at different periods of one year. Results showed that the concentrations of BPs in the coastal waters were dependent on seasonal variation. The highest level in summer and the ecological risk should be considered based on the risk quotient values. These results demonstrated that the present DGT method is suitable for measuring, characterization, and risk assessment of BPs in freshwater and marine environment.

Development of organic-diffusive gradients in thin films technique for measuring freely dissolved concentrations of tetracyclines using a commercial SPE packing

The freely dissolved concentrations (FDCs) of pollutants are related to their bioavailability in the environment, and the diffusive gradients in thin films technique (DGT) can obtain the FDC of an analyte. Aiming for the detection of the FDCs of tetracyclines (TCs), we used a polyacrylamide hydrogel comprising acrylamide and acrylaide agarose cross-linker as diffusive and binding gels, and a commercial solid-phase extraction (SPE) packing, namely polymer sorbent (PLS), as an adsorption material in the binding gel for the preparation of the organic-diffusive gradients in thin films (o-DGT) devices. The results showed that the diffusion coefficients of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in the diffusive gels were 1.08 × 10-6, 1.08 × 10-6 and 1.03 × 10-6 cm2/ s at 25 °C, respectively. The binding gel showed excellent performance with adsorption capacities of 534.88-569.42 µg/disc for TC, 527.18-565.98 µg/disc for OTC and 1320.12-1320.86 µg/disc for CTC, respectively. The uptake efficiencies were 94.21-111.12, 71.25-88.44 and 76.10-86.62% for TC, OTC and CTC, respectively, with the TCs concentration of 0.05-10 mg/L. The adsorption kinetics of TCs could be described with a pseudo-second-order model (POSM, R2 >0.97). According to the result of adsorption kinetics, the adsorption rate of TCs in the binding gel was not as fast as that of heavy metals, suggesting that the TCs concentrations at the boundary of binding gels in the o-DGT devices could not decrease to zero. After correction of the boundary concentration, the FDCs accounted for 30.30-56.90, 48.10-64.68 and 16.55-50.16% for TC, OTC and CTC, respectively, while their concentrations ranged from 0.2 to 10.0 mg/L. Our results suggested that SPE packing might be an ideal adsorption material for o-DGT binding gels, and that adsorption kinetics should be corrected when calculating the FDCs of organic pollutants.

Superficially capped amino metal-organic framework for efficient solid-phase microextraction of perfluorinated alkyl substances

Perfluorinated alkyl substances (PFASs) were ubiquitously in the surface and groundwater. It is crucial and urgent to develop a rapid and ultrasensitive analysis method for the quantification of trace-level PFASs. Herein, a highly hydrophobic sorbent by capping phenylsilane groups on the surfaces of NH₂-UiO-66(Zr) nanocrystals was used for efficient solid-phase microextraction (SPME) of PFASs in water samples. It was found that the superficially capped nanocrystals (NH₂-UiO-66(Zr)-hp) exhibited both faster extraction kinetics and higher enrichment capacity than the non-capped nanocrystals. The extraction of eleven kinds of PFASs by NH₂-UiO-66(Zr)-hp fiber reached equilibrium in 20 min. The enrichment factors of the NH₂-UiO-66(Zr)-hp fiber ranged from 6.5 to 48, with a preference for long-chain PFASs over short-chain PFASs. It was proposed that superficial capping eliminated competitive moisture adsorption on the surfaces of the non-capped nanocrystals, thus facilitating the adsorption of PFASs through hydrophobic interaction. By using this new sorbent, the limits of detection of the SPME method as low as 0.035 to 0.616 ng·L^-1 were achieved for the target PFASs. The recoveries of PFASs in the environmental water samples were 80.9%-120%. This study presents a new strategy for developing an efficient sorbent for PFASs by surface hydrophobic modification.

Use of glioma to assess the distribution patterns of perfluoroalkyl and polyfluoroalkyl substances in human brain

Human brain has a complex structure and is able to perform powerful functions. Blood-brain barrier blocks the entry of foreign substances and maintains the homeostasis of the brain. However, some exogenous substances are still able to pass through the blood-brain barrier, with distribution patterns yet to be clarified. Perfluoroalkyl and polyfluoroalkyl substances (PFASs), including perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs), a precursor (perfluorooctane sulfonamide that can be degraded to other substances), and emerging PFASs, were analyzed for the first time in living human brain glioma. The target compounds were detected and quantified in 25 out of 26 glioma samples. The concentration range of ∑PFAS was < RL-51 ng g^-1 wet weight (applied to all reported concentrations), with a median of 2.9 ng g^-1. The most abundant compound was PFCAs (40%), followed by PFSAs (28%), emerging PFASs (22%), and perfluorooctane sulfonamide (10%). Abundant alternatives PFASs, including short-chain PFCAs, short-chain PFSAs, and emerging PFASs (52% of ∑PFAS), were found in the glioma samples, supporting the notion that low molecular weight exogenous compounds have high permeability to cross the blood-brain barrier and accumulate in brain tissue. Gender difference was not significant (p > 0.05) in the concentrations of PFASs in the glioma samples. Concentrations of PFASs increased with increasing age, from 0.61 ng g^-1 (0-14 years old) to 1.6 ng g^-1 (>48 years old), with no significant linear correlation with age. The present study suggested that glioma is an effective indicator for monitoring exogenous contaminants in brain tissues.

Effects of biofouling on the uptake of perfluorinated alkyl acids by organic-diffusive gradients in thin films passive samplers

While organic-diffusive gradients in thin films (o-DGT) passive samplers have been used to assess organic contaminants in water, the effects of biofouling on accurate analyte quantification by o-DGT are poorly understood. We evaluated the effects of biofouling on the uptake of six common perfluoroalkyl substances (PFAS) using a previously developed polyacrylamide-WAX (weak anion exchange) o-DGT without a filter membrane. Linear uptake (R² > 0.91) over 21 days was observed in fouled samplers. The measured sampling rates (R_s) and accumulated masses of PFAS in pre-fouled o-DGT were significantly lower (p < 0.05, 20-39% relative error) than in control-fouled samplers. However, compared to clean o-DGT (no biofouling), the R_s of most PFAS in control-fouled samplers (i.e., those with clean diffusive and binding gels initially) were not affected by biofouling. Under flowing (∼5.8 cm s^-1) and static conditions, the measured diffusive boundary layer (DBL) thicknesses for clean o-DGT were 0.016 and 0.082 cm, respectively, whereas the effective in situ biofilm thicknesses for fouled o-DGT were 0.018 and 0.14 cm, respectively. These results suggest that biofilm growth does not have significant effects on target PFAS sampling by o-DGT under typical flowing conditions (≥2 cm s^-1). However, rapid surface growth of biofilm on o-DGT deployed in quiescent waters over long periods of time may exacerbate the adverse effects of biofilms, necessitating the estimation of biofilm thickness in situ. This study provides new insights for evaluating the capability of o-DGT samplers when biofilm growth can be significant.

A critical review of diffusive gradients in thin films technique for measuring organic pollutants: Potential limitations, application to solid phases, and combination with bioassays

Diffusive gradient in thin films (DGT) for organics has received considerable attention for studying the chemical dynamics of various organic pollutants in the environment. This review investigates current limitations of DGT for organics and identifies several research gaps for future studies. The application of a protective outer filter membrane has been recommended for most DGT applications, however, important questions regarding longer lag times due to significant interaction or adsorption of specific groups of compounds on the outer membrane remain. A modified DGT configuration has been developed that uses the diffusive gel as the outer membrane without the use of an extra filter membrane, however use of this configuration, while largely successful, remains limited. Biofouling has been a concern when using DGT for metals; however, effect on the performance of DGT for organics needs to be systemically studied. Storage stability of compounds on intact DGT samplers has been assessed in select studies and that data is synthesized here. DGT has been used to describe the kinetic desorption of antibiotics from soils and biosolids based on the soil/biosolid physical-chemical characteristics, yet applications remain limited and requires further research before wide-scale adoption is recommended. Finally, DGT for organics has been rarely, albeit successfully, combined with bioassays as well as in vivo bioaccumulation studies in zebrafish. Studies using DGT combined with bioassays to predict the adverse effects of environmental mixtures on aquatic or terrestrial biota are discussed here and should be considered for future research.

Development and evaluation of a ceramic diffusive layer based DGT technique for measuring organic micropollutants in seawaters

Diffusive gradients in thin-films (DGT) technique has been well demonstrated as a robust tool for measuring organic micropollutants (OMPs) in the aquatic environment. However, potential adsorption of the OMPs on organic polymer filters and flow rate of waters can affect the measuring results of the DGT method, hence tedious work should be conducted to reduce these interferences. In the present study, a novel DGT technique coupled with a ceramic diffusive layer was developed to measure the OMPs in seawaters. The ceramic diffusive layer exhibited adsorption inertness to the OMPs with various logK_ow values. Moreover, the ceramic diffusive layer based DGT technique was proved to be less affected by the flow rate than the traditional DGT with agarose diffusive layer. The developed DGT device exhibited kinetic accumulation for the targets during a 6-d deployment, and measurement of the OMPs by the DGT method was independent with pH and ionic strength. Finally, the developed DGT sampler was applied in coastal waters of Dalian, and eight OMPs were detected with levels ranging from 1.58 to 13.1 ng/L. The development of the ceramic diffusive membrane can lead to simplification of the DGT applications, promoting the progress of the OMPs monitoring technology.

Development and Applications of Novel DGT Passive Samplers for Measuring 12 Per- and Polyfluoroalkyl Substances in Natural Waters and Wastewaters

Extensive and long-term use of per- and polyfluoroalkyl substances (PFASs) has caused their widespread distribution in aquatic systems. A new diffusive gradients in thin-films (DGT) passive sampling method based on weak anion exchanger (WAX) binding layer is developed here for monitoring five perfluoroalkyl carboxylic acids (PFCAs), five perfluoroalkanesulfonic acids (PFSAs) and two PFASs (6:2 FTSA and GenX) in waters. Performance of WAX-DGTs was independent of environmental conditions, namely pH (3.03-8.96), ionic strength (1-500 mM), and DOM content (4-30 mg L^-1). Diffusion coefficients (D) of the 12 PFASs in the diffusive gels were measured, 9 for the first time. Linear correlations between D and perfluoroalkyl chain lengths (CF₂) were established to obtain D for congener chemicals with the similar functional group and structure. The binding capacity of the WAX-DGT sampler was at least 440 μg PFASs per sampler, sufficient for applications in waters across a wide range of conditions and PFASs concentrations. Successful applications of WAX based DGT samplers in a wastewater treatment plant (WWTP) and three rivers has demonstrated that DGT is a powerful tool for monitoring, surveillance and research of these 12 PFASs in aquatic systems, and can be extended to wider suites of PFs in future.