Estrogenic Activity Measurements in Water Using Diffusive Gradients in Thin-Film Coupled with an Estrogen Bioassay

Development of diffusive gradients in thin-films technique for monitoring polycyclic aromatic hydrocarbons in coastal waters

Addressing the challenge of accurately monitoring polycyclic aromatic hydrocarbons (PAHs) in aquatic systems, this study employed diffusive gradients in thin-films (DGT) technique to achieve methods detection limits as low as 0.02 ng L-1 to 0.05 ng L-1 through in situ preconcentration and determination of time-integrated concentrations. The efficacy of the developed DGT samplers was validated under diverse environmental conditions, demonstrating independence from factors such as pH (5.03-9.01), dissolved organic matter (0-20 mg L-1), and ionic strength (0.0001-0.6 M). Notably, the introduction of a novel theoretical approach to calculate diffusion coefficients based on solvent-accessible volume tailored for PAHs significantly enhanced the method's applicability, particularly for organic pollutants with low solubility. Field deployments in coastal zones validated the DGT method against traditional grab sampling, with findings advocating a 4 to 7-day optimal deployment duration for balancing sensitivity and mitigating lag time effects. These results provide a sophisticated, efficient solution to the persistent challenge of monitoring hydrophobic organic pollutants in aquatic environments, broadening the scope and applicability of DGT in environmental science and providing a robust tool for researchers.

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.

Adaptation of the o-DGT for the sampling of 12 hormones: calibration, performance evaluation, and recommendation

This work highlights the methodology for the development of diffusive gradients in thin films (o-DGT) through its adaptation for 12 natural and synthetic hormones belonging to three different families (estrogens, progestins, and androgens). A reliable strategy must be applied during o-DGT lab adaptation to avoid issues related to the analysis (i.e., presence of matrix effects in grab or passive samples) but also to the o-DGT configuration (i.e., undesirable sorption or desorption, lack of performance with insufficient elution or unreliable diffusion coefficient). To avoid analytical issues due to the presence of salts in grab samples, CaCl₂ exposure solutions must be used on a lab-scale development to monitor the hormone concentration. The selected o-DGT was composed of an Oasis® HLB binding gel and a diffusive gel in agarose because they provided better performance than polyacrylamide gels (i.e., higher elution factors and more repeatable diffusion coefficients). The elution factors of the binding gel were then from 0.79 ± 0.13 to 1.04 ± 0.13 (RSD < 15%) and the diffusion coefficients at 25 °C were from 4.07 ± 0.24 to 5.49 ± 0.28 × 10^-6 cm² s^-1 (RSD < 9%). A laboratory exposure to a synthetic solution was performed to check the consistency with the DGT quantification model validating the calibration parameters for all hormones (except 17α-ethinylestradiol with a bias of 40%). Therefore, the o-DGT configuration is suitable for sampling hormones in the natural environment with LOQ_DGT ranging from 0.3 to 6.6 ng L^-1.

Appraisal on the role of passive sampling for more integrative frameworks on the environmental risk assessment of contaminants

Over time multiple lines of research have been integrated as important components of evidence for assessing the ecological quality status of water bodies within the framework of Environmental Risk Assessment (ERA) approaches. One of the most used integrative approaches is the triad which combines, based on the weight-of-evidence, three lines of research, the chemical (to identify what is causing the effect), the ecological (to identify the effects at the ecosystem level) and the ecotoxicological (to ascertain the causes of ecological damage), with the agreement between the different lines of risk evidence increasing the confidence in the management decisions. Although the triad approach has proven greatly strategic in ERA processes, new assessment (and monitoring) integrative and effective tools are most welcome. In this regard, the present study is an appraisal on the boost that passive sampling, by allowing to increase information reliability, can give within each of the triad lines of evidence, for more integrative ERA frameworks. In parallel to this appraisal, examples of works that used passive samplers within the triad are presented providing support for the use of these devices in a complementary form to generate holistic information for ERA and ease the process of decision-making.

Development and applications of diffusive gradients in thin films for monitoring pharmaceuticals in surface waters

Pharmaceutical contaminants in surface water have raised significant concerns because of their potential ecological risks. In particular, coronavirus disease 2019 (COVID-19)-related pharmaceuticals can be released to surface water and reduce environmental water quality. Therefore, reliable and robust sampling tools are required for monitoring pharmaceuticals. In this study, passive sampling devices of diffusive gradients in thin films (DGTs) were developed for sampling 35 pharmaceuticals in surface waters. The results demonstrated that hydrophilic-lipophilic balance (HLB) was more suitable for DGT-based devices compared with XAD18 and XDA1 resins. For most pharmaceuticals, the performance of the HLB-DGT devices were independent of pH (5.0-9.0), ionic strength (0.001-0.5 M), and flow velocity (0-400 rpm). The HLB-DGT devices exhibited linear pharmaceutical accumulation for 7 days, and time-weighted average concentrations provided by the HLB-DGT were comparable to those measured by conventional grab sampling. Compared to previous studies, we extended DGT monitoring to include three antiviral drugs used for COVID-19 treatment, which may inspire further exploration on identifying the effects of COVID-19 on ecological and human health.

Validation and application of diffusive gradient in thin-film (DGT) equipped novel cyclodextrin polymer gels for monitoring endocrine disrupting chemicals (EDCs) and environmental risk assessment in the Taihu lake basin

Taihu Lake is the most important drinking water source of the major cities in the Yangtze River Delta. The pollution of endocrine disruptors (EDCs)in Taihu Lake has been increasing recently, the accurate determination is an important guide for predicting its health risks and developing appropriate controls. Monitoring organic pollutants in water using the diffusive gradient in thin film technique (DGT) has attracted much attention due to more accuracy and convenience than the grab sampling methods. In this study, a novel cyclodextrin polymer (CDP) synthesized by the simple and green method in water was taken as an adsorbent for the binding gel. Four endocrine-disrupting chemicals (EDCs), bisphenol A (BPA), 17α-ethinylestradiol (EE2), 17β-estradiol (E2), and estriol (E3), were taken as models to determine the diffusion coefficients (4.68 × 10^-6, 3.38 × 10^-6, 3.34 × 10^-6 and 4.31 × 10^-6 cm²/s) and to test the performance of DGT, such as adsorption capacity and deployment time (1-5 day). The assembled CDP-DGT was adopted to determine four EDCs in a simulated water environment (3-9 of pH, 0.001-0.5 M of ionic strength (IS), and dissolved organic matter (DOM) of 0-20 mg/L). The ability of CDP-DGT sampling was verified in the Jiuxiang River and was carried out for a large-scale field application of in situ sampling EDCs in Taihu Lake basin. The results show that the total EDCs concentration range and the estradiol equivalent concentrations (EEQ) in Taihu Lake and its main rivers are 2.78 ng/L to 11.08 ng/L and 2.62 ng/L to 10.91 ng/L, respectively. The risk quotients (RQs) of all sampling sites in the region were greater than 1, indicating that EDCs pose a serious threat to aquatic organisms in the area. Therefore, the monitoring of EDCs in the Taihu Lake basin should be further strengthened.

Novel hyphenation of DGT in-situ passive sampling with YES assay to ascertain the potency of emerging endocrine disruptors in water systems in New Zealand

This study represents the first attempt to investigate selected estrogenic compounds that include 17α-ethynylestradiol (EE2), 17β-estradiol (E2) bisphenol A (BPA), and bisphenol AF (BPAF) along the drinkable water, from river-to-tap, and wastewater, from effluent-to-treated wastewater, treatment processes of the Hamilton City Council and the monitoring of the freshwater, from source-to-outfall, of the Waikato River in New Zealand. This was accomplished by the adoption of a novel combination of diffusive gradients in thin films (DGTs) in-situ passive sampling coupled with high-performance liquid chromatography/mass spectrometry analysis (HPLC/MS) and the Yeast Estrogen Screen (YES). Estradiol equivalency quantities, integrated in time, were evaluated theoretically (cEEQ) by DGT-HPLC/MS and experimentally (EEQ) by DGT-YES assay. cEEQ and EEQ highlighted that primary treatments are not suitable for estrogens and bisphenolic plastics removal both at drinkable and wastewater treatment plants in Hamilton where they worsen the water quality in terms of estrogenicity making these pollutants more available in the water phase. All downstream sites monitored along the Waikato River showed higher cEEQ and EEQ, moreover the Waikato River water quality showed a moderate worsening moving from Taupo (source) to Tuakau (outfall). The most polluted sites were downstream of Hamilton city and Huntly township wastewater treatment plants that serve the main conurbations in the area. cEEQ and EEQ generally showed good agreement at low concentrations but differed substantially at more polluted sites where cEEQ consistently underestimated estrogenic potency, possibly due to DGT accumulation of estrogenic compounds not quantified by HPLC/MS.

Estrogenic activity and ecological risk of steroids, bisphenol A and phthalates after secondary and tertiary sewage treatment processes

Effluents of sewage treatment plants (STPs) are an important source of estrogenic substances to the receiving water bodies affecting their ecological safety. In this study, steroids, bisphenol A (BPA) and phthalates were assessed in the secondary (SE) and tertiary effluent (TE) of three typical urban STPs in Beijing (China). In addition, the overall estrogenic activity in these effluents was assessed by an in-vitro bioassay (ERE-CALUX). Results showed that the concentrations and activities of estrogenic compounds in TE were lower than those in SE. The residual concentration of 17β-estradiol (E2) was the highest among the detected steroids, accounting for 51.6 ± 5.1% in SE and 57.5 ± 24.8% in TE. The residual level (25.2-41.6 ng/L) of BPA in effluents was significantly higher than that of steroids (0.2-28.8 ng/L). The residual concentration of diethyl phthalate was the highest among the detected phthalates accounting for 47.1 ± 5.1% in SE and 37.6 ± 11.5% in TE. Steroids and BPA had a higher removal rate (83.5% and 96.7%) in secondary and tertiary treatment than phthalates (68.8% and 83.1%). The hydrophobic characteristics of these estrogenic compounds determined the removal mechanism. The removal of steroids, BPA, dimethyl phthalate and diethyl phthalate (LogKow= 1.61-4.15) mainly occurred through biodegradation in the water phase, while the removal of dibutyl phthalate, butylbenzyl phthalate and di(2-ethylhexyl) phthalate (LogKow= 4.27-7.50) mainly occurred in the solid phase after adsorption on and sedimentation of the suspended particulate matter. According to ERE-CALUX, the estrogenic activity in the final STP effluents was 3.2-45.6 ng E2-equivalents/L, which is higher than reported levels in the effluents of European STPs. Calculation of estrogenic equivalents by using substance specific chemical analysis indicated that the dominant contributor was E2 (56.4-88.4%), followed by 17α-ethinylestradiol (EE2) (4.1-34.8%), both also exerting a moderate risk to the aquatic ecosystem. While the upgrade of treatment processes in STPs has efficiently reduced the emission of estrogenic substances, their ecological risk was not yet phased out.

Determination of diffusion coefficients in agarose and polyacrylamide gels for 112 organic chemicals for passive sampling by organic Diffusive Gradients in Thin films (o-DGT)

The diffusive gradient in thin film technique was recently adapted to organic compounds. The diffusional coefficient (D) is a key parameter needed to calculate the time-weighted average concentration. In this study, two methods are used for D measurement in two gels (agarose and polyacrylamide): the diffusion cell method (D_cell) and the slice stacking method (D_stack). Thus, D were discussed and compared for 112 organic compounds, including pesticides, hormones, and pharmaceuticals. D_stack tends to be higher than D_cell. It could be explained by the presence of a non-negligible diffusive boundary layer thickness in diffusion cell. Consequently, the use of sampling rates (R_S) should be more adequate to determine water concentration, for a given bulk flow velocity. D_stack also corresponds to the diffusion in gel only, allowing the determination of the maximal R_S, and would be considered as a reference value that can be adjusted to in situ conditions, by applying the appropriate DBL thickness. The range and variability of D values found in the literature and obtained in this work were discussed. Relationships between D and compound physicochemical properties (molecular mass, log Dow, polar surface area, van der Waals volume) were investigated. We did not find clear and robust correlation between D and any single physicochemical property, for the set of compounds tested.

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 application of diffusive gradients in thin-films for in situ sampling of the bitterest chemical - denatonium benzoate in waters

Denatonium benzoate (DB), a commonly used bitter agent in numerous products, has recently been recognized as a waterborne contaminant due to concern about its potential persistence, mobility and toxicity (PMT). However, its occurrence, levels and fate in global aquatic environments are largely unknown. In this study, a new sampling method, based on diffusive gradients in thin films (DGT) with mixed-mode cation exchange (MCX) as the binding agent, was developed for measuring DB in waters. MCX shows a rapid adsorption and high capacity for DB. DB is linearly accumulated by MCX-DGT. pH (6-8), ionic strength (0.01-0.5 M), or DOM (0-10 M) do not show any significant effect on the MCX-DGT performance, confirming its reliability. The DGT measurements in a wastewater treatment plant (WWTP) are comparable to those by paralleled grab sampling. The field results suggest DB is persistent in WWTPs and could be a potential domestic wastewater indicator. Therefore, MCX-DGT is a promising technique for understanding the environmental occurrence, levels and fate of DB. This is a first report of using DGT for DB monitoring and of DB occurrence in Chinese environments. Further exploration of DGT as a reliable passive monitoring tool for a wide range of PMT substances in different applications is warranted.

Field evaluation of diffusive gradients in thin-film passive samplers for wastewater-based epidemiology

There is a need for a simple water sampling technique to enable routine monitoring of community drug consumption through wastewater-based epidemiology (WBE). This study investigates the potential use of diffusive gradients in thin films to sample organic compounds (o-DGT) for WBE. Three types of resin gels (HLB, XAD 18, and XDA-1) within o-DGT samplers each were deployed in triplicate at the inlets of two sewage treatment plants of Southern Asian cities. The target compounds included 15 illicit drugs and 18 antibiotics. A comprehensive evaluation was undertaken regarding each resin's ability to accumulate the target compounds and accuracy by comparing active samples. The organic compounds accumulated on each resin gel were characterised at the molecular level using Fourier transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The results showed that the HLB resin performed better than the XAD 18 and XDA-1 resins. Based on calculations using the HLB-DGT data, methamphetamine and heroin were the two most popular illicit drugs consumed among the studied populations, and were followed by ketamine and codeine, which agreed well with the authoritative reports and reference data. The total drug consumption in Hanoi was one order of magnitude higher than that in Guangzhou, thus implying a probably more serious drug situation in the former. Overall, the findings of this study demonstrate that o-DGT passive samplers are a promising tool for WBE studies, particularly at WWTPs or in urban streams where an automatic sampler for taking composite water samples is absent.

Using Estrogenic Activity and Nontargeted Chemical Analysis to Identify Contaminants in Sewage Sludge

Diverse organic compounds, many derived from consumer products, are found in sewage sludge worldwide. Understanding which of these poses the most significant environmental threat following land application can be investigated through a variety of predictive and cell-based toxicological techniques. Nontargeted analysis using high-resolution mass spectrometry with predictive estrogenic activity modeling was performed on sewage sludge samples from 12 wastewater treatment plants in California. Diisobutyl phthalate and dextrorphan were predicted to exhibit estrogenic activity and identified in >75% of sludge samples, signifying their universal presence and persistence. Additionally, the application of an estrogen-responsive cell bioassay revealed reductions in agonistic activity during mesophilic and thermophilic treatment but significant increases in antagonism during thermophilic treatment, which warrants further research. Ten nontarget features were identified (metoprolol, fenofibric acid, erythrohydrobupropion, oleic acid, mestranol, 4'-chlorobiphenyl-2,3-diol, medrysone, scillarenin, sudan I, and N,O-didesmethyltramadol) in treatment set samples and are considered to have influenced the in vitro estrogenic activity observed. The combination of predictive and in vitro estrogenicity with nontargeted analysis has led to confirmation of 12 estrogen-active contaminants in California sewage sludge and has highlighted the importance of evaluating both agonistic and antagonistic responses when evaluating the bioactivity of complex samples.

Cysteine-modified silica resin in DGT samplers for mercury and trace metals assessment

Diffusive gradients in thin-films (DGT) is an in situ passive sampling technique to assess labile trace metal concentrations in different environmental matrix. The technique is consisting of a diffusive domain backed up by a resin gel that binds free metals and metal complexes that dissociate in the diffusive domain. This technique requires specific resin for special metals, for example mercury (Hg), since the classic resin (Chelex-100) gel is not applicable for Hg measurement. A simultaneous determination of Hg with other metals by the DGT was not yet reported. Two biomolecule-based resins were prepared by glutaraldehyde immobilisation of cysteine onto 3-amino-functionalised silica and 3-aminopropyl-functionalised silica, respectively. The load of functional groups on modified resins was qualitatively and quantitatively characterised. The modified resins were applied in the DGT technique and the uptake efficiency, elution efficiency, and linear accumulation of analytes of the DGT were tested. This novel DGT technique, using two cysteine-modified resins, can accumulate Hg and other metals in a broad range of pH and ionic strength in solutions. In the Belgian coastal zone (BCZ), the concentrations of Hg and other trace metals sampled by cysteine-modified resin-DGTs were similar as those by the other two DGT assemblies for Hg and other trace metals, respectively. The cysteine-modified silica resin combined the features of Chelex-100 resin and 3-mercaptopropyl silica resin and allowed simultaneous determination of labile Hg and other trace metals. The resin with a higher load of functional groups also showed higher performance in the further application in the DGT technique.

Simultaneous determination of mercury, cadmium and lead in fish sauce using Diffusive Gradients in Thin-films technique

Fish sauce is a popular seasoning liquid originating from southeastern Asian cuisine, consisting of fermented fish, salt and additional ingredients. Fish can contain high amounts of metals, some of which are hazardous for human health. Therefore, authorities responsible for food safety and quality should monitor the levels of these contaminants in fish and fish deviated products. In this work, the passive sampling technique of Diffusive Gradients in Thin-films (DGT) containing Chelex-100 and Purolite S924 resin gels, is used for the determination of dissolved mercury (Hg), cadmium (Cd) and lead (Pb) in fish sauce. The DGT performance test showed linear accumulation of Hg, Cd and Pb on the binding gels versus deployment time. A wide range of pH and salt concentration did not affect the performance of the DGT. The effective diffusion coefficients of Hg, Cd and Pb in diffusive gels were determined by applying a series of deployments in fish sauce solution. Besides the direct sampling with the DGT technique, fish sauce samples were also digested using a microwave oven. Analyses of DGT and microwave oven digested samples were performed with Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS). Both methods were then used for the analysis of fish sauces from local retail stores. Due to the preconcentration ability of DGT, lower detection limits of Hg, Cd and Pb could be achieved compared to the microwave digestion method. The DGT technique offers a more sensitive method for trace element analysis in complex food matrices.

Performance of the organic-diffusive gradients in thin-films passive sampler for measurement of target and suspect wastewater contaminants

Although passive sampling is widely accepted as an excellent tool for environmental monitoring, their integration with suspect or non-targeted screening by high-resolution mass spectrometry has been limited. This study describes the application of the organic-diffusive gradients in thin-films (o-DGT) passive sampler as a tool for accurate measurement of both targeted and suspect polar organic contaminants (primarily pharmaceuticals) in wastewater. First, performance of o-DGT was assessed alongside the polar organic chemical integrative sampler (POCIS) and active sampling at two wastewater treatment facilities using targeted analyses. Overall, water concentrations measured by o-DGT, POCIS, and 24-hr integrative active samples were in good agreement with each other. There were exceptions, including a systematic difference between o-DGT and POCIS at certain sites that we propose was a result of site-specific conditions and a difference in sampling rates between the two techniques. The second component of this work involved suspect screening of the o-DGT extracts using high-resolution, high mass accuracy quadrupole time-of-flight mass spectrometry (QTOF). Lamotrigine, venlafaxine, and des-methylvenlafaxine were three suspect compounds identified and selected as proof-of-concept case studies to determine the feasibility and accuracy of o-DGT for estimating water concentrations based upon predicted sampling rates using a previously validated o-DGT diffusion model. Semi-quantification of the suspect compounds was conducting using an average surrogate response factor based on the suite of compounds measured by the targeted analyses. This, combined with the modelled sampling rates provided time-weighted average wastewater concentrations of the identified suspects within a factor of 2 of the true value, confirmed by isotope dilution with mass labelled internal surrogates. To the knowledge of the authors, this work is the first to demonstrate the utility of the o-DGT passive sampler as a potential environmental screening tool that can be integrated into the rapidly advancing field of non-targeted high resolution mass spectrometry.

Adaptation of diffusive gradients in thin films technique to sample organic pollutants in the environment: An overview of o-DGT passive samplers

The adaptation of the diffusive gradients in thin films technique (DGT) to sample organic pollutants in the environment, called o-DGT has been performed since 2011 for various types of organic compounds (e.g. pesticides, pharmaceuticals, hormones, endocrine disrupting chemicals, household and personal care products). To sample these different compounds, configuration of the samplers (mainly receiving phase and diffusive gel) has to be adapted. Up-to-date, sampling of 142 organic compounds by this passive sampler have been tested. This review provides the state-of-art of o-DGT passive sampler development, describing theory and modelling, calibration, configuration of the devices, and field applications. The most used configurations were agarose-XAD-18 and agarose-HLB configuration. o-DGT can be used to sample soils and most of natural waters (range of pH 4-9 and ionic strength 0.001-0.1 M). This review discusses current limitation of o-DGT in light of the feedback of DGT use to sample inorganic contaminants. It mainly concern the low sampling rates currently obtained by o-DGT compared to other passive samplers. This weakness could be compensated in the future with new sampler's design allowing an increase in exposure area.

Bioavailability and metabolism in a soil-crop system compared using DGT and conventional extraction techniques

Traditional extraction methods (soil solution and solvent extraction) are simple to use and conventionally employed to assess pesticide chemical form and bioavailability in soils. However, whilst convenient for regulatory testing, it has been suggested that these approaches may be too crude or are poor predictors of bioavailability, due to their arbitrary original development to detect 'total' concentration using exhaustive extraction. The diffusive gradients in thin films (DGT) technique has been widely used to measure chemical speciation in situ and shown to reliably predict bioavailability of a range of contaminants (e.g. heavy metals, radionuclides, nutrients) in soil systems, because it dynamically samples contaminants from/re-supplied to the soil solution phase. Experiments were therefore conducted with 5 soils of different properties to compare DGT and the two conventional extraction approaches for sampling atrazine (ATR) and its metabolites from soils and for predicting their uptake by maize tissues. After 23 days aging, a large proportion of total ATR was still available for solvent (acetonitrile) extraction and the major constituent in soils was parent ATR. The best correlations of total ATR concentrations in maize and total ATR measured in soil were with DGT and soil solution measurements. This is encouraging, in jointly supporting one of the established methodologies traditionally used in pesticide testing (i.e. soil solution) and a widely used method (i.e. DGT), which has been validated previously for a range of contaminants. The poorer performance of solvent extraction (a procedure widely used for pesticide testing) is perhaps to be expected, given that solvents will not truly mimic the conditions encountered in soil-plant systems.

Effect of corn straw biochar application to sediments on the adsorption of 17α-ethinyl estradiol and perfluorooctane sulfonate at sediment-water interface

The immobilization of organic contaminants in sediment-water systems is of growing concern. Using biochar as sorbent amendment to reduce the mobility of pollutants in the sediment-water interface is becoming increasingly popular as a low-cost and environmentally friendly option. In this study, we mixed sediment from the Weishan Lake with biochar (0%, 2%, and 5% (w/w)) derived from corn straw to investigate the adsorption of perfluorooctane sulfonate (PFOS) and 17α-ethinyl estradiol (EE2). Biochar addition significantly improved the adsorption rates and capacities of EE2 and PFOS on sediments by the factors 1.7-3.5; the organic carbon concentration in the sediment was the main factor influencing this process. The sorption of EE2 and PFOS to sediment was near-linear (Freundlich exponent 1/n of 0.799-0.805), but non-linear for biochar (0.430-0.476) and sediment+biochar (0.370-0.421). The mobility of PFOS in the water-sediment system after biochar addition was significantly reduced, with a considerable increase (about three times) in the sediment-water distribution coefficient K_d. Compared to EE2, PFOS is anionic compound and contains hydrophobic C-F chains and hydrophilic S-O groups, making it more susceptible pH influences and resulting in interactions with-OH, -C=O, Si-O-Si, -O-Si, and -Al-O-Al groups via hydrogen bonding, ligand exchange, and surface complexation. We suggest that biochar amendment at ～5% is a viable approach to immobilize EE2 and PFOS at the sediment-water interface.

In situ measurement of estrogenic activity in various aquatic systems using organic diffusive gradients in thin-film coupled with ERE-CALUX bioassay

Organic-diffusive gradients in thin-film samplers (o-DGT), were developed and applied for accumulation of estrogen and estrogen-like compounds on a XAD18 resin and deployed in situ in the effluents of Beijing Gaobeidian Wastewater Treatment Plant (GWWTP) and Brussels North Wastewater Treatment Plant as well as in several aquatic systems in Belgium, including the Zenne River, the Belgian Oostende Harbor and the North Sea. Estrogenic compounds accumulate on the XAD18 resin and the estrogenic activity of the resin extract was measured with the Estrogen Responsive Elements-Chemically Activated LUciferase gene eXpression (ERE-CALUX) bioassay. With this result and by applying Fick's diffusion law, it is possible to calculate the estrogenic activity in the aquatic system, if the diffusion boundary layer (DBL) is known or negligible compared to the hydrogel diffusive layer thickness. The DBL thickness in our study varied from 0.010 to 0.023 cm and ignoring the DBL thickness would for instance, underestimate the estrogenic activity by 10-20%. Estrogenic activities in the secondary effluent of GWWTP were the highest (29 ± 4 ng E2-equivalents L^-1), while the lowest level was found at the Belgian Oostende Harbor (0.05 ± 0.01 ng E2-equivalents L^-1). Comparable estrogenic activities in water samples measured by o-DGT and grab sampling were obtained, confirming that o-DGT can be efficiently used in various aquatic systems. The advantage of our sampling and measuring method is that very low, time averaged estrogenic activities can be determined, with a minimum of sample treatment. The risk of sample contamination is very low as well as the cost of the whole analytical procedure.

In situ measurements of micronutrient dynamics in open seawater show that complex dissociation rates may limit diatom growth

In this first in situ study of the dynamic availability of phytoplankton micronutrients, a SeaExplorer glider was combined with Diffusive Gradients in Thin Films and deployed in the Mediterranean Sea. On the basis of their labile metal complex pools, we discovered that Fe and Co can be potentially limiting and Cu co-limiting to diatom growth, contrary to the generally accepted view that phosphorus (phosphate) is the growth limiting element in the Mediterranean Sea. For flagellates and picoplankton, phosphorus remains the main element limiting growth. Our in situ measurements showed that organic complexes of Fe and Cu (>98% of total dissolved concentration), dissociate slower than inorganic complexes of Co, Cd and Ni (>99% of total dissolved concentration being free ions and inorganic complexes). This strengthens the potential growth limiting effect of Fe and Cu versus phosphate, which is present as a free ion and, thus, directly available for plankton.

Investigation and application of diffusive gradients in thin-films technique for measuring endocrine disrupting chemicals in seawaters

Endocrine disrupting chemicals (EDCs) can be released to coastal waters and affect the endocrine system of marine organisms. To monitor their levels in seawaters, a simple, robust passive sampling method, the diffusive gradients in thin-films (DGT) technique, was developed with XDA-1 resin as a binding agent. Six EDCs (including three estrogens, two pesticides and bisphenol A) were used to assess the performance of the DGT. The XDA-1 binding gel showed adequate ability for adsorbing EDCs in seawaters. The DGT sampler exhibited linear accumulation for the EDCs during a 15-day deployment and diffusion coefficients and sampling rates were calculated. The DGT measurement was independent of pH in the range 7.0-9.0 and ionic strength in the range 0.4-0.8 M. Field applications of this DGT in a coast of Dalian (China) showed comparable results to those from grab sampling. Five EDCs were detected with concentrations ranging from 0.7 to 19.4 ng L^-1. This study is a first attempt to apply DGT sampler for determining EDCs in seawaters.