Gradients In Thin Films Technique Research Articles

A bibliometric analysis and assessment of priorities for heavy metal bioavailability research and risk management in contaminated land.

Risk assessment has been recognized as an important tool for evaluating heavy metal pollution and providing risk-based information for decision makers. In order to accurately assess the risk of heavy metals in contaminated soil to human health, it is necessary to conduct bioavailability studies on heavy metals in soil. Bioavailability of heavy metals in soils and the implications for risk assessment and land management/remediation has evolved over the decades and now has considerable practical and economic implications internationally. This article aims to explore its evolution by undertaking a bibliometric analysis of the research fields which have addressed heavy metal bioavailability in soils, with a focus on the risk assessment of contaminated land and human exposure to soil-borne metals. Bibliometric analysis techniques are applied to monitor and assess the changing research literature on the bioavailability of heavy metals in contaminated soils. Over 5000 articles were found for the period 1979-2020. The purpose was not to perform an exhaustive literature review, but to draw out trends and patterns in the literature, and to make observations on past and current priorities. Key words were extracted from the analysis and the roles of different countries in driving the research literature identified. Three phases in literature/subject development were identified. Between 1979 and 2000 (initial phase, 213 articles), studies used extraction procedures and solubility studies to investigate the roles of soil properties on metal form/speciation and focused on bioavailability to (crop) plants in agricultural soils. Between 2001 and 2010 (slow development phase, 1105 articles), attention switched to metals introduced in soil amendments and wastes, metal impacts on soil microbial processes, and incorporating bioavailability in risk assessment. More rigorous techniques were being used, such as the diffusive gradients in thin films technique, to better understand kinetic and metal speciation in soils and the quantitative relationship to bioavailability. By 2011-2020 (rapid development phase, 3137 articles), research was being conducted in many countries (site specific, often industrially contaminated and urban sites), with a focus shift to health risk assessment, remediation, and bioavailability to various ecological receptors (e.g., humans and animals), with the development of many methods of bioavailability (e.g., simulated gastrointestinal tract enzymolysis methods). Some priorities for research on soil heavy metal bioavailability are identified.

Analysis of phosphorus and sulfur effect on soil selenium bioavailability based on diffusive gradients in thin films technique and sequential extraction.

Human intake of selenium (Se) mainly occurs through the food chain, and is largely dependent on the bioavailability of soil Se. Sulfur (S) and phosphorus (P) also as essential nutrients for plants, their antagonistic with Se effects on Se bioavailability should be considered. We conducted pot experiments to investigate the interaction effect on the bioavailability of Se in the soil using a sequential extraction method and diffusive gradients in thin films (DGT). The results showed that the root and shoot Se of pak choi increased at most 340%-360% with S and P application, while the Se uptake by pak choi was slightly inhibited when S and P application was 100mgkg-1. With high S and P application, pak choi Se had a high bioaccumulation factor (BAF) and low translocation factor (TF), and soil Soluble-Se (SOL-Se) increased 178%-299%, which due to the competitive adsorption of S, P with Se and changes in soil pH that lead to the transformation of soil Se fractions. In addition, the available Se concentration in soil measured by the DGT (CDGT-Se) increased by 866% with exogenous S and P application, and its source was HA-Se. However, CDGT-Se failed to show a good linear relationship with the Se content of pak choi. The application of DGT to assess the bioavailability of Se in soils where Se is present in the steady state needs to be further explored. We discuss the effect of S and P application on the bioavailability of soil Se and provide evidence for agricultural production and rational fertilizer use on Se-rich land.

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.

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.

Selective and simultaneous high resolution 2-D imaging of AsIII, CrIII and SbIII and dissolved oxygen by developing a new DGT technique comprising a hybrid sensor

A new diffusive gradients in thin films technique (HR-MPTS DGT) with mercapto-functionalized attapulgite in a binding gel was developed for simultaneous two-dimensional (2-D) chemical imaging of AsIII, CrIII and SbIII selectively at the submillimeter scale, combined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. The HR-MPTS DGT exhibited selective accumulation of AsIII, SbIII and CrIII (> 97%), yet negligible accumulation of AsV, SbV and CrVI (< 2%). Accumulation of AsIII, CrIII and SbIII on the binding gel had a linear relationship (R2 > 0.99) with the corresponding standardized laser ablation signals, proving the feasibility of LA-ICP-MS analysis. Analysis for AsIII, CrIII and SbIII was provided with favorable analytical precision (relative standard deviation <10%). With the purpose of evaluating the dynamics of AsIII, CrIII, SbIII and O2 in the rooting zone, a hybrid sensor, which comprises the HR-MPTS gel overlying an O2 planar optode, was deployed in rhizosphere sediments. Results showed that the consumption of both AsIII and SbIII due to the oxidation extended ~4.48 mm into the sediments, which was consistent with the extension length of the oxidized sediment layers around the roots created by O2 leakage.

Desorption kinetics of antipsychotic drugs from sandy sediments by diffusive gradients in thin-films technique

Dynamic processes of organic contaminants in sediments can have important toxicological implications in aquatic systems. The current study used diffusive gradients in thin-films (DGT) devices in sandy sediments spiked with nine antipsychotics and in field sandy sediments. Samplers were deployed for 1 to 30 days to determine the flux of these compounds to DGT devices and the exchange rates between the porewater and sediment solid phase. The results showed a continuous removal of antipsychotics to a binding gel and induced a mobile flux from the DGT device to the adjacent sediment solution. A dynamic model, DGT-induced fluxes in soils and sediments, was used to derive rate constants of resupply of antipsychotics from solid phase to aqueous phase (response time, Tc) and distribution coefficients for labile antipsychotics. The largest labile pool was found for lamotrigine and carbamazepine in spiked sediments. Carbamazepine, clozapine, citalopram, and lamotrigine were resupplied rapidly by sediments with Tc (25–30 min). Tc values of bupropion and amitriptyline were the longest (≈5 h), which exhibited slow desorption rates in sediments. In field sediments, high resupply was found for carbamazepine and lamotrigine, which did not show higher labile pool. The Tc values were obviously higher in the filed sediments (52–171 h). Although the adsorption process is dominant for most studied antipsychotics in both spiked sediments and field sediments, the kinetic resupply of antipsychotic compounds may not be accurately estimated by laboratory-controlled incubation experiments. More studies are needed to explore the mechanisms of desorption kinetics by using in situ DGT technique in the field.

Diffusive Gradients in Thin-films technique for uranium monitoring along a salinity gradient: A comparative study on the performance of Chelex-100, Dow-PIWBA, Diphonix, and Lewatit FO 36 resin gels in the Scheldt estuary.

Monitoring of uranium in the environment using the Diffusive Gradients in Thin-films (DGT) technique gains in importance as it can provide unique information about the bioavailability of the element and allows its long-term in-situ measurement. Hence, in this study, four DGT binding phases (Chelex-100, Dow-PIWBA, Diphonix, and Lewatit FO 36 resins) were evaluated for uranium monitoring to assess the robustness of their performance in estuarine and marine environments. These DGTs were deployed along the Scheldt estuary (Belgium and the Netherlands) over four campaigns between 2014 and 2021. The DGT performance (ratio of the DGT-determined vs. dissolved U concentration in grab water sample) varied with the water salinity. The Chelex-100 DGTs generally provided good performance in freshwater (median ratios close to 1.0), but an inverse correlation with the increasing salinity was observed (median ratios 0.7at the stations with salinity >5). The Lewatit FO 36 DGTs provided good performance in the salinity range 0-18 (median ratios 1.0). However, a strong negative influence was observed at stations with high salinity levels (>18, ratio 0.6) and during the long-term deployment in seawater (ratios <0.5 over deployment periods ≥2 days). The Dow-PIWBA and Diphonix DGTs provided overall similar results with excellent performances along the whole salinity gradient (median ratios 1.1 and 1.0, respectively). Nevertheless, the long-term deployment trial in seawater (salinity ∼27) revealed the robustness of Diphonix DGTs that provided outstanding results even after 28 days of deployment (ratio 1.0). The differences in the performance of tested DGT resins were mostly given by the changes of U speciation along the salinity gradient. The speciation modelling of U showed that calcium uranyl carbonate complexes dominate along the Scheldt estuary (from 97 to 86% seawards) with increasing fraction of UO2(CO3)34- (from 2 to 14%) towards the mouth.

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.

Evaluation of the Bioavailability of Metals in Sediment from the Southern Coastal Wetland of the Qiantang Estuary by Using Diffusive Gradients in Thin Films Technique

Evaluation of the Bioavailability of Metals in Sediment from the Southern Coastal Wetland of the Qiantang Estuary by Using Diffusive Gradients in Thin Films Technique

Simulated Bioavailability of Heavy Metals (Cd, Cr, Cu, Pb, Zn) in Contaminated Soil Amended with Natural Zeolite Using Diffusive Gradients in Thin-Films (DGT) Technique

The aim of this study was to investigate the effect of natural zeolite amendment to contaminated soil on the heavy metal (Cd, Cr, Cu, Pb and Zn) simulated bioavailability over a three-month period of storage. Two pot experiments were created by amending soil with two different amounts of natural zeolite (3 and 6 wt.%). During the experiment, pH level, metal concentrations in soil solution (Csol) and metal concentrations in soil by the diffusive gradients in thin-films technique (CDGT) were determined. When the zeolite was added to the soil, a significant decrease (p = 95%, n = 3) for Cd and Pb concentrations, both in Csol and in CDGT, was observed. The Cu, Cr and Zn concentrations also showed a decreasing trend, but the changes in their concentrations were not statistically significant. The R ratio between CDGT and Csol was calculated for each metal in order to assess the resupply of metals from the soil solid phase to soil solution. The R values significantly decreased for Cd and Pb, showing a low resupply from the solid phase in the samples with added zeolite.

Effective immobilization of arsenic in waters and sediments using novel zirconium-loaded lanthanum-modified bentonite capping

A novel zirconium–loaded clay material (abbreviated as Zr-LMB) was synthesized using lanthanum-modified bentonite (LMB) and zirconium oxychloride octahydrate (ZrOCl2·8 H2O) to immobilize arsenic (As) in waters and sediments. The optimal mass ratio of ZrOCl2·8 H2O to LMB was found to be 1:17. The adsorption capacities of As(III) and As(V) on Zr-LMB were 3.86 and 5.36 mg/g, respectively. Zr-LMB adsorption of As(III) and As(V) was unaffected by common pH, and the 30-d capping of Zr-LMB in sediments had almost no impact on pH in overlying waters. The 30-d capping of Zr-LMB largely weakened the concentration gradient of dissolved As and labile As measured by diffusive gradients in thin films technique (DGT, DGT-labile) for diffusion from the surface sediment to the overlying water. Additionally, dissolved As and DGT-labile As in three As-contaminated sediments (the added levels of As were 0, 10 and 20 mg/kg) obviously decreased, with maximum reduction efficiencies of 58.0%, 74.4% and 67.5% for dissolved As, and 34.7%, 78.3% and 56.2% for DGT-labile As, respectively. The effective depth of Zr-LMB capping on immobilizing dissolved As was up to 80 mm below the sediment–water interface. The results demonstrated that the novel Zr-LMB is a potential absorbent for As immobilization in waters and sediments.

Investigation of diffusion and binding properties of uranium in the diffusive gradients in thin-films technique

Environmental context Monitoring uranium concentrations and speciation in aquatic systems is important for pollution control and for environmental studies. Although an in situ speciation technique based on diffusion and uptake of uranium has been developed, known as DGT, there were uncertainties over some parameters affecting the accuracy of the measurements. This study resolved those uncertainties by investigating diffusion and binding properties of uranium in DGT and provided confidence in monitoring uranium in the environment. Rationale Diffusive gradients in thin-films (DGT) ha been used for uranium speciation measurements since 2006, but interpretational difficulties have arisen due to uncertainties in the pH dependence of U diffusion coefficients (D) within the diffusive gel. This work tested the hypothesis that differences in measured D values between laboratories are due to methodological artifacts. Methodology The properties of uranium binding and diffusion of U within DGT were systematically investigated at different conditions between pH 3–8 and ionic strength from 1 to 500 mmol L−1. Previous uncertainties were attributed to loss of U by adsorption within the diffusion cell, identified by mass balance calculations, and a binding efficiency dependent on the type of binding gel. Results The diffusion coefficient in an agarose cross-linked polyacrylamide gel measured using Metsorb DGT of 5.26 ± 0.17 × 10−6 cm2 s−1 agreed well with both values obtained using a pre-conditioned diffusion cell (&lt; 7% difference) and by modelling. The binding efficiencies for Chelex DGT (BChelex = 0.86–0.89) and Fe-oxide DGT (BFe-oxide = 0.64 were smaller than for Metsorb DGT (BMetsorb = 1). No significant differences were found for BChelex at different pH. Discussion This work demonstrated that the diffusion coefficient of uranium is independent of pH and the binding gel used, provided the binding efficiency (B) is taken into account. These findings indicate that DGT equipped with either Metsorb or Chelex binding gels should be capable of measuring U for a wide range of environmental conditions provided the appropriate diffusion coefficients and binding efficiencies are used.

The Use of Stable Zinc Isotope Soil Labeling to Assess the Contribution of Complex Organic Fertilizers to the Zinc Nutrition of Ryegrass.

Manure and sewage sludge are known to add significant amounts of zinc (Zn) and other metals to soils. However, there is a paucity of information on the fate of Zn that derives from complex organic fertilizers in soil–plant systems and the contribution of these fertilizers to the Zn nutrition of crops. To answer these questions, we grew Italian ryegrass in the presence of ZnSO4, sewage sludge, and cattle and poultry manure in an acidic soil from Heitenried, Switzerland, and an alkaline soil from Strickhof, Switzerland, where the isotopically exchangeable Zn had been labeled with 67Zn. This allowed us to calculate the fraction of Zn in the shoots that was derived from fertilizer, soil, and seed over 4 successive cuts. In addition, we measured the 67Zn:66Zn isotope ratio with the diffusive gradients in thin films technique (DGT) on soils labeled with 67Zn and incubated with the same fertilizers. After 48 days of growth, the largest fraction of Zn in the ryegrass shoots was derived from the soil (79–88%), followed by the Zn-containing fertilizer (11–20%); the least (<2.3%) came from the seed. Only a minor fraction of the Zn applied with the fertilizer was transferred to the shoots (4.7–12%), which indicates that most of the freshly added Zn remained in the soil after one crop cycle and may thereby contribute to a residual Zn pool in the soil. The 67Zn:66Zn isotope ratios in the DGT extracts and the shoots measured at cut 4 were identical, suggesting that the DGT and plant took up Zn from the same pool. The proportion of Zn derived from the fertilizers in the DGT extracts was also identical to that measured in ryegrass shoots at cut 4. In conclusion, this work shows that stable Zn isotope labeling of the soil available Zn can be used to precisely quantify the impact of complex organic fertilizers on the Zn nutrition of crops. It also demonstrates that DGT extractions on labeled soils could be used to estimate the contribution of Zn fertilizers to plant nutrition.

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 (Dcell) and the slice stacking method (Dstack). Thus, D were discussed and compared for 112 organic compounds, including pesticides, hormones, and pharmaceuticals. Dstack tends to be higher than Dcell. It could be explained by the presence of a non-negligible diffusive boundary layer thickness in diffusion cell. Consequently, the use of sampling rates (RS) should be more adequate to determine water concentration, for a given bulk flow velocity. Dstack also corresponds to the diffusion in gel only, allowing the determination of the maximal RS, 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.

In situ monitoring of phthalate esters (PAEs) pollution and environmental risk assessment in Poyang Lake Basin by DGT Technology using cyclodextrin polymer as binding phase

Poyang Lake is the first freshwater lake in China, which is an important drinking water source. In recent years, industrial pollution has led to the increased phthalate acid esters (PAEs) in Poyang Lake. PAEs are a class of typical endocrine disruptors that can accumulate in organisms and interfere with their secretion systems. Thus, the accurate determination of PAEs in Poyang Lake is important for health risk prediction and the development of corresponding control means. Monitoring organic pollutants in water using the diffusive gradient in thin films technique (DGT) has attracted much attention due to more accuracy and convenience than the traditional methods. This study used an inexpensive amphiphilic cyclodextrin polymer (PBCD) as the sorbent for the binding gel. This new binding gel has an ultra-high specific surface area and excellent adsorption performance. Diffusion coefficients of the five PAEs were determined, and the performance of DGT such as adsorption capacity and deployment time (1–4 days) was tested using five PAEs as models. The assembled PBCD-DGT was used to examine the performance in a complex simulated water environment. The sampling capability of PBCD-DGT was verified in Yangshan Lake, and a large-scale field application was conducted in Poyang Lake basin. The results of 11 sampling points showed that the concentration ranges of dimethyl phthalate, diethyl phthalate, diallyl phthalate, dipropyl phthalate, and dibutyl phthalate were 434–2594 ng/L, 40–314 ng/L, 80–527 ng/L, 45–308 ng/L, and ND-182 ng/L, respectively. The health risk index (HI) and ecological risk quotient (RQ) values of PAEs in the Poyang Lake watershed were far below 1, indictating a lower health and ecological risk. Considering that PAEs are bioaccumulative and persistent, it is very necessary to continue to pay attention to its pollution status and health and ecological risk changes in Poyang Lake Basin in the future.

Development and Applications of an In Situ Probe for Multi-Element High-Resolution Measurement at Soil/Sediment-Water Interface and Rice Rhizosphere

The biogeochemistry of multi-elements, such as sulfur (S), phosphorus (P) and arsenic (As), is interlinked especially at interfaces of soil/sediment–water and plant rhizosphere. To explore the biogeochemical behavior of multi-elements such as S-P-As at interfaces, an in situ and high-resolution technology is required. In this study, we developed an in situ probe (LDHs-DGT) based on the diffusive gradients in thin-films technique using a single binding layer to realize the co-measurement of multi-elements including sulfide and oxyanions. Mg-Al layered double hydroxides (LDHs) were synthesized and incorporated into the probe’s binding layer. Laboratorial characterization showed that the LDHs-DGT probe had a high capacity for sulfide, phosphate and arsenate and can effectively determine their levels across a wide range of solution conditions, i.e., pH from 5 to 8 and ionic strengths from 0.005–0.01 mol L−1 NaNO3. The application potential of the LDHS-DGT probe in capturing the concentration profiles of sulfide and oxyanions across the soil/sediment–water interface at a centimeter scale was demonstrated. The synchronous co-variations of labile sulfide and phosphate were observed along an intact river sediment core, demonstrating the redox driven behaviors of oxyanions at aerobic–anaerobic transition zones. Moreover, the LDHS-DGT probe was further used to acquire the dynamic distributions of multi-elements in the plant rhizosphere at a two-dimensional millimeter scale. Compared to treatments of sodium sulfate and mercaptopygorskite fertilization, the addition of elementary S promoted the reduction of sulfate to sulfide along the whole growth stage and thus inhibited the activation of toxic metals in the rice rhizosphere. Collectively, this study provides a tool for convenient measurement of nutrients and metal(loid)s across soil–water/root interfaces at high resolution and thus, a broad application prospect of the tool in sustainable agriculture is expected.

Predicting soil cadmium uptake by plants in a tailings reservoir during 48-year vegetation restoration

Plant uptake can reduce soil cadmium (Cd) pollution, while how to exactly predict plant Cd uptake in industrial or mining areas during vegetation restoration remains unexplored. Taking Heteropogon contortus as the object plant, we predicted plant Cd uptake in the Majiatian tailings reservoir during 48-year vegetation restoration by the methods of soil total Cd, DGT (diffusive gradients in thin films technique) and acetic acid (HAc) extraction. Meanwhile, we explored the effects of soil properties on the accuracy of the prediction. Total Cd concentrations in the soils exhibited a better prediction of plant Cd uptake relative to the methods of HAc extraction and DGT. However, the DGT method effectively predicted plant Cd uptake at low Cd supply (lower than 0.42 μg/L), probably because of the dominant diffusion limitation by plants. The prediction of plant Cd uptake by HAc extraction was improved when combined with soil pH. Our results indicate that with increasing external Cd inputs during the vegetation restoration, soil total Cd and traditional extraction method in combination with soil properties are effective ways to predict plant Cd uptake, especially when the Cd fractions cannot be measured by DGT. However, the DGT method works once plant Cd uptake dominated by diffusion limitation despite the interference in soil properties.

In situ application of the diffusive gradients in thin film technique in aquaculture ponds for monitoring antibiotics, hormones, and herbicides.

In recent years, as the abuse of antibiotics, hormones, and herbicides has worsened in aquaculture industry, it is important to monitor the concentrations of those trace contaminants in aquaculture water more effortlessly. The aim of this study was to develop a reliable sampling method for chemical monitoring in aquaculture ponds based on the technique of diffusive gradients in thin films (DGT). A binding material (XDA-1 resin) with high adsorption capacity for antibiotics, hormones, and herbicides was selected. In laboratory, the diffusion coefficients of 11 antibiotics, 3 hormones, and 3 herbicides of the XDA-1-DGT devices were tested and ranged from 1.0×10-6 to 8.7×10-5 cm2/s. During the in situ application of XDA-1-DGT devices in different aquaculture ponds, concentrations of 11 antibiotics, 3 hormones, and 3 herbicides in aquaculture water (CSOLN) via grab sampling were also analyzed and found ranging from 0.03 to 6.3 ng/L, lower than the results based on DGT (CDGT) (1.2-1.3×102 ng/L). The values of CDGT/CSOLN were larger than one unit, suggesting that the rates of resupply of target chemicals (antibiotics, hormones, and herbicides) by the desorption and diffusion of pond water were higher than the rates of uptake by XDA-1-DGT, and pond water was proved a sufficient reservoir of antibiotics for DGT application. The value of Log (CDGT/CSOLN) of 1.1 derived from the application in the aquaculture ponds of 14 regions in Eastern China can be a reference value for future chemical monitoring based on DGT technique. And the accuracy of this value was found hardly affected by the physical and chemical properties of chemicals with pKa ranging from -1 to 12, Log Kow ranging from 0 to 4.5, and Log solubility ranging from 0.0 to 4.0.

Inputs of Total and Labile Dissolved Metals from Six Facilities Continuously Discharging Treated Wastewaters to the Marine Environment of Gran Canaria Island (Canary Islands, Spain).

The presence of ten metals (Cd, Ni, Pb, Cr, Cu, Zn, Al, Fe, Mn, and Co) was investigated in the final discharge of six facilities, including four wastewater treatment plants, which were continuously discharging treated wastewater to the coastal environment in Gran Canaria Island. A four-day sampling campaign was carried out at each facility in July 2020, in which both the spot samplings technique and the diffusive gradient in thin-film technique (DGT) were carried out to measure total dissolved metals and the in situ labile metal fraction, respectively. After the necessary sample preparation steps, measurements were carried out by ICP-MS for both samplings. Raw data referred to the spot total dissolved and DGT-labile metal concentrations were reported. In general, the average metal concentrations were dispersed in a broad range. As expected, the highest metal contents were found in those facilities with larger industrial contributions. The values of annual average environmental quality standards (AA-EQS) were used to assess the total dissolved metal concentrations for every metal in every final discharge. In only one of the studied facilities, some metals (Ni and Zn) exceeded these EQS within the receiving waterbody, highlighting the need for more efficient treatment targeted towards a specific discharging-water quality. In addition, the total dissolved and labile metal daily fluxes of discharge were calculated to estimate the contribution of every effluent to the receiving water bodies.

Efficiency of a new allylagarose-assembled DGT in measuring Cd, Zn, and Pb bioavailability in sludge-treated soil

The purpose of this study was to assess and validate measures of cadmium (Cd), lead (Pb), and zinc (Zn) bioavailability in a contaminated calcareous soil treated with sewage sludge (0, 10, and 30 g kg −1 ) under peppermint ( Mentha pipertia L.) cultivation using new allylagarose-assembled diffusive gradients in thin-films technique (DGT). To achieve the best gel composition, various diffusive hydrogels were made from different amounts of acrylamide monomer (15, 20, and 25%) and allylagarose cross-linker (0.3, 0.4, and 0.6%). The DGT assembled with 15% acrylamide and 0.3% allylagarose was the best hydrogel based on the obtained swelling rate (3.2) and diffusion coefficients of Cd (5.81 ×10 cm 2 s −1 ), Pb (8.07 cm 2 s −1 ), and Zn (6.13 cm 2 s −1 ). Sewage sludge application increased resupply (R-value) and effective concentration (C E ) of Cd, Pb, and Zn. The highest amounts of C E -Zn (2202 μ g l −1 ), Cd (982.5 μ g l −1 ), and Pb (1847 μ g l −1 ) were observed in soil treated with 30 g kg −1 sewage sludge. Comparison of correlation revealed that 0.3% allylagarose-measured C E -Zn and Pb had a significant logarithmic correlation with the corresponding plant metals concentrations, while C E -Cd was linearly correlated with the plant Cd concentration. These results support the conclusion that the combination of 15% acrylamide and 0.3% allylagarose as a diffusive gel in DGT is a robust gel to predict metal bioavailability and can be reliably used to replace the patented gel cross-linked with agarose. • Increasing percentages of cross-linker led to a reduction in gel pore size. • The high swelling hydrogel facilitated the metals diffusion through the hydrogel. • Increasing sewage sludge level resulted in increasing the re-supply (R) of metals. • 15% acrylamide and 0.3% allylagarose gave the best estimate of bioavailability.