Gradients In Thin Films Technique Research Articles

Use of diffusive gradients in thin-film technique to predict the mobility and transfer of nutrients and toxic elements from agricultural soil to crops-an overview of recent studies.

The purpose of this review was to survey the recent applications of the diffusive gradients in thin films (DGT) technique in the assessment of mobility and bioavailability of nutrients and potentially toxic elements (PTEs) in agricultural soil. Many studies compared the capabilities of the DGT technique with those of classical soil chemical extractants used in single or sequential procedures to predict nutrients and PTE bioavailability to crops. In most of the published works, the DGT technique was reported to be superior to the conventional chemical extraction and fractionation methods in obtaining significant correlations with the metals and metalloids accumulated in crops. In the domain of nutrient bioavailability assessment, DGT-based studies focused mainly on phosphorous and selenium labile fraction measurement, but potassium, manganese, and nitrogen were also studied using the DGT tool. Different DGT configurations are reported, using binding and diffusive layers specific for certain analytes (Hg, P, and Se) or gels with wider applicability, such as Chelex-based binding gels for metal cations and ferrihydrite-based hydrogels for oxyanions. Overall, the literature demonstrates that the DGT technique is relevant for the evaluation of metal and nutrient bioavailability to crops, due to its capacity to mimic the plant root uptake process, which justifies future improvement efforts.

A new simple index for characterizing the labile heavy metal concentration in soil by diffusive gradients in thin films technique

Diffusive gradients in thin films technique (DGT) is recognized as a more reliable method for determining labile heavy metal (HM) concentration in soil than traditional destructive methods. However, the current DGT measurement index, CDGT, theoretically underestimates the true labile concentration (Clabile) of HMs in soil and lacks direct comparability with the conventional soil HM content indices due to unit differences. Here, we proposed CDGT-W, a new simple index which is defined as the HM accumulation in the binding layer, normalized to the weight of soil (optimized water content = 100% of the maximum water holding capacity) filled in the open cavity-type DGT device over a specified deployment time (optimized time = 24 h). The procedure for measuring CDGT-W is analogous to that of CDGT but includes precise determination of water content (water/dry soil) and the mass of soil filled in the cavity. We conducted measurements of Cu, Pb, Cr(Ⅵ) and As(V) as CDGT-W, CDGT, solution concentration (Csoln), and CaCl2 extractable concentration (CCaCl2) on three soils with a diverse range of HM concentrations. CDGT-W showed significant linear correlations with all other tested indexes. The ratios of CDGT-W to CCaCl2 varied between 0.30 and 0.98 for all HM–soil combinations with only one exception, a range much greater than CDGT/Csoln (typically <0.1) but lower than 1. This suggested that CDGT-W may more accurately reflect Clabile than CDGT (theoretically underestimates Cliable) and CCaCl2(likely overestimates Cliable). Additionally, CDGT-W measurements for these four HMs exhibited a broad measure concentration range and a low detection limit (mg/kg level). Consequently, CDGT-W may offer a more reliable alternative to CDGT for characterizing Clabile in unsaturated soils.

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.

A recyclable SERS-DGT device for in-situ sensing of sulfamethazine by Au@g-C3N4NS in water

Although diffusion gradient in thin-film technique (DGT) has realized the in-situ sampling Sulfamethazine (SMT), the traditional DGT devices cannot be served as sensing devices but in-situ sampling devices. Here we report a recyclable surface enhanced Raman scattering (SERS) responsive DGT sensing device (recyclable SERS-DGT Sensing Device) capable of in-situ sensing of SMT in water. This is achieved by innovatively utilizing a recyclable SERS responsive liquid suspension of Au nanoparticles supported on g-C3N4 (Au@g-C3N4NS) as DGT binding phase. Au@g-C3N4NS is synthesized via in-situ growth method and embed in DGT binding phase, which exhibits good SERS activity, aqueous stability recyclable and adsorption performance. The SERS-DGT Sensing Device is valid for measuring SMT under a wide range of conditions (i.e., deployment time 24∼180 h, concentrations range of 1.031∼761.9 ng mL−1, pH 5∼9, ionic strength 0.0001∼0.05 mol L−1 NaCl, DOM concentrations 0∼100 mg L−1, four recycles). Furthermore, substrate combined with DGT binding phase, can integrate the sampling, pretreatment and SERS detection of SMT, which can be recycled, improving the reliability and efficiency of environmental monitoring. In this article, recyclable SERS-DGT Sensing Device, a platform for recyclable in-situ sensing of antibiotics, holds great potential for environmental monitoring.

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

Cadmium (Cd) contamination of selenium (Se)-rich soils may jeopardize the nutritional benefits of Se-biofortified crops. This study employed diffusive gradients in thin-films (DGT) technique and DIFS (DGT-induced fluxes in soils) model to understand the interdependency and driving factors of Se and Cd distribution and desorption kinetics across 50 soils from south China with naturally elevated levels. DGT-labile Se was the highest (up to 2.66 μg L−1) in non-carbonate/shale-derived soils, while Cd was maximal (5.53 μg L−1) in carbonate-based soils, reflecting soil background concentrations and soil characteristics. Over one-third of the soils showed labile Se:Cd molar ratio below 0.7, suggesting Cd phytotoxicity risks. The DIFS-derived response times (Tc) and desorption rate constants (k−1) suggested that Se was resupplied to the soil solution faster than Cd in soils with higher pH and SOM level, but Se resupply was still restricted due to the rapid depletion of its labile pool. As the first study of Se and Cd release kinetics in soils, our results reveal dependence on soil parent materials, with low labile Se:Cd soils presenting greater Cd hazards. By elucidating Se and Cd lability and interactions in soils, our findings help to inform management strategies to balance reduced Cd risk with adequate Se availability.

In Situ Evaluation of Cr(VI) Bioavailability and Rhizosphere Effects in Reduced Cr-Contaminated Soil Based on Diffusive Gradients in Thin Films Technique

The transformation between Cr(III) and Cr(VI) occurs in Cr-contaminated soil, which can be regulated by root-soil interactions, under natural conditions. In situ investigation of the effectiveness of different reductants in reducing Cr(VI) to Cr(III), and thereby the reoccurrence risk in reduced Cr-contaminated soil, can improve the understanding of Cr biogeochemistry and toxicity. Traditional and high-resolution diffusive gradients in thin films (DGT) were used to measure Cr(VI) availability and rhizosphere effect controlling the chemical behaviors of Cr(VI) in the rice rhizosphere microdomain. The Cr(VI) concentration in the soil solution (Csoln) of the rhizosphere region varied according to the reductant type and followed the order: Molasses > CaS4 >Fe(II). Rice root activity increased the Csoln in the rhizosphere region by 2.16 μg/L, 1.90 μg/L, and 1.08 μg/L for Fe(II), CaS4, and Molasses treatments, respectively. The Cr(VI) concentration measured by DGT (CDGT) in the reduced Cr-contaminated soils increased from 0.96–1.17 μg/L in the bulk region to 1.23–1.76 μg/L in rhizosphere region. The variation in the effective concentration of Cr(VI) (CE) was similar to that of Csoln in the rice rhizosphere microdomain. Csoln accounted for 14.71–19.36% of the CE, further suggesting that bioavailable Cr(VI) mainly originated from the replenishment from the solid phase. The sequence of the average Cr(VI) flux in the reduced Cr-contaminated soil was Molasses, CaS4, and Fe(II). Except for Molasses, there was no obvious Cr(III) in Fe(II) and CaS4. For Fe(II), a higher phosphate flux in the rhizosphere microdomain hindered Cr(VI) uptake. High-resolution imaging provides a theoretical basis for the bioavailability evaluation and remediation of Cr-contaminated soil. Compared with CaS4 and Molasses, Fe(II) was the most effective reductant for remediating Cr-contaminated soils.

Bio-accessibility and mobilization dynamics of soil vanadium during a 48-year vegetation restoration in a vanadium titano-magnetite tailings reservoir

Bio-accessibility of vanadium (V) in soils determines the effectiveness of vegetation restoration in the vanadium titano-magnetite tailings reservoirs because of persistent V toxicity, yet the variations in the bio-accessibility and mobilization of V in the soils with vegetation restoration remain elusive. Here, the bio-accessibility and mobilization of V in the soil-water interface were investigated along a 48-year vegetation restoration chronosequence in the Majiatian tailings reservoir using the diffusive gradients in thin films technique (DGT) and DGT-induced flux model. We found a low concentration of DGT-extracted V along the vegetation restoration chronosequence and the V fraction was dominated by the residual form, indicating a low V bio-accessibility in the soils. The bio-accessibility of V increased along the chronosequence because of the increased V resupply from solid phase, especially from the organic V fraction and the clay bound V. Low supply coefficient (R = 0.25) revealed a limited release of V from solid phase to soil solution. The kinetic resupply processes of V and its key regulating parameters were stage-specific during the vegetation restoration. The pool size of labile V in the soils determined the rapid V supply at the early and late stages, while the low desorption rate of V from the solid to liquid phase regulated the slow supply regime at the middle stage. The results of the present study highlight the importance of the long-term monitoring of soil V mobilization in the tailings reservoir because of the increased bio-accessibility and the dynamic supply of V during the vegetation restoration.

Evaluation of novel biomass-derived materials as binding layers for determining labile mercury in water by diffusive gradient in thin-films technique

In this work, several binding gels were successfully prepared in Diffusive Gradient in Thin-film (DGT) that targeted the inclusion of novel biomass-derived materials for the determination of the labile fraction of mercury (Hg) in water. First, five biomass-derived materials were tested and the descending order as a function of the average percentage of Hg removal in solution was feathers > biochar > cork > canola meal > rice husk. The best two materials were treated and pulverized into powder to be embedded in a hydrogel; and so, feathers were pyrolyzed preserving the sulfur contained in their keratin structure (FBC), and biochar (BC) was modified and pyrolyzed with sublimated sulfur (SBC) to increase the Hg sorption sites in its structure. Analysis by Energy Dispersive X-ray fluorescence (EDXRF) spectrometry confirmed that the different pyrolysis procedures increased sulfur absorption successfully. The efficiency of the new gels (BC, SBC and FBC) in agarose was evaluated by comparative Hg uptake tests, showing a larger efficacy in the following order: SBC > BC > FBC. To assess the suitability of their application in freshwater environments, novel DGT devices were also evaluated to determine their diffusion coefficients (D). This test was conducted under controlled laboratory conditions, with particular focus on the potential competence of trace elements (Mn, Cu, Zn, Ni, Pb, Cd and As), which are commonly present in natural waters affected by mining. A stronger linear relationship between the Hg uptake by binding layers and the deployment time were obtained for the DGT devices with SBC (R2 = 0.948) vs. BC (R2 = 0.885). Therefore, the D obtained for Hg were 8.94 × 10−6 cm2 s−1 for DGT-SBC and 5.12 × 10−6 cm2 s−1 for DGT-BC devices at 25 °C, both within the same order of magnitude reported by previous studies. The good performance obtained by DGT-SBC devices is a promising result and indicates the potential for valorization of waste materials in the DGT technique.

Application of two-dimension, high-resolution evidences to reveal the biogeochemical process patterns of trace metals in reservoir sediments

Pollutions of trace metals (TMs) in reservoirs are blooming due to TMs were trapped efficiently in reservoir sediments by dams. Despite the mobilization of TMs in sediments have been well-documented, the patterns of biogeochemical processes occurred in sediments remain poorly understanding. Herein, a deep reservoir was selected to investigate the patterns of TMs biogeochemical processes in sediments by using high-resolution ZrO-Chelex-AgI diffusive gradient in thin films technique (HR-ZCA DGT) and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). 2-dimension high-resolution (2D-HR) images showed significant differential spatial enrichment of TMs (V, Mn, Fe, Co, Zn and Sb) in sediments, indicating strong heterogeneity in sediments. Correlations of TMs within microniches (diameter < 1 mm) in horizontal were usually different even contrast with that in vertical profile, suggesting distinct biogeochemical process patterns occurred in vertical vs. in horizontal. Further analyses from 2D-HR images showed the distributions of TMs in microniches reflected their mobilization that was driven by microenvironmental conditions. In contrast, distributions in sediment vertical profile recorded the diagenesis in different deposition depth. The diagenesis in sediment vertical is continuously accumulated by the discrete, microniches mobilization of TMs in horizontal. Collectively, our findings evidenced that 2D-HR data is an update complement to 1-dimension data for better interpret the biogeochemical process patterns of TMs in sediments, that have implication for water management to metals pollution in reservoir ecosystems.

Aging rice straw reduces the bioavailability of mercury and methylmercury in paddy soil

Straw amendment is a prevalent agricultural practice worldwide, which can reduce air pollution and improve soil fertility. However, the impact of aging straw amendment on the bioavailability of mercury (Hg) and methylmercury (MeHg) in paddy soil remains unclear. To investigate this, incubation experiments were conducted using the diffusive gradient in thin-film technique. Results showed that amendments of dry-wet aging (DRS), photochemical aging (LRS), and freeze-thaw aging rice straw (FRS) reduced the bioavailable MeHg in paddy soil by 2.2–27.6%, 13.5–69.8%, and 23.5–86.1%, respectively, compared to fresh rice straw (RS) amendment. This result could be due to changes in soil properties such as soil pH and overlying water Fe and Mn as well as microbial abundance (including Clostridiaceae, Firmicutes, and Actinobacteriota). Simultaneously, The LRS and FRS amendments reduced bioavailable Hg in paddy soil by 20.0–40.8% and 17.1–48.6%, respectively, while DRS increased the bioavailable Hg by 15.8–120.0%. This could be attributed to changes in soil oxidation-reduction potential and overlying water SO42− content. Additionally, the results of sand culture experiments showed that the concentrations of Hg uptake by rice seedlings were 97.1–118.2%, 28.1–35.6%, and 198.0–217.1% higher in dissolved organic matter (DOM) derived from DRS, LRS, and FRS than RS, indicating that aging straw leached DOM may promote the Hg bioavailable when straw amendment. This result could be due to lower molecular weight and higher CO functional group content. These results provide new insight into how aging straw amendment affects the bioavailability of Hg and MeHg in paddy soil under different climates.

Development and evaluation of diffusive gradients in thin-films technique with a novel titanium peroxide binding gel for in situ measurement of Tl in natural waters and sediments

Speciation of thallium (Tl) controls its fate and biogeochemical behaviors. Thus, a sensitive and accurately approach for Tl monitoring is of great demand due to its ultra-low concentration and sensitivity to redox change. In this study, diffusive gradients in thin-films technique (DGT) assembled with novel titanium peroxide (TP) binding gels (TP-DGT) was developed for in situ measurement of dissolved Tl(I) and Tl(III) in waters and sediments. Laboratory test showed a linear mass accumulation of Tl(I) and Tl(III) on the TP binding gels with the deployment time from 4 to 72 h. A fascinating performance of this novel DGT was achieved in a pH range of 4–9, ionic strength range of 0.1–200 mmol L−1, and humic acid concentration of 0–30 mg L−1 with a low detection limit of 0.3 ng L−1 for Tl(I) and 0.6 ng L−1 for Tl(III). The TP binding gels own excellent stability (1–365 d) and high capacity (73.5 μg Tl disc−1) which are suitable for long-term monitoring. Field application in a river indicated that TP-DGT could work effectively, comparable to the grab sampling in waters. For the first time, the TP-DGT coupled with oxygen optode was successfully applied to map 2D distribution patterns of Tl and oxygen simultaneously in the rhizosphere of M. verticillatum L. This study confirms TP-DGT is a promising tool for routine monitoring of Tl in waters and for investigating biogeochemical processes of Tl in sediments.

Hydrogeochemistry of groundwater surrounding a pyrite mine in southern China: Assessment of the diffusive gradients in thin films technique for in situ monitoring

Acid mine drainage (AMD) resulting from pyrite mining causes hydrogeochemical evolution of groundwater and, in particular, the consequent release of potentially toxic elements (PTEs), posing health risks to populations dependent on groundwater. In this study, hydrogeochemical characteristics and evolutionary mechanisms were systematically illustrated via multivariate statistical methods and hydrogeochemical methods based on groundwater samples (n = 40) collected in a pyrite mining area in southern China. The diffusive gradients in thin films (DGT) technique was applied to evaluate the accuracy of metal content detection in groundwater at low concentrations. Based on principal component analysis (PCA), the groundwater dataset was classified into four types: brackish water dominated by sulfate, brackish water dominated by Ca-HCO3, low-mineralized water with the presence of PTEs, and freshwater in its natural state. The main controlling factors of hydrogeochemistry are evaporative crystallization and water–rock interactions. Fe, Mn, Pb, and Cd were detected in groundwater in the study area at levels exceeding World Health Organization (WHO) parameter values, and the highly toxic trace metal Tl was detected at levels up to 20 μg/L. The assessment of the applicability of the DGT technique to groundwater systems showed that reliable DGT detection results could be obtained under neutral or alkaline conditions at low Mn and Cd levels. This study highlights the evolution of the groundwater hydrogeochemistry under the combined influences of human activities such as mining and remediation management. In particular, the release of PTEs can affect human health, while the adoption of in situ DGT technology can provide strong support for studying these issues.

High-resolution imaging of O2 dynamics and metal solubilization in the rhizosphere of the hyperaccumulator Leersia hexandra Swartz

The mobilization of trace metals in the rhizosphere can be affected by the redox potential, which is closely related to the O2 dynamics. This study examined the distributions of O2 and trace metals in the rhizosphere of the subaquatic hyperaccumulator Leersia hexandra Swartz under chromium (Cr) stress using planar optodes and the diffusive gradients in thin films technique coupled with laser ablation inductively coupled plasma mass spectrometry. The O2 concentrations and oxidized areas in the rhizosphere significantly increased with increases in the light intensity, air humidity, and atmospheric CO2 concentrations (p < 0.05). The O2 concentration first increased with increasing ambient temperatures, then decreased when the temperature increased from 25 to 32 ℃. The O2 concentration in the rhizosphere was significantly decreased under Cr stress (p < 0.05), with a prolonged response time to the altered ambient temperature. Cr stress led to decreased mobilities of As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sb, V, W, and Zn in the rhizosphere, which were negatively correlated with the concentrations of O2. These results provide new insights into the role of changes in the O2 concentration induced by the roots of hyperaccumulator plants in controlling the mobility of trace metals in soils.

Calibration comparison between two passive samplers -o-DGT and POCIS- for 109 hydrophilic emerging and priority organic compounds

The Polar Organic Chemical Integrative Samplers (POCIS) is the most widely used passive sampler for hydrophilic compounds, but unsuitable for certain ionic organic contaminants. The Diffusive Gradient in Thin-Film technique (o-DGT) has shown positive results for both ionic and hydrophilic compounds. However, a calibration step is now needed to evaluate kinetic constant of accumulation for a wide range of molecules.In this study, o-DGT and POCIS were compared for the sampling of three families of micropollutants of potential risk to aquatic environments: 53 pesticides, 36 pharmaceuticals and 20 hormones. A calibration experiment was conducted to compare the kinetic models and constants from a scientific and practical perspective. The results are discussed in a single table that summarizes the performance of both passive samplers for the 109 compounds of interest. The advantage of o-DGT is that it allows linear accumulation for 72 compounds versus only 33 with POCIS. The mean times to equilibrium obtained with o-DGT are higher than those obtained with POCIS. These results confirm that the presence of a diffusion gel delays the achievement of equilibrium during compound accumulation. Therefore, o-DGT can be considered for situations where POCIS cannot be used due to non-linear accumulation over a typical 14-day deployment period. However, overall sampling rates and mass transfer coefficients also appear reduced with o-DGT, which is explained by the smaller exchange surface area, as well as the consideration of an additional diffusive layer in this device. This paper also showed that the most appropriate membrane to sample polar compounds with o-DGT was a polyethersulfone polymer with a pore size of 5 μm.

Short-term arsenic mobilization, labilization, and microbiological aspects after gasoline and diesel addition in tropical soils.

The effect of the presence of gasoline and diesel on the speciation and mobility of inorganic arsenic species in tropical topsoils was investigated. Topsoil samples (n = 25) were contaminated with gasoline and diesel (500mgkg-1) in laboratory and were incubated under unsaturated conditions and regular aeration for 21days. Speciation analysis and chemical fractionation were performed in the pore water from control, gasoline, and diesel-contaminated soil samples. Arsenic concentrations were compared to microbiological parameters (microbial metabolic quotient and soil basal breathing) and the presence of ArsM-harboring bacteria. The spike of gasoline and diesel to the topsoils increased pore water As3+ (H3AsO3) concentration. Arsenic mobilization was lower compared to previously reported data for other sources of organic matter (biochar, litter, and a mixture of sphagnum peat moss and composted poultry manure). However, gasoline or diesel addition mobilized As fractions that were adsorbed to the solid phase, in approximately 60% of the soils. Methylation presented an important role in the As3+ regulation in control soils, which was no longer observed after gasoline or diesel addition. The quantification of the labile fractions sampled by the diffusive gradients in thin films technique showed that the increased As concentration in the gasoline or diesel-contaminated soils mostly included inert species. Dissolved organic carbon content seems to be an important control mechanism of the labile As concentration. The increase in As mobility seems to pose a more concerning scenario due to As leaching than to plant uptake.

Benzoylthiourea based polymers as new binding agents for diffusive gradients in thin films technique in labile mercury determination in freshwaters

In this study, the diffusive gradient in thin film (DGT) has been developed using three new materials derived from benzoylthiourea (PBTU, BTP1 and BTP2) for the determination of bioavailable mercury (Hg). The efficiency of these DGT devices was compared with the well-established 3-mercaptopropyl functionalized silica gel (3MFS) in laboratory and field conditions. It was found that PBTU lacked of consistency for handling and assembling in the DGT device, whereas the other two polymers provided mechanically stable binding gels and extracted satisfactorily Hg. However, BTP2 showed no correlation between Hg uptake and Hg present in the aqueous solution, and therefore, BTP1 gels was chosen as the binding layer used for DGT technique. The calculated diffusion coefficient of DGT-BTP1 was 4.0 × 10 −6 cm 2 s −1 at 25 °C in 0.8 mm thick diffusion layer and 2.3% w/v of material in gel, whereas for DGT-3MFS, the D value was 9.1 × 10 −6 cm 2 s −1 . Moreover, it was found that neither the pH (range 4.5 – 9.5) nor the ionic strength (range 0.005–0.1 mol L −1 ) significantly affected the binding behavior of Hg (p > 0.05). Finally, the DGT-BTP1 devices were successfully used for in-situ measurements of Hg in Quito River (Colombia), impacted by artisanal gold mining, and were compared with DGT-3MFS. Results showed a good performance with values of the labile Hg concentration between 5 to 8% of the total Hg in water. This study demonstrates that benzoylthiourea based DGT is a useful tool for in situ monitoring of Hg in freshwaters. • Three new materials derived from benzoylthiourea were used for DGT technique. • BTP1 extracted satisfactorily Hg, with a diffusion coefficient of 4.0 × 10 −6 cm 2 s −1 . • DGT-BTP1 was suitable for aqueous solutions with a wide pH and ionic strength range. • These devices were successfully used in a Colombian river highly impacted by Hg. • Benzoylthiourea based DGT was a useful tool for in situ monitoring of Hg in freshwaters.

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 (CDGT/Csoln 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 Kow 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.

Simultaneous measurement of multiple labile heavy metals in soils by diffusive gradients in thin film technique

Simultaneous measurement of multiple labile heavy metals in soils by diffusive gradients in thin film technique

Prediction model for Cd accumulation of rice (Oryza sativa L.) based on extractable Cd in soils and prediction for high Cd-risk regions of southern Zhejiang Province, China.

Soil environmental quality in China for agricultural land always considers the effect of total cadmium (Cd) in soil, ignoring the bioavailability of soil Cd. The 139 paired rice (Oryza sativa L.) and soil samples were collected from the Cd-contaminated paddy fields of southern Zhejiang Province, China. The objectives of this study were to establish accurate prediction models for Cd accumulation in brown rice based on bioavailable Cd and physiochemical properties of soils and to evaluate the safety of rice production in Cd-contaminated paddy. The bioavailable Cd in soils was extracted and evaluated by using CaCl2, HNO3, diethylenetriamine pentaacetic acid (DTPA), diffusive gradients in thin-films technique (DGT), and sequential extraction method proposed by the European Community Bureau of Reference; 100 pairs of data were used as training sets, and the remaining 39 sets were used as validation sets. Stepwise multiple linear regression analysis and random forest analysis showed that total Cd in soil could roughly indicate the content of Cd in rice, while extractable Cd could better explain the accumulation of Cd in rice grain and DTPA and DGT extractive technologies are the most evaluative. The validation sets also showed that the prediction model has a good fit. Based on the prediction model for Cd in brown rice based on soil pH and DGT extractive Cd, the Monte Carlo simulation showed that 74.32% and 89.35% of the estimated brown rice hazard quotient (HQ) of the daily Cd intake of adults and children in safe utilization paddy sites could exceed the safe level of 1, respectively. Additionally, the threshold values for extractable Cd by DGT or DTPA for rice safe production were 3.4μg/kg or 0.13mg/kg when the pH in soils was below 5.5. The results further proved the threshold concentration of extractable Cd for predicting high-risk soils of Cd contamination in brown rice.

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.