DGT Technique Research Articles

Development of the Diffusive Gradient in Thin Film (DGT) Method with CaO/Biochar Binding Agent from Eggshells and Rice Straw Waste for Determining the Concentration of Phosphate

Phosphorus, often found in the form of phosphate in the environment, especially aquatic environments, has been identified as the primary contaminant that causes algae blooms and eutrophication. Phosphate adsorption in the aquatic environment was carried out by comparing the adsorption capabilities of eggshell (CaO), rice straw (BC) and CaO/biochar materials at mass variations of 1:1, 1:2 and 2:1 from the use of eggshell and rice straw waste. Each material was synthesized using ball milling and pyrolysis methods. The adsorption isotherm and kinetics of the material are by the Langmuir adsorption isotherm and are pseudo-second-order (PSO) adsorption kinetics. The CaO/biochar 1:2 material shows the highest phosphate adsorption capacity at pH 12 with a contact time of 24 hours. CaO/biochar 1:2 was applied in the phosphate adsorption process using the Diffusive Gradient in Thin Film method as a binding agent, which acts as an adsorbent. The DGT technique is an in situ sample preparation technique for identifying the presence of phosphate, a labile species. The binding agent material was characterized using FTIR, XRD, and BJH-BET instruments. The success of synthesizing CaO/biochar 1:2 binding gel and ferrihydrite was demonstrated by the appearance of the same adsorption as the diffusive gel using FTIR. The CaO/biochar binding gel demonstrated that it is a better material compared to the ferrihydrite binding gel for phosphate adsorption, achieving CDGT values of 10.1727 mg/L and 2.5959 mg/L at pH 5 and 3, respectively, with a phosphate concentration of 10 mg/L. These findings underscore the potential of CaO/biochar as a more effective material for phosphate removal applications.

Bioassessment of Cd and Pb at Multiple Growth Stages of Wheat Grown in Texturally Different Soils Using Diffusive Gradients in Thin Films and Traditional Extractants: A Comparative Study.

The bioavailability of heavy metals in soil is a crucial factor in determining their potential uptake by plants and their subsequent entry into the food chain. Various methods, including traditional chemical extractants and the diffusive gradients in thin films (DGT) technique, are employed to assess this bioavailability. The bioavailability of heavy metals, particularly cadmium (Cd) and lead (Pb), is also influenced by soil texture and their concentrations in the soil solution. The primary objectives of this experiment were to compare and correlate the assessment of the Cd and Pb bioavailability using the DGT technique and traditional extractants across two soil textural classes: sandy clay loam (SCL) and clay loam (CL) at two contamination levels: aged contaminated (NC) and artificially contaminated (AC). The specific objectives included assessing the bioavailability of Cd and Pb at different growth stages of the wheat plant and correlating the DGT-based bioassessments of Cd and Pb with their concentrations in various plant parts at different growth stages. This study also compared the effectiveness of the DGT method and traditional extraction techniques in assessing the bioavailable fractions of Cd and Pb in soil. The regression analysis demonstrated strong positive correlations between the DGT method and various extraction methods. The results showed that the wheat plants grown in the AC soils exhibited lower root, shoot, and grain weights compared to those grown in the NC soils, indicating that metal contamination negatively impacts plant performance. The concentrations of Cd and Pb in the wheat tissues varied across different growth stages, with the highest levels observed during the grain filling (S3) and maturity (S4) stages. It is concluded that the in situ assessment of Cd and Pb though DGT was strongly and positively correlated with the Cd and Pb concentration in wheat plant parts at the maturity stage. A correlation and regression analysis of the DGT assessment and traditional extractants showed that the DGT method provides a reliable tool for assessing the bioavailability of Cd and Pb in soils and helped in developing sustainable soil management strategies to ensure the safety of agricultural products for human consumption.

Application of biochar prepared from wheat bran as the binding phase in diffusive gradient in thin films technique for determination of mercury in natural waters

A novel binding gel for the DGT technique, containing biochar produced through the pyrolysis of wheat bran, was developed. The results of this study indicate that wheat bran biochar (WBBC) is a porous material with a surface area of 25 m2/g. The primary functional group on the surface of WBBC was identified as a carbonyl group, although some hydroxyl and imino groups were also detected. Furthermore, the findings demonstrate that the accumulation of Hg on WBBC was significantly influenced by an increase in ionic strength, particularly in NaCl solution, owing to Hg’s high affinity for chloride ions. The performance of the DGT with WBBC binding gel was also affected by solution pH, with the optimal pH for WBBC application falling within the range of 3–7. The diffusion coefficient of Hg, depending on the matrix environment, varied between 5.44 and 6.99 × 10−6 cm2/s. When applying the newly designed DGT technique to spiked samples of river water, an R value of 0.68 was achieved. The results of this work proved that modified DGT technique allows for a cost-effective analysis of Hg in natural waters with lower salinity, while retaining the fundamental properties of the binding gel incorporating a particulate adsorbent with anchored functional groups.Graphical

In situ Measurement of Phosphate using Fe3O4/Chelex®100-Agarose-Oxalic Acid Hydrogel in Diffusive Gradient in Thin Films

ABSTRACT. This study would be the first to develop a novel combination of Chelex®100 and Fe3O4 as a mixed binding gel for in situ phosphate measurement employing Diffusive Gradient in Thin Films (DGT). Fe3O4 and Chelex®100 were utilized as binding agents within a single binding layer for phosphate measurements in laboratory and natural water settings. The synthesized Fe3O4 was identified as magnetite and consisted of micro-sized particles. The pore size of the mixed binding gel ranged from 22.39 to 112.5 µm. Incorporating Chelex®100 with Fe3O4 in oxalic acid cross-linked agarose did not diminish phosphate adsorption efficiency. As adsorption time and phosphate concentration in solution increased, the quantity of adsorbed phosphate in the mixed binding gel also increased. Optimal phosphate elution was achieved using a basic solution, with a phosphate elution efficiency of 95.3 ± 0.4% observed with 0.4 M NaOH. The diffusion coefficient measured using the mixed binding gel was 1.08 times greater than that of polyacrylamide cross-linked with an agarose derivative (APA) gel, typically employed in the DGT technique. Phosphate concentration measurement with Fe3O4/Chelex®100-agarose oxalic acid in a DGT passive sampler at pH 4-8 yielded values twice those in bulk solution. Similar results were obtained when measuring phosphate in a 0.01 – 0.1 M NaNO3 solution. A T-test showed that the phosphate concentration obtained from mixed binding layer-DGT as an alternate passive sampler was not significantly different from grab sampling. This study underscores the suitability of Fe3O4-Chelex®100 impregnated in agarose-oxalic acid gel for monitoring phosphate in natural water via DGT. Keywords: Agarose, diffusive gradient in thin films, mixed binding gel Fe3O4, oxalic acid.

Trace elements fractionation in anaerobic digestates: Recommendation for using diffusive gradients in thin films passive samplers

This study proposes an evaluation of the Diffusive Gradients in Thin films (DGT) technique to assess the labile fraction of trace metals and metalloids in anaerobic digestates. Experiments were performed in presence and absence of air to determine whether maintaining anaerobic conditions is mandatory during DGT deployments. A theoretically expected linear accumulation profile was observed for Fe, Mn, Ni, Mo, and As(III) in a manure-derived digestate and for Mn in distillery waste-derived digestate, whereas Al and Cu were detected without a consistent trend over time. The DGT technique can thus be used to evaluate the labile fraction of some trace elements in these digestates. The labile fraction of some elements was shown to evolve over 72 h when deployments were performed in the presence of air. We thus strongly recommend to systematically perform time-series deployments to identify and consider only the elements with a linear accumulation trend and to maintain anaerobic conditions.

Nutrients and Rare Earth Elements in Surface Sediments of Hongze Lake (China) Using the DGT Technique: Spatial Distribution Pattern and Probabilistic Risk

Nutrients and Rare Earth Elements in Surface Sediments of Hongze Lake (China) Using the DGT Technique: Spatial Distribution Pattern and Probabilistic Risk

The alternation of flood and ebb tide induced arsenic release and migration from coastal tidal flat sediments in Yellow Sea wetlands: An ex-situ study

Periodic floods and ebb tides driven by seawater affect arsenic (As) behavior in coastal wetlands, which is not fully understood. In this study, we combined DGT, high-throughput sequencing, and real-time quantitative polymerase chain reaction (qPCR) techniques for the first time to investigate the effects of flood and ebb tide on As transformation and mobility in a typical coastal tidal flat wetland by laboratory experiments. In the flood-tide stage, more As was released into the water solution, and As(III) concentration in water solution was notably higher (51 μg/L) than in the ebb-tide stage, especially in SA (sodium acetate addition) treatment. As-methylation also occurred in this stage. The release of As was attributed to the reductive dissolution of amorphous and crystalline Fe oxides bound As induced by microbes. Fusibacter, Sva1033, Bradyrhizobium, Ralstonia, and Desulfobacter were primarily involved in the reduction of As, Fe, and S. The copy numbers of arsC were 20–148 times higher than arrA, suggesting that the detoxification reduction pathway was the primary mechanism of direct As-reduction in the flood-tide stage. However, 2-D high-resolution DGT techniques revealed that the concentrations of As(III) and total As in pore water of sediments in the ebb-tide stage were higher than those in the flood-tide stage. The detected aioA gene indicated that As was oxidized in the sediment surface, resulting in As stabilization by crystalline iron minerals, whereas more As(III) were accumulated in pore water. The reduction pathway mediated by arrA may play a prominent role in the ebb-tide stage. This study provides new insights into As release processes in coastal wetlands in seawater environments, which further deepens our understanding of As biogeochemical cycling behavior in different natural environments.

Development and Field Application of a Diffusive Gradients in Thin-Films Passive Sampler for Monitoring Three Polycyclic Aromatic Hydrocarbon Derivatives and One Polycyclic Aromatic Hydrocarbon in Waters

Polycyclic aromatic hydrocarbon (PAH) derivatives are widely present in the environment, and some are more hazardous than their parent PAHs. However, compared to PAHs, PAH derivatives are less studied due to challenges in monitoring as a result of their low concentrations in environmental matrixes. Here, we developed a new passive sampler based on diffusive gradients in thin films (DGT) to monitor PAH derivatives and PAHs in waters. In the laboratory study, the XAD18-DGT device exhibited high adsorption rates and was demonstrated to be suitable for deployment in environmental waters on the timescale of months. The diffusion coefficients, D, were 5.30 × 10−6 cm2 s−1, 4.51 × 10−6 cm2 s−1, 4.03 × 10−6 cm2 s−1 and 3.34 × 10−6 cm2 s−1 for 9-fluorenone (9-FL), 1-chloroanthraquinone (1-CLAQ), 9-nitroanthracene (9-NA) and phenanthrene (Phe), respectively, at 25 °C. The DGT device’s performance was independent of pH, ionic strength, deployment time and storage time, indicating it can be widely used in natural waters. In the field study, the target pollutant concentrations measured by the DGT are in good accordance with those determined via grab sampling. Then, the DGT devices were utilized to quantify PAH derivatives and PAHs in several rivers in Hefei, China. This work demonstrates the feasibility of using the DGT technique to detect trace PAH derivatives and PAHs in waters.

Development and validation of diffusive gradients in thin-films for in situ monitoring of ionic liquids in waters.

Due to their wide applications, occurrence and "PFAS-like" environmental behaviors, ionic liquids (ILs) represent a new challenge for the environmental monitoring community, who require robust analytical methods that can determine accurately and efficiently their environmentally relevant concentrations. A new passive sampling method based on the diffusive gradients in thin films (DGT) technique was developed for the measurement of imidazole-based ILs in waters using a mixed-mode cation exchange (MCX) resin as the adsorbent. The selected binding gel had a high binding capacity (>170 μg per disc) for ILs. Diffusion coefficients measured using a diffusion cell correlated well with alkyl chain lengths (r2 = 0.95) and retention times (r2 = 0.88), providing a simple and rapid prediction approach for other ILs. The assembled MCX-DGT sampler exhibited a linear accumulation for at least 120 h. MCX-DGT also showed good performance under typical freshwater conditions (pH 5-8, ionic strength 0.001-0.01 M, and humic acid 0-5 mg L-1), while still being problematic for aquatic conditions with higher ionic strength (>0.1 M) or DOM (>10 mg L-1). Laboratory deployment (for up to 3 days) in spiked natural freshwater (SNW) resulted in linear mass uptakes for the short-chain ILs (C2-C8), and their DGT-measured concentrations agreed well with solution concentrations. However, MCX-DGT significantly overestimated the concentrations of the long-chain ILs (C10-C12) when deployed in SNW for one day or more, which is attributed to the strong competitive adsorption of the long-chain ILs by natural organic matter. In situ field evaluation along with grab sampling found no target ILs in a wastewater treatment plant and its receiving river, implying that these new chemicals might not be widely used in South China now. This is the first report on the DGT technique for ILs and might provide an effective tool for monitoring short chain length ILs in the aquatic environment in the near future.

A critical review of the quantification, analysis and detection of radionuclides in the environment using diffusive gradients in thin films (DGT): advances and perspectives

Abstract This critical review explores the quantification, analysis, and detection of radionuclides in the environment using the diffusive gradients in thin films (DGT) technique. Radionuclides, unstable isotopes emitting ionising radiation, are present in the environment due to natural and anthropogenic sources for which concerns are raised about their impact on human health and ecosystems. DGT offers a unique passive sampling approach for understanding the behaviour of radionuclides and other trace elements. This review provides insights into method development, real case scenarios, advantages, limitations, and future perspectives of DGT in radionuclide analysis. In terms of method development, various isotopes have been analysed with varying significance based on origin, concentration, risks, and persistence. Notably, U, Th, Pu, Am, Cm, 99Tc, 226Ra, 137Cs, 134Cs, 232U, 237Np, and 152Eu have been measured, revealing their diverse roles in environmental radioactivity. Real case scenarios illustrate applications in uranium mining, water quality monitoring, and metal speciation studies, shedding light on mobility, bioavailability, and ecological impacts. DGT’s advantages include in-situ monitoring, time-averaged mean concentrations, and comprehensive speciation insights. Challenges include potential influences from biofouling, temperature changes and specifically the possible degradation of the binding and diffuse layer due to ionising radiation in long term exposures. In addition, the distinction between fully labile free metal ions and partially labile metal-ligand complexes introduces a potential limitation in the DGT technique, hence being an opportunity for future studies. Looking forward, DGT is expected to contribute to radiation dose modelling, environmental risk assessment, and water quality monitoring, with ongoing developments enhancing its utility and accuracy.

Impact of Eucalyptus residue leaching on iron distribution in reservoir sediments assessed by high-resolution DGT technique.

Blackwater occurs every winter in reservoirs with Eucalyptus plantations. The complexation reaction between ferric iron (Fe3+) and Eucalyptus leachate tannic acid from logging residues (especially leaves) is the vital cause of water blackness. However, the effect of Eucalyptus leaf leaching on the dynamic of iron in sediments and its contribution to reservoir blackwater remain unclear. In this study, two experiments were conducted to simulate the early decomposition processes of exotic Eucalyptus and native Pinus massoniana leaves in water (LW) and water-sediment (LWS) systems. In LW, high concentrations of tannic acid (>45.25 mg/L) rapidly leached from the Eucalyptus leaves to the water column, exceeding those of Pinus massoniana leaves (<1.80 mg/L). The chrominance increased from 5~10 to 80~140, and the water body finally appeared brown instead of black after the leaching of Eucalyptus leaves. The chrominance positively correlated with tannic acid concentrations (R=0.970, p<0.01), indicating that tannic acid was vital for the water column's brown color. Different in LWS, blackwater initially emerged near the sediment-water interface (SWI) and extended upward to the entire water column as Eucalyptus leaves leached. Dissolved oxygen (DO) and transmission values in the overlying water declined simultaneously (R>0.77, p<0.05) and were finally below 2.29 mg/L and 10%, respectively. During the leaching of Eucalyptus leaves, the DGT-labile Fe2+ in sediments migrated from deep to surface layers, and the diffusive fluxes of Fe2+ at the SWI increased from 12.42~19.93 to 18.98~26.28 mg/(m2·day), suggesting that sediment released abundant Fe3+ into the aerobic overlying water. Fe3+ was exposed to high concentrations of tannic acid at the SWI and immediately generated the black Fe-tannic acid complex. The results indicated that the supplement of dissolved Fe3+ from sediments is a critical factor for the periodic blackwater in the reservoirs with Eucalyptus plantations. Reducing the cultivation of Eucalyptus in the reservoir catchment is one of the effective ways to alleviate the reservoir blackwater.

Monitoring localized changes of Cr(VI) bioavailability related to root-induced changes around rice roots

Transformation between Cr(III) and Cr(VI) occurs in Cr-contaminated soils. Although redox conditions and biotic/microbial activity are known to be important factors in determining Cr transformation and accumulation in soil-rice systems, how spatial trends and specific soil processes regulate Cr behaviour around lowland/flooded rice roots are poorly understood. In this study, the Cr(VI) bioavailability was evaluated using the diffusive gradients in thin film (DGT) technology. Root activity reduced Cr(VI) bioavailability. The Cr(VI) flux near rice roots was 1.27–3.92 times lower than that in bulk soil (0.94 ng cm−2 h−1). The radial extension of the strong influence zone (R1) in the rhizosphere of C-LYZ was smaller than that in Hui-LY985. Although Fe(II) and S2− were involved in Cr(VI) reduction, they were not the primary influence, especially for the rhizosphere region. The high phosphate concentration in the C-LYZ rhizosphere hindered Cr(VI) uptake. The DGT technique overcomes the limitations of traditional research methods, revealing the spatial variability in Cr(VI) and its interactions with other elements in the rhizosphere, thereby providing theoretical basis for bioavailability evaluation and remediation of Cr-contaminated soils.

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 meandiffusion 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. TheoreticalRs 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.

Iron bound phosphorus predominates the contribution of phosphorus to lake system from terrigenous source: The evidence from the small watershed scale

The reduction of exogenous emissions of phosphorus (P) is a crucial measure for resolving eutrophication in lakes. However, the input of terrigenous materials still potentially contributes to an increase of P load in lake systems. In this study, we examined the phosphate oxygen isotope (δ18OP) of various P fractions in soils and sediments in a small lake watershed, namely, Shijiuhu watershed. The high-resolution in-situ diffusive gradients in thin films (DGT) technology was also used to survey the dynamic processes of P diffusion from sediment particles to the water. The results demonstrated that lighter δ18OP values (16.2–19.5‰) for individual P fractions in lake sediments were detected compared to other land-use patterns, indicating the cumulative biological P recycling on anaerobic condition. Fe bound P (Fe-P) overall had heavier δ18OP values (17.3–24.8‰) than some of Ca bound P (Ca-P) and equilibrium values, suggesting that Fe-P conserved the parental isotope signatures from terrigenous source and could act as the ideal tracer for the lake sediments. The mixing effect of terrigenous detrital input and biological mineralization made the source identification uncertain by using Ca-P, which had a wider range of δ18OP values (13.0–26.6‰). Additionally, significantly positive correlation (r = 0.551–0.913, p<0.05) between soluble reactive P (SRP) and Fe2+ in interstitial water obtained using DGT measurement revealed the conspicuous release and desorption of solid Fe-P toward the water. High diffusion fluxes from the sediments toward the overlying water further demonstrated that the desorption of Fe-P in the soil-originated sediments toward the solution conspicuously facilitated the accumulation of SRP in lake water. The first-time application of δ18OP isotope combined with in-situ DGT techniques certified that it's feasible for the contribution confirmation from terrigenous to lacustrine environments, and presented the direct evidence for management strategy making about P control and eutrophication restoration at the catchment scale of lakes.

Bioavailability Assessment of Heavy Metals and Organic Pollutants in Water and Soil Using DGT: A Review

In recent years, the diffusive gradients in the thin films (DGT) technique has also been increasingly applied to assess the bioavailability of heavy metals and organic pollutants in the soil. The combination of binding and diffusion phases made from different materials allows for the targeted determination of different target substances. This review briefly introduces the compositions and development of the DGT technique and analyzes the composition structure of DGT and the impact of environmental factors, such as pH, ion strength (IS), and dissolved organic matter (DOM), on the bioavailability evaluation of heavy metals and organic pollutants in soil. Finally, the application potential and broad application prospects of the DGT technique were expected. In addition, standardized DGT technique methods and calibration procedures are conducive to the establishment of a more stable and reliable measurement system to enhance the robustness of the DGT technique application in the soil.

Predicting the Kinetics of Resupply of Organic Pollutants from Sediments Using Diffusive Gradients in Thin Film Samplers and their Bioavailability to Aquatic Invertebrates.

The present study used diffusive gradients in thin film (DGT) samplers deployed in situ at a wastewater-impacted site (Clarkboro Ferry) for 20 days to develop a predictive model between time-weighted mean concentrations of seven selected antipsychotic compounds in water and those in resident benthic invertebrates, specifically crayfish (Faxonius virilis). The model was further combined with a model of desorption of antipsychotic compounds to predict kinetics at the sediment-water interface. Antipsychotic compounds were mostly detected in adult crayfish and internal concentrations were similar among targeted compounds, except for lesser concentrations of duloxetine. The model, based on the mass balance of organic chemicals, to predict uptake by organisms exhibited good agreement with measured values (R2 = 0.53-0.88), except for venlafaxine (R2 = 0.35). At the sediment-water interface, positive fluxes were observed for antipsychotic compounds and the results from DGT-induced fluxes in sediments (DIFS) coupled with equilibrium hydroxyl-β-cyclodextrin extraction further indicated partial resupply of antipsychotic compounds from sediments to the aqueous phase, despite the labile pool being relatively limited. The results of the present study affirm that DGT techniques can be used as a predictive tool for contamination in benthic invertebrates and can simulate the ability of contaminant resupply from sediments. Environ Toxicol Chem 2023;42:1696-1708. © 2023 SETAC.

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.

Ecotoxicological risk of antibiotics and their mixtures to aquatic biota with the DGT technique in sediments

Antibiotics are emerging contaminants and widely used in human healthcare, livestock, and aquaculture. The toxicity posed by antibiotics and their mixtures in sediments depends on their bioavailability. Now, the bioavailability of organic materials can be determined accurately by the diffusive gradients in thin films (DGT) technique. This technique was used for the first time ever in this study to evaluate in detail the integral toxicity of antibiotics in sediments to aquatic biota. Zhelin Bay was selected as a case study, because it is the largest mariculture area in eastern Guangdong, South China. Two antibiotics, chlortetracycline (CTC) (A) and sulfachlorpyridazine (SCP), were detected at average concentrations of 2.83 and 1.14 ng/ml, respectively. The other fifteen antibiotics were undetectable. The single risk assessment based on the risk quotient (RQ) of CTC and SCP shows that a relatively low risk has occurred. After this careful assessment of probabilistic ecotoxicological risks, the combined toxicity of antibiotic mixtures (CTC and SCP) clearly indicates that the toxicity probability of surface sediments to aquatic organisms was relatively low (0.23%).

Use of carminic acid immobilized in agarose gel as a binding phase for DGT: A new approach for determinations of rare earth elements

Recently, rare-earth elements (REEs) have attracted great interest due to their importance in several fields, such as the high-technology and medicine industries. Due to the recent intensification of the use of REEs in the world and the resulting potential impact on the environment, new analytical approaches for their determination, fractionation and speciation are needed. Diffusive gradients in thin films are a passive technique already used for sampling labile REEs, providing in situ analyte concentration, fractionation and, consequently, remarkable information on REE geochemistry. However, data based on DGT measurements until now have been based exclusively on the use of a single binding phase (Chelex-100, immobilized in APA gel). The present work proposes a new method for the determination of rare earth elements using an inductively coupled plasma‒mass spectrometry technique and a diffusive gradients in thin films (DGT) technique for application in aquatic environments. New binding gels were tested for DGT using carminic acid as the binding agent. It was concluded that acid dispersion directly in agarose gel presented the best performance, offering a simpler, faster, and greener method for measuring labile REEs compared to the existing DGT binding phase. Deployment curves obtained by immersion tests in the laboratory show that 13 REEs had linearity in their retention by the developed binding agent (retention x time), confirming the main premise of the DGT technique obeying the first Fick's diffusion law. For the first time, the diffusion coefficients were obtained in agarose gels (diffusion medium) and carminic acid immobilized in agarose as the binding phase for La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, which were 3.94 × 10−6, 3.87 × 10−6, 3.90 × 10−6, 3.79 × 10−6, 3.71 × 10−6, 4.13 × 10−6, 3.75 × 10−6, 3.94 × 10−6, 3.45 × 10−6, 3.97 × 10−6, 3.25 × 10−6, 4.06 × 10−6, and 3.50 × 10−6 cm2 s−1, respectively. Furthermore, the proposed DGT devices were tested in solutions with different pH values (3.5, 5.0, 6.5 and 8) and ionic strengths (I = 0.005 mol L−1, 0.01 mol L−1, 0.05 mol L−1 and 0.1 mol L−1 – NaNO3). The results of these studies showed an average variation in the analyte retention for all elements at a maximum of approximately 20% in the pH tests. This variation is considerably lower than those previously reported when using Chelex resin as a binding agent, particularly for lower pH values. For the ionic strength, the maximum average variation was approximately 20% for all elements (except for I = 0.005 mol L−1). These results indicate the possibility of a wide range of the proposed approach to be used for in situ deployment without the use of correction based on apparent diffusion coefficients (as required for using the conventional approach). In laboratory deployments using acid mine drainage water samples (treated and untreated), it was shown that the proposed approach presents excellent accuracy compared with data obtained from Chelex resin as a binding agent.

Probabilistic ecotoxicological risk assessment of heavy metal and rare earth element mixtures in aquatic biota using the DGT technique in coastal sediments

Heavy metals (HMs) are routine contaminants due to their extensive use worldwide. Rare earth elements (REEs) are emerging contaminants because of their global exploitation for use in the high-tech sector. Diffusive gradients in thin films (DGT) are an effective method for measuring the bioavailable component of pollutants. This study represents the first assessment of the mixture toxicity of HMs and REEs in aquatic biota using the DGT technique in sediments. Xincun Lagoon was chosen as the case study site because it has been contaminated by pollutants. Nonmetric multidimensional scaling (NMS) analysis reveals that a wide variety of pollutants (Cd, Pb, Ni, Cu, InHg, Co, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb) are primarily impacted by sediment characteristics. Appraisal of single HM-REE toxicity reveals that the risk quotient (RQ) values for Y, Yb and Ce notably exceeded 1, demonstrating that the adverse effects of these single HMs and REEs should not be ignored. The combined toxicity of HM-REE mixtures in terms of probabilistic ecological risk assessment shows that the Xincun surface sediments had a medium probability (31.29%) of toxic effects on aquatic biota.