Use of the diffusive gradients in thin films technique to evaluate (bio)available trace metal concentrations in river water

Geochemical distribution and speciation of Tl and other trace metals in upper Beijiang River in South China: Approach of in-situ DGT monitoring

Mining activities frequently result in severe contamination of river water. This study aimed to better understand the spatial distribution characteristics of Tl and other metals (e.g., Al, Cd, Co, Mn, Ni, Zn, Pb, V, As, Mo, and Sb), and to assess their risks to human health. Surface water samples were collected from the upper Beijiang River (South China) via grab sampling and the diffusive gradients in thin-films (DGT) technique. The concentrations of Tl measured by grab sampling and δ-MnO₂-DGT ranged from 0.045 μg L^-1 to 0.231 μg L^-1 and from 0.056 μg L^-1 to 0.131 μg L^-1, respectively. Most of the metals monitored were below the threshold levels allowed by the drinking water standard in China, except for As, Sb, and Mn at specific sampling sites. The concentrations of other metals measured by grab sampling were higher than those measured using the DGT technique because of the differences in speciation during these measurements. The hazard quotient (5.43 × 10^-4-8.0 × 10^-1 for grab sampling and 2.23 × 10^-4-2.8 × 10^-1 for DGT technique) for the monitored trace metals demonstrated minimal health risk to human beings. The pollution status of these toxic metals in the study area was generally acceptable. As was found to be potentially the most harmful metal in the studied area, with hazard quotients at some sampling sites calculated by grab sampling of >1. It has previously been suggested that As is the most important non-carcinogenic contaminant. The combination of grab sampling and the DGT technique provides a comprehensive understanding of trace metals, especially Tl, in terms of potential bioavailability and ecological assessment.

Diffusive gradients in thin films (DGT): A suitable tool for metals/metalloids monitoring in continental waterbodies at the large network scale

The contribution of Diffusive Gradients in Thin films (DGT) passive sampling to continental water quality monitoring was assessed in a real measurement network (6 sampling campaigns, 17 stations). Ten metals/metalloids (Al, Zn, Ni, Cd, Cu, Pb, Cr, As, Se and Sb) were studied using the control laboratory's working conditions with grab and DGT passive sampling. The DGT field deployments were robust, with a 3% sampler loss rate and a <65% average relative deviation between duplicates. Compared to grab sampling, DGT showed a similar quantification frequency for half of the targeted elements but showed a higher frequency for the other half (e.g., Cd quantification at 20% with grab sampling vs. 97% with DGT). Similar concentration trends were established using DGT and grab sampling at most sites throughout the year. Notably, for some elements, trends were only provided by DGT sampling. A study of several DGT blanks showed that the device contamination was occasional and originated primarily from cross-contamination during the disassembly step. Considering this contamination, the operational sensitivity by DGT was at least between 1 and 5 times greater in comparison to that by grab sampling. Estimations of the economic cost revealed that measurement networks cost 2 to 3 times more when monitored by DGT compared to standard grab monitoring. However, the information obtained based on each type of sampling method is different. Grab sampling is easy to implement and can highlight high contamination peaks. The DGT concentrations are averaged over time and are relevant to chronic exposure evaluations. Considering the good performance of the DGT sampling highlighted in this study and its complementarity with grab sampling in terms of water quality assessments, a combination of these two types of sampling, which can be affordable, should improve the water quality evaluation within monitoring networks.

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

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

Limitations of Applying Diffusive Gradients in Thin Films to Predict Bioavailability of Metal Mixtures in Aquatic Systems with Unstable Water Chemistries

The present study accessed the use of diffusive gradients in thin film (DGT) as a surrogate for estimating the bioavailability and bioaccumulation of copper (Cu) and zinc (Zn) in a freshwater mussel. We coupled DGTs with mussels and deployed them in a constructed wetland. Water quality parameters were measured for a 4-d period on 3 continuous occasions during 12-d trials in the summer and winter; metal speciation was modeled for each occasion. Higher cumulative rainfall and water turbidity during the summer trial resulted in higher particulate metal concentrations compared to the winter trial. Mussel accumulated metals did not correlate with DGT-measured metals but positively correlated with particulate metals in the summer because filtering particulate food mainly contributed to the bioaccumulation. In contrast, the winter trial suggested a positive correlation between metal bioaccumulation and DGT-measured metals because uptake of dissolved organic matter (DOM) from water mainly contributed to the bioaccumulation, and the labile metal species complexed with DOM generally overlapped with DGT-targeted metals. Though Cu has a higher affinity for organic ligands than Zn, the interactions between Cu and Zn in the mixture did not impede their uptake and bioaccumulation. The deployment duration when DGTs and mussels are coupled to compare metal bioavailability should be no less than 12 d so that mussels have enough time to accumulate contaminants from the environmental media. In summary, DGT is a convenient surrogate for biomonitoring, but it may not fit the real environment such as the aquatic system with unstable water chemistries. Geochemical modeling is good at calculating metal speciation but inferior to DGT in predicting bioavailability and mimicking bioaccumulation. Environ Toxicol Chem 2020;39:2485-2495. © 2020 SETAC.

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

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

Trace metal mobility in sub-seabed sediments by CO2 seepage under high-pressure conditions

Carbon capture and storage (CCS) is the third contributor to cumulative carbon emission reductions required by the second half of this century. Although this is a promising technology for reducing atmospheric CO₂, it is only affordable if the confinement of the gas is guaranteed for hundreds of years. Hence, it is of paramount importance to figure out and predict the chemical and biological effects associated with potential CO₂ leakage, to provide decision makers with a good basis for choosing technology and potential storage sites. To this end, a titanium reactor (1.4 m³) was used to study CO₂ seepage under realistic sub-seabed conditions (30 bar pressure and 7 °C). The injection of CO₂ was calibrated to decrease the pH value from 8.1 to 7.3, which may be the pH found near a leakage point. This pH value also coincides with predictions for near-future ocean pH under current CO₂ emissions worldwide. The results from this study demonstrate that there are some elements, i.e., Fe, Co, Pb, Ce, Zn and Cu, present in deep marine sediments, that are strongly affected by the reduced pH levels related to CO₂ addition. The dissolved concentrations of Fe, Pb and, to a lesser extent, Cr increased, due probably to weakening of the Fe/Mn shuttle by increased dissolved concentrations of CO₂. Desorption processes from oxyhydroxide surfaces due to acidification may explain the release of Co, Ni and Ce observed during the experiment. The increased CO₂ concentration also led to increased metal bioavailability, suggested by higher values for labile metal species. Conversely, Cd mobility seems not to be affected by CO₂-associated acidification. It is concluded that the determination of those elements most affected by CO₂-related acidification in a sub-seabed CO₂ storage perimeter (i.e., sediment, sediment-water interface and water column) would be a simple and effective technique to verify suspected leakage.

Evaluation of the DGT technique for predicting uptake of metal mixtures by fathead minnow (Pimephales promelas) and yellow lampmussel (Lampsilis cariosa)

Diffusive gradients in thin films (DGT) were assessed for their predictive capability of fathead minnow and yellow lampmussel bioaccumulation in copper (Cu) and lead (Pb) mixed metal exposures. Nine treatments with a matrix of 3 Cu and 3 Pb concentrations were utilized. Exposures were coupled, with organisms and DGT exposed in tanks for 6 days. The Cu measured in fish, mussel, and DGT was found not to be influenced by Pb treatment, whereas Pb accumulation was impacted by the interaction of Cu and Pb treatment. The Pb accumulation increased with increasing Cu concentration, which was attributed to the different speciation of Cu and Pb in the water where Cu binds preferentially to ligands, decreasing its bioavailability and concomitantly displacing Pb from complexing sites. The DGT values were significantly correlated with accumulated Cu and Pb in the fish, but not with Pb in the mussel. In addition, DGT was determined to better predict aquatic organism bioaccumulation of Cu than the inorganic Cu fraction calculated by the speciation model, because DGT accumulated not only inorganic metal fractions but also complexes of metal and organic matter. The present study provides insights into metal speciation in polluted environments, extends the understanding of using DGT as a tool for estimating metal bioavailability, and provides implications for the selection of geochemical modeling, biological sampling, and passive sampling techniques for monitoring trace metal contamination. Environ Toxicol Chem 2019;38:61-70. © 2018 SETAC.

Evaluation of diffusive gradients in thin films for prediction of copper bioaccumulation by yellow lampmussel (Lampsilis cariosa) and fathead minnow (Pimephales promelas)

Using a coupled method of diffusive gradients in thin films (DGT) exposure with aquatic organism bioassays, we assessed the use of DGT as a tool for estimating copper (Cu) bioavailability in contaminated waters. The DGT-accumulated Cu fraction could possibly be used as a surrogate for other assessments of metal bioavailability. The Cu concentrations in fathead minnow (Pimephales promelas) and yellow lampmussel (Lampsilis cariosa) soft tissue were compared with DGT-accumulated Cu after 2, 4, and 6 d of exposure to a Cu concentration series in static, water-only assays. The DGT-accumulated Cu was found to include free Cu ions, labile inorganic Cu complexes, and labile dissolved organic matter Cu complexes, compared with Cu speciation output from the biotic ligand model. Regressions of Cu concentrations between DGT and fathead minnow at 4 and 6 d of exposure demonstrated linear relationships. The Cu bioaccumulated in yellow lampmussel was overpredicted by DGT at Cu concentrations greater than 10 µg L^-1 , which may be caused by internal regulation of Cu. The speciation component of the biotic ligand model predicted relationships between inorganic Cu and animal-accumulated Cu that were similar to predicted relationships between DGT-indicated Cu and animal-accumulated Cu at all deployment durations. Environ Toxicol Chem 2018;37:1535-1544. © 2018 SETAC.

Evaluating water quality and ecotoxicology assessment techniques using data from a lead and zinc effected upland limestone catchment

Point and diffuse sources associated with historical metal ore mining are major causes of metal pollution. The understanding of metal behaviour and fate has been improved by the integration of water chemistry, metal availability and toxicity. Efforts have been devoted to the development of efficient methods of assessing and managing the risk posed by metals to aquatic life and meeting national water quality standards. This study focuses on the evaluation of current water quality and ecotoxicology techniques for the metal assessment of an upland limestone catchment located within a historical metal (lead ore) mining area in northern England. Within this catchment, metal toxicity occurs at circumneutral pH (6.2-7.5). Environmental Quality Standards (EQSs) based on a simple single concentration approach like hardness based EQS (EQS-H) are more overprotective, and from sixteen sites monitored in this study more than twelve sites (>75%) failed the EQSs for Zn and Pb. By increasing the complexity of assessment tools (e.g. bioavailability-based (EQS-B) and WHAM-F_TOX), less conservative limits were provided, decreasing the number of sites with predicted ecological risk to seven (44%). Thus, this research supports the use of bioavailability-based approaches and their applicability for future metal risk assessments.

Prediction of the bioavailability of potentially toxic elements in freshwaters. Comparison between speciation models and passive samplers

The aim of this work is to predict the bioavailability of the Potentially Toxic Elements (PTEs) Cd, Pb, Hg, Ni, Cu, Zn, As, Cr and Se in 6 sites within the Ebro River basin. In situ Diffusive gradient in thin-films (DGTs) and classical sampling have been used and compared. The potentially bioavailable fractions of each PTE was estimated by modelling their chemical speciation using three programs (WHAM 7.0, Visual MINTEQ 3.1 and Bio-met), following the suggestions published in recent European regulations. Results of the equilibrium-based models WHAM 7.0 and Visual MINTEQ 3.1 indicate that As, Cd, Ni, Se and Zn, predominate as free metals ions or forming inorganic soluble complexes. Copper, Pb and Hg bioavailability is conditioned by their affinity to dissolved humic substances. According to Visual MINTEQ 3.1, Cr is subjected to redox reactions, being Cr (VI) present (at low concentrations) in the studied rivers. According to Bio-met model, the bioavailability of Cu and Zn is highly influenced by soluble organic matter and water hardness, respectively. For most PTEs, the bioavailability estimated by deploying DGTs in river waters tends to be slightly lower than the estimation obtained with speciation models, since in real conditions more environmental factors take place comparing to the finite number of parameters considered in models.

Evaluation of trace metals bioavailability in Japanese river waters using DGT and a chemical equilibrium model

To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water. In this study, we employed the diffusive gradients in thin-films (DGT) to determine the bioavailability of metals (Ni, Cu, Zn, and Pb) in Japanese water systems. The DGT results were compared with a chemical equilibrium model (WHAM 7.0) calculation to examine its robustness and utility to predict dynamic metal speciation. The DGT measurements showed that biologically available fractions of metals in the rivers impacted by mine drainage and metal industries were relatively high compared with those in urban rivers. Comparison between the DGT results and the model calculation indicated good agreement for Zn. The model calculation concentrations for Ni and Cu were higher than the DGT concentrations at most sites. As for Pb, the model calculation depended on whether the precipitated iron(III) hydroxide or precipitated aluminum(III) hydroxide was assumed to have an active surface. Our results suggest that the use of WHAM 7.0 combined with the DGT method can predict bioavailable concentrations of most metals (except for Pb) with reasonable accuracy.

DGT as surrogate of biomonitors for predicting the bioavailability of copper in freshwaters: an ex situ validation study

The present report is the companion study of our previous study in which we investigated the impact of the dissolved organic matter, water cationic composition and pH on the bioavailability and the bioaccumulation of copper (Cu) in aquatic mosses (Fontinalis antipyretica). The impact had been assessed under laboratory controlled conditions and modelled using a two-compartment model calibrated under a wide range of water compositions (Ferreira et al., 2008, 2009). Herein are reported the validation stage of the abovementioned approach for contrasted geochemical field conditions. Experiments were performed with aquatic mosses that were exposed for 7d to two nominal Cu concentrations (5 and 15μgL(-1)) in a flow-through field microcosm supplied with four contrasting natural waters. At the end of the exposure period, a 6-fold difference in the bioaccumulated Cu contamination levels was found among the four deployment sites, suggesting a significant control of the water quality on the metal bioaccumulation by aquatic mosses. In parallel, the so-called 'labile' Cu concentration for the same four field conditions was determined using a DGT device (Diffusive Gradient in Thin film). By coupling these DGT measurements and a cation competition model involving Ca(2+), Mg(2+), Na(+) and H(+), the time-dependent Cu concentrations in aquatic mosses were predicted; these simulation results were compared to the actual bioaccumulation of Cu in mosses. We found that any bioaccumulation model that ignores water characteristics is not suitable to predict the Cu accumulation by aquatic mosses under various water quality conditions. Instead, we found that our approach integrating DGT measurements and cationic composition was able to reproduce the Cu bioaccumulation kinetics by aquatic mosses for a wide range of water quality conditions. In conclusion, the DGT approach was demonstrated to be a dynamic in situ measuring technique that can be used as a surrogate of bioindicators if the cationic correction is taken into account.

Monitoring of (bio)available labile metal fraction in a drinking water treatment plant by diffusive gradients in thin films

A performance study of diffusive gradients in thin films (DGT) and inductively coupled plasma optical emission spectrometry (ICP-OES) was applied for the monitoring of the labile fraction of metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in Sant Joan Despí Drinking Water Treatment Plant located in the South of Barcelona's Metropolitan Area (Spain). The DWTP monitoring protocol was optimized by working for 1 day of deployment (24 h) with the DGT device in contact with both treated and river water matrixes. Additionally, it was demonstrated that an increase in the deployment time of 1 week did not decrease the evaluated concentrations of the studied metals. The quality parameters of the DGT device and ICP-OES determination, such as limit of quantification, accuracy expressed as relative error (%) and reproducibility expressed as relative standard deviation, were evaluated. Good results were obtained for all the metals in ultrapure water; limits of quantification ranged from 1.5 μg L( - 1) for cadmium to 28 μg L( - 1) for zinc when deployment time of 24 h was used and from 0.2 μg L( - 1) for cadmium to 4 μg L( - 1) for zinc when this time was increased by 1 week. Accuracy and precisions lower than or equal to 10% were obtained at a parametric concentration value of the metals regulated in the European Drinking Water Guidelines (98/83/EC). DGT deployment was tested in river and treated water, and good results were obtained for Cd, Ni, Co and Zn, whereas for the other metals, a continuous control of their metallic labile fractions was monitored. Therefore, DGT device allows the continuous monitoring of the labile metal species in a drinking water treatment plant.

Ferrihydrite containing gel for chemical imaging of labile phosphate species in sediments and soils using diffusive gradients in thin films

We report on a novel binding gel for phosphate, based on ferrihydrite, and its use in diffusive gradients in thin films (DGT) for measuring labile phosphate species in waters, sediments, and soils. An existing method of binding layer preparation was modified to overcome potential problems with deterioration of ferrihydrite due to conversion to goethite. The gel was characterized regarding its suitability for conventional DGT measurements as well as for measuring two-dimensional distributions of P with high spatial resolution using laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS). The effects of pH, ionic strength and storage time of gels on phosphate binding were investigated and the kinetics of binding and the maximum binding capacity were determined. The gel is shown to have a considerably higher P capacity than the conventional ferrihydrite DGT binding layers. LA-ICPMS analysis of DGT standards with P concentrations ranging from 0.088 ± 0.005 to 4.47 ± 0.16 μg cm(-2) resulted in reproducible calibration curves which could be described using a simple power function. We demonstrate that the new gel is well suited for analyzing small-scale changes of P concentrations in soils. Moreover, the gel can be used as an alternative to conventional DGT gels that incorporate powdered ferrihydrite, with improved characteristics for the determination of labile phosphate.

Diffusive gradient in thin FILMS (DGT) compared with soil solution and labile uranium fraction for predicting uranium bioavailability to ryegrass

The usefulness of uranium concentration in soil solution or recovered by selective extraction as unequivocal bioavailability indices for uranium uptake by plants is still unclear. The aim of the present study was to test if the uranium concentration measured by the diffusive gradient in thin films (DGT) technique is a relevant substitute for plant uranium availability in comparison to uranium concentration in the soil solution or uranium recovered by ammonium acetate. Ryegrass (Lolium perenne L. var. Melvina) is grown in greenhouse on a range of uranium spiked soils. The DGT-recovered uranium concentration (C(DGT)) was correlated with uranium concentration in the soil solution or with uranium recovered by ammonium acetate extraction. Plant uptake was better predicted by the summed soil solution concentrations of UO(2)(2+), uranyl carbonate complexes and UO(2)PO(4)(-). The DGT technique did not provide significant advantages over conventional methods to predict uranium uptake by plants.

Dissolved organic matter from treated effluent of a major wastewater treatment plant: characterization and influence on copper toxicity

A combination of reverse osmosis (RO) concentration and DAX-8/XAD-4 resin adsorption techniques is used to isolate the various constituents of urban dissolved organic matter (DOM) from inorganic salts. Three fractions: hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) accounting respectively for 35%, 20% and 45% of extracted carbon, are isolated from effluents of a major French wastewater treatment plant. This atypical DOC distribution, in comparison with natural water where the HPO fraction dominates, shows the significance of HPI fraction which often gets neglected because of extraction difficulties. A number of analytical techniques (elemental, spectroscopic: UV, FTIR) allow highlighting the weak aromaticity of wastewater effluent DOM (EfOM) due to fewer degradation and condensation processes and the strong presence of proteinaceous structures indicative of intense microbial activity. Copper toxicity in the presence of DOM is estimated using an acute toxicity test on Daphnia Magna (Strauss). Results reveal the similar protective role of each EfOM fraction compared to reference Suwannee river fulvic acid despite lower EfOM aromaticity (i.e. specific UV absorbance). The environmental implications of these results are discussed with respect to the development of site-specific water quality criteria.