Diffusive Gradients In Thin Research Articles

Comparison of sediment bioavailable methods to assess the potential risk of metal(loid)s for river ecosystems

A heavily impacted river basin (Caudal River, NW Spain) by Hg and Cu mining activities, abandoned decades ago, was used to evaluate the environmental quality of their river sediments. The obtained results compared with reference values established by the US EPA and the Canadian Council of Ministers of the Environment for river sediments, have shown that the main elements of environmental concern are arsenic (As), mercury (Hg) and, to a lesser extent, copper (Cu), which reach concentrations up to 1080, 80 and 54 mg kg−1, respectively. To understand the role that river sediments play in terms of risk to ecosystem health, a comparison has been made between the total content of metal(oid)s in the sediments and the bioavailable contents of the same elements in pore water, passive DGT (Diffusive Gradients in Thin films) samplers and the sediment extractant using acetic acid. A good correlation between the As and Cu contents in the DGTs and the pore water was found, resulting in a transfer from the pore water to the DGT of at least 47 % of the Cu and more than 75 % of the As when the concentrations were low, with a deployment time of 4 days. When As and Cu concentrations were higher, their transfer was not so high (above 23.6 % for As and 19.3 % for Cu). The transfer of Hg from the pore water to the DGT was practically nil and does not seem to depend on the content of this metal. The fraction extracted with acetic acid, conventionally accepted as bioavailable, was clearly lower than that captured by DGTs for As and Cu (≤5 % and ≤8.5 % of the total amount, respectively), while it was similar for Hg (0.2 %).

BIOPOLÍMERO QUITOSANA NA ADSORÇÃO DE GLIFOSATO: USO NO MONITORAMENTO OU REMEDIAÇÃO AMBIENTAL

In this work, low molecular weight chitosan was used to adsorb the herbicide glyphosate in aqueous solution. Considering the possibilities of remediation and monitoring in aquatic environments, chitosan was formatted into thin discs 0.8 mm thick and 2.5 cm in diameter. The films were characterized by SEM, EDS and FTIR. In the adsorption study, a chitosan disc was able to adsorb 100% of a 5 mgL-1 glyphosate solution. Pseudo-first-order, pseudo-second-order and Elovich kinetic models were applied and it was found that chemisorption predominates in the adsorption process. Thus, chitosan films can act very well as a material for remediating water bodies contaminated by glyphosate. For monitoring studies, the possibility of using chitosan films in DGT (Diffusive Gradients in Thin Films) technique was verified and the diffusive material used was 1.5% agarose film (m/v). The diffusion coefficient of glyphosate in the agarose gel was determined 7.94 x 10-10 m2s-1.

Determination of the Isotopic Composition of Aqueous Mercury in a Paddy Ecosystem Using Diffusive Gradients in Thin Films.

Measuring the isotopic composition of Hg in natural waters is challenging due to the ultratrace level of aqueous Hg (ng L-1). At least 5 ng of Hg mass is required for Hg isotopic analysis. Given the low Hg concentration in natural waters, a large volume of water (>10 L) is typically needed. The conventional grab sampling method is time-consuming, laborious, and prone to contamination during transportation and preconcentration steps. In this study, a DGT (diffusive gradients in thin films) method based on aminopropyl and mercaptopropyl bi-functionalized SBA-15 nanoparticles was developed and extended to determine the concentration and isotopic composition of aqueous Hg for the first time. The results of laboratory analysis showed that Hg adsorption by DGT induces ∼ -0.2‰ mass-dependent fractionation (MDF) and little mass-independent fractionation (MIF). The magnitude of MDF exhibits a dependence on the diffusion-layer thickness of DGT. Since Hg-MDF can occur in a broad range of environmental processes, monitoring the δ202Hg of aqueous Hg using the DGT method should be performed with caution. Field results show consistent MIF signatures (Δ199Hg) between the DGT and conventional grab sampling method. The developed DGT method serves as a passive sampling method that effectively characterizes the MIF of Hg in waters to understand the biogeochemical cycle of Hg at contaminated sites.

Potential of granular complexes of lime and montmorillonite for stabilizing soil cadmium and the underlying mechanisms

Cadmium (Cd) contaminated soils were widely remediated by alkaline materials in powder, while the effects of granular materials are still unknown. This study was conducted to prepare granular materials based on hydrated lime and montmorillonite with ratios of 1:1, 1:2, and 1:3 (LM1, LM2, and LM3); their effects and mechanisms on stabilizing Cd in hydroponic, pot, and field conditions were further explored. The results showed that powdery materials caused intense pH elevations within 30–60 min and dissolved-Cd reductions within 8–100 min. However, granular materials significantly delayed these effects; the highest solution pH and lowest dissolved-Cd occurred after 250 min. The LM1 granules induced a much higher reduction of dissolved-Cd (99.8%) than that in the LM2 (53.6%) and LM3 granules (14.3%) due to the generation of more cadmium carbonate precipitates. Additionally, the soil pH gradually decreased after an intense elevation induced by powdery materials, but the LM1 granules maintained the soil pH at approximately 7.0, resulting in a lower level of CaCl2-extractable Cd (0.03 mg kg−1) than the LM1 powder (0.22 mg kg−1) after 30 d of cultivation. Similar to lime powder, a small spatial variation (Std. of 3.45) of DGT (diffusive gradient in thin films) extractable Cd in soil profile was observed in the LM1 granules, revealing a homogeneous stabilization effect induced by the LM1 granules. Accordingly, the LM1 granules induced a higher reduction in brown rice Cd (50.9%) than that in the LM1 powders (35.1%). Thus, the granular material of hydrated lime and montmorillonite (1:1) h the potential to replace lime powder in the remediation of Cd-contaminated field.

Monitoring of Heavy Metal Pollution in Water and Sediments at the Mid-Black Sea Region by Using Passive Sampling Method Diffusive Gradients in Thin Films

Determining the potential bioavailability of heavy metals, evaluating according to adapted regulations is essential to efficiently conserve our coastal and estuarine waters. In this study, it is aimed to determine the industrial pollution and various other pollution sources that the Black Sea Basin is exposed to by using DGT (Diffusive Gradients in Thin Films) method and grab (manuel) sampling method in water and sediment and to evaluate the existing pollution according to quality standards. In Samsun, seasonal samples were collected from five different sampling stations, namely Akkiraz Stream, Hıdırellez Stream, Organized Industrial Zone (OIZ) Channel, Şabanoğlu Stream and Selyeri Stream, which are selected from Tekkeköy region where industry is intensively active. In order to determine the heavy metal content in both water and sediment samples, the DGT method was chosen for passive sampling and the grab sampling method was used for active sampling, and the efficiency of the methods was evaluated. According to the results of the study, the heavy metal concentration in grab sampling for water samples in descending order Al> Fe> Zn> Pb> Ni> Cu; In the samples taken with DGT, they are listed as Al> Fe> Zn> Cu> Ni> Pb. There were significant relationships between the total metal concentrations of sediment (Csed) and water (Csu) in grab sampling and metal concentrations sediment (Csed-DGT) and water (Csu-DGT) measured by DGT. It was found that the sensitivity and performance of sampling with DGT was 2-10 times higher compared to grab sampling. The high resolution in situ DGT technique for the assessment and management of the potential release risk of heavy metals at the water-sediment interface is a complementary method that contributes to the standard grab sampling method.

Desorption kinetics of heavy metals in the gleyic layer of permafrost-affected soils in Arctic region assessed by geochemical fractionation and DGT/DIFS

An in-situ DGT (diffusive gradient in thin films) technique was deployed to gleyic-layer soils identified in the active layer of eight Arctic islands for the release-resupply processes of labile Cd, Zn, and Pb during the thawing season. The capability to maintain the initial soil concentration of these metals is highly dependent upon landscape elevation and soil texture, which determines the labile pool size of metals (Kdl). Cd and Zn had larger labile pools compared to Pb, indicating a larger resupply capacity for those metals. The rate at which the soil system can supply metal from solid phase to solution, represented as response time (Tc), of Zn and Cd was very short (<1 min), indicating rapid resupply. The longer Tc for Pb (~5 min) was consistent with its slower desorption. In fluctuating permafrost-affected areas, the increasing elevation, which causes heterogeneity in soil texture, organic matter, and pH, resulted in lower Kdl and higher Tc for Cd, Zn, and Pb. Combined with BCR methods, labile Cd was associated with Fe oxides, Zn was associated with both Fe and Mn oxides, and Pb was associated with Mn oxides and also highly bound to micro-aggregates and dissolved organic matter.

Millimetre-resolution mapping of citrate exuded from soil-grown roots using a novel, low-invasive sampling technique.

The reliable sampling of root exudates in soil-grown plants is experimentally challenging. This study aimed at developing a citrate sampling and mapping technique with millimetre-resolution using DGT (diffusive gradients in thin films) ZrOH-binding gels. Citrate adsorption kinetics, DGT capacity, and stability of ZrOH gels were evaluated. ZrOH gels were applied to generate 2D maps of citrate exuded by white lupin roots grown in a rhizotron in a phosphorus-deficient soil. Citrate was adsorbed quantitatively and rapidly by the ZrOH gels; these gels can be stored after sampling for several weeks prior to analysis. The DGT capacity of the ZrOH gel for citrate depends on the ionic strength and the pH of the soil solution, but was suitable for citrate sampling. We generated for the first time 2D citrate maps of rhizotron-grown plants at a millimetre resolution to measure an illustrated plant response to phosphorus fertilization, demonstrating that DGT-based citrate sampling is suitable for studying root exudation in soil environments, at high spatial resolution. The change of binding material would also allow sampling of other exudate classes and exudation profiles of entire root systems. These aspects are crucial in cultivar breeding and selection.

Advances in Understanding Mobilization Processes of Trace Metals in Marine Sediments.

Different mobilization mechanisms control the metal distribution in surface sediments of the Belgium coastal zone (BCZ) and the anoxic Gotland basin (GB). This mobilization was studied using DGT (diffusive gradients in thin films): vertical one-dimensional (1D) profiles of Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn were measured at 5 mm intervals, while two-dimensional (2D) high-resolution (100 μm) images of smaller zones of the sediment profile were obtained on separate DGT probes. Removal of dissolved Cd, Cu, and Pb in BCZ sediments caused steep vertical gradients at the sediment-water interface that were well replicated in 1D profiles and 2D images. While 1D profiles showed apparent coincident maxima of Co, Mn, and Fe, 2D images revealed mutually exclusive Co and Fe mobilization. Correlation analysis supported this observation and showed a consistent linkage between Co and Mn. Sharp maxima of some metals in the vertical 1D profiles of GB sediment were attributed to localized mobilization in microniches. Examination of an ∼1 mm diameter Cu and Ni maximum in 2D, defined by ∼300 data points, showed that the metals were supplied from localized decomposition of reactive organic material, rather than from reductively dissolving Fe or Mn oxides, and that they were removed as their sulfides.

Tracking anthropogenic sources in a small catchment using Zn-isotope signatures

Tracking metal pollution in surface water is a major environmental, public-health and economic issue. Knowledge of the behaviour of metals such as zinc (Zn), in stream sediments and water, is a key factor to improving river water quality. Because the isotopic compositions of Zn can be used as an environmental tracer for tracking the sources of man-made materials and its transport into water and soil, we have used Zn isotopes for studying the anthropogenic impact on a watershed. As a case study, we chose a small watershed in the Loire River basin, near Orléans (France). The Egoutier spring issues in a pristine area, but its water is affected a few kilometres downstream by liquid effluents from a wastewater treatment plant (WWTP) and farther down still by diffuse pollution from road traffic. We sampled the liquid effluents as well as water and sediments along an upstream to downstream transect. For liquid samples, we took “grab” samples and integrated samples using passive DGT (Diffusive Gradients in Thin films) samplers. The advantages of DGT are (1) to pre-concentrate in-situ the Zn dissolved in water—avoiding a time-consuming chemical preparation—and (2) to integrate the potential variations of Zn isotopic signature over time. The mobile fraction of sediments—that released by the leaching in 0.2N HCl—was also investigated. The δ66/64Zn values in water and sediments along the upstream/downstream profile clearly showed the anthropogenic input of WWTP effluents in the river, which was still visible several kilometres downstream in water. This dissolved anthropogenic contribution is easily transported along the transect and only slightly fixed by adsorption on sediments, probably due to their low clay-mineral content. For the farthest downstream sample, affected by road traffic, the pollution source is difficult to discern due to the similar δ66/64Zn values in WWTP effluents and in road-traffic particles. Here, the use of DGT has proved to be a major asset: during a rainfall event, road traffic particles were leached by rainwater, forming runoff with a relatively high Zn content that flowed into the river, and DGT monitoring showed it to be an adequate method for discerning discontinuous anthropogenic input into the river water.

Control of internal phosphorus release from sediments using magnetic lanthanum/iron-modified bentonite as active capping material

The non-magnetic capping materials are difficult to be recycled from the water bodies after their application, leading to the increase in the cost of the sediment remediation. To address this issue, a capping material, i.e., magnetic lanthanum/iron-modified bentonite (M-LaFeBT) was prepared by loading lanthanum onto a magnetic iron-modified bentonite (M-FeBT) and used to control the internal phosphorus (P) loading in this study. To determine the capping efficiency and mechanism of M-LaFeBT, the impact of M-LaFeBT and M-FeBT capping on the mobilization of P in sediments was investigated, and the stabilization of P bound by the M-LaFeBT and M-FeBT capping layers was evaluated. Results showed that M-LaFeBT possessed good magnetic property with a saturated magnetization of 14.9 emu/g, and exhibited good phosphate adsorption ability with a maximum monolayer sorption capacity (QMAX) of 14.3 mg P/g at pH 7. Moreover, M-LaFeBT capping tremendously reduced the concentration of soluble reactive P (SR-P) in the overlying water (OL-water), and the reduction efficiencies were 94.7%–97.4%. Furthermore, M-LaFeBT capping significantly decreased the concentration of SR-P in the pore water and DGT (diffusive gradient in thin films)-labile P in the profile of OL-water and sediment. Additionally, most of P bound by the M-LaFeBT capping layer (approximately 77%) was stable under natural pH and reducing conditions. The phosphate adsorption ability for M-LaFeBT was much higher than that for M-FeBT, and the QMAX value for the former was 4.86 times higher than that for the latter. M-LaFeBT capping gave rise to a higher reduction of DGT-labile concentration in the profile of OL-water and sediment than M-FeBT capping. The P adsorbed by the M-LaFeBT capping layer was more stable than that by the M-FeBT capping layer. Results of this study demonstrate that M-LaFeBT is promising for utilization as an active capping material to intercept sedimentary P release into OL-water.

Novel, recyclable active capping systems using fabric-wrapped zirconium-modified magnetite/bentonite composite for sedimentary phosphorus release control

A zirconium-modified magnetite/bentonite composite (M-ZrFeBT) was synthesized, characterized and combined with water-permeable fabric to construct novel, recyclable active capping systems for sedimentary phosphorus (P) release control. Three fabric-wrapped M-ZrFeBT capping devices with different shapes were designed, i.e., CAP-1, CAP-2 and CAP-3, and they are disc-shaped, cuboid-shaped and spindle-shaped capping devices, respectively. The behavior and mechanism for phosphate adsorption onto M-ZrFeBT was studied. The impact of CAP-1, CAP-2 and CAP-3 capping on the mobilization of P in sediments was investigated. The results showed that M-ZrFeBT possessed good phosphate adsorption ability, with a largest monolayer adsorption capacity of 8.02 mg P/g. The replacement of Fe/Zr bound hydroxyl groups with phosphate through ligand-exchange reactions to generate the inner-sphere Fe-O-P and Zr-O-P bonding played a key part in the uptake of phosphate from water by M-ZrFeBT. Sediment capping with fabric-wrapped M-ZrFeBT not only brought about a significant decline in the concentrations of soluble reactive P (SRP) and DGT (diffusive gradient in thin films)-labile P (LPDGT) in the overlying water, but also gave rise to the diminished SRP and LPDGT concentrations in the upper sediment. Most (96.5%-98.2%) of P bound by the M-ZrFeBT in the capping layers was in the form of NaOH extractable inorganic P, HCl-extractable P and residual P, which were considered to be hard to be released back into the water column under common pH and oxygen-deficient conditions. The reduction of pore water SRP and LPDGT in the upper sediment layer induced by the adsorption of SRP on the M-ZrFeBT-based capping layer played a key part in the interception of SRP liberation from the sediment solid into the overlying water. Results indicate that fabric-wrapped M-ZrFeBT capping is promising for controlling the internal P loading from sediments in shallow freshwater bodies.

Study of orthophosphate detection method using DGT (diffusive gradients in thin films) device with modified binding layer Fe-chitosan-bentonite biocomposite in aquatic system

In this work, a study of orthophosphate detection technique in the aquatic system has been conducted. The detection technique used in this study was Diffusive Gradients in Thin Films (DGT) with Fe-Chitosan-Bentonite (Fe-CSBent) biocomposite as the binding agent. The phosphate species diffused through the polyacrylamide gel and then bound by Fe-CSBent as the binding agent on the binding layer. The adsorption of phosphate by Fe-CSBent is through electrostatic attraction, inner sphere complexation, and ion-exchanged. The synthesized Fe-CSBent biocomposite was characterized using Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis, and the synthesized diffusive gel and binding gel were characterized using FTIR analysis. In this experiment, we examined the DGT-Fe-CSBent capability in orthophosphate binding with parameters such as the deployment time, pH of the solution and the presence of co-existent anion i.e. sodium tripolyphosphate (STPP). The mass of bound orthophosphate can be calculated after eluted the binding gel with acid and then measured with the molybdenum blue method using UV-Vis spectrophotometry. Based on the experiment, DGT-Fe-CSBent bound the orthophosphates more efficiently in concentration of 2.2970 μg/mL with 90.208 % efficiency, compared to DGT-CSBent in concentration of 1.7333 μg/mL with 79.874 % efficiency. It was also known that the presence of STPP influenced the amount of orthophosphate concentration bound by Fe-CSBent in the binding gel. DGT-Fe-CSBent device that was made to be selective in predicting bioavailable phosphate, but the presence of other phosphate species such as sodium tripolyphosphate may be influenced orthophosphate bound by DGT.

To what extent can the biogeochemical cycling of mercury modulate the measurement of dissolved mercury in surface freshwaters by passive sampling?

Mercury (Hg) is a pollutant of global concern owing to its great toxicity even at very low concentrations. Its toxicity depends on its chemical forms evidencing the importance to study its speciation. Dissolved Hg (Hg(d)) and methylmercury (MeHg(d)) monitoring in surface freshwaters represents a great challenge because of their very low concentrations and substantial temporal variability at different timescales. The Hg(d) temporal variability depends on the environmental conditions such as the hydrology, water temperature, redox potential (Eh), and solar photo cycle. Passive samplers represent an alternative to improve the assessment of Hg(d) and MeHg(d) concentrations in surface freshwaters by integrating their temporal variability. An original sampling strategy was designed to assess the relevance of 3-mercaptopropyl DGT (Diffusive Gradient in Thin films) to integrate in situ the temporal variations of labile Hg (Hg(DGT)) and MeHg (MeHg(DGT)) concentrations. This strategy was implemented on two rivers to study the dynamics of Hg(d), Hg(DGT), MeHg(d) and MeHg(DGT) at diurnal and annual timescales. We evidenced that Hg(DGT) and MeHg(DGT) concentrations were generally consistent with discrete sampling measurements of Hg(d) and MeHg(d) in dynamic surface freshwaters. However, Hg(DGT) concentrations were overestimated (2–16 times higher) in case of low flow or low water depth, low suspended particulate matter (SPM) concentrations and elevated daily photoperiod. The most probable hypothesis is that such conditions promoted Hg0 production, and resulted in Hg0 uptake by DGT. Thus, attention should be paid when interpreting Hg(DGT) concentrations in surface freshwaters in environmental conditions that could promote Hg0 production.

Assessment of iron-modified calcite/zeolite mixture as a capping material to control sedimentary phosphorus and nitrogen liberation.

Calcite/zeolite mixture (CZ) can be used to construct a capping layer for the simultaneous management of phosphorus (P) and nitrogen (N) liberation from sediments into the overlying water (OVER-water). However, its control efficiency of sedimentary P release still needs to be improved. To address this issue, an iron-modified CZ (Fe-CZ) was synthesized, characterized, and employed as a capping material to simultaneously prevent P and N release from sediments into OVER-water. Batch and microcosm incubation experiments were performed to study the efficiency and mechanism for the control of P and N release from sediments by capping Fe-CZ. Results showed that sediment capping with Fe-CZ resulted in the significant reduction of soluble reactive P (SRP) and ammonium-N (NH3-N) in OVER-water, with reduction rates of 77.8-99.7% and 54.0-96.7%, respectively. Furthermore, the Fe-CZ capping layer decreased the SRP concentration in the pore water (PORE-water) at depth of 0-30mm and reduced the concentration of PORE-water NH3-N at depth of 0-50mm. Moreover, the Fe-CZ capping layer gave rise to the great decrement of the concentration of the labile P measured by DGT (diffusive gradient in thin films) technology (P-DGT) in the profile of OVER-water and sediment. Additionally, the Fe-CZ capping resulted in the reduction of redox-sensitive P (P-BD) in the 0-50mm sediment and caused the transformation of P-BD to calcium-bound P (P-HCl) and residual P (P-RES) in the 0-10mm sediment as well as to P-RES in the 10-20mm sediment. Results of this work indicate that the Fe-CZ capping has a high potential for the simultaneous management of P and N release from sediments, and the decrease of the contents of sediment P-DGT, sediment P-BD, PORE-water SRP and PORE-water NH3-N as well as the conversion of mobile P to more stable P in the top sediment should have a significant role in the simultaneous interception of sedimentary P and N liberation into OVER-water by the Fe-CZ capping.

Effect of ageing of bare and coated nanoparticles of zinc oxide applied to soil on the Zn behaviour and toxicity to fish cells due to transfer from soil to water bodies

This study evaluated the influence of ageing of ZnO nanoparticles (NPs) applied to soil on the potential availability and chemical speciation of Zn, and also of their toxicity to aquatic organisms due to transfer of contaminants from soil to water. To this end, soil samples were spiked with two types of bare nanoparticles: b1ZnO NPs (rod- and elongated-shaped) and b2ZnO NPs (near-spherical shaped) and ZnO NPs coated with (3-aminopropyl)triethoxysilane (cZnO NPs) within the 0–800 mg Zn kg−1 soil dose range, and were left to age for 0, 30, 60 and 90 days. The available concentration and speciation of Zn in soil were determined by the DGT (diffusive gradients in thin films) technique and sequential extraction procedures, respectively. The toxicity of the aqueous extracts from the ZnO NP-treated soils was assessed in vitro in established fish cell lines (RTG-2). The highest distribution percentages of the applied Zn occurred in the organically complexed (OC), followed by the exchangeable (EXC) fraction, for all NP types, applied doses and incubation times. The toxicity of NPs depended on their intrinsic properties: b1ZnO NPs affected the membrane function, reductase enzyme activity and, to a lesser extent, reactive oxygen species (ROS) levels of fish cells, whereas b2ZnO NPs and cZnO NPs affected mainly ROS generation. Ageing increased Zn soil availability, but toxicity to fish cells showed no trend over time. The particle dissolution of ZnO NPs did not explain the observed toxicity, hence a nanoparticles-specific effect should be assumed. The findings of this study seem to indicate that the transfer of ZnO NP from contaminated soils to aquatic ecosystems should be addressed.

Distribution character of localized iron microniche in lake sediment microzone revealed by chemical image.

DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (CDGT(Fe)) are investigated for Fe remobilization character. There are 902 CDGT(Fe) values between 1000 and 2000 μg L-1, 463 values between 2000 and 3000 μg L-1, and 112 values over 3000 μg L-1 in all chemical maps. Based on the linear correlation relationships between CDGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. CDGT(Fe) peak flux in the center of Fe microniche and the low CDGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large CDGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large CDGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones.

Influence of amendments on metal environmental and toxicological availability in highly contaminated brownfield and agricultural soils.

The immobilizing effects of wood biochar (BW2%) and iron grit (Z1%) applied alone or in combination (BW2% + Z1%) to agricultural (M750) and brownfield (MAZ) soils highly contaminated by metals were assessed in a greenhouse experiment. The results showed that Z1% and BW2% + Z1% were the most efficient amendments to reduce Cd, Cu, Pb, and Zn mobility, environmental availability, and phytoavailability in the M750 soil. The oxidation of Z1% allowed part of the Cu and Zn pools present in exchangeable or carbonate-bound forms (labile fraction) to complex in less mobile forms. In this soil, the metal chemical extractions (0.01 M CaCl2 and 0.05 M EDTA) and the DGT (diffusive gradient in thin films) devices to assess metal in soil solution and soil pore water (SPW) also highlighted the immobilizing characteristic of Z1%. In most cases, the addition of BW2% to Z1% (BW2% + Z1%) did not improve this effect, except for the dissolved Pb and Zn concentrations in the M750 soil solution. It was also observed that Cd, Pb, and Zn passed throughout DGT mimicking the biological cell membrane were reduced by all amendments of the M750 soil corroborating metal concentrations measured in rye grass shoots. In the MAZ soil, metals were less available as shown by their low extractability rate, low capacity of metal resupply from the solid phase to pore water, and low phytoavailability. The poor metal availability could be explained by the high levels of carbonate and organic matter contents in this soil. Nevertheless, a decrease of the Cu environmental availability and the Cu concentrations in rye grass shoots grown on the MAZ soil was also observed in the soil amended with Z1% alone or in combination with BW2%. From a health point of view, the most effective amendment to reduce human exposure through ingestion of soil particles for the M750 and MAZ soils was BW2% for Cd and BW2% + Z1% for Pb. However, the presence of rye grass minimized the amendments' beneficial effects.

Flow period influence on uranium and trace elements release in water from the waste rock pile of the former La Commanderie uranium mine (France)

Uranium mining activities expose uranium ore and mine tailings to the surface environment, where the release of radionuclides is facilitated by weathering at rates exceeding those typically found in nature. Therefore, close to former uranium mining sites, radionuclides and especially uranium concentrations in water may surpass local background levels. The methodology proposed herein, entails coupling, gamma-ray mapping, water sampling and chemical analyses including DGT (Diffusive Gradient in Thin Film) measurements, provides new insights into describing the environment of the La Commanderie site (France). Gamma-ray mapping allows identifying water seepage, output from a waste rock pile, as a potential pathway for radionuclides into the environment. Water seepage monitoring has shown: a low pH value (4.2), high sulfate content (179 mg.L−1) and high uranium concentrations of up to 436 μg.L−1. These recordings indicate that an acid mining drainage (AMD) process is occurring inside or under the oxidized parts of the waste rock pile. Monitoring data over three flow periods revealed the release of the highest uranium concentrations during a high-flow period downstream of the site, which is compliant with local regulations. The AMD process is also responsible for the release of significant amounts of Fe, Mn and As within the immediate environment in both dissolved and particulate forms. Changes in dissolved oxygen concentration and redox potential during low flow periods, modify the speciation of Fe (in AMD waters) which acts as a scavenger for other elements such as As, Mn and U. The use of DGT under environmental conditions, and specifically AMD waters, seems to be relevant in comparison to filtered spot water sampling strategies. Moreover, based on DGT measurements, the dissolved part of the released uranium is considered as labile with concentrations above the environmental standards for freshwater organisms.

High-resolution imaging of phosphorus mobilization and iron redox cycling in sediments from Honghu Lake, China

Phosphorus (P) pollution is a significant environmental problem in lakes, especially in lakes highly impacted by human activities, e.g., Honghu Lake. Years of farming activities have led to a complex occurrence of P in the sediment which has not been studied in detail. Iron redox cycling is a key mechanism controlling P adsorption–desorption behavior, and its study is an effective means of assessing P dynamics, which could provide basic theoretical data for the control of internal phosphorus in such lakes. The high-resolution ZrO-Chelex DGT (ZrO-Chelex diffusive gradients in thin films) and HR-Peeper (high-resolution dialysis sampler) techniques were used to assess labile P, labile Fe, and soluble reactive P (SRP) in five sediment samples from four functional areas of Honghu Lake. The temperature, pH, and dissolved oxygen levels of water samples were measured in situ using a portable water quality analyzer, and the dissolved organic carbon (DOC) concentration was analyzed with a TOC analyzer after 0.45 μm membrane filtration. Total Fe concentrations were determined using the phenanthroline colorimetric approach. Sediment porosity was calculated based on weight loss after drying for 6 h at 105 °C. One-dimensional changes in labile P and Fe in different functional areas of the lake were quite heterogeneous, and there was a significant linear correlation between labile P and Fe near the sediment–water interface (SWI). Sediment samples HH-2 and HH-5 exhibited positive P diffusion flux (F) and tended to be a P source, while sites HH-1, HH-3, and HH-4 tended to take in P from overlying water. The ratio (R) of labile P to SRP was used as an indicator of potential soluble reactive P release from sediments into the surrounding water and initially increased at four sampling sites, then decreased deeper in the sediment except at site HH-4. The results indicated that the tendency of P released from sediments or uptake from overlying water was distinct in different functional areas and that iron redox cycling was a key mechanism controlling P dynamics in the sediments of Honghu Lake. Thus, the iron–phosphorus relationship can provide an accurate assessment of P release processes in a surface water environment.

Time weighted average concentrations measured with Diffusive Gradients in Thin films (DGT)

Time weighted average (TWA) concentrations can improve the assessment of water quality. DGT (Diffusive Gradients in Thin films) devices have been suggested as simple tools to measure TWA metal concentrations, but the connection of TWA with cDGT has not been rigorously discussed. It is shown here that cDGT is the average DGT-labile concentration along the deployment, which suggests that it is well suited to correlate with toxicity effects. In terms of real species, cDGT is a good estimator of the TWA concentration for simple metal solutions (no ligands are present) when the accumulation takes place under perfect sink conditions. Differences between cDGT and the TWA concentration for short pulses (<40 min), when the transient regime becomes relevant, are reported. In the presence of complexes, cDGT contains the TWA of the product of the labile fraction times the diffusivity of the complex (relative to that of the free metal). This means that cDGT can underestimate the TWA of the total metal concentration due to the presence of complexes less mobile than the free metal or not fully labile. These findings are illustrated with Cd, Ni, Mg or Ni + nitrilotriacetic acid (NTA) solutions. When only one complex is relevant, as in the Ni + NTA system, a simple correction factor can yield the TWA concentration from cDGT.