Determination of labile species of As(V), Ba, Cd, Co, Cr(III), Cu, Mn, Ni, Pb, Sr, V(V), and Zn in natural waters using diffusive gradients in thin-film (DGT) devices modified with montmorillonite

Determination of Labile Cadmium in Soils Using a New Sodium Alginate-Polyglutamic Acid-Diffusive Gradient in Thin Films

Sodium alginate-polyglutamic acid was used to develop a new diffusive gradient in thin films (SA-PGA-DGT) device, which was proven to be suitable for the investigation of labile Cd in soil. The adsorption capacity of Cd was calculated to be approximately 16.8 μg/cm² , which was hardly affected by factors including pH (5-9), ionic strength (0.1-100 mM), and the presence of other metals (Pb, Cu, Ni, and Cr). The SA-PGA gel has dense and uneven pores with large specific surface area, which ensures the adsorption of Cd by functional groups of the gel. A kinetics study indicated that the adsorption rate of Cd by the binding gel can be described as a pseudo-second-order reaction. Deployment of the SA-PGA-DGT in the soils of Tang Gu (located in Binhai New District, Tianjin, China) showed a strong positive linear correlation between Cd measured by the device and exchangeable Cd measured by the Tessier method (R = 0.73, p < 0.01). Cadmium determined by the SA-PGA-DGT device was less affected by soil properties. This new SA-PGA-DGT has obvious advantages over other methods in respect of the labile Cd analysis in soil. The innovative novel device expands the variety of existing DGT technologies and can be utilized to monitor the level of labile Cd in soil effectively. Environ Toxicol Chem 2021;40:1559-1569. © 2021 SETAC.

Speciation of Inorganic Compounds in Aquatic Systems Using Diffusive Gradients in Thin-Films: A Review

The speciation of trace metals in an aquatic system involves the determination of free ions, complexes (labile and non-labile), colloids, and the total dissolved concentration. In this paper, we review the integrated assessment of free ions and labile metal complexes using Diffusive Gradients in Thin-films (DGT), a dynamic speciation technique. The device consists of a diffusive hydrogel layer made of polyacrylamide, backed by a layer of resin (usually Chelex-100) for all trace metals except for Hg. The best results for Hg speciation are obtained with agarose as hydrogel and a thiol-based resin. The diffusive domain controls the diffusion flux of the metal ions and complexes to the resin, which strongly binds all free ions. By using DGT devices with different thicknesses of the diffusive or resin gels and exploiting expressions derived from kinetic models, one can determine the labile concentrations, mobilities, and labilities of different species of an element in an aquatic system. This procedure has been applied to the determination of the organic pool of trace metals in freshwaters or to the characterization of organic and inorganic complexes in sea waters. The concentrations that are obtained represent time-weighted averages (TWA) over the deployment period.

Evaluating the Performance of a Diffusive Gradient in Thin Film Embedded with Montmorillonite for the Determination of Labile Cd, Pb, Mn, and Zn in Natural River Water

Montmorillonite (MMT), a natural clay mineral with high ion-exchange capacity and trace metal adsorbability, has been demonstrated to be a suitable binding phase in the diffusive gradient in thin film (DGT) technique for the determination of labile trace metals in synthetic water samples. However, in situ working performance of DGT-MMT with natural river water has not yet been investigated. The present study examined the performance of a DGT containing montmorillonite (MMT) for the in situ isolation and determination of labile Cd, Pb, Mn, and Zn fractions in Lach Tray River water, North Vietnam. The repeatability and accuracy of the DGT-MMT probe were assessed on the basis of seven measurement replicates performed on Cd2+, Pb2+, Mn2+, and Zn2+ standard solutions. Then, the DGT-MMT probes were deployed in Lach Tray River water at different sampling sites to determine the labile metal fractions present in river water. By comparing the total and dissolved metal concentrations in the river water, the distributions of the four tested trace metals were constructed. The proportions of the dissolved fractions of Cd, Pb, Mn, and Zn were 46.7–73.7%, 38.5–63.9%, 36.4–41.6%, and 49.8–67.7%, respectively. The results also showed that the high accuracy and reproducibility of the DGT-MMT data were comparable with measurements obtained by the commonly used DGT-Chelex-100 method. In comparison with the data obtained from anodic stripping voltammetry (ASV), a traditional technique for the determination of non-in situ speciation of trace metals, labile metal concentrations measured by DGT-MMT were in similar ranges. These findings indicate that naturally available montmorillonite can be used as an alternative binding material in DGT probes for the in situ determination of labile metal concentrations in natural watercourses.

Assessing the uranium DGT-available fraction in model solutions

The uranium speciation in humic acid (HA) and fulvic acid (FA) model solutions was investigated by diffusive gradients in thin films (DGT). A reference solution was used to normalize the DGT data from different samples. This approach was used to assess uranium DGT-available fraction (F_U), which was calculated from experimental data and reflect both the mobility and lability of uranium species. F_U decreased with increasing HA or FA concentrations, because more uranium was able to bind the strong binding sites of HA or FA. When copper was spiked, F_U increased due to the competition between copper and uranium. In HA model solutions, an increase of ionic strength could increase F_U, and when pH was greater than 7, F_U increased significantly. The DGT uptake factor (φ), which can be obtained from data fitting, is the ratio of the product of diffusion coefficient and lability degree of the unknown sample to that of the reference solution. In U-HA-NaHCO₃ solutions, UO₂(CO₃)₂^2- had a relatively high φ value and might be the most DGT-available species. This approach allows the comparison of DGT data from different samples, and combining with a data fitting procedure, it can be used to investigate the distribution of metal species.

The Intercalation of CORM-2 with Pharmaceutical Clay Montmorillonite (MMT) Aids for Therapeutic Carbon Monoxide Release

The pharmaceutical clay montmorillonite (MMT) is, for the first time, explored as a carbon monoxide-releasing material (CORMat). MMT consists of silicate double layered structure; its exfoliation feature intercalate the CORM-2 [RuCl(μ-Cl)(CO)3]2 inside the layers to suppress the toxicity of organometallic segment. The infrared spectroscopy (IR) confirmed the existence of ruthenium coordinated carbonyl ligand in MMT layers. The energy-dispersive X-ray spectroscopy (EDX) analysis showed that ruthenium element in this material was about 5%. The scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that the layer-structure of MMT has been maintained after loading the ruthenium carbonyl segment. Moreover, the layers have been stretched out, which was confirmed by X-ray diffraction (XRD) analysis. Thermogravimetric (TG) curves with huge weight loss around 100-200 °C were attributed to the CO hot-release of ruthenium carbonyl as well as the loss of the adsorbed solvent molecules and the water molecules between the layers. The CO-liberating properties have been assessed through myoglobin assay. The horse myoglobin test showed that the material could be hydrolyzed to slowly release carbon monoxide in physiological environments. The half-life of CO release was much longer than that of CORM-3, and it has an excellent environmental tolerance and slow release effect.