Gradients In Thin Films Devices Research Articles

Back Accumulation of Diffusive Gradients in Thin-Films Devices with a Stack of Resin Discs To Assess Availability of Metal Cations to Biota in Natural Waters.

Determining species, concentrations, and physicochemical parameters in natural waters is key to improve our understanding of the functioning of these ecosystems. Diffusive Gradients in Thin-films (DGT) devices with different thicknesses of the resin or of the diffusive disc can be used to collect independent information on relevant parameters. In particular, DGT devices with a stack of two resin discs offer a simple way to determine dissociation rate constants of metal complexes from the accumulation of the target metal in the back resin disc. In this work, simple approximate expressions for the determination of the dissociation rate constant are reported and applied to a model Ni nitrilotriacetic complex as well as to Zn complexes in the Mediterranean Osor stream. Once the physicochemical parameters are known, one can plot the labile fraction of the metal complexes in terms of the thickness of the diffusion domain. These plots reveal a strong dependence on the nature of complexes as well as on the characteristics of the diffusion domain, and they are of high interest as predictors of availability to biota whose uptake is limited by diffusion.

A new DGT technique based on nano-sized Mg2Al layered double hydroxides with DTPA for sampling of eight anionic and cationic metals.

In this work, a new resin gel incorporated with layered double hydroxide nanoparticles modified with diethylenetriaminepentaacetic acid is developed for application in diffusive gradients in thin-film devices (abbreviated as LDHs DGT) to monitor eight anions and cations (such as Fe, Mn, Co, Ni, Cu, Cd, Pb, and As) in natural waters and soils. The accumulated anions and cations were quantitatively recovered by one-step elution using 0.5mol·L-1 HNO3 with an optimized elution time of 30min. The performance of the LDHs DGT was independent of solution pH (5-8) and ionic strengths (5-100mmol·L-1). The capacities of the LDHs DGT for Mn(II), Fe(II), Co(II), Ni(II), Cu(II), As(V), Cd(II), and Pb(II) individually are determined to be 202.9, 363.6, 246.9, 88.8, 99.5, 75.3, 159.8, and 671.7μg·cm-2. During the field deployments in anature river, LDHs DGT measured concentrations of cations and anions were almost like those measured by the traditional sampling method (except Fe(II), Cd(II), and Co(II)). In addition, bioavailable Cd measured by LDHs DGT correlated well with Cd in rice grains (R2 = 0.55), indicating that LDHs DGT is a reliable tool for assessing the risk of Cd.

Recent nanomaterials development and application in diffusive gradients in thin-film devices

Recent nanomaterials development and application in diffusive gradients in thin-film devices

Effects of a mixture of ligands on metal accumulation in diffusive gradients in thin films (DGT)

Environmental contextThe availability of trace metals to aquatic organisms is influenced by the natural ligands present in water. We investigate the influence of the composition of the system on the availability of metal cations as nutritive or toxic species. The focus is on clarifying whether availability measured in single-ligand systems with diffusive gradients in thin film devices can be used to predict accumulation in mixtures. AbstractNatural waters contain mixtures of ligands, which collectively affect the availability of trace metals. The individual contribution of each complex to the overall metal flux received by a sensor can be described in terms of its lability degree. The question arises as to whether the mixture entails specific non-additive effects, i.e. to what extent is it possible to predict the collective behaviour of the mixture from the values of the lability degree of each single ligand system (SLS). For this reason, a series of experiments with diffusion gradients in thin films (DGT) devices were carried out to measure nickel accumulation from synthetic media comprising either nitrilotriacetic acid (NTA), ethylenediamine (EN) or mixtures of both ligands. The results were compared with numerical simulations. It is shown that NiNTA becomes more inert in the mixture than in the SLS that contains the same concentration of free Ni and NiNTA, whereas the opposite is true for the Ni bound to EN, which becomes more labile in the mixture than in the SLS. This unprecedented behaviour arises when one of the ligands (NTA, forming strong and partially labile complexes) is present under non-excess conditions. As NiNTA and NiEN have an opposite influence on the lability degree of each other, the sum of partial fluxes calculated from the lability degrees obtained in SLSs yields a reasonable estimate of DGT performance in the mixture. Experimental accumulations in the mixture are just slightly below the predicted values, with errors lower than 11 % when NTA concentrations vary from 20 to 100 % of the total Ni concentration.

Changes in soil bacterial communities and diversity in response to long-term silver exposure.

Silver-induced selective pressure is becoming increasingly important due to the growing use of silver (Ag) as an antimicrobial agent in biomedical and commercial products. With demonstrated links between environmental resistomes and clinical pathogens, it is important to identify microbial profiles related to silver tolerance/resistance. We investigated the effects of ionic Ag stress on soil bacterial communities and identified resistant/persistent bacterial populations. Silver treatments of 50-400 mg Ag kg(-1) soil were established in five soils. Chemical lability measurements using diffusive gradients in thin-film devices confirmed that significant (albeit decreasing) labile Ag concentrations were present throughout the 9-month incubation period. Synchrotron X-ray absorption near edge structure spectroscopy demonstrated that this decreasing lability was due to changes in the Ag speciation to less soluble forms such as Ag(0) and Ag2S. Real-time PCR and Illumina MiSeq screening of 16S rRNA bacterial genes showed β-diversity changes, increasing α-diversity in response to Ag pressure, and immediate and significant reductions in 16S rRNA gene counts with varying degrees of recovery. These effects were more strongly influenced by exposure time than by Ag dose at these rates. Ag-selected dominant OTUs principally resided in known persister taxa (mainly Gram positive), including metal-tolerant bacteria and slow-growing Mycobacteria.

Key Role of the Resin Layer Thickness in the Lability of Complexes Measured by DGT

Analysis of the dynamic features of diffusion gradients in thin film devices (DGT) indicates that the penetration of complexes into the resin layer dramatically increases their lability. This should be taken into account when interpreting DGT measurements in terms of the dynamics of solution speciation. The experimental accumulation of Cd by DGT sensors in Cd-NTA systems confirmed these theoretical analyses. A computational code, which allows a rigorous digital simulation of the diffusion-reaction processes in the gel and resin layers, was used to model the results and to demonstrate the effect of the complex penetration into the resin layer on the lability degree. These findings suggest that DGT renders all complexes much more labile than if the resin-diffusive gel interface was considered as a perfect planar sink, explaining why DGT often measures a high proportion of the metal in a natural water. This information is relevant since some studies have stressed the importance of labile complexes as a source of bioaccumulated metal.