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

Abstract

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.

Anthropogenic activities influence the mobilization of trace metals and oxyanions in coastal sediment porewaters

“…The R value equals the fraction of labile dissolved concentration to total dissolved concentration in porewater and is by definition smaller than one, since it only includes the free ions and the weakly bound inorganic complexes (Galceran et al, 2021;Gao et al, 2019). Moreover, this labile fraction is much more sensitive to redox changes in the porewater than the non-labile fraction (organic complexed metals and metal colloids), because in aquatic systems strongly bound metals or colloids have a higher stability due to the formation of coordination bonds (de Paiva Magalhães et al, 2015).…”

Surface Water Processes in Coping with Anthropogenic Impact in a Coastal Eastern Mediterranean Region

“…Additionally, pH can affect the bioavailability of metals in freshwater. Therefore, as the pH decreases, the free metal ion concentration might increase, which leads to metal desorption from colloidal and particulate matter and to the dissociation of some inorganic and organic metal complexes [7]. Furthermore, organic matter (OM) is well known for its ability to interact with metallic micropollutants, affecting their transport and fate in the aquatic environment [8] [9] as well as their bioavailability, biodegradation, and toxicity towards organisms [10] [11] [12] [13].…”

A simple, green and low-cost agarose-based binding layer for simultaneous determination of cations and anions in aquatic systems using DGT

“…2 This technique uses the diffusion properties to distinguish the chemical species that are sampled by the binding phase. The chemical species sampled by DGT mainly are free ions and kinetically labile complexes (easily dissociated complexes 3 ). In addition, DGT is able to preconcentrate analytes, giving time-integrated information about their concentration at trace and ultra-trace levels.…”