Release of solutes in environmental systems can occur as both chronic or acute events, associated with both naturally occurring processes and pollution. Environmental monitoring and analysis often rely on grab sampling, which provides a snapshot in space and time. However, solute variability in natural systems makes constraining a representative baseline challenging. Inaddition, environmental risk is typically governed by the lability, bioavailability, and speciation of solutes; but these properties can be altered during sample handling, preservation, and storage. Therefore, the accuracy of solute measurements and associated risk assessments might be limited when using traditional snapshot sampling and subsequent laboratory analysis. Diffusive gradients in thin films (DGT) help address these limitations. DGT tech- niques collect solutes selectively in situ over time, preserving speciation and providing pre-concentrated, low-matrix solutions for sensitive chemical analysis. The sampling device consists of a binding layer, a dif- fusive hydrogel, and a protective filter held in a small plastic housing. The bind- ing layer immobilizes target analytes via ion-exchange or complexation, maintaining a concentration gradient. This gradient drives a flux of labile solute species into the device. Both the hydrogel and binding layers are tailored to the intended use and target solute. Devices can be deployed in rivers, lakes, seawater, sediments, soils or controlled laboratory systems for hours to weeks, enabling them to capture continuous baseline concentrations. Analytes are later extracted from the binding layer by elution and quantified through laboratory analysis. Based on Fick’s first law of diffusion, these data are converted into time-integrated concentrations or fluxes. DGT therefore provides context on environmental supply dynamics and risks, supporting monitoring of contamination, nutrient cycling, and changing ecosystems. For example, DGT has been used to study toxic trace metals, nutrients, radionuclides, organic contaminants, and isotopic signa- tures across aquatic and terrestrial envi- ronments. When combined with chemical imaging, DGT has also resolved microscale solute patterns of elemental mobilization, retention, or transformation around plant roots, sediment–water interfaces, and pollution hotspots.
Author: Antonia Siebenbrunner
Journal: Nature Reviews Earth & Environment