An Evaluation of DGT Performance Using a Dynamic Numerical Model

Lehto, Niklas J.; Davison, William; Zhang, Hao; Tych, Włodek

doi:10.1021/es061215x

Cited by 48 publications

(65 citation statements)

References 30 publications

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“…[83] It was successfully modelled using a similar approach to TusseauVuillemin et al [82] but assuming that binding of metal to the resin was controlled by stability and rate constants rather than being instantaneous. [73] The DGT measurement was shown to be independent of the stability constant for metal binding to the resin, provided it was greater than a threshold value. A similar model was used to calculate the lability degree defined as the ratio of the actual contribution of the complex to the metal flux to the maximum contribution reached if the complex was labile (Eqn 10).…”

Section: Accounting For Complexationmentioning

confidence: 96%

“…For simple solutions, relatively weak binding is sufficient to lower analytes to negligible concentrations and so the measurement is expected to be independent of the binding agent. [73] Possible explanations include the binding of Hg to Chelex being kinetically limited and the binding agent affecting Hg hydrolysis.…”

Section: Concentration Of Analyte In the Binding Layermentioning

confidence: 99%

“…The mass that accumulates before steadystate being reached should be considered. Lehto et al [73] used a dynamic numerical model that accommodates the time to steady-state to calculate mass accumulated for various values of t, Dg and D, and compared the mass to that obtained assuming steady-state throughout (i.e. using Eqn 1).…”

Section: Accounting For Complexationmentioning

confidence: 99%

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Progress in understanding the use of diffusive gradients in thin films (DGT) – back to basics

2012

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Environmental context. It is now nearly 20 years since the introduction of the technique of diffusive gradients in thin films, which can provide information on solute concentrations and dynamics in sediments, soils and water. The interpretation of these measurements in terms of concentrations relies on simple equations and associated assumptions. This review examines how well they have stood the test of time.Abstract. Diffusive gradients in thin films (DGT) is now widely used to measure a range of determinands in waters, soils and sediments. In most cases the mass accumulated is interpreted in terms of a labile form of the component being measured using a simple equation that applies to steady-state conditions. During the past decade several publications have revealed phenomena that question some of the assumptions necessary for use of the simple equation. This review systematically examines the available evidence relating to appropriate geometry, possible charge effects, binding of solutes and ligands to the diffusive gel and filter, the rate of reaction with the binding layer, the effects of solution complexation and kinetic limitation, necessary time for deployment and the measurement of nanoparticles. DGT emerges as a robust monitoring tool for labile components in solution. Although there is evidence, for some conditions, of binding of metals and, more moderately, humic substances to the diffusive gel and filter membrane, this is unlikely to affect DGT measurement in natural waters for deployment times exceeding a few days. Detailed speciation and kinetic studies require a more thorough interpretation of the mass accumulated by DGT. A coherent theory has emerged for relatively simple solutions, but systems with complex heterogeneous ligands, as is the case for natural waters, are challenging. The size discrimination of DGT is still poorly known. Systematic measurements with well characterised nanoparticles are required to define the distribution of pore sizes in the gels and to establish the contribution of natural colloids to the DGT measurement.

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Section: Accounting For Complexationmentioning

confidence: 96%

Section: Concentration Of Analyte In the Binding Layermentioning

confidence: 99%

Section: Accounting For Complexationmentioning

confidence: 99%

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Progress in understanding the use of diffusive gradients in thin films (DGT) – back to basics

2012

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“…4). The obtained average (n = 3) mass accumulated after 5 h, for each GFL disc with 3.8 cm 2 effective window area, was 167, 156, 123 and 129 ng for Pb, Cu, Ni, and Fe, respectively (Fig.4) It is important to realize that as long as the capacity of the DGT gel is not exceeded, all metals will accumulate in the resin linearly and the binding affinity of the respective cations is without importance (Davison and Zhang 1994;Warnken et al 2004b;Lehto et al 2006). The binding affinity of the respective trace metals only becomes important if the deployment is so long that the saturation level of the DGT is approached (see below).…”

Section: Sandwich Sensormentioning

confidence: 98%

“…At very high Fe concentrations of 1 mM, as found, for example, in the porewaters of some harbor sediments, capacity is likely to be reached with this sandwich system, precluding its use for Fe, Mn, and possibly Cd. However, all other relevant trace metals will remain unaffected by any potential Fe(II) saturation, as they bind more strongly to the resin (Warnken et al 2004b;Lehto et al 2006). They would displace Fe(II) and continue to bind once capacity is exceeded.…”

Section: Mesocosm Experimentsmentioning

confidence: 99%

A combined sensor for simultaneous high resolution 2‐D imaging of oxygen and trace metals fluxes

Ståhl

Warnken

Sochaczewski

et al. 2012

Limnology & Ocean Methods

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A new sandwich sensor, consisting of an O 2 planar optode overlain by a thin (90 μm) DGT layer is presented. This sensor can simultaneously resolve 2-D O 2 dynamics and trace metal fluxes in benthic substrates at a high spatial resolution. The DGT layer accumulates metals on a small particle size (0.2 μm) chelating resin and records the locally induced trace metal flux during the deployment, whereas the planar optode resolves the O 2 dynamic in near real time at the same location in the sediment. Despite its ultrathin composition, the DGT layer has high carrying capacity for trace metals with no saturation problems during application to typical coastal-or contaminated sediments. Combined with laser ablation, accumulated metal fluxes could be resolved at a resolution of ~200 μm, whereas the O 2 images had a resolution of ~100 μm. A 2-D diffusion-reaction model showed that the enhanced smearing and reduced response time of the O 2 signal associated with the additional DGT layer were marginal. To test sensor performance at realistic conditions, it was applied to an artificial burrow system consisting of permeable dialysis tubing flushed with oxygenated seawater. The measurements demonstrated localized mobilization of Ni, Cu, and Pb close to the burrow wall, where O 2 was elevated. The latter was also confirmed for Cu and Pb in natural sediments irrigated by the polychaete Hediste diversicolor. The sandwich sensor has great potential for investigating interrelations between O 2 dynamics and metal mobilization in complex benthic systems such as burrows, rhizospheres, permeable sands, and microbial mats.

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The temperature and flow dependence of nitrate concentration and load estimates based on diffusive gradients in thin films

et al. 2022

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Concentrations determined using diffusive gradients in thin films (DGT) have been used to derive time‐averaged loads in streams and rivers. However, DGT provide time‐weighted average concentrations that assume the independence of concentration and flow. Additionally, dynamic and coordinated changes in temperature, flow, and concentration are potential sources of bias in concentration and load calculations. We modeled scenarios in which temperature and flow were correlated to varying degrees with concentration and evaluated the consequences for DGT concentration and load calculations. As the correlation between solution flow and concentration moved toward 1 and –1, the load determined by DGT either overestimated or underestimated the actual load by as much as 30%. In DGT‐based load estimates, the degree of potential bias should be assessed, and the concentration‐flow relation should be characterized. As the correlation of analyte concentration and temperature approached 1 and –1, the deviation of the concentration determined by DGT from the actual concentration increased. In most cases, this bias was < 2%; however, if the changes in concentration and temperature were large (∼10 mg L–1 and ∼10 °C), the bias exceeded 5%. Concentration and temperature are unlikely to be perfectly or strongly correlated or anti‐correlated in natural systems and thus should not affect the accuracy of DGT concentration calculations in most circumstances. The more solution temperature, flow, and concentration were uncorrelated, the closer DGT‐derived concentration and load were to the actual solution concentration and load.

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An Evaluation of DGT Performance Using a Dynamic Numerical Model

Cited by 48 publications

References 30 publications

Progress in understanding the use of diffusive gradients in thin films (DGT) – back to basics

Progress in understanding the use of diffusive gradients in thin films (DGT) – back to basics

A combined sensor for simultaneous high resolution 2‐D imaging of oxygen and trace metals fluxes

The temperature and flow dependence of nitrate concentration and load estimates based on diffusive gradients in thin films

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