SEGH Articles

Diffusive gradients in thin films (DGT): An emerging technique for bioavailability assessment of chemicals in the environment

08 April 2014
As a rapidly developing passive sampling method for the labile forms of chemicals in waters, sediments and soils, the diffusive gradients in thin films (DGT) technique has significant advantages over conventional methods: in situ measurement, time averaged concentrations and high spatial resolution.

The diffusive gradients in thin films (DGT) technology provides a novel approach for the in situ measurement of the labile forms of chemical elements, such as phosphorus (P), sulphur (S), arsenic (As) and metals in waters, sediments and soils. It was invented in Lancaster in 1993. The simple device uses a hydrogel binding layer impregnated with Chelex resin or other binding agents to accumulate ions. The binding layer is overlain by a diffusive layer of hydrogel and a filter. Ions have to diffuse through the filter and diffusive layer to reach the binding layer. It is the establishment of a constant concentration gradient in the diffusive layer that forms the basis for measuring chemical element concentrations in solutions quantitatively. The effect of temperature can be predicted from the known temperature dependence of the diffusion coefficient.

 Compared with conventional methods, DGT has significant advantages:

  • In situ measurement
  • Time averaged concentrations
  • High spatial resolution

The in situ measurement avoids the artificial influences including contamination of sample collection and treatment which may change the forms of chemicals.  The time averaged concentration reflects representative measurement over a period of time. The high-resolution information captures biogeochemical heterogeneity of interested elements distributed in microenvironments, such as in rhizosphere and the vicinity of the sediment-water interface. Moreover, DGT is a dynamic technique by simultaneously considering the diffusive of solutes and their kinetic resupply from the solid phases. All the advantages of DGT significantly promote the collection of “true” information of the bioavailable or labile forms of chemicals in the environment, with potential applications in agriculture, environmental monitoring and mining industry.


The fundamental theory behind DGT is Fick’s first law of diffusion. For deployment, the unit is emerged in water or inserted into sediments or in close contact with wet soils. The labile forms of chemical elements diffuse through the filter and diffusive gel, adsorbed on the binding gel, and then quantified.

The analytes that can be measured by DGT are determined by the binding agent in use. The binding agent for the first DGT was Chelex resin for the measurements of metal ions. After that, the ferrihydrite gel was used to measure phosphorus, and silver iodide was included in the gel to take up sulphide. Recently the Zr-oxide gel was developed to measure phosphorus and inorganic arsenic with high capacities. The agents are also combined to enable simultaneous measurements of multiple analytes. For example, the hydrous zirconium oxide (Zr-oxide) has been combined with silver iodide to measure both phosphorus and sulphide, and combined with Chelex to measure phosphorus and iron.

Another significant development in DGT is the 2D high resolution measurement, which provides new evidences for the micro-scale geochemical heterogeneity. The scales have generally reached sub-millimetre level using various technologies, including proton induced X-ray emissions (PIXE), computer-imaging densitometry (CID), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and 2D slicing.

The field applications are still at the early testing stage. Further studies are needed to properly interpret the DGT measured results under complex environmental conditions, and standard procedures and guideline values based on DGT are required to pave the way for its routine applications in environmental monitoring.

Contact: Dr. Chaosheng Zhang, School of Geography and Archaeology, National University of Ireland, Galway, Ireland; Prof. Shiming Ding, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China.



Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Fate and partitioning of heavy metals in soils from landfill sites in Cape Town, South Africa: a health risk approach to data interpretation 2019-06-14


    The fate and persistence of trace metals in soils and sludge from landfill sites are crucial in determining the hazard posed by landfill, techniques for their restoration and potential reuse purposes of landfill sites after closure and restoration. A modified European Community Bureau of Reference’s (BCR) sequential extraction procedure was applied for partitioning and evaluating the mobility and persistence of trace metals (As, Cd, Cr, Cu, Ni, Pb, Sb, Se, Zn) in soils from three landfill sites and sludge sample from Cape Town, South Africa. Inductively coupled plasma optical emission spectroscopy was used to analyze BCR extracts. The mobility sequence based on the BCR mobile fraction showed that Cu (74–87%), Pb (65–80%), Zn (59–82%) and Cd (55–66%) constituted the mobile metals in the soils from the three sites. The mobility of Cu, Zn and Ni (> 95%) was particularly high in the sludge sample, which showed significant enrichment compared to the soil samples. Geo-accumulation index (Igeo) and risk assessment code were used to further assess the environmental risk of the metals in the soils. Exposure to the soils and sludge did not pose any non-cancer risks to adult and children as the hazard quotient and hazard index values were all below the safe level of 1. The cancer risks from Cd, Cr and Ni require that remedial action be considered during closure and restoration of the landfill sites.

  • An investigation into the use of < 38 µm fraction as a proxy for < 10 µm road dust particles 2019-06-13


    It is well documented that a large portion of urban particulate matters is derived from road dust. Isolating particles of RD which are small enough to be inhaled, however, is a difficult process. In this study, it is shown for the first time that the < 38 µm fraction of road dust particles can be used as a proxy for road dust particles < 10 µm in bioaccessibility studies. This study probed similarities between the < 10 and < 38µm fractions of urban road dust to show that the larger of the two can be used for analysis for which larger sample masses are required, as is the case with in vitro analysis. Road dust, initially segregated to size < 38 µm using sieves, was again size segregated to < 10 µm using water deposition. Both the original < 38 µm and the separated < 10 µm fractions were then subject to single particle analysis by SEM–EDX and bulk analysis by ICP-OES for its elemental composition. Dissolution tests in artificial lysosomal fluid, representative of lung fluid, were carried out on both samples to determine % bioaccessibility of selected potentially harmful elements and thus probe similarities/differences in in vitro behaviour between the two fractions. The separation technique achieved 94.3% of particles < 10 µm in terms of number of particles (the original sample contained 90.4% as determined by SEM–EDX). Acid-soluble metal concentration results indicated differences between the samples. However, when manipulated to negate the input of Si, SEM–EDX data showed general similarities in metal concentrations. Dissolution testing results indicated similar behaviour between the two samples in a simulated biological fluid.

  • Degradation of petroleum hydrocarbons in unsaturated soil and effects on subsequent biodegradation by potassium permanganate 2019-06-13


    To date, the oxidation of petroleum hydrocarbons using permanganate has been investigated rarely. Only a few studies on the remediation of unsaturated soil using permanganate can be found in the literature. This is, to the best of our knowledge, the first study conducted using permanganate pretreatment to degrade petroleum hydrocarbons in unsaturated soil in combination with subsequent bioaugmentation. The pretreatment of diesel-contaminated unsaturated soil with 0.5-pore-volume (5%) potassium permanganate (PP) by solution pouring and foam spraying (with a surfactant) achieved the total petroleum hydrocarbon (TPH) removal efficiencies of 37% and 72.1%, respectively. The PP foam, when coupled with bioaugmentation foam, further degraded the TPH to a final concentration of 438 mg/kg (92.1% total reduction). The experiment was conducted without soil mixing or disturbance. The relatively high TPH removal efficiency achieved by the PP–bioaugmentation serial foam application may be attributed to an increase in soil pH caused by the PP and effective infiltration of the remediation agent by foaming. The applied PP foam increased the pH of the acidic soil, thus enhancing microbial activity. The first-order biodegradation rate after PP oxidation was calculated to be 0.068 d−1. Furthermore, 94% of the group of relatively persistent hydrocarbons (C18–C22) was removed by PP–bioaugmentation, as verified by chromatogram peaks. Some physicochemical parameters related to contaminant removal efficiency were also evaluated. The results reveal that PP can degrade soil TPH and significantly enhance the biodegradation rate in unsaturated diesel-contaminated soil when combined with bioaugmentation foam.