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

SEGH Events

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

  • Status, source identification, and health risks of potentially toxic element concentrations in road dust in a medium-sized city in a developing country 2017-09-19


    This study aims to determine the status of potentially toxic element concentrations of road dust in a medium-sized city (Rawang, Malaysia). This study adopts source identification via enrichment factor, Pearson correlation analysis, and Fourier spectral analysis to identify sources of potentially toxic element concentrations in road dust in Rawang City, Malaysia. Health risk assessment was conducted to determine potential health risks (carcinogenic and non-carcinogenic risks) among adults and children via multiple pathways (i.e., ingestion, dermal contact, and inhalation). Mean of potentially toxic element concentrations were found in the order of Pb > Zn > Cr(IV) > Cu > Ni > Cd > As > Co. Source identification revealed that Cu, Cd, Pb, Zn, Ni, and Cr(IV) are associated with anthropogenic sources in industrial and highly populated areas in northern and southern Rawang, cement factories in southern Rawang, as well as the rapid development and population growth in northwestern Rawang, which have resulted in high traffic congestion. Cobalt, Fe, and As are related to geological background and lithologies in Rawang. Pathway orders for both carcinogenic and non-carcinogenic risks are ingestion, dermal contact, and inhalation, involving adults and children. Non-carcinogenic health risks in adults were attributed to Cr(IV), Pb, and Cd, whereas Cu, Cd, Cr(IV), Pb, and Zn were found to have non-carcinogenic health risks for children. Cd, Cr(IV), Pb, and As may induce carcinogenic risks in adults and children, and the total lifetime cancer risk values exceeded incremental lifetime.

  • Erratum to: Preliminary assessment of surface soil lead concentrations in Melbourne, Australia 2017-09-11
  • In vivo uptake of iodine from a Fucus serratus Linnaeus seaweed bath: does volatile iodine contribute? 2017-09-02


    Seaweed baths containing Fucus serratus Linnaeus are a rich source of iodine which has the potential to increase the urinary iodide concentration (UIC) of the bather. In this study, the range of total iodine concentration in seawater (22–105 µg L−1) and seaweed baths (808–13,734 µg L−1) was measured over 1 year. The seasonal trend shows minimum levels in summer (May–July) and maximum in winter (November–January). The bathwater pH was found to be acidic, average pH 5.9 ± 0.3. An in vivo study with 30 volunteers was undertaken to measure the UIC of 15 bathers immersed in the bath and 15 non-bathers sitting adjacent to the bath. Their UIC was analysed pre- and post-seaweed bath and corrected for creatinine concentration. The corrected UIC of the population shows an increase following the seaweed bath from a pre-treatment median of 76 µg L−1 to a post-treatment median of 95 µg L−1. The pre-treatment UIC for both groups did not indicate significant difference (p = 0.479); however, the post-treatment UIC for both did (p = 0.015) where the median bather test UIC was 86 µg L−1 and the non-bather UIC test was 105 µg L−1. Results indicate the bath has the potential to increase the UIC by a significant amount and that inhalation of volatile iodine is a more significant contributor to UIC than previously documented.