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

  • Genotoxic effects of PM 10 and PM 2.5 bound metals: metal bioaccessibility, free radical generation, and role of iron 2018-10-09


    The present study was undertaken to examine the possible genotoxicity of ambient particulate matter (PM10 and PM2.5) in Pune city. In both size fractions of PM, Fe was found to be the dominant metal by concentration, contributing 22% and 30% to the total mass of metals in PM10 and PM2.5, respectively. The speciation of soluble Fe in PM10 and PM2.5 was investigated. The average fraction of Fe3+ and Fe2+ concentrations in PM2.5 was 80.6% and 19.3%, respectively, while in PM2.5 this fraction was 71.1% and 29.9%, respectively. The dominance of Fe(III) state in both PM fractions facilitates the generation of hydroxyl radicals (·OH), which can damage deoxyribose nucleic acid (DNA), as was evident from the gel electrophoresis study. The DNA damage by ·OH was supported through the in silico density functional theory (DFT) method. DFT results showed that C8 site of guanine (G)/adenine (A) and C6 site of thymine (T)/cytosine (C) would be energetically more favorable for the attack of hydroxyl radicals, when compared with the C4 and C5 sites. The non-standard Watson–Crick base pairing models of oxidative products of G, A, T and C yield lower-energy conformations than canonical dA:dT and dG:dC base pairing. This study may pave the way to understand the structural consequences of base-mediated oxidative lesions in DNA and its role in human diseases.

  • A systematic review on global pollution status of particulate matter-associated potential toxic elements and health perspectives in urban environment 2018-10-08


    Airborne particulate matter (PM) that is a heterogeneous mixture of particles with a variety of chemical components and physical features acts as a potential risk to human health. The ability to pose health risk depends upon the size, concentration and chemical composition of the suspended particles. Potential toxic elements (PTEs) associated with PM have multiple sources of origin, and each source has the ability to generate multiple particulate PTEs. In urban areas, automobile, industrial emissions, construction and demolition activities are the major anthropogenic sources of pollution. Fine particles associated with PTEs have the ability to penetrate deep into respiratory system resulting in an increasing range of adverse health effects, at ever-lower concentrations. In-depth investigation of PTEs content and mode of occurrence in PM is important from both environmental and pathological point of view. Considering this air pollution risk, several studies had addressed the issues related to these pollutants in road and street dust, indicating high pollution level than the air quality guidelines. Observed from the literature, particulate PTEs pollution can lead to respiratory symptoms, cardiovascular problems, lungs cancer, reduced lungs function, asthma and severe case mortality. Due to the important role of PM and associated PTEs, detailed knowledge of their impacts on human health is of key importance.

  • Interactions between polycyclic aromatic hydrocarbons and epoxide hydrolase 1 play roles in asthma 2018-10-06


    Asthma, as one of the most common chronic diseases in children and adults, is a consequence of complex gene–environment interactions. Polycyclic aromatic hydrocarbons (PAHs), as a group of widespread environmental organic pollutants, are involved in the development, triggering and pathologic changes of asthma. Various previous studies reported the critical roles of PAHs in immune changes, oxidative stress and environment–gene interactions of asthma. EPHX1 (the gene of epoxide hydrolase 1, an enzyme mediating human PAH metabolism) had a possible association with asthma by influencing PAH metabolism. This review summarized that (1) the roles of PAHs in asthma—work as risk factors; (2) the possible mechanisms involved in PAH-related asthma—through immunologic and oxidative stress changes; (3) the interactions between PAHs and EPHX1 involved in asthma—enzymatic activity of epoxide hydrolase 1, which affected by EPHX1 genotypes/SNPs/diplotypes, could influence human PAH metabolism and people’s vulnerability to PAH exposure. This review provided a better understanding of the above interactions and underlying mechanisms for asthma which help to raise public’s concern on PAH control and develop strategies for individual asthma primary prevention.