Users

The many hundreds of users of DGT® throughout the world have deployed it in all continents, even including Antarctica and the Arctic.

Widely applicable, users include diverse industries, from mining to agriculture, environmental consultants, government agencies, universities and research institutes.

DGT® has pioneered many research areas, including 2D imaging of solutes in sediments and soils, but it is also used routinely. DGT has been adopted as a routine method for water quality monitoring and assessment by about 100 environmental agencies, monitoring stations, soil testing laboratories, fisheries and consultancy companies. For example, many Australian farmers use it to assess phosphate deficiencies of their soils. (Above field-trial image curtesy of Sean Mason)

DGT Case Studies

A few examples of the many uses of DGT passive samplers are found in this series of Case Studies.

Major comparative survey of contaminants in coastal waters using DGT (more...)

MONITOOL, New tools for monitoring the chemical status in transitional and coastal waters under the Water Framework Directive, is a major European Research programme that champions the use of DGT. It aims to establish how well Environmental Quality Standards can operate using DGT measurements rather than the existing definitions based on dissolved concentrations (metals), total concentrations (organic contaminants) or concentrations in biota (hydrophobic organics). Extensive work packages are underway to compare DGT measurements with traditionally collected data over a wide geographical area. The collaborators are making measurements in the Atlantic regions embracing the Canary Islands, Portugal, Spain, France, Ireland and the UK, with additional measurements in the North and Mediterranean Seas. The main research partners are:

Dublin City University, Ireland
Instituto Tecnológico de Canarias, Spain
Instituto Português do Mar e da Atmosfera, Portugal
Fundación AZTI, Spain
Institut Français de Recherche pour l’ Exploitation de la Mer, France
Centre for Environment, Fisheries and Aquaculture Science, UK
Università degli Studi di Cagliari, Italy
Instituto Superior Técnico, Portugal

Monitool has made available a series of videos which explain the rationale of the programme and show sampling campaigns in action. An outstanding set of practical, instructional videos go step by step through the detailed protocols the partners have adopted for DGT preparation, field deployment and preparation for analysis.

Speciation of Trace Metals in the Baltic Sea (more...)

The Baltic Sea

DGT was used by a consortium of universities, from Lulea, Stockholm and Oxford, and the Swedish Natural History Museum, to study metal speciation in the Landsort Deep of the Baltic Sea. They compared in situ measurements by DGT with samples taken for ultrafiltration. For Cd, Mn and Zn the DGT measured concentrations agreed very well with concentrations measured after filtration through a 1 kDa filter. Filters specified as 1 kDa approximately corresponds to a pore size of 2 nm, comparable to the pore size of the DGT diffusive gel of 2-3 nm. This good agreement between techniques indicates that for these metals there were no significant metal ligand complexes. For Cu and to some extent Ni, DGT labile concentrations were lower than the measurements by ultrafiltration. This indicated the presence of strongly binding Cu complexes, small enough to pass through membranes, but insufficiently labile to be measured by DGT. This study provided a clear demonstration of the capability of DGT to make reliable measurements of trace metals at very low concentrations.

Adapted from J. Forsberg, R. Dahlqvist, J. Gelting-Nystrom, J. Ingri, Trace metal speciation in brackish waters using diffusive gradients in thin films and ultrafiltration: comparison of techniques, Env. Sci. Technol., 40 (2006), 3901-3905.

Horizontal bars are measurements from DGT deployed for typically 2 weeks. Squares are measurements after 1 kDa ultrafiltration.

Continuous monitoring of phosphate from an agricultural catchment (more...)

Installing the THOË sampler in a creek

Agricultural activities have the potential to increase dramatically the concentrations of nutrients into water courses. A recent study by Luode Consulting demonstrated the importance of continuous monitoring of phosphate concentrations. They used a programmable sampler that automatically deployed DGT devices with an iron oxide binding layer (LSNP-NP) in a small creek downstream of farmland. The THOË automatic sampler, which is available through AEL, was programmed to exposed DGT devices over twelve 24-hour periods. To demonstrate this innovative technique provided an improvement over traditional sampling, several spot samples were collected and analyzed using classical colorimetric determination by CFA (Continuous Flow Analysis).

THOË’s integrated temperature logger was used to record water temperatures over the study period (0.2-6.5°C) to allow accurate determination of the daily dissolved phosphate concentrations from the DGT measurements.

During the study period the THOË autosampler permitted the identification of a severe pollution event with phosphates concentrations reaching over 10 times the lowest values recorded. The pollution event was traced back to manure being cleaned out of a cow house. It could have easily been missed if reliance was placed solely on spot samples.

Daily phosphate concentrations determined in a small creek using a THOË sampler

Monitoring trace metals in a marine effluent outfall in New Caledonia (more...)

While mining is an important part of the New Caledonian economy, being the third top nickel producer in the world, New Caledonia is also home to the third largest barrier reef in the world. This barrier reef and its associated lagoons were listed as a world heritage site in 2008. Given the biological diversity present in these ecosystems, it is essential to ensure these industrial activities do not have any detrimental effects on the marine environment, by performing adequate monitoring.

One mining operator has their marine outfall located within one of the world heritages zones and uses DGT passive samplers, deployed automatically using THOË, to monitor dissolved metals concentrations in the waters adjacent to the outfall. The THOË automatic sampler, which is available through AEL, can be programmed to deploy and retrieve sequentially up to 12 DGT passive samplers for any desired time periods and intervals between deployments.

Deployed on mooring lines six THOË samplers have been used for over three years to provide time series data on dissolved metal concentrations. Positioned at increasing distances from the outfall, monitoring is conducted over two-month periods and several times a year at a depth of approximately 35 meters. Local regulatory authorities require the company to ensure compliance with strict release limits, but it must also demonstrate no detrimental effects are observed in the surrounding environment. For this reason, continuous monitoring is preferred over grab sampling. In addition to the continuous data collected, sampling logistical costs have been vastly reducing with only two trips required every two months.

Further case studies on:

Hexavalent chromium and dissolved metals in rivers,
Monitoring dissolved metals in a port,
Investigating shallow hydrothermal sources of trace elements
that use DGT with the CHLOË automatic deployment system are available under the USER Stories section of the AEL CHLOË website.

DGT videos

Some users have created their own training videos for using DGT passive samplers.

Deployment in streams and storm overflows Two videos prepared by The New Zealand National Institute of Water & Atmospheric Research Ltd (NIWA) show in detail how to go about deploying DGT devices in these situations.

Automated system for DGT deployment AEL/Technicap market a fully programmable sampler, called THOË for automatically deploying DGT devices. This video shows its use at sea.

Complete DGT deployment procedure The programme MONITOOL that assess the effectiveness of DGT for regulatory water quality monitoring has a series of detailed videos. They illustrate detailed protocols for preparing DGT passive samplers prior to deployment, the deployment procedure, retrieval and laboratory preparation prior to analysis. Other videos give the aims of the programme and show actual field situations of deployment in coastal locations.

Speciation and bioavailability of plutonium using DGT A consortium of Swiss institutes provide a video showing the methods they used to undertake this exacting work using DGT passive samplers.