The device, known as DGT (Diffusive Gradients in Thin films), has previously been used to measure contaminants in Antarctica, as well as tropical and temperate environments.
For the first time at Casey research station last summer, a team, led by Professor Dianne Jolley of the University of Wollongong,* aimed to test the device in the Antarctic environment and correlate metal concentrations measured by the device, with toxicity to Antarctic organisms.
“There are some sites in Antarctica where human activities have left a legacy of metal and other contaminants,” Professor Jolley said.
“Metals may be locked up in soil in mineral form and unavailable to organisms, or they may occur as ions that are free to interact with the environment.
“We want to understand what concentration of these metals are free or ‘bioavailable’. Once we know this, we may be able to predict how toxic the metals are to organisms living in those environments.
“This information will allow metal concentration thresholds to be established which, if exceeded, will trigger decisions on whether a site should be remediated.”
While DGT could provide a way to measure these bioavailable metal ions, Dr Jolley said the team also needed to conduct further tests on the device’s performance in extreme temperatures, and confirm its suitability in field and laboratory-based applications.
The team was specifically looking at five metals — copper, cadmium, nickel, lead and zinc — which occur in fuels, and historic general tip waste, old laboratory and photography chemicals, and batteries.
University of Wollongong PhD student, Darren Koppel, helped deploy DGTs in nearshore waters and freshwater melt streams, and collected soils and sediments for testing in the laboratory. Testing sites were selected from contaminated, partially remediated and pristine areas, to reflect the broad range of site conditions and potential metal concentrations.
Mr Koppel said the DGTs are effectively a three-layered sandwich that is applied to wet samples.
“The first layer is filter paper that only lets dissolved metals pass through,” he explained.
“The second layer is a water-based gel that sets up a gradient to facilitate the diffusion of dissolved contaminants. The final layer is a resin that binds the specific metal ions that we’re studying.”
To measure contaminants in nearshore environments around Casey, the team put DGTs in plastic baskets and moored them in place with a buoy. For soils, samples were taken back to the laboratory and wetted down, and probes were placed on their surface.
To measure contaminants in marine sediments, cricket-bat shaped DGTs were placed in large containers of marine sediment and seawater in the laboratory, or in fresh meltwater streams in the field.
The bat shape allows the sediment DGTs to measure a depth profile of the metals — from the overlying water to a sediment depth of about 10cm. The interface between the sediment and surface water is where many organisms dwell and feed, and much of the chemistry happens.
“One of the aims of this project was to see how useful DGTs are in the polar environment,” Mr Koppel said.
“We had some challenges with the sea ice at our marine sites, which moved some of the DGT moorings and we lost two of the 11 that we deployed.
“As temperatures changed over the summer months we also found that some melt streams froze over during the experiment, making the DGTs inoperable.”
The devices were collected after one to two weeks in soils and sediments, and four weeks in waters, and the binding resins were removed. The resins are now being analysed for the five metal concentrations. The results will reflect the free metal concentrations that are available, over time, to interact with organisms.
“We’ve also taken samples of the sediments, soils and waters to look at the total concentration of metals in each, so that we can compare that to the concentrations measured by the DGTs,” Mr Koppel said.
“This will allow us to judge how much biologically available metal is leaching into the environment and potentially posing a risk to Antarctic organisms.”
If the DGTs function well in Antarctic conditions, the team will be able to compare the results with research on toxicity thresholds for a range of Antarctic organisms.
This ecotoxicological research has been conducted by a team at the Australian Antarctic Division, led by Dr Catherine King†, over the past 10 years.
Dr King’s team has been assessing the toxicity of a range of contaminants on marine and terrestrial Antarctic organisms (Australian Antarctic Magazine 27: 3, 2014). This season they continued tests with the five metals, individually and in mixtures, on an aquatic micro-invertebrate and a moss collected from areas where the DGTs were deployed.
“If the DGTs are found to be suitable for Antarctic conditions, we’ll be able to deploy them at suspected sites of contamination to see if there’s a risk of toxicity to the organisms living there,” Dr King said.
“They will be a useful addition to our current ecotoxicology tool kit, and will provide a further line of evidence to direct our remediation activities and prioritise sites for clean-up.”
Australian Antarctic Division
*Australian Antarctic Science Project 4326
†Australian Antarctic Science Project 4100