Open Cut » Environment
This project builds on the opportunity identified through Project C23037, which showed that the Diffusive Gradients in Thin Films (DGT) technique may be appropriate for assessing bioavailable metal concentrations in streams of the Fitzroy River Basin (FRB). The Project C23037 conducted a trial using DGT to measure metals in water of FRB streams that receive coal mine water discharge. The results of that project showed that the fractions of these metals measured by the DGT technique were significantly lower than dissolved metal concentrations and were varied among elements.
The DGT unit facilitates metal speciation measurements by two ways (1) the diffusive hydrogel and filter membrane control the compounds that can diffuse sufficiently rapidly to contribute appreciably to the accumulated amount of metal (2) the thickness of the diffusion and resin layers can discriminate the measurable species by limiting the time available for dissociation of metal complexes. As the DGT was designed with a diffusive layer that 'mimics' biological membrane uptake, it has been suggested that the DGT could provide a measure of the bioavailable fraction of metals, which is more likely to represent the metal fraction that would be potentially related to ecotoxicity.
This project investigated whether Cu and Ni measured by DGT are equivalent to the bioavailable concentration of Cu and Ni that causes toxicity to two local tests species, a tropical alga (Chlorella sp.) and a temperate zooplankton (Ceriodaphnia cf. dubia). The anticipated application of the outcome of this study would be to develop more realistic tools to monitor and assess environmental risks to the aquatic ecosystem in river receiving mine water discharges through a more accurate measurement of the bioavailable fraction of metal contaminants.
The findings of this research demonstrated that DGT can be used as a conservative tool to monitor bioavailable Cu and Ni in mine related water with lower cost than laboratory measurement of the bioavailable fractions. This study has provided important additional information regarding the applicability of the DGT technique for monitoring bioavailable Cu and Ni concentrations.
Monitoring of river waters receiving controlled released water can be implemented by using DGT samplers to conservatively monitor the resulting bioavailable Cu and Ni fractions, while integrating metal concentrations over the deployment period. This provides a substantial benefit over grab samples, which may miss pulses of dissolved metals due to timing of sample collection among other factors. Ease of deployment and the relatively low installation cost of DGT samplers, they can be deployed at multiple depths and locations to provide an integrative monitor of the risk of metal pollution in a waterbody.
This work has shown that the DGT technique can provide a conservative estimate of bioavailable Cu and Ni concentrations. The effect of DOC on the DGT measurement could be potentially minimised by using of longer deployment times. However, further investigation on a suitable deployment time that could minimize the effect of DOC on the DGT measurement is required to establish the extent of such effects for a range of realistic conditions. This will improve the estimation of bioavailable metal concentrations in FRB waterways.