Evaluation of rehabilitation options for Mount Lyell using whole-effluent toxicological tests on freshwater organisms
Supervising Scientist Report 122
Humphrey C, Templeman S, Camilleri C and Klessa D
Supervising Scientist, 1997
ISBN 0 642 24322 0
- SSR122 - Evaluation of rehabilitation options for Mount Lyell using whole-effluent toxicological tests on freshwater organisms (PDF 3.2 MB)
A century of continuous copper mining and processing at the Mount Lyell Mine, Queenstown, Tasmania, has resulted in severe environmental impacts both in the mine area and off-site. Amongst the impacts arising from discharge of metal-enriched acid drainage, slag and tailings are the pollution of fresh and marine waters and the deposition of tailings and slag in Queen and King Rivers and Macquarie Harbour.
Part of the objective of the Mount Lyell Remediation Research and Development Program (MLRRDP), established in 1995 as a joint Tasmanian and Federal Government program to develop a strategy for remediating the environmental effects of past mining at Mount Lyell, is to assess the effectiveness of various remediation options in enabling return of life to the polluted Queen and King Rivers. Results of toxicity tests on freshwater organisms may be usefully applied to this problem but proposals for such study were initially discounted as it was anticipated that future concentrations of copper in the receiving waters downstream of the mine would be well above those concentrations for which, based on published guidelines, aquatic life could be sustained and protected (eg ANZECC 1992).
Interim results from other MLRRDP projects and associated studies, however, suggested that these original premises may not have been correct; thus (i) copper concentrations would be reduced substantially in the lower King River (to ~ 20-60 m g/L) if 90% of the acid drainage was treated by neutralisation (DELM, unpub), and (ii) ameliorative effects were observed amongst marine organisms exposed to Macquarie Harbour waters containing 10-42 µg Cu/L - a result, it was suggested, of copper adsorption to colloidal iron, manganese and aluminium oxides/hydroxides (Stauber et al 1996).
The impetus for carrying out an initial investigation of freshwater toxicity was to determine whether the countering of acid mine drainage at source, in association with any possible ameliorative effects present in freshwaters of the Queen and King Rivers downstream of the Mount Lyell mine, would allow biological recovery of the Queen and King Rivers to take place. Results using 'whole-effluent' toxicity testing techniques could then be used to estimate the effectiveness of various remediation options canvassed to reduce acid drainage from mining operations at Mount Lyell, including neutralisation, in allowing the return of aquatic life to the Queen and King Rivers. Specifically, the project was designed to estimate the percentage of acid mine drainage that would be required to be neutralised with lime to produce an effluent mix in which aquatic life could survive.
Two temperate cladoceran species, Daphnia carinata and Ceriodaphnia dubia s. l., were tested initially using various ratios of neutralised (to pH 6.5) to raw Mount Lyell mine acid drainage, 65:35, 80:20 and 95:5, each serially diluted with West Queen River water. Both cladoceran species proved intolerant of the soft naturally-acidic diluent water though one partially-successful test using C. dubia s. l. established that all concentrations of 65:35 and 80:20 neutralised acid drainage water were toxic to test organisms, resulting in 100% (or near) mortality. From these preliminary results it was concluded that the options of 65:35 and 80:20 neutralisations would be unlikely to support the recovery of aquatic life to the King and Queen Rivers.
Further toxicity tests were conducted using test species that occur naturally in soft acidic stream waters. Two species, a cladoceran, Moinodaphnia macleayi, and a freshwater cnidarian, Hydra viridissima, were assessed for their ability to survive and breed in West Queen River water. Eventually, M. macleayi like the previous cladoceran species used, proved intolerant of West Queen River water though H. viridissima reproduced successfully in this water at 20° C.
On the basis of earlier results, the neutralisation regimes were changed to 95:5 and 99:1 for further testing of Hydra viridissima. Four H. viridissima population growth tests, including two initial range finding tests, were conducted using a range of concentrations from 95:5 and 99:1 neutralisation regimes. The NOEC, LOEC and EC50 for each neutralisation regime were derived from pooled test data with copper concentrations corresponding to these test end-points shown to be very similar. Averaged between the two neutralisation regimes, copper concentrations corresponding to NOEC, LOEC and EC50 were ~15, 18 and 28 m g/L respectively.
Using the results of another MLRRDP project, it was shown that, of the constituents present in neutralised mine effluent, projected Cu concentrations would probably be most limiting to biological recovery in the receiving waters downstream of the Mount Lyell mine. The responses of the cladoceran Ceriodaphnia dubia s. l. and cnidarian Hydra viridissima to copper present in neutralised mine effluent were generally consistent when compared with each other (NOECs of ~12 and 15 m g/L respectively) and with other C. dubia data. Equivalent NOEC values for Cu found in this study were generally higher than guideline values from Australia and elsewhere. Nevertheless, the results indicate, in contrast to those reported for the marine environment (Macquarie Harbour), that no comparable ameliorative effects were present in the stream waters around the Mount Lyell mine that would support the viability of any suggested remediation options for assisting recovery of aquatic life.
In a separate study establishing concentration boundary limits for metals, including Cu and Al, within the King and Queen Rivers under a variety of flow conditions and scenarios of mine effluent treatment (principally neutralisation), the greatest potential for biological recovery was shown to be in the King River upstream of the delta and the least, at the confluence of Haulage Creek with the Queen River. The lowest projected concentration of total soluble Cu in the Queen River under various acid neutralisation regimes was an estimate of 366 m g/L (Klessa et al 1997), far exceeding the equivalent NOEC value (~15 m g/L) found in this study. None of the neutralisation options, therefore, would facilitate the return of life to the Queen River.
For the King River, the maximum protection afforded to aquatic organisms was that prevailing under a scenario of 99% neutralisation (to pH 6.5) of acid drainage and maximum dilution with the power station below Lake Burbury operating; under these conditions projected Cu concentration would approach 10 m g/L (Klessa et al 1997). However, with the power station not operating (12 hours in a 24 hour cycle), estimates of Cu concentration in the King River would range between 74 and 235 m g/L. Because the NOEC value is intermediate between these diurnal ranges, the potential may be present for some partial recovery of life in the King River. Additional toxicity tests employing pulsed and episodic exposure of test organisms to neutralised acid drainage would be required to resolve this issue.