By Ray Smith
HOBART — The 1992 honours thesis of Alexandra de Blas, which studied the impact of the Mt Lyell Mining and Railway Company on Macquarie Harbour and Strahan, was published last week. Its appearance was delayed 16 months by threats from the company to sue anyone associated with publication of the research.
The study raised concerns over acid drainage from the Mt Lyell mine, which has had a ministerial exemption to pollute since 1974. It also reported mercury concentrations in fish in Macquarie Harbour at or above the level recommended by the National Health and Medical Research Council.
The quantity of acid drainage into the Queen River is unknown. Currently alkaline tailings, which neutralise the acid drainage, are dumped into the river at Queenstown by Mt Lyell. The drainage, however, will continue after the mine closes on December 15.
Water from the Queen River flows into the King River, and then into Macquarie Harbour. Large fish kills have occurred in the harbour, but it is uncertain whether these are the result of pollution from Mt Lyell or from other sources. According to a Department of the Environment and Land Management report, there is some evidence that King River water was implicated.
The pollution could be problematic for fish farms located in Macquarie Harbour, and for other industries such as tourism, which are playing an increasingly significant role in the town's economy. Leases for fish farms in the areas affected have been withdrawn. Nowadays only 7% of the population of Strahan is employed by the mining industry.
The study, in addition to mercury, in fish, found high concentrations of copper were in oysters in the harbour.
Macquarie Harbour is used by many Strahan residents for fishing and recreational purposes, and it is estimated that 20% of the Strahan population could be eating fish with excessive levels of mercury.
The Mt Lyell mine is considered to be the major source of copper in the Harbour. The source of the mercury is less certain. However, information provided by Mt Lyell to de Blas showed that the tailings discharged into the Queen River frequently contain measurable amounts of mercury. Mt Lyell dumps 1.5 million tonnes of tailings into the Queen River annually. Other possible sources remain uninvestigated, such as Hydro-Electric Commission (HEC) dams.
The first part of a state government environmental study, a response to de Blas' thesis, is to be released by early July. It is being funded by, amongst others, Mt Lyell Mining and Railway Company, and the HEC.