Sediment Metal Concentration Survey Along the Mine-Affected Molonglo River, NSW, Australia

Abstract

Metal concentrations were measured in sediments of the mine-affected Molonglo River to determine current metal concentrations and distribution along the river. Compared with an uncontaminated site at 6.5 km upstream of the Captains Flat mine, sediments collected from the river at ≤12.5 km distance below the mine had a significantly higher percentage of finely divided silt and clay with higher concentrations of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). The measured metal concentrations in the mine affected sites of the river were in the following order: Zn = 697-6818 > Pb = 23-1796 > Cu = 10-628 > Cd = 0.13-8.7 µg/g dry mass. The highest recorded metal concentrations were Cd at 48, Cu at 45, Pb at 240, and Zn at 81 times higher than the background concentrations of these metals in the river sediments. A clear sediment metal-contamination gradient from the mine site to 63 km downstream was established for Cd, Cu, Pb, and Zn in the river sediments. Compared with sediment metal concentrations before a major flood in 2010, only Zn concentrations increased. For all of the mine-affected sites studied, Cd and Zn concentrations exceeded the (ANZECC/ARMCANZ, Australian and New Zealand guidelines for fresh and marine water quality. Australian and New Zealand Environment and Conservation Council/Agriculture and Resource Management Council of Australia and New Zealand, 2000) interim sediment-quality guidelines low values for Cd (1.5 µg/g dry mass) and the high value for Zn (410 µg/g dry mass). Existing metal loads in the riverbed sediments may still be adversely affecting the river infauna.

The freshwater bivalve Corbicula australis as a sentinel species for metal toxicity assessment: An in situ case study integrating chemical and biomarker analyses

“…This area of the river has a legacy of sediment metal contamination following 8 decades of mining for zinc, copper, lead, silver, and gold. The locations were chosen based on previous work that characterized sediment metal concentrations at 10 locations along a 70-km stretch of the Molonglo River, upstream and downstream of the Captains Flat mine, showing that concentrations of zinc, lead, cadmium, and copper were elevated in sediments downstream of the mine relative to those upstream [24]. The locations were chosen based on previous work that characterized sediment metal concentrations at 10 locations along a 70-km stretch of the Molonglo River, upstream and downstream of the Captains Flat mine, showing that concentrations of zinc, lead, cadmium, and copper were elevated in sediments downstream of the mine relative to those upstream [24].…”

“…Three locations downstream of the Captains Flat mine (Railway, Briars Sharrow, and Burbong; 12.5 km, 32 km, and 47 km, respectively) were selected to represent a decreasing metal contamination gradient, and 1 location 6.5 km upstream of the mine (Reference) was selected to represent relatively clean conditions ( Figure 1). The locations were chosen based on previous work that characterized sediment metal concentrations at 10 locations along a 70-km stretch of the Molonglo River, upstream and downstream of the Captains Flat mine, showing that concentrations of zinc, lead, cadmium, and copper were elevated in sediments downstream of the mine relative to those upstream [24].…”

“…Once metals are incorporated into river sediments, they persist for decades, during which they can alter community structure and biodiversity through toxic effects on aquatic biota [21,22]. During this time, tailing dump collapses, mine spigot dam spills, and acid mine drainage contributed significant loads of zinc, lead, copper, and cadmium to the river [23], resulting in contamination of river sediments along a 50-km stretch of the river [24]. During this time, tailing dump collapses, mine spigot dam spills, and acid mine drainage contributed significant loads of zinc, lead, copper, and cadmium to the river [23], resulting in contamination of river sediments along a 50-km stretch of the river [24].…”

“…Periodic mining and processing of ore, primarily for zinc, copper, and lead, with some silver and gold, occurred between 1882 and 1962 at Captains Flat, in the upper catchment of the Molonglo River (New South Wales, Australia). During this time, tailing dump collapses, mine spigot dam spills, and acid mine drainage contributed significant loads of zinc, lead, copper, and cadmium to the river [23], resulting in contamination of river sediments along a 50-km stretch of the river [24]. Metal exposure affects the oxidative stress pathway in organisms through increased production of reactive oxygen species (ROS) and suppression or increased expression of antioxidants and other oxygen reduction enzymes, increasing susceptibility to lipid peroxidation [25].…”

“…Figure modified from Marasinghe Wadige et al[24], where sediment metal concentration data for other indicated sites are available. Deployment locations for in situ Corbicula australis metal exposure were: location 1, Reference (6.5 km upstream of the mine); location 5, Railway (12.5 km downstream of the mine); location 7, Briars Sharrow (23 km downstream of the mine); and location 8, Burbong (47 km downstream of the mine).…”