Assessment of heavy metals and metalloids from historical mine practices in the Leichhardt River, Queensland, Australia

Abstract

An ecological risk assessment was undertaken of the aquatic ecosystem at the Leichhardt River, Mount Isa to assess the effects of metal or metalloid contamination of the Leichhardt River, from residual contamination of mine sediments largely resulting from mine practices in the 1940’s. The assessment of sediments in the Leichhardt River involved comparison of the concentrations of heavy metals and metalloids with the ANZECC/ARMCANZ (2000) interim sediment quality guidelines (ISQGs). Results of the ecological risk assessment indicated that all sites including the background site exceeded one or both the ISQG-High and ISQG-Low trigger values based on total concentrations. A lesser number of sites exceeded the ISQG-Low trigger values once the 1 M hydrochloric acid extract was used as an indication of bioavailability. To assess the significance of the exceedances of the ANZECC ISQG trigger levels, a toxicity assessment was undertaken using aquatic macroinvertebrate species. The test results indicated that only the zone of sediment in the Leichhardt River within Mount Isa city and adjacent to the Velodrome (Sites 3 and 4), associated with acidic sediment from oxidised sulfide mineralisation and elevated metal and metalloid concentrations had potential to be toxic to aquatic biota and required further assessment. However, all sites where sediments exceeded the ANZECC ISQG-Low trigger required toxicity assessment. Only Sites 3 and 4 exhibited sediment toxicity with both aquatic test species. Following completion of the Leichhardt River Remediation Project in May 2008 further ecological risk assessment of sediment was undertaken with test organisms. The ecotoxicity testing of the remediated Leichhardt River sediment showed no further effects to test species and indicated that the remediation of sediment within the city area was completed satisfactorily