Abstract

Iron Cove catchment (~1500 ha) on the southern shores of Port Jackson (Sydney) has been highly urbanised (>90%) for a considerable time (1800s). A map of the area was divided into squares 200 by 200 m and a soil sample was taken randomly in each defined area from the dominant land use type in each square (n = 374). The objectives of the study were to determine the distribution and sources of heavy metals (Cu, Pb, Zn) in surface soils over the catchment and to assess soil quality in terms of guidelines and bioavailability of these metals.

The concentrations of Cu, Pb, and Zn were determined for total soil and on a normalised basis. These metals are elevated across the whole catchment, with mean total concentrations for Cu, Pb, and Zn of 62, 410, and 343 mg/kg and 50 percentiles of 44, 203, and 224 mg/kg, respectively, whereas mean enrichment over background is 2, 5.5, and 4.6 times, respectively. Such a wide, regional metal enrichment is probably related to atmospheric deposition from industry inside and beyond the catchment. The highest concentrations of most metals were in soils from the north-east part of the catchment in an area where dwellings and buildings are oldest and where major roads and railway lines converge. Normalise data suggest sources of these metals are roads, railway lines, and older lead-painted houses. Independent studies in the catchment support roads as being an important source of metals in the area. Total soil chemistry indicates that 34, 33, and 56% of the samples were above the Australian and New Zealand Environment and Conservation Council (ANZECC) and National Health and Medical Research Council (NH&MRC) guidelines for Cu, Pb, and Zn, respectively, and selective extraction procedures (EDTA and HCl) indicate that 46–86% of these metals may be bioavailable.