Relationship between metals leached and soil type from potential acid sulphate soils under acidic and neutral conditions in western Australia

Metal contaminants are likely to be mobilised from soil when in contact with acidic drainage. Soils containing sulphide are often associated with significant quantities of trace metals. Understanding the source of metal pollution is of significant concern for management because sulphide-containing soils are found in close proximity to estuaries, lowland rivers and lakes. This study focuses on Western Australian soils, which are typically sandy and well weathered. Two leachate trials, a batch and a column method, investigated the possibility of characteristic leachate signatures with respect to future traceability of metal contamination from soil drainage. Leaching signatures were assessed for four soil types (grey sand (GS), iron-rich sand (FeRS), silty sand (SS) and peat) found coastally between Perth and Albany, in Western Australia. Trace metals leached from the four soil types showed significant differences for both the metals leached and the concentrations for the column leaching trial. No nickel (<1.0 μgL^-1) but relatively high concentrations of arsenic were leached from the peat site. The FeRS leachates contained chromium, copper, high aluminium and relatively high iron. The GS leached extremely high iron and relatively high manganese concentrations. In comparison, only small concentrations of nickel, iron, aluminium, arsenic and manganese leached from the SS columns. Selenium did not leach above reporting limits (<1.0 μg L^-1) from any of the soil types. This work suggests that leachate signatures from different soil types exist and that soil type should be considered when determining the risk of aquatic impact associated with acidic drainage.