Establishing geochemical background variation and threshold values for 59 elements in Australian surface soil.

Area of Science:

• Geochemistry
• Environmental Science
• Soil Science

Background:

• The National Geochemical Survey of Australia collected over 1300 sediment samples across 81% of the continent.
• Analysis focused on 59 elements in the <2mm fraction of top and bottom soil layers.

Purpose of the Study:

• Establish geochemical background variation for 59 elements in Australian surface soil.
• Determine geochemical threshold values to differentiate background from anomalous concentrations.
• Compare derived thresholds with Western Australia's ecological investigation levels (EILs) for potentially toxic elements (PTEs).

Main Methods:

• Sediment sampling across 1186 catchments at a density of 1 site/5200km².
• Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis following aqua regia digestion.
• Statistical methods including cumulative probability distributions, Tukey inner fence, and 98th percentile for threshold determination.

Main Results:

• No widespread diffuse contamination by PTEs was found at a continental scale in Australian soils.
• Western Australia's EILs for Manganese (Mn) and Vanadium (V) were found to be unrealistically low.
• Most investigated PTEs showed few sites requiring attention, suggesting localized contamination or mineral potential rather than widespread pollution.
• Geochemical thresholds were established for 59 elements, including critical 'high-tech' elements.

Conclusions:

• Continental-scale geochemical data provide a baseline for Australian soils.
• Existing EILs for some PTEs may require revision based on natural background variations.
• Statistical methods are effective in defining geochemical thresholds for environmental assessment and resource exploration.