Using geochemical indices to establish background concentration ranges in Australian sediments

Background concentrations of metals in sediments and soil are the naturally occurring metals with no human-derived inputs. Being able to determine background concentrations is becoming increasingly important in Australia as it is used as part of the risk assessment process on contaminated sites. The current study utilised the National Geochemical Survey of Australia (NGSA): The Geochemical Atlas of Australia (GAA) data to form the first Australia-wide assessment of background concentration in sediments using a geochemical index approach. A continental-scale geochemistry database for catchment-outlet-sediments was obtained from the NGSA: GAA covering 1315 sites across all Australian states and territories. Our aim was to develop geochemical indices (Hamon et al. 2004) by determining the degree of association between index metals (Al, Fe and Mn) and other trace elements (Sb, As, Cd, Cr, Cu, Pb, Hg, Ni, Ag and Zn) for assessing background concentration ranges and relationships in Australian sediments. Geochemical indices developed were shown to be a relatively good statistical approached to determine relationships between index elements and natural concentrations of heavy metals in Australian sediments For instance, linear relations between Fe and Cu (r2=0.70, P<0.001), Ni (r2=0.67, P<0.0001), and Cr (r2=0.66, P<0.001) showed good fits. The data based generated by the GAA, offered a means to determine the natural background concentrations of heavy metals in sediment across Australia. The calculated natural background geochemical relationships will provide assistance in the separation of naturally enriched sites compared to human-impacted environments.