g. Miller et al., 1999 and Taylor and Hudson-Edwards, 2008). Surface Enrichment Ratios >2 indicate surface soil contamination (cf. Taylor et al., 2010 and Mackay et al., 2013). Eighty percent of Cu floodplain SER values are >2, with a maximum of 8.8. Given that Cu was the

primary metal being extracted at LACM, these values demonstrate that the spill has had a marked impact on the floodplain surface relative to deeper sediment concentrations. Although the upper Saga and Inca catchment possess highly mineralised bedrock geology, the SER values signaling pathway coupled with a lack of sediment-metal variation at depths <2 cm confirms that the in situ geology is not a significant factor in explaining the surface enrichment of Cu. The Glencore Xstrata Mount Isa Mines Pty Ltd mining and smelting facility, one of the Australia's largest emitters of Cu to the atmosphere (∼46,000 kg in 2011–12; NPI, 2013), lies ∼140 km upwind of the study catchment. Parry (2000) demonstrated that, at distances greater than 50 km from the mining and smelting operations, surface soil metal concentrations returned to background levels. Therefore, it is unlikely that emissions from Mount Isa Mines have contributed significantly to the surface enrichment of Cu in the floodplain sediment. The effect of Cu contamination on floodplain sediment

quality is evident as far as ∼40 km downstream, but any residual effect has dissipated by ∼47 km downstream, where the Barkly Highway crosses the Saga-Inca catchment (Fig. 2 and Fig. 6). In contrast to Cu, the floodplain surface sediment concentrations of As, Cr and Pb are highly variable. Given that the majority of As, Cr and Pb concentrations Autophagy inhibitor mouse are below or near the mean background concentrations, Sclareol these are probably natural variations rather than the result of impacts arising from the mine spill. Although the vertical soil-metal profiles for Cr and Pb indicate a slight surface enrichment in 60% and 70% of pits, respectively, the SERs are <2, which could be attributable to natural variations in local sediment chemistry. In addition, As displayed no clear soil-metal profile patterns. Thus, considering variability in both lateral

floodplain sediment-metal and the absence of significant surface enrichment, it is evident that As, Cr and Pb cannot be used to delineate the effect of the mine spill. Furthermore, concentrations are below the threshold of concern with respect to Australian Sediment (ANZECC and ARMCANZ, 2000 – ISQG low and high) and Canadian Soil Guidelines (CCME, 2007). Soil-metal profiles for Ni and Al revealed inverse relationships to Cu, with an increase in concentration with depth. Given that Al is a structural element in clays, this increase with depth is probably due to in situ clay mineral variation (e.g. weathering) rather than anthropogenic influence (Siegel, 2002). The cause of the down profile increase in Ni concentration is less definitive.