The influence of controlled fire on the mobilization of Potentially Toxic Elements (PTE) in a mined landscape : Implications for land management and environmental health

Controlled fires conducted in fire prone areas are an efficient and economic option to reduce the frequency and intensity of wild fires that result in damage to human property, infrastructure and ecosystems. However, in a similar way to wild fires, controlled fires affect many of the physical and bio-geochemical properties of the forest soil, and may remobilize Potentially Toxic Elements (PTE) from vegetation and soil organic matter. The objective of this study is to investigate the mobilization of PTEs in a mined landscape after a controlled fire and to describe their temporal variations in concentrations. Soil samples were collected two days before and two days after the controlled fire, at the end of each season, and after a major rainfall in September 2016, from a legacy mine site in Maldon, Central Victoria, Australia, and analysed for PTE concentrations. The results revealed PTE mobility after the controlled fire, and most of the PTEs (As, Cd, Cu, Mn, and Zn) evidenced an increase in concentration (1.2, 1.5, 1.1, 2.9, and 1.7 times respectively) and other PTEs (Hg, Cr and Pb) shown a decrease (1.4, 1.1 and 1.1 times respectively) immediately after the fire. The increase in PTE concentration immediately after the fire is postulated to be associated with the addition of PTE enriched ash to the soil and the reduction is due to the volatilization of elements during fire. The PTEs, which increased their concentrations immediately after the fire show a temporal decrease in concentration in the post-fire soil environment due to the removal of ash and surface soil by rainfall runoff, leaching and wind activity. However, Hg shows an increase in concentration after the major rainfall event. Although, median concentrations of As, Hg, Pb, Cu and Zn exceeded the Australian and Victorian top soil averages, only As and Hg are considered to be a risk to human and aquatic ecosystems health due to their elevated concentration and toxicity. Climate change and the resulting projection for increased forest fire frequency illustrates a growing concern given the expected concomitant increase in PTE mobilization. Preparing appropriate land and water management strategies, and addressing environmental health practice and policy, specifically at the legacy mining areas require a review. This study highlights the significant risk these sites pose.Doctor of Philosoph