Legacy mercury emissions and releases from colonial-era gold mining in Australia

Legacy gold mining in Australia, closely tied to 19th-century colonisation and predating environmental protection laws, has left substantial mercury (Hg) contamination. Historical records in Walhalla, Victoria, indicate that Hg loss via the amalgamation process between 1867 and 1889 ranged between 2.65 tonnes and 34.4 tonnes, with further emissions in the following two decades. Dendrochemical analysis of exotic gymnosperms planted in Walhalla provides the first chronological record of colonial-era Hg emissions in Victoria. Local Bhutan cypress (Cupressus torulosa) and Douglas fir (Pseudotsuga menziesii) show elevated Hg during the peak of mining (1885-1914), reaching 44 ± 17 ng g^-1 and 29 ± 9 ng g^-1 respectively. Additionally, soils near gold-processing sites contain Hg at concentrations 2.5 orders of magnitude greater than background concentrations (41 ± 34 mg kg^-1). Stringers Creek sediments exceed the Australian high risk sediment guideline by 22 times (3.3 ± 3.4 mg kg^-1). Methylmercury (MeHg; 9.4 ± 10.8, max 32 ng g^-1) content of some waterfall sediments is in the global top 10 %. The nonlinear MeHg - total Hg relationship (Spearman ρ = 0.93, p = 0.005) suggests reduced methylation efficiency under high Hg loading. In soils, the relationship between total Hg vs. organic matter relation (R² = 0.47) indicates organic content is a driver of Hg retention. This study establishes an "emission-dendrochemistry-environment" evidence chain, confirming 19th-century mining as a major Australian Hg source with enduring ecological impacts and provides critical information that must be incorporated into national Hg management strategies.