Environmental metals in Australian historic lichens, fungi and wildfire ash
thesisposted on 28.03.2022, 03:06 authored by Li Qin Wu
Australia has a well-established record of environmental metal (e.g. Cu, Pb and Zn) contamination dating back to early mining activities in South Australia in the 1840s. Over the last two centuries, base metal mining and processing, industrial development, the use of leaded petrol in motor vehicles and urban expansion have generated large-scale emissions and depositions of metals into the environment. To date, work to reconstruct the historic and contemporary extent of human impact on environmental contamination in Australia, using biological archives and the products of wildfires, has been spatially limited. This thesis focuses on reconstructing the historic and contemporary records of trace metal atmospheric emissions using two lichen genera and one fungus collected over a 150-year period from the Greater Sydney area and from central and southern Victoria. Recycling of industrial Pb is assessed via measurement of ash residue released from four Australian wildfires that occurred in 2012 and 2013. The Pb isotope ratios of lichens, fungi, air filters,ash, river sediments, soils and rocks are also determined and combined with published isotopic data of various potential emission sources to elucidate the relative importance of each likely emission source. The findings in this thesis show that early metal mining activities have been responsible for elevated Cu, Pb and Zn levels observed in lichen and fungi archives dating back to the 1880s,particularly in central and southern Victoria. Elevated median Pb and Zn values were also measured in archival samples from the leaded petrol era (1932–2001) for both the Greater Sydney and central and southern Victoria regions. Peak Pb enrichments (relative to upper crustal Pb concentrations) were found in the Greater Sydney samples during this time. Lower median Pb levels were found in samples collected post 2002, following the cessation of leaded petrol consumption in 2002. The Pb concentrations measured in ash residues were low,with the exception ash samples from the Duffys Forest on the northern outskirts of Sydney,where median Pb values were an order of magnitude above the local background soil and rock samples. The Pb isotope ratios of lichen and fungi samples in the Greater Sydney area and from central and southern Victoria show a marked fall from the period of 1850–1931 to the period of 1932–1984, following the introduction of leaded petrol in 1932. The Pb isotopic compositions of wildfire ash demonstrate that, in addition to lithogenic Pb, anthropogenic inputs from former leaded petrol deposition are identifiable. Despite the removal of Pb from petrol, the contemporary lichen and fungi samples and wildfire ash deposits investigated in this study demonstrate that emissions from metal sources are persistent in the environment. Thus, while the data indicates that contemporary impacts from environmental emissions are reduced, the evidence shows that the consequences of the legacy of contamination persist. The issue of environmental metal contamination remains a significant and ongoing challenge for scientists addressing accurately the sources and deleterious consequences of toxic metal emissions on both environmental systems and human health.