Abstract
Waterways in the Southern Hemisphere, including on the Australian continent, are facing increasing levels of mercury contamination due to industrialization, agricultural intensification, energy production, urbanization, and mining. Mercury contamination undermines the use of waterways as a source of potable water and also has a deleterious effect on aquatic organisms. When developing management strategies to reduce mercury levels in waterways, it is crucial to set appropriate targets for the mitigation of these contaminated waterways. These mitigation targets could be (1) trigger values or default guideline values provided by water and sediment quality guidelines or (2) background (pre-industrialization) levels of mercury in waterways or sediments. The aims of this study were to (1) quantify the differences between existing environmental guideline values for mercury in freshwater lakes and background mercury concentrations and (2) determine the key factors affecting the spatial differences in background mercury concentrations in freshwater lake systems in Australia. Mercury concentrations were measured in background sediments from 21 lakes in Australia. These data indicate that background mercury concentrations in lake sediments can vary significantly across the continent and are up to nine times lower than current sediment quality guidelines in Australia and New Zealand. This indicates that if waterway managers are aiming to restore systems to ‘pre-industrialization’ mercury levels, it is highly important to quantify the site-specific background mercury concentration. Organic matter and precipitation were the main factors correlating with background mercury concentrations in lake sediments. We also found that the geology of the lake catchment correlates to the background mercury concentration of lake sediments. The highest mercury background concentrations were found in lakes in igneous mafic intrusive regions and the lowest in areas underlain by regolith. Taking into account these findings, we provide a preliminary map of predicted background mercury sediment concentrations across Australia that could be used by waterway managers for determining management targets.
Highlights
Mercury is a highly toxic compound, especially in its methylated form (Ullrich et al, 2001)
Background mercury concentrations in sediments compared to sediment quality guidelines Background mercury concentrations in the 21 Australian lakes ranged from 15.6 ng/g to 249 ng/g
These results indicate that existing sediment quality guidelines in Australia can overestimate Australian background sediment mercury concentrations by at least nine times (Figure 2)
Summary
Mercury is a highly toxic compound, especially in its methylated form (Ullrich et al, 2001). Anthropogenic activities such as fossil fuel combustion (Fabris et al, 1999), industrialization (Navarro et al, 1993), mining (Davies et al, 2018), and agricultural intensification (Denton and Breck, 1981) have led to increasing levels of mercury contamination in aquatic environments. Lintern et al: Background concentrations of mercury in Australian freshwater sediments. The development of mines, and industrialization (Lintern et al, 2015) These studies indicate that it was only with European settlement and industrialization that the metal concentrations in aquatic sediments started to fluctuate significantly.
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