Maxwell Warren, Paul Winn and Larissa Schneider
An ANU (School of Culture, History, and Language; Fenner School of Environment and Society) and Hunter Community Environment Centre collaboration
Mercury is an incredibly toxic heavy metal, which can bioaccumulate and biomagnify through food chains. Over the past century, human activities have increased atmospheric mercury concentrations by 300-500% above natural levels. The predominant anthropogenic sources of mercury emissions worldwide are artisanal and small-scale gold mining (about 38%) followed by stationary combustion of coal (about 21%), non-ferrous metal production (about 15%) and cement production (about 11%).
In response to the rapid increase in global mercury emissions, the United Nation’s Minamata Convention on Mercury adopted a treaty in 2013 to protect the human health and the environment from anthropogenic emissions of mercury. The Treaty includes a ban on new mercury mines, the phase-out of existing ones, the phase out and phase down of mercury use in a number of products and processes, and control measures on emissions to air and on releases to land and water. Despite it entering into force in 2017 and having signed the international agreement, the Australian Government is yet to ratify the Minimata Convention.
Researchers from the Australian National University, and members of The Hunter Community Environment Centre (HCEC) are collaborating in a research project on the history of mercury deposition in Lake Macquarie. Lake and reservoir sediments often contain valuable records of sediment that yield history and sediment-associated contaminant, and therefore, can be helpful to interpret the changes in mercury deposition through time.
Lake Macquarie is a particularly interesting place to study mercury contamination because it has a long industrial history, which includes former and current industries: a lead and zinc smelter, a fertiliser plant and a steel foundry, at the North Side, and a total of three power plants on the South Side.
Reconstructing the history of mercury contamination in this area is important as Lake Macquarie, located 90km North of Sydney in the Hunter Region, hosts numerous important ecosystems, as well as large human population centres. Much of the local population of the City of Lake Macquarie live on the Lake’s shores together with two operating coal-fired power plants; Vales Point and Eraring (Figure 2).
Coal fired power plants emit mercury through the burning of coal and other fossil fuels. The heavy reliance on this form of electricity generation has led to large quantities of mercury and other toxic chemicals being released to the atmosphere. In addition, coal plants generate large quantities of coal ash that includes mercury and other metals, which is often cleaned out of the facilities with water, and then stored in ash dams. These are low, exposed, earthen walled containment facilities which, without proper construction and maintenance, often allow wind-blown ash and leach to contaminate nearby areas and wash into the lake.
Studies have shown that metals such as cadmium, lead, nickel, zinc, and copper and metalloids such as selenium and arsenic, have significantly increased in sediments of South Lake Macquarie since the commissioning of power stations. Nothing is known about mercury to date, due to its particularities as a chemical element and the need for specific analytical setup to conduct reliable measurements. Because of these chemical particularities, we cannot translate the findings from other metals to understand the effects of industrialisation on the natural levels of mercury in the Lake.
This collaborative research between the ANU and the HCEC set out to assess the impact of the local coal plants on Lake Macquarie’s Hg concentration, comparing the Hg levels to the years the plants were constructed, decommissioned, or changed. Members of the HCEC collected sediment cores from a site near the ash dam of Vales Point Power Stations (Figure 3) so ANU researchers could analyse the mercury concentration and date sediments to understand mercury changes over time; seen in Figure 3.
The group is specifically interested in checking changes in mercury in South Lake Macquarie, as a result of the construction of new plants, decommissioning of old ones and as a reflect of new policy and technologies put in place by power stations for better ash handling procedures after coal is burnt.
The results of our initial research are shown in Figure 4. Results clearly show a rise in mercury in the sediment over time, increasing alongside the commissioning of the power stations and ash dams surrounding Lake Macquarie. The period of most significant rise was with the commissioning of Vales Point and Munmorah power plants. The most significant decrease of mercury was at the time Vales Point Power Station was retrofitted with bag filters, which are devices to reduce particle emissions from the stacks.
Another important finding is that mercury in the surface sediments of the lake are being deposited considerable distances from the power stations (Figure 5). This is a different finding than other metals, such as cadmium and lead, which have their hot spot in the lake near the power stations (link to previous study showing this). The most plausible explanation to these findings is mercury’s chemical behaviour. Mercury requires minimal heat to vaporise, being extremely volatile. When the power station burns coal, ~ 98% of mercury is emitted into the air and not captured by bag filters, meaning that the substance is easily dispersed atmospherically, while only small amounts (under 2%) of mercury found in the bottom ashes of coal-fired power plants.
Mercury different from other metals and can travel great distances before cooling and falling to the Earth’s surface; and thus the readings from the samples collected are likely not just from ash dam procedures but also from atmospheric transport and deposition. Mercury is able to contaminate areas and lifeforms great distances from where it is emitted. Please note that, apart from power stations, urbanisation and other industries around the lake may also have contributed to the inputs of Hg into the lake.
As Australian coal-fired power stations rely on outdated emission control mechanisms, vapourised mercury is travelling within a very large radius of power stations. Regulations, including Australia ratifying the Minamata Convention on Mercury, will help monitoring, reporting, and reducing Hg emissions in Australia.
Comparing the concentrations of mercury measured in Lake Macquarie to Default Guideline Value (DGV) for mercury, established by the Australian and New Zealand Guidelines for freshwater sediments (150 ng/g threshold value), we can conclude that mercury concentrations in Lake Macquarie is below the DGV value and currently no health issue is expected for organisms living in the lake in relation to mercury contamination in sediments. However, mercury has been increasing since the commissioning of power stations. Action must be taken in order to prevent further mercury deposition in the Lake and surrounding environments. If no action is taken, mercury may exceed the guidelines value in the coming years and represent a significant threat to the health of wildlife and people feeding on fish and other animals from the lake.
If Australia ratifies the Minamata Convention, coal-fired power stations will be required to retrofit their stations with technology and other improvements aimed at reducing mercury emissions. Technology is available that can reduce mercury emissions by 99%, which would significantly reduce mercury deposition in Lake Macquarie. At the moment, 114 countries have ratified the Minamata Convention. The results of this research highlight the importance of this Convention to be ratified in Australia.
Maxwell Warren has just completed his fourth and final year as an Environmental and Social Studies student at Fenner School of Environmental Science at the Australian National University. He has worked in this research for his Special Topic Project with the aim to learn about the mercury biogeochemical cycle in Australia, to understand how industries have affected the natural cycle of mercury in Lake Macquarie, and to provide Australia with knowledge that will help on the compliance of the Minamata Convention when Australia ratifies it. The help of the Hunter Community Environment Centre (HCEC) has been essential to succeed with this project and demonstrate the importance of developing collaborative work between universities and community centres in environmental research projects.