Using tree rings to track atmospheric mercury pollution in Australia: the legacy of mining in Tasmania.

Historical records of mercury (Hg) deposition in lake sediments have commonly been used to monitor historic atmospheric concentrations. In the Australian environment, however, freshwater lakes are limited, restricting the region for which depositional archives of Hg can be derived. In this study we show that dendrochemistry can provide a record of atmospheric concentrations at the annual scale. We measured Hg concentrations in growth rings of two tree species in Tasmania-Huon Pine (Lagarostrobus franklinii) and Celery Top Pine (Phyllocladus aspleniifolius) at a site in western Tasmania, a region that has been heavily mined over the past 150 years. Although much previous work has linked atmospheric Hg to gold mining, the evidence in this study suggests that smelters in Queenstown and Zeehan, not gold mining activities, were the main sources of Hg emissions to the atmosphere in this location. Huon Pine had significantly higher background Hg concentrations (x̄= 5.62 ng/g) than Celery Top Pine (x̄= 2.95 ng/g). No significant increase in Hg concentration during the peak copper smelting phase (1896 to 1935) was observed for Celery Top Pine, while a 1.4 fold-increase was observed for Huon Pine. Our results show that Huon Pine is one of the most efficient bioaccumulators of Hg worldwide, and represents a significant Hg reservoir in the region, making it a good proxy for track historical Hg emissions in western Tasmania. This case study illustrates the potential of using long-lived trees in Australia to track and monitor Hg contamination in the environment over time. It also assists the Australian government to identify the main emission source of Hg in western Tasmania. The ability to measure Hg in the environment is essential if Australia ratify the Minamata Convention.