Using tree rings to track atmospheric mercury pollution in Australia: the

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Using tree rings to track atmospheric mercury pollution in Australia: the legacy of mining in Tasmania. Larissa Schneider, Kathryn Allen, Meg Walker, Christine Morgan, and Simon Haberle Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b06712 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 16, 2019

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Environmental Science & Technology

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

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in Tasmania.

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Larissa Schneider1,2 *, Kathryn Allen3, Meg Walker4, Christine Morgan4, Simon Haberle1,2

5 6 7

1

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2601, Australia

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2 ARC

Archaeology and Natural History, College of Asia and the Pacific, Australian National University, Canberra, ACT

Centre of Excellence for Australian Biodiversity and Heritage, Australian National University, Canberra,

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ACT 2601, Australia

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3 School

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3121, Australia

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4 School

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ACT, 2601. Australia

of Ecosystem and Forest Sciences, University of Melbourne, 500 Yarra Boulevard, Richmond, Victoria

of Archaeology and Anthropology, College of Arts and Social Sciences, Australian National University,

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* Corresponding author: Larissa Schneider. Archaeology and Natural History, College of Asia

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and the Pacific, Australian National University, Canberra, ACT 2601, Australia. Email:

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[email protected]

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1-

INTRODUCTION

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Mining has been central to Australia’s culture and development since early European

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settlement 1. This mining has resulted in contamination of surrounding environments with

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mercury (Hg), potentially posing a threat to both biota and the human population

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Understanding the sources and extent to which Hg concentrations have increased from their

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background values is crucial to putting this contamination legacy into perspective and to protect

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the health of current and future generations.

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In areas where no historical monitoring programme is available, isolated lakes with small

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contained catchments are ideal proxies to track historical atmospheric Hg fluxes as lakes act as

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natural sinks for the deposition of atmospheric contaminants, including Hg

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general, has a dry climate with a mean surface runoff of 50 mm per year 6. Consequently, there

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are relatively few natural lakes on the continent, making it particularly difficult to measure

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historical atmospheric fluxes. Identification of other possible natural sinks is thus necessary in

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order to track the history of heavy metals such as Hg in the environment.

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Trees have long been recognised as archives of environmental pollution over time

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studies have examined their potential to track pollution in urban centres or around contaminated

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sites (e.g. 10,15–18. Essentially, the chemical makeup of the annual woody increment at least partly

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reflects the chemistry of the environment during the year of formation

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concentration in each ring can be precisely allocated to a calendar year, allowing for high

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precision records of Hg contamination in the local environment

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dendrochronology is a promising tool for tracing the history of Hg contamination in Australia.

4,5.

19.

2,3..

Australia, in

7–14.

Many

As such, Hg

10,14,20.

Therefore,



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To date there has been no prior attempt to investigate the potential of any Australian tree species

48

as bioindicators of Hg contamination.

49

In this study we measure Hg concentrations in growth rings of two Australian softwood tree

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species, Huon Pine (Lagarostrobos franklinii) and Celery Top Pine (Phyllocladus aspleniifolius)

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to test their potential to track historical Hg contamination in the former mining areas of

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Queenstown, Zeehan and Roseberry, Tasmania. We aim to: (1) test the applicability of

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dendrochemical analysis in these two species to monitor historical Hg emissions in Tasmania, (2)

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understand the Hg bioaccumulation patterns in these species, (3) identify the main source of Hg

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in West Tasmania, one of the most important mining regions in Australia. If successful, these

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trees will provide a low-impact and high-benefit method to monitor atmospheric Hg

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contamination in western Tasmania and support the Australian Government to implement and

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comply with the Minamata Convention. Our study will be the first to try to track Hg in the

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environment over time in the Southern Hemisphere.

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2- MATERIALS AND METHODS

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2.1-

Historical setting

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Western Tasmania is a mountainous area predominantly underlain by intensely folded and

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faulted Cambrian and pre-Cambrian quartzite rocks and conglomerate units that are intersected

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with highly mineralised volcanic belts 21. This highly mineralised area of western Tasmania has a

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history of mining since 1860s, when gold begin to be prospected in western Tasmania (Figure 1).

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Although interest in mining in western Tasmania was initially sparked by gold, other minerals

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were mined in the region from the 1880s and specific activities in the main mining centres, 3 ACS Paragon Plus Environment

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Zeehan, Roseberry and Queenstown. A detailed description of mining in these three centres is

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provided in the Supporting Information.

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72 73 74 75 76 77

Figure 1 – Map of western Tasmania showing the main mining centres: Zeehan, Rosebery and Queenstown. This map represents the average circulation of air masses in this area during the period 1961-1990 , demonstrating air trajectories and directions of atmospheric particles and associated metals released from Queenstown, Rosebery and Zeehan (adapted from Schneider et al. 2018). On the bottom left side is a close up on the location of the trees that had ring samples collected in this study.



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2.1.1- Zeehan

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Zeehan was established as a mining field in 1882 as a result of the discovery of numerous silver-

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lead deposit (Figure 1). Silver was initially the main mineral extracted and sustained human

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settlements around Zeehan

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concentration mills and two smelters required to locally refine ore 23.

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Zeehan smelters were forced to close between 1909-1911 due to the lack of suitable technology

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to process the ore. Smelters reopened in 1912 24 and in 1923, a new flotation circuit was devised

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and milling and roasting were implemented in the Zeehan smelters to process the high grade zinc

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ores from Rosebery. In 1948, the Zeehan smelters closed down 25.

22.

In 1898, the owners of major mines invested in the four

87 88

2.1.2- Rosebery

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After the gold era in western Tasmania (1860 – 1900), zinc and lead sulphide were discovered in

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the slopes of Mount Black at Rosebery. Rosebery ores were sent to Zeehan for smelting

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the smelters in Zeehan were closed. Since this closure, the ores from Rosebery were sent to

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overseas smelters. Production is ongoing at the Rosebery mine. As the smelter activities were

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restricted to Zeehan, Rosebery was most likely a minor atmospheric emitter of metals to the

94

atmosphere.

24

until

95 96

2.1.3- Queenstown

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In 1896, large scale mining and pyritic smelting was established in Queenstown

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town became the largest copper producer in the British Empire and the Southern Hemisphere 27.

99

In 1922, a flotation method was put in place, reducing atmospheric contamination from the

26,

where the


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smelters. In contrast to the eleven large furnaces required for the previous smelting process, the

101

new process using the floatation method only required one small furnace 26.

102

Between 1940 and 1960, the Queenstown mine faced several problems due to low copper prices

103

and high processing cost. In 1964 the smelter closed down and copper concentrates were shipped

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to smelters on the Australian mainland and overseas. The mine (Copper Mines of Tasmania -

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CMT) has been closed for the last four years for care and maintenance since two successive

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accidents resulting in the death of two workers in 201328.

107 108

2.2- Study site and field sampling

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The west coast receives high orographic rainfall produced by air masses rising over mountains

110

29,30.

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with a mean annual temperature of 11 °C at sea level, and 6°C at 1000 m altitude 31.

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Both Huon Pine (Lagarostrobos franklinii) and Celery Top Pine (Phyllocladus aspleniifolius) are

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softwood species endemic to Tasmania

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hundred (Celery Top pine) or even thousands (Huon pine) of years 33–36. Their longevity allowed

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for the essential establishment of baseline palaeoenvironmental conditions before mining started.

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The potential of these two species to track Hg contamination in the area was, therefore, tested in

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this study.

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Twenty Huon pine and twenty Celery Top pine trees were sampled close to the confluence of

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Newell Creek and the King River (Figure 1), approximately 10 km south of Queenstown. This

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site was chosen as part of a broader study around the ability to use the wood properties, and

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isotopic properties (18O, 13C) from low elevation trees for both climate reconstruction purposes

122

and ecological studies (e.g. Drew et al, 2013; Allen et al., 2013; Loader et al., in prep).

Precipitation can be as high as 3,400 mm and the annual temperature range is 3 – 21 °C,

32,

that produce annual tree rings and live for several



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Trees used in this study were selected based on their relative longevity at the site (> 200 years)

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and their relatively straight and untwisted form. The stand sampled stretched approximately 1.5

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km along Newell creek, all Huon Pine on the northern side of the creek and the majority of

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Celery Top pine on the southern side of the creek (Figure 1). From each tree, a total of three

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cores were obtained; two 5 mm cores were taken with a standard 40 cm increment borer and one

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10 mm diameter core taken with a Tanaka drill fitted with a hollow drill bit.

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Samples were air dried and then glued to mounts and sanded with successively finer grades of

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sand paper until the cellular detail in the rings became visible. Ring widths in the samples were

131

then visually crossdated (matching of patterns of ring width amongst cores) and measured using

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a Velmex measuring stage attached to a linear encoder and computer. Visual crossdating was

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then checked using the quality control software, COFECHA 37. Low elevation trees of both these

134

species are typically difficult to crossdate

135

although missing rings due to ring wedging produced as a response to disturbance at the local

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scale, or branch abscission (especially in Celery Top pine) may be present.

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Due to the poor crossdating of the specimens at the site and the possibility of missing, but not

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false rings, we selected five samples of Huon pine and four of Celery top pine, all with relatively

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large and clear rings that extended back to ~1800 AD or before. These samples were least likely

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to include missing rings and, if any were missing, this would be unlikely to be an issue due to the

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5-yr resolution used for this study (see below). These nine tree cores were then transported to

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the Australian National University for Hg analyses at the Palaeoworks Laboratory (see

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http://palaeoworks.com).

34,38

but neither species is apt to produce false rings,

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2.4- Chemical analyses

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Wood samples were sanded to remove possible contamination on the external layer using Norton

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Wet or Dry sand paper sheets 230 x 280mm - 800 and 1000 Grit. Based on the tree ring dating

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previously performed, a clean razor blade was used to cut the cores into 5-year increments.

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When the rings were tight (successive rings were very small), a 10-yr increment was used in

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order to obtain the required mass. Cut increments were stored in a clean glass vial, covered with

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parafilm and placed on a FreeZone Plus 6 freeze-drier (Labconco, Kansas City, MO) and

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lyophilized at -50 ºC for 48 hours. Dried samples were then ground into finer pieces and

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approximately 100 mg of each sample was placed in quartz sample boats for analysis.

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Total Hg concentration was determined by thermal decomposition, amalgamation, and atomic

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absorption spectrometry using a Milestone Direct Mercury Analyser (DMA-80 Tri-cell;

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Milestone, Bergamo, Italy) using the USEPA method 7473 (USEPA, 1998). Two blanks and two

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Standard Reference Materials (SRMs) were analysed for every 36 samples. A replica sample was

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run for every 10 samples and results for these were within 10% of the original sample and

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reported as the mean between the replicas. SRM 1515 (apple leaves) from the National Institute

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of Standards & Technology were analysed and results were in agreement with the SRM reports.

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2.5- Statistical analyses

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Data were analysed using the statistical package R 3.5.1 39 with p < 0.05 as the level of statistical

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significance. The assumption of normality was checked using the Shapiro-Wilk test and the

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equality of variances checked using the Bartlett test. As data did not meet the assumptions of



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normality and homoscedasticity, they were log (x)-transformed in order to use parametric tests,

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which are typically more powerful than non-parametric tests when data is normally distributed.

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An independent-sample t-test was conducted to compare Hg concentrations between tree species,

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with Hg concentrations in each tree ring sample (5 or 10-year increment) as the dependent

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variable and tree species as the independent variable. A paired-samples t-test was conducted to

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compare Hg concentrations in tree rings before smelting and during smelting period. A

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stratigraphic diagram of Hg concentrations in tree rings over the years was performed using the

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R package analogue (https://cran.r-project.org/web/packages/analogue/analogue.pdf).

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3- RESULTS AND DISCUSSION

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Mercury concentrations for the individual Celery Top Pine and Huon Pine trees for the period

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between 1710 and 2007 are reported in Supplementary Table 1. These data are used to compare

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Hg concentrations between species, across the pre- to during pyritic smelting and with other

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similar studies around the world.

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3.1- Temporal variation of mercury concentrations in tree rings

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Mercury concentrations in tree rings over time, for both species, are illustrated in Figure 2. As

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Hg has historically been used as part of gold prospecting in Tasmania, our initial hypothesis was

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that commencement of gold mining would lead to increased Hg concentrations in trees. No

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historical description of the amount of Hg used in the gold mining era of western Tasmania is

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available in the literature, however, it is estimated that a significant amount of Hg would have


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been used to recover the 837 kg of alluvial gold recovered from the area between 1866 and 1890

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40.

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For a long time, studies on Hg emissions from gold mining suggested that most Hg used in the

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amalgamation process in artisanal mining was lost to the atmosphere

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mercury in the tree rings increased from background concentrations at ca. 1900 (Figure 2). This

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increase occurred 20 years after the instigation of gold mining in the area, suggesting that

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although gold mining activities were carried out within the sampled stand, the quantity of Hg

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emitted from roasting the amalgam was not significant enough to be recorded in the local trees.

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Our results are consistent with other recent studies demonstrating that Hg loss during the heating

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stage of the Au-Hg amalgam is not as significant as first thought because most Hg ends up

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buried at mine-sites or in rivers to which they drained 43,44.

41,42.

Our results show that

199 200 201

Figure 2- Temporal profile of Hg concentration in tree rings of Celery Top Pine (Phyllocladus aspleniifolius) and Huon Pine (Lagarostrobos franklinii) in Queenstown, Tasmania, Australia.



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Notably, however, peak concentrations of Hg in the Newall reek trees coincide with the

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commencement of pyritic smelting for copper and zinc 45. The main source of Hg concentrations

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likely to have affected these trees, therefore, is the Queenstown pyritic smelters. Two lines of

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evidence support this argument. Firstly, Hg concentrations in tree rings begin to increase at the

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same time as pyritic smelting started in Queenstown in 1896 and peaked between 1910 and 1920

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when smelting in Queenstown was also at its peak

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begin to decrease in parallel with the introduction of the flotation method in the Queenstown

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smelter in 1922, which concentrated the ore before the smelting process 26. This new method was

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introduced due to the decrease in the copper content of the Mount Lyell pyrite to 0.6 % and

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required only one small furnace instead of eleven large furnaces prior to 1922, considerably

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decreasing emissions of heavy metals to the atmosphere.

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collection apparatus was placed in the chimney of the smelter and it has been claimed that only

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7% of the 52 tons of valuable flue dust escaped up the chimney each 24 h until the last days of

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the smelter

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1934 is also believed to have decrease the atmospheric Hg emissions 47 and hence uptake by the

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trees.

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The smelting activities in Zeehan are also likely to have affected Hg uptake by tree rings as the

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prevailing wind direction means that trees are located downstream from these activities. A study

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in the area using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT)

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forward trajectories, determined with the average circulation of air masses over Tasmania during

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the period 1961-1990

46.

26.

Second, Hg concentrations in tree rings

26.

Furthermore, in 1934 a dust

This installation of a dust collector apparatus by the smelter company team in

48,

shows that the particles from Zeehan and Queenstown smelters are


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carried to the trees’ location by air masses with high frequency (Figure 1), further supporting the

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contribution of smelters to Hg uptake by these trees.

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3.2- Mercury concentrations before and during pyritic smelting phase

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Background Hg concentration was 2.9 ± 0.7 ng/g for Celery Top Pine and 5.6 ± 0.8 ng/g for

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Huon Pine (Table 1, Supplementary Table 1). With the onset of pyritic smelting, Hg

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concentrations in tree rings increased to 4.2 ± 1.0 ng/g in Celery Top Pine and 12.7 ± 2.5 ng/g in

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Huon Pine (Table 1 and Supplementary Table 1).

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There was a significant difference in the Hg concentrations in Huon Pine between pre-smelting

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(before 1880) and pyritic smelting phase (1900-1930) t(51) = -10, p = 0.000) (Figure 3). There

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was no significant increase in Hg concentration in the wood of Celery Top Pine with the onset of

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pyritic smelting t(29) = -6.4, p = 0.06. These differences in Hg concentrations before and during

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pyritic smelting phase yield an average Hg concentration increase of 0.5-fold for Celery Top

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Pine and an average 1.4-fold for Huon Pine (Table 1, Figure 3). Huon Pine, therefore, should be

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chosen over Celery Top Pine in monitoring programs to track past Hg contamination in

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Tasmania.



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Figure 3 – Mercury concentrations (ng/g) in Celery Top Pine (Phyllocladus aspleniifolius) and Huon Pine (Lagarostrobos franklinii) before and during pyritic smelting. Notched boxplots represent the median and interquartile range (IWR); whiskers extend to the most extreme data points up to 1.5 times the IQR; Red stars indicate outliers.

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Table 1 – Mean Hg concentration, standard deviation and fold-increase per individual tree before and during mining phase.

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Tree Species --> Celery Top Pine Tree ID --> CTP02 CTP03 CTP04 CTP07 HP15 Background Mean Hg concentration (ng/g) 4.5 1.7 2.2 3.4 5.8 1700 to 1900 Standard deviation 1.6 0.4 1.5 2.1 0.7 Mining phase Mean Hg concentration (ng/g) 4.9 2.0 4.3 5.7 11.7 1900 to 1930 Standard deviation 1.4 0.2 2.5 1.7 4.6 Fold-increase from background 0.1 0.1 1.0 0.7 1.0 Period

Huon Pine HP16 HP19 HP20 HP21 3.3 10.6 3.6 4.8 1.0 2.5 0.6 0.6 10.6 21.4 10.8 9.2 1.6 8.3 3.5 3.8 2.2 1.0 2.0 0.9

254 255

3.3- Mercury concentrations between species

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Mercury concentration differed significantly between species. Huon Pine had significantly

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higher Hg concentrations (x̄= 9.1, SD= ± 5.1 ng/g) than Celery Top Pine (x̄= 3.5, SD= ± 1.7

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ng/g), (t(163) = -11.5, p= 0.000) (Figure 4). This difference in the ability to bioaccumulate Hg is

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likely due to anatomy and physiology.

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Given the apparent response to Hg produced by the pyritic smelting process rather than by

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artisanal gold mining, our results suggest that Huon Pine and Celery Top Pine are taking up Hg

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from the atmosphere rather than from the soil. If Hg uptake by these trees species was mainly

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through soil, then much larger increases in Hg concentrations would have been expected at the

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time of peak gold mining (1881-1900 AD)

265

in Hg concentrations in tree rings at this time (Figure 4). Our results are consistent with

266

greenhouse and laboratory studies that have also shown that leaves are the main Hg uptake

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pathway for trees 49–52,52 while Hg uptake from soil is generally limited due to barriers against Hg

268

entry from the root system to the upper part of superior plants 15,18,53.

26,40.

In contrast, there is no evidence of an increase

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Figure 4 – Mercury concentrations (ng/g) in Celery Top Pine (Phyllocladus aspleniifolius) and Huon Pine (Lagarostrobos franklinii). Red stars indicate outliers. On the right side are illustrations of the foliage of Huon Pine and Phyllodes of Celery Top Pine, the likely route by which Hg is taken up from the atmosphere. Huon Pine picture taken by Simon Mustoe and Celery Top Pine picture by Tatiana Gerus.

275 276

Although Celery Top Pine foliage has a larger surface area, this species has a lower atmosphere-

277

foliage Hg absorption rate than Huon Pine, suggesting that surface area is not the most

278

significant factor driving Hg uptake by these trees. The difference in Hg concentrations between

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species may be related to stomatal absorption and the rate of gas exchange by epidermal

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components that affect the rate of Hg uptake by the trees

51.

281

disseminated over the outer (exposed) surface of the leaf

54,55,

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numerous stomata occur in irregular lines, mainly on the lower surface of the phyllodes 54. The

283

location of the stomates on the underside of leaves in tree species could result in any Hg

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deposited on the surface being washed off rather than entering the stomata. This is in agreement

Huon Pine stomates are well while in

Celery Top Pine


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with studies on Populus species, which also have stomata on the underside of the leaf surface

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and have lower Hg concentrations than Pinus species 56.

287

Nonstomatal processes are also important factors affecting Hg uptake by trees. Previous studies

288

have demonstrated that Hg absorption to the epicuticular wax is directly influenced by the

289

composition and properties of the epicuticular wax, which plays an important role in the Hg

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diffusion rate to epidermal cells 57–59 and spatially across the leaf 60–62. Thicker wax, such as that

291

on the Celery Top phyllodes, tends to result in less uptake of Hg

292

surface of Celery Top pine phyllodes may also prevent Hg entering its stomata (pers. comm. G.

293

Jordan, University of Tasmania) and therefore contribute to its lower Hg uptake relative to Huon

294

pine.

60,63,64.

Therefore, the waxy

295 296

3.4- Mercury concentrations within species

297

Within-species differences in Hg concentrations were also observed. For Huon Pine, HP15 and

298

HP19 showed the highest Hg concentrations of all tree individuals while CTP02 had the highest

299

Hg concentrations amongst Celery Top Pines individuals (Supplementary Figure 1,

300

Supplementary Table 1). Underlying geology, light availability, temperature, and catalase

301

activity are known factors to influence Hg uptake in trees

302

importance of these factors at this stage is premature and would require collection of more data,

303

but results clearly demonstrate the importance of analysing several individuals of the same

304

species in the same geographical area in order to obtain a mean rate of Hg uptake that evens out

305

the differences by individuals.

65–67.

Speculation about the relative



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Tree age has also been reported as a factor leading to differences in Hg uptake amongst

307

individuals of a single species

308

changes in stomata and cuticular properties, and the saturation of absorption sites in cuticles is

309

reached more quickly with increasing tissue age. In this study, however, Hg concentrations differ

310

in trees of similar age (Supplementary Table 2).

13,68.

Older trees have been found to take up less Hg due to

311 312

3.5- Comparison with other species

313

Mercury concentrations in reported in the rings of other tree species around the world are

314

reported in Table 2. The Hg concentrations in Celery Top Pine (2.9 ng/g) fall in line with the

315

range of values reported for other tree species. Huon Pine, with higher background

316

concentrations (5.6 ng/g), has similar Hg background concentrations to European Beech (4.1

317

ng/g) and Mountain Birch (5.1 ng/g). This higher background concentration as well as the

318

significant increase in Hg concentration under contaminated conditions results suggest that Huon

319

Pine ranks as one of the top three Hg bioaccumulators (together with Betula alba and Quercus

320

robur), and is therefore a good indicator of Hg atmospheric flux Table 2. Further, the longevity

321

of Huon Pine enables long term historical Hg monitoring.

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Table 2 – Mercury concentrations (ng/g) in tree species from around the world, and for Huon Pine and Celery Top Pine (this study). Background Contaminated Hg concentration (ng/g) in bole wood American beech Fagus grandifolia 1.5 Not reported Balsam fir Abies balsamea 1.5 Not reported Yellow birch Betula alleghaniensis 2.1 Not reported Red maple Acer rubrum 0.8 Not reported Sugar maple Acer saccharum 0.9 Not reported Red spruce Picea rubens 2 Not reported 1.7 Not reported White ash Fraxinus americana White pine Pinus strobus 2.3 Not reported Norway Spruce Picea abies 2.2 Not reported European beech Fagus sylvatica 4.1 Not reported Picea mariana Black spruce Not reported 30 Pinus sp. Poplar 0.9 to 2.1 3.3 to 5.7 BDL 0.4 Silver maple Acer saccharinum Willow Salix rubens 2.2 2.1 Red maple Acer rubrum 0.1 0.4 Red oak Quercus rubra 0.7 1.6 Mountain birch Betula pubescens 5.1 20 Birch wood Betula alba Not reported 13.4 Oak wood Quercus robur Not reported 16.4 11.5 Pine wood Pinus sylvestris Not reported Huon Pine Lagarostrobos franklinii 5.6 12.7 Celery Top Pine Phyllocladus aspleniifolius 3.2 4.2 Popular name

331

Scientific Name

Location

Reference

USA Yang et al., 2018 USA Yang et al. 2018 USA Yang et al. 2018 USA Yang et al. 2018 USA Yang et al. 2018 USA Yang et al. 2018 USA Yang et al. 2018 USA Yang et al. 2018 Czech Republic Hojdová et al., 2011 Czech Republic Hojdova et al 2011 Canada Zhang et al., 1995 USA Wright et al., 2014 Canada Siwik et al., 2010 Canada Siwik et al 2010 Canada Siwik et al 2010 Canada Siwik et al 2010 Norway Reimann et al., 2007 Spain Nóvoa-Muñoz et al., 2008 Spain Nóvoa-Muñoz et al., 2008 Spain Nóvoa-Muñoz et al., 2008 Australia this study Australia this study

332 333

3.6- Directions for Future Studies

334

In order to begin to comply with the Minamata Convention on Mercury, Australia needs to

335

identify sources of Hg in the environment and be able to track concentrations over time. Details

336

about the Minamata Convention on Mercury and the participation of Australia are given in

337

Supporting Information. The results in this study provide crucial information that will help

338

government decision makers understand the main sources of Hg in Australia. This is a vital first

339

step in complying with the Minamata Convention on Mercury, which Australia has signed and is

340

anticipated to ratify in the near future.



Page 20 of 26

341

A lack of isolated lakes suitable for monitoring Hg emissions in Australia means that other Hg

342

proxies need to be found to facilitate this. Our study shows that some tree species can provide a

343

useful archive of information about Hg in the environment. The technique used in this study is

344

rapid and is capable of high temporal resolution with extremely low detection limits. There is the

345

potential to use this technique to analyse the wood of tree species on the Australia mainland in

346

regions known to have long mining legacies, thereby providing a feasible solution to the lack of

347

long-term Hg monitoring in the country.

348

This study has focussed on an area rich in long-lived species with known annual rings and with a

349

long history of mining. In fact, the bulk of Australian tree-ring chronologies originate from

350

Tasmania. While the successful development of tree-ring chronologies on mainland Australia has

351

so far been limited, this does not mean it will not be possible to use these species as bioindicators

352

of heavy metals like Hg. Current work is making significant headway in identifying features,

353

other than ring width, that can be matched across trees of various species

354

prep, Oliver, UWA, unpublished data). This work holds great promise with regard to the

355

production of highly tree-ring series that can provide sub-decadal – annual information. In

356

addition, as discussed by Heinrich and Allen 69, 14C dating is a powerful dating tool resolved that

357

can be used alongside Hg analysis to establish a chronology of concentrations. Furthermore, at

358

least two Callitris species (also softwoods) have been the basis of annually dated chronologies in

359

Western Australia

360

scope to examine the potential of additional tree species as bio-indicators.

361

In Australia, gold smelters and coal-combustion in power stations are the two main sources of

362

Hg emissions to the atmosphere 73. Currently, Kalgoorlie gold mining and smelter is estimated to

363

be the largest Hg emitter in Australia

70–72

33,38

(Gillen et al, in

(Allen et al, in revision for Austral Ecology). There is thus considerable

74,

and Callitris preisii in the region may prove a useful 19

ACS Paragon Plus Environment

Page 21 of 26


364

indicator of environmental Hg. Similarly, long-lived (200+-year) eucalypt species in the Hunter

365

and LaTrobe valleys, where major power stations are located, should be investigated for their

366

potential to provide records of Hg concentrations in the atmosphere.

367 368

Supporting information available: Background on the Minamata Convention and its status in

369

Australia and detailed historical setting description for the mining activities in West Tasmania.

370

Figures and Tables with detailed data is also available in supporting information. This material is

371

available free of charge via the internet at http://pubs.acs.org

372 373

Acknowledgements

374 375

Financial assistance for the research was obtained from the Department of Archaeology and

376

Natural History at the Australian National University. L. Schneider was supported through a

377

postdoctoral fellowship from the School of Culture, History and Language. K. Allen was

378

supported by LP 120104320. We thank Neil Allen, Ralph Bottrill and Les Hay for sharing their

379

detailed knowledge on geology and the history of mining in western Tasmania.

380 381 382

References

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Using tree rings to track atmospheric mercury pollution in Australia: the

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