Spatial distribution of mercury and other potentially toxic elements using epiphytic lichens in Nova Scotia

Chemosphere 241 (2020) 125064

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Spatial distribution of mercury and other potentially toxic elements using epiphytic lichens in Nova Scotia Sara J. Klapstein a, *, Allison K. Walker b, Cardy Hallett Saunders b, Robert P. Cameron c, John D. Murimboh d, Nelson J. O’Driscoll a a

Earth and Environmental Science Department, Acadia University, Wolfville, NS, B4P 2R6, Canada Department of Biology, Acadia University, Wolfville, NS, B4P 2R6, Canada Nova Scotia Department of Environment, Protected Areas Branch, Canada d Chemistry Department, Acadia University, Wolfville, NS, B4P 2R6, Canada b c

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Epiphytic lichens were used as passive samplers for air pollution.
Data support the hypothesis that lichen Hg is from historical longrange transport.
Potentially toxic elements had concentrations similar to other remote regions.
Element clustering indicated both long-range atmospheric and mineral sources.
Provides baseline data for identifying changes in trace metal distribution.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 May 2019 Received in revised form 18 July 2019 Accepted 4 October 2019 Available online 7 October 2019

The use of naturally occurring epiphytic lichens can be an effective tool for regional monitoring of mercury (Hg) and other potentially toxic elements (PTEs). Nova Scotia, Canada is a hotspot for mercury and other trace metal accumulation in ecosystems; partially attributed to long-range transport of air pollution. The relative contribution of local and international sources of Hg to local air in Nova Scotia is unknown. This study assessed the potential of epiphytic lichens (Usnea spp.) as passive samplers for PTE air pollution in Nova Scotia. Lichens (n ¼ 190) collected across mainland Nova Scotia were analyzed for PTEs. Results indicate that there are 3 distinct clusters of PTEs which suggest patterns and sources for each elemental cluster. Hg was correlated with longitude and prevailing wind direction, and Hg was not significantly different in site-specific hotspot sampling nor year of sampling. Our data support the hypothesis that Hg in lichens is from historical and ongoing long-range transport and diffuse emission patterns rather than localized pollution sources. PTE concentrations were shown to have median values that are similar to other remote regions (such as the Antarctic) however the maximum values were observed to be substantially higher for some elements (e.g. lead, cadmium). This research supports the use of lichens as biomonitors and provides a baseline for future monitoring efforts to identify changes in PTE distribution in Nova Scotia with ongoing industrial activity and a changing climate. Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved.

Handling Editor: Dr Patryk Oleszczuk Keywords: Lichen Mercury Potentially toxic elements (PTEs) Metals Nova scotia Pollution

* Corresponding author. E-mail address: [email protected] (S.J. Klapstein). https://doi.org/10.1016/j.chemosphere.2019.125064 0045-6535/Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved.

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1. Introduction In highly industrialized or urbanized areas with known point sources, active samplers are useful for monitoring targeted contaminant total emissions, however, passive samplers allow for better detection of non-point sources of potentially toxic elements (PTEs) and better spatial resolution (McLagan et al., 2018). Passive samplers are superior, in terms of background exposures, to active sampling instruments because they provide time-averaged concentration data over a duration (McLagan et al., 2016) rather than a snapshot in time. Passive samplers can be manufactured or can be in situ living organisms. Tree bark, needles, leaves, and epiphytic lichens have all been shown to be effective air quality bioindicators of local and global air pollution (Chiarantini et al., 2017, 2016; Cocozza et al., 2016) and declines in lichen biodiversity have been measured in response to air pollution (Cameron et al., 2007; Loppi, 2019). There is ongoing widespread monitoring of trace metals in moss and lichen (Kłos et al., 2018), and research specifically targeting epiphytic lichen monitoring at contaminated mining sites
pez Berdonces et al., 2017) and chemical manufacturing plants (Lo (Sensen and Richardson, 2002). Epiphytic lichens have several characteristics which make them particularly attractive as passive samplers for atmophile elements including: (i) large surface area; (ii) good distribution with ease of collection; and (iii) slow growth rate with long lifespan (Bargagli, 2016). The repeated surveying of in situ epiphytic lichens as PTE biomonitors provides a relatively inexpensive method with good spatial resolution to quantify patterns in trace metal distribution over time in remote areas (Bargagli, 2016). Background concentrations of PTEs provide context when interpreting the spatial distribution of pollution sources and health risks to organisms. Nova Scotia has a wide variety of mineral deposits spread throughout the province. PTEs including but not limited to arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) have been liberated from geogenic sources through a range of human activities including coal-fired power generation, chemical manufacturing, €rup, 2003). Gold waste incineration, metal smelting, and mining (Ja mining was carried out in 64 mining districts in the Meguma Terrane of Nova Scotia from 1861 to 1942 (Bates, 1987). This extensive mining has led to a large quantity of mine tailings containing high concentrations of arsenopyrite throughout areas of southeastern Nova Scotia, many of which are publicly accessible and near residential areas. Gold mining has historically used Hg during the amalgamation and extraction process, and much of this Hg still remains in tailings and poses an ecological risk (Parsons et al., 2012). Atmospheric deposition of Hg originally from anthropogenic sources such as fossil fuel burning and mining activities has decreased in some areas in recent years due to emission controls (Castro and Sherwell, 2015; Zhang et al., 2012). This reduction of emissions and subsequently a reduction in atmospheric Hg deposition should result in mid-latitude temperate ecosystem recovery and some food webs have exhibited reductions in the Hg concentrations of top predator fish in recent years (Braaten et al., 2019; Zhou et al., 2017). However, recovery from the legacy effects of Hg deposition in heavily-impacted regions may take decades due to the time-lags between atmospheric depositional patterns, ecosystem storage, production of methylmercury for biological uptake, and food web transfer. In some ecosystems, atmospherically-deposited Hg may be stored in sediments and released over a long time span. Hg may also be removed from the water column by photoreduction reactions (O’Driscoll et al., 2017, 2004) and subsequent volatilization to the atmosphere and deposition downwind where the cycle repeats. An important aspect in identifying Hg-sensitive ecosystems is to develop an effective

quantification of the relative distribution of atmospheric Hg deposition. The Mercury Deposition Network (MDN) is part of the National Atmospheric Deposition Program (NADP) which is tasked with analyzing spatial trends in Hg deposition. Recent analyses of temporal trends in Hg deposition from these databases indicate that total Hg in wet deposition has been decreasing at many sites since 1997, including the site located in Kejimkujik National Park (KNP), Nova Scotia (Herrick, 2009; Weiss-Penzias et al., 2016). However, it is important to note that these measurements, while useful for monitoring, are incomplete since the wet samples are filtered resulting in the loss of any particle bound Hg. There are very limited data available for depositional inputs of reactive gaseous Hg and particulate Hg in Canada, specifically Atlantic Canada, with the exception of a few sites (e.g. KNP). As such, biomonitors may be a useful addition to monitoring applications as they may better reflect a diversity of Hg species that are retained on the solid surface. This study used epiphytic lichens as biomonitors of spatial PTE distribution in Nova Scotia. In our study, Usnea spp. (mainly trichodea, longissima, and strigosa species), were collected across mainland Nova Scotia and analyzed for PTE concentrations. This genus of lichen was chosen due to its intermediate pollutiontolerance (Cameron et al., 2007), abundance in Nova Scotia, and ease of collection and identification to the genus level. Measured PTE concentrations were then analyzed using spatial techniques and statistical modeling to observe the clustering of PTEs and to group the elements non-hierarchically. Sources of PTEs were inferred based on spatial clustering of elements, corresponding mineralogy, and a lack of positive or negative correlation between elements. Additionally, Hg concentrations were tested with environmental parameters, such as longitude andwind direction. 2. Materials and methods 2.1. Field collection and sample preparation Collection locations with easily accessible roads were chosen at an approximate spacing of 10 km to have good spatial resolution across the province of Nova Scotia, Canada (n ¼ 190). Therefore, the sampling design was influenced by access and to where these lichens grew in 2015, 2016, and 2017. Additionally, two target areas were specifically sampled in 2017 to determine if these target sites had higher Usnea Hg concentrations. The target areas were from a region of historical gold-mining (labelled “gold” in figures) and a region known to be a biological hot spot for Hg in organisms (Evers et al., 2007; Little et al., 2015), (labelled “keji” in figures). All lichen collections were from live coniferous trees (spruce [Picea] and fir [Abies]) at a height of approximately 2 m set back from roads (minimum 50 m upwind) to minimize the direct influence of road traffic on air quality. Lichen identifications were confirmed using DNA barcoding; ITS rDNA barcode sequences obtained during this study were deposited in the online reference DNA sequence database, NCBI Genbank (https://www.ncbi.nlm.nih.gov/genbank/) under accession numbers KY471545 e KY471547. Specimens from this study were deposited in Acadia University’s E.C. Smith Herbarium under ACAD number 043317 (Usnea spp.) Powder-free nitrile gloves were worn during collection to prevent contamination of the sample and GPS coordinates at each sample location were recorded. The sample was immediately placed in a brown paper bag or HDPE zippered bag and samples were stored in the dark at room temperature until cleaning. Each sample was cleaned of debris such as twigs, bark, or spider silk. Following the cleaning procedure, samples were dried (either freeze dried or oven dried at low temp), cryoground using liquid

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nitrogen in a clean mortar and pestle, and stored in 50 mL polypropylene tubes until analysis. Due to the large number of samples (n ¼ 190), only analytical replication was performed. 2.2. Mercury and PTE analyses Total mercury (THg) concentrations were determined in all 190 lichen samples on a Nippon Instruments MA-3000 Mercury Analysis System using thermal pyrolysis with gold amalgamation atomic absorption (USGS method 7473). Certified Reference Material was analyzed throughout the analyses for quality control and quality assurance (DORM4 recovery: 94.3 ± 8.16% SD; n ¼ 46). Analytical triplicates (n ¼ 15) yielded a mean of 10.3% RSD and the method detection limit (MDL) was calculated as 3x the standard deviation of blanks (0.01 ng, n ¼ 18). Other PTE concentrations, including iron (Fe), aluminum (Al), zinc (Zn), selenium (Se), chromium (Cr), lead (Pb), arsenic (As), nickel (Ni), copper (Cu), cobalt (Co), cadmium (Cd), and tin (Sn), were determined in lichen samples with sufficient remaining mass (n ¼ 95) using a PerkinElmer SCIEX DRC-e Inductively Coupled Mass Spectrometer (ICP-MS) after digestion to a liquid. Following EPA Method 3050B, ~0.5 g of homogenized lichen was digested in 5 mL of 1:1 nitric acid and deionized water for 30 min and then 5 mL of concentrated nitric acid for an additional 90 min at 95  C in a Hot Block. The digest was cooled and 2 mL of deionized water and 0.5 mL of hydrogen peroxide were added for complete digestion and then placed back in the Hot Block for 30 min. The digest was then cooled to room temperature, diluted to 50 mL with deionized water and vacuum filtered to 0.45 mm using a DigiTUBE filtration setup. The filtrate was then analyzed. Digest blanks and Certified Reference Material (AgroMAT CP-1) were processed during each digestion. ICP-MS analyses included external 5e7 point calibration curves and every 8 samples we included an analytical duplicate and an analytical spike of digest matrices. Method detection limits (MDLs) were calculated for each element as 3x the standard deviation of a low 0.5 mg/kg standard (n ¼ 7; reported in Table 1). 2.3. Data analyses Concentration ranges, medians, and MDL were reported for each of the elements and the corresponding analytical techniques. PTE concentrations were not normally distributed (Shapiro-Wilk; pvalue’s < 0.001) and Spearman-rank correlations were performed between each of the elements to compile correlation matrices. Subsequently, PTEs were delineated into clusters of correlative elements using significance at 95%. These clusters were then used to infer similar elemental sources: long-range transport, mineralogic,

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Table 2 Spearman-rank correlation tables of A): Cluster 1 elements e mineral source (Strong), B) Cluster 2 elements e mineral source (weak). and C) mercury (Hg) and iron (Fe) with copper (Cu) concentrations. All correlations are significant at 95% significance, except those in italics. A). A) Cluster 1

As

Se

As Se Fe

0.87 0.82

0.76

B) Cluster 2

Al

Cr

Co

Ni

Zn

Sn

Pb

Al Cr Co Ni Zn Sn Pb Cu Cd

0.73 0.53 0.52 0.27 0.40 0.58 0.45 0.04

0.51 0.53 0.3 0.36 0.52 0.44 0.05

0.79 0.53 0.06 0.36 0.48 0.36

0.48 0.02 0.29 0.3 0.39

0.04 0.15 0.264 0.35

0.33 0.42 0.14

0.34 0.08

Cu

0.05

C) Other Elements

Hg

Fe

Hg Fe Cu

0.03 0.32

0.28

or other. These concentrations were also compared between Ecoregions and Ecodistricts using the Ecological Land Classification for Nova Scotia. Concentrations of Hg were ln-transformed for further analyses (Shapiro-Wilk W ¼ 0.985, p ¼ 0.051). To test for suspected hot spots in the Hg dataset, we used sites targeted for lichen sampling (“gold” and “keji”) and compared them with “ambient” Hg concentrations from the other sites across Nova Scotia using a two-way ANOVA with Site Category and Year of Collection as factors. Determination of significance between factor levels was performed using Tukey’s Honest Significant Tests. To test for a long-range Hg source, correlations between both latitude and longitude with Hg concentrations were used. Additionally, prevailing wind directions in Nova Scotia were averaged across January 2015eJune 2016 from an Environment and Climate Change Canada weather station in KNP to determine a calmer prevailing wind direction of 202.5 and a stronger wind direction of 315 . These wind directions were used to calculate the normalized distance that air parcels travelled along those directions between the lichen samples and could represent a long-range transport source for elements. Testing this relationship is relevant because long-range transport from combustion sources has resulted in enhanced Hg deposition in the province (Herrick, 2009; WeissPenzias et al., 2016; Roberts et al., 2019). These normalized

Table 1 Summary of lichen potentially toxic element (PTE) concentration minimums, maximums, median (mg/kg) and corresponding method detection limit (MDL; mg/kg). All trace PTEs except Hg were analyzed using ICP-MS analysis. Mercury analysis was performed using thermal pyrolysis with gold amalgamation atomic absorption. Element

Minimum (mg/kg)

Maximum (mg/kg)

Median (mg/kg)

MDL (mg/kg)

Fe Al Zn Se Cr Pb As Ni Cu Co Cd Sn Hg

32.94 18.89 7.94 0.20 0.90 0.37 0.13
31,484.96 5514.49 285.51 70.47 55.75 50.60 25.16 11.24 5.64 3.53 2.64 1.11 0.52

179.79 59.77 21.14 0.70 1.10 1.36 0.38 0.38 1.58 0.10 0.09 0.05 0.14

21.9 6.8 8.7 8.0 8.5 1.5 3.7 3.5 3.5 2.8 7.5 17.5 0.01 (ng)

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distances were tested for Pearson product-moment correlations with the ln-transformed lichen Hg concentrations. 2.4. Spatial analyses Kriging in ArcGIS was used to create a smooth surface map layer for each element, thus providing predicted element concentration values in unmeasured areas. Kriging is a geospatial statistical analysis procedure that interprets values between points of known values. The interpretation procedure incorporates spatial autocorrelation - samples that are close together in space are more likely to be similar, compared with those that are further apart. This spatial correlation is used to explain variations in the surface map (Matheron, 1963; McGrath et al., 2004). Unlike other methods (e.g. inverse distance weighted), kriging is a statistical method that makes use of a variograms to calculate the spatial autocorrelation between points at graduated distances (Krige, 1952; Webster and Oliver, 2001). Thus, kriging is considered more advanced than some other interpolation methods, such as the inverse distance weighted method (Ha et al., 2014). There are several different kriging models including circular, spherical, Gaussian, linear and exponential. Ordinary spherical kriging was chosen as the optimized model by iteratively testing alternate models (Khalil et al., 2013; Li et al., 2001). The spherical model provided the minimized standard mean and root mean square error. 3. Results 3.1. Concentrations of PTEs in lichens

Table 3 Correlation table of mercury (Hg) concentrations with latitude (South / North), longitude (West / East), prevailing and strong wind directions from Kejimkujik National Park (KNP) from January 2015 to July 2016. Correlations not significant at 95% significance level are in italics. Hg concentration Trend South / North West / East Prevailing wind (202.5 ) Strong wind (315 )

r 0.08 0.14 0.12 0.09

Cluster 1 elements, are almost identical (Fig. 1A and Fig. 1B, respectively). Geospatial maps of select Cluster 2 elements, Cu (Fig. 2A), Pb (Fig. 2B), Ni (Fig. 2C), and Cr (Fig. 2D) showed higher concentrations of these Cluster 2 elements in Digby county on the west side of Nova Scotia. The Geospatial map for Hg concentrations (Cluster 3) had one area of higher concentrations located primarily in Annapolis County, near KNP (Fig. 3). Lichens collected from two targeted sampling regions were compared with ambient Hg concentrations in lichens on mainland Nova Scotia to determine if these regions were hot spots for Hg in Usnea lichens (Fig. 4). Usnea from the historical gold-mining area of Guysborough and Halifax counties (“gold”) were not significantly different from the Hg concentrations in lichens collected in other areas of Nova Scotia (“ambient”; p ¼ 0.93). Usnea from within KNP (“keji”) tended to have higher Hg concentrations from background (“ambient”) lichens and gold-mining area (“gold”) lichens (Fig. 4), though they were not statistically significant (p-values >0.19).

The concentrations of PTEs in Usnea spp. varied greatly (Table 1). PTEs with higher concentrations were Al (18.9e5514.5 mg/kg), Fe (32.9e31,485.0 mg/kg), and Zn (7.9e285.5 mg/kg). The Hg in lichens showed a wide concentration range of between 61.6 and 518.4 mg/kg. The other PTEs measured (As, Cd, Co, Cr, Cu, Ni, Pb, Se, and Sn) were between 24 mg/kg and 70 mg/kg (Table 1) and the medians were similar to those measured at other remote locations, however higher maximum ranges were observed for some elements. 3.2. PTE groupings We found strong correlations between some of the PTEs in the lichens. This led to a delineation in the data which suggests the elements in the lichens had different sources. Cluster 1, which is indicative of a mineral source, included As, Se, and Fe (Table 2A). The correlations between these PTEs were all significant at the 99% level: AseSe (r ¼ 0.87), AseFe (r ¼ 0.82), and SeeFe (r ¼ 0.76). Cluster 2 also suggests a geogenic or mining/industrial source, including: Al, Cr, Co, Ni, Zn, Sn, Pb, Cu, and Cd (Table 2B). Most were significantly correlated with each other at the 95% level (r’s > 0.26) except for: i) Sn and Co (r ¼ 0.06), Ni (r ¼ 0.02), and Zn (r ¼ 0.04), ii) Pb and Zn (r ¼ 0.15), and iii) Cd and Al (r ¼ 0.04), Cr (r ¼ 0.05), and Cu (r ¼0.11). Cluster 3 was defined as Hg, as Hg was not correlated with any of the other PTEs reported in this study except for Cu (r ¼ 0.32, p ¼ 0.001), in Cluster 2 (Table 2C). Additionally, there were some Cluster 2 elements that were negatively correlated with Cluster 1 elements. Cr, Ni, and Cd were significantly negatively correlated with As and Se (all r-values ranged from 0.22 to 0.36), and Cu was significantly correlated with Fe (r ¼ 0.28, p < 0.01). 3.3. Spatial distributions of PTEs Geospatial maps of As and Se, which are highly correlated

Fig. 1. Concentration distribution of select Cluster 1 elements in Usnea spp. across mainland Nova Scotia: A) arsenic (As), and B) selenium (Se).

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Fig. 2. Concentration distribution of select Cluster 2 elements in Usnea spp. across mainland Nova Scotia: A) copper (Cu), B) lead (Pb), C) nickel (Ni), and D) chromium (Cr).

Scotia. Prevailing wind direction (202.5 ) was also weakly correlated with Hg concentration (r ¼ 0.12, p ¼ 0.09) but strong wind direction (r ¼ 0.09, p ¼ 0.21) and latitude (r ¼ 0.08, p ¼ 0.27) were not correlated with Hg concentration (Table 3). A spatial plot of Hg concentration shows high variability of Hg concentrations across Nova Scotia (Fig. 3). Concentrations of elements were also compared with the Ecological Land Classification for Nova Scotia. No patterns emerged using Ecoregion (n ¼ 9 categories) nor Ecodistrict (n ¼ 39 categories). 4. Discussion 4.1. Concentrations and clustering patterns in PTEs

Fig. 3. Concentration distribution of mercury (Hg; Cluster 3) in Usnea spp. across mainland Nova Scotia.

Lichen samples collected in different years were also not significantly different in Hg concentration (p-values>0.42). Concentrations of Hg in lichens were weakly correlated with longitude at 90% statistical significance (r ¼ 0.14, p ¼ 0.05), with higher concentrations of Hg in lichens on the west side of Nova

This is the first study to assess the utility of Usnea spp. as biomonitors for a broad range of PTEs (Hg, Al, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Se, Sn, and Zn) in Canada. The use of biomonitors for PTE distribution is novel in Nova Scotia. Previous research on lichens in Nova Scotia has focused on species identification and characterization of species distributions in relation to pollution and therefore as spatial indicators of that pollution (Cameron et al., 2007). The concentrations of PTEs found in lichens in this study is in a similar range to what was observed in other studies of lichens (Cocozza rina et al., 2018). While the median PTE values are et al., 2016; Zve similar between studies, for many of the elements (e.g. As, Cd, Pb,

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to be more resistant rock (e.g. granites of Cape Breton Highlands and Cobequid Hills) (Davis and Browne, 1996), which is naturally less erodible. Cluster 2 may be linked to mineral deposits in Digby and Cumberland Counties such as gold deposits (Fig. 2 shows spatial distribution for Cu, Pb, Ni, and Cr). In Fig. 2A, it is clear that Cu has more variability across Nova Scotia than the other Cluster 2 elements. This suggests that Cu likely has sources both in Digby and Cumberland counties. Cluster 3 had a large range of concentrations, with great spatial variation but the highest concentrations of Hg located in the central southwestern region of mainland Nova Scotia, mainly in Annapolis County. The lack of correlation between Hg and most other elements suggests that Hg in lichens likely has a different origin than the other PTEs. The Hg source likely originates from long-range transport of the elemental gaseous form of Hg (Hg0), as this species of Hg is most likely to be transported long distances compared to reactive gaseous Hg or particulate Hg. The lack of correlation between Hg and other PTEs measured is not surprising as other studies have also found similar lack of correlation with other metals such as Cd and Pb (Carignan et al., 2009), and As, Cd, Co, Cr, Mn, Ni, Fe, Pb, and rina et al., 2014). Zn (Zve 4.2. Identifying sources of Hg

Fig. 4. Mercury (Hg) concentrations in lichen, summarized for each of the site categories during hotspot analyses: ambient ¼ background provincial Hg concentrations, n ¼ 130; gold ¼ sites of historic intensive gold mining, n ¼ 34; keji ¼ sites within Kejimkujik National Park (KNP), a documented biological hotspot for biological Hg concentrations (Evers et al., 2007), n ¼ 25. There were no significant differences between site categories even at 90% significance (p > 0.10).

Co, Ni, Cr) the maximum concentrations were observed to be substantially higher in Nova Scotia. The range and median of Hg concentrations measured in our study are comparable other global studies (Table 4). We created three clusters of PTEs based on the correlative capacities between the various PTEs measured. Cluster 1 included: As, Fe, and Se (Table 2A), Cluster 2 included: Al, Cr, Co, Ni, Zn, Sn, Pb, Cu, and Cd (Table 2B), and Cluster 3 was comprised solely of Hg. Although there were some weaker correlations between Cluster 1 and Cluster 2, the distinct correlation strength of Cluster 1 (all rvalues>0.76) led to this delineation in the data. Cluster 1 is a strong mineral signature with higher concentrations grouping in areas more dominated by the Halifax Formation (Fig. 1), which consists of several types of slate. The slates are softer and more erodible than surrounding granites and greywacke and also tend to be more mineral rich (Roland, 1982), leading them to release Hg more readily. Soil over the slates is often very thin, and frequently there is only a thin organic layer over the slate. In some areas, the bedrock slate is exposed, interacting with air and water. The adjacent granites also have thin soils, but these rocks are much harder and less erodible (Davis and Browne, 1996) than slates. In other areas of the province with slates and other softer more erodible bedrock, overburden is much deeper, thus less rock is exposed and there is less potential for atmospheric interaction with the elements contained therein. Where there is rock exposure, there normally tends

Two potential hot spot regions for Hg were investigated and our data show that the Hg in the lichens we examined is likely of atmospheric origin. Lichens collected near gold-mine tailings did not have significantly higher Hg compared to background lichen concentrations. Interestingly, samples collected near the area of KNP in south central Nova Scotia that experienced a wildfire in 2016 had some of the highest concentrations of Hg (>500 mg/kg). While it is unclear if this is related to the higher relative Hg observed in lichens used in this study, the results are consistent with previous findings of high levels of Hg in biota and lichens (Usnea spp. Hg median 176 mg/kg; maximum of 660 mg/kg) in this area (Rencz et al., 2003). Rencz et al. (2003) suggested that bioaccumulation patterns in KNP may be tied to atmospheric inputs. Orihel et al. (2007) also observed that in experimentally manipulated freshwater ecosystems, increased Hg(II) atmospheric deposition resulted in a linear increase of Hg in food webs, suggesting that new atmospheric inputs of Hg may be a significant factor in Hg aquatic bioaccumulation. Therefore, continued and increased monitoring of atmospheric Hg deposition using lichens may help predict Hg uptake projections in food webs. The higher Hg in lichens observed near KNP could be a result of recent forest fires and the release of Hg from surface soils as seen in other studies of wildfires (Webster et al., 2016). However, lichens collected in and near the “keji” hotspot did not have significantly higher Hg concentrations in 2017 compared to lichens collected in 2015 and 2016 before the wildfire (p-values>0.68) just north of the park. Additionally, samples were not collected in the same locations before and after the fire but more generally over the area (~400 km2); any fire induced release of Hg would likely have had a small impact radius and Hg may have been in particulate form, with deposition occurring close to the fire. In which case it is unlikely that the lichen species chosen captured an episodic release of Hg from soils related to this fire event. Therefore, the higher concentrations of Hg in lichens in the area of KNP are likely a long-term signature (consistent with results of Rencz et al. (2003); Table 4), not significantly impacted by the 2016 wildfire. Xu et al. (2017) performed a source-apportionment analysis for Hg speciation in air at KNP and determined that all forms (gaseous elemental, gaseous oxidized, and particulate Hg) were dominated by contributions from photochemistry and re-emission. This suggests that

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factors affecting loss from surface soils might be important in the spatial patterns observed. For our study, the THg concentrations were measured in unwashed, homogenized lichens. Future work should include the separation of Hg into absorbed versus particulate as this distinction could be more indicative of episodic disturbance events such as fire, mining, and resuspension). 4.3. Spatial analysis patterns To look at spatial drivers of PTE distribution we compared the analyzed concentrations to Ecological Land Classification for Nova Scotia. We found no patterns in the PTE distribution related to Ecoregion (n ¼ 9; largely controlled by climate) nor Ecodistrict (n ¼ 39; determined based on relief, geology, landform, soils, and vegetation). For a relatively small province, Nova Scotia is highly heterogenous in habitat types and these categories are still too general as small pockets (<1 km2) of lichen-bearing trees can be found easily throughout Nova Scotia. Mixed forests and subtle transitions are common, frequently flowing between sub-boreal and Acadian forest. The sampling strategy for this study was opportunistically random, primarily controlled by access and where these lichens grow. This sampling limitation likely reduced the ability to explore hypothesis-testing questions but allowed us to ask broad spatial questions and provide a starting point for biomonitoring with lichens in the province. As and Se in lichen were found to coincide with mineral occurrences in Annapolis County (arsenopyrite) and the distribution of gold (not measured) deposits and historic abandoned gold mines near Lunenburg, Mahone Bay, and New Germany in Lunenburg County (Chatterjee, 1983; Nova Scotia Department of Natural Resources, 2010). Arsenopyrite is known to occur in gold-bearing quartz veins and surrounding host rocks in Nova Scotia. As a consequence, historic gold mining in Nova Scotia, has resulted in the distribution of many As-rich tailings areas across the province. Copper coincided with occurrences of copper mineral occurrences in Cumberland and Colchester Counties (malachite, chalcocite, chalcopyrite), Digby neck and peninsula (malachite, chalcocite), and Yarmouth County (chalcopyrite, tetrahedrite), and around Lunenburg, Mahone Bay, New Germany, and New Ross (chalcopyrite) (Chatterjee, 1983; Nova Scotia Department of Natural Resources, 2010). Lead coincided with mineral occurrences of galena near Meteghan, along St. Mary’s Bay (directly opposite Digby peninsula) and in Colchester County (Chatterjee, 1983; Nova Scotia Department of Natural Resources, 2010). The sampling resolution of our study may not have been sufficiently sensitive to pick up on point source emissions or hotspot reemissions. In New Brunswick, Hypogymnia physodes has been shown to be an effective biomonitor of decreasing Hg

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concentrations with distance from a chlor-alkali plant (Sensen and Richardson, 2002) with concentrations returning to background levels (100e200 mg/kg) within about 3 km of the plant. The majority of lichen samples in our study fell within or below 200 mg/kg (n ¼ 169/190) and represent this background signature for Hg concentrations. Deviations from these lower concentrations appeared in the southwestern side of Nova Scotia, with higher variation of Hg concentrations within these sampling locations. The source of Hg in lichens was further investigated as there have been high historic deposition rates of Hg in Atlantic Canada with the source being long range transport of industrial Hg emissions from Northeastern USA and Ontario Canada (Government of Canada, 2002; Roberts et al., 2019). We compared the Hg concentrations across the specific sampling locations (latitude, longitude; Table 3). The southwestern region of the province had the highest range and relative Hg concentrations (Fig. 3) with only a very weak correlation of Hg concentration with longitude (r ¼ 0.14). Western sampling locations had greater variability of lichen Hg, with concentration variability decreasing at the eastern locations. Because atmospheric Hg is readily transported by atmospheric currents, we also tested whether Hg in lichens was related to prevailing (202.5 ) and strong (315 ) wind directions (Table 3). Lichen Hg concentrations were significantly correlated (r ¼ 0.12) with the distance that prevailing winds tracked across Nova Scotia from southwest to northeast. Cheng et al. (2013) used the concentration-weighted trajectory model to examine atmospheric Hg speciation and concentration in air at an urban coastal site in Nova Scotia. Potential source areas both with and without identifiable local Hg emissions were identified, suggesting non-point source emissions and natural emission as being drivers of Hg concentrations. Here we used a more detailed empirical approach to examine Hg distribution regionally using lichens as natural passive monitors to search with greater spatial detail for correlations with point sources and mineral and/or geomorphological patterns (Cheng et al., 2013). The type of analysis used in Cheng et al. (2013) could be applied in a future lichen monitoring program in Nova Scotia. Our study provides unique baseline data, supporting the use of common Usnea lichens for monitoring distributions of PTEs in Nova Scotia and the Acadian/Boreal forest transition region in general. Southwest Nova Scotia is an ecological hot spot for Hg, with higher Hg concentrations found among a range of animals (fish, invertebrates, and birds) (Clayden et al., 2013; Evers et al., 2007; Little et al., 2015; Wyn et al., 2010). Our spatial mapping of Hg in lichen samples showed some of the highest Hg concentrations in this region, and specifically, both within and north of KNP (Fig. 3). This suggests that these higher Hg concentrations in lichens may be related to non-point source emissions downwind and could explain why we did not find high Hg concentrations near historical gold-

Table 4 Concentrations of mercury (Hg; mg/kg) in various lichens found globally. Region Northern Quebec, Canada Northern Alaska, USA Greenland New Brunswick, Canada Victoria Land Hudson Bay, Canada Chilean Patagonia

Lichen

[Hg] Range (mg/kg) [Hg] Mean (mg/kg) References

Alectoria ochroleuca, Cornicularia divergens, Cretaria nivalis 10e270 Cetraria cucullata 20e112 Cetraria nivalis 29e89 Hypogymnia physodes 88e148 Umbilicaria decussata 90e1661 Evernia, Usnea, Bryoria 80e2060 Nephroma antarcticum Usnea spp. Graham Land Usnea sphacelata 140e240 Poland Hypogymnia physodespp 50e200 James R. I., Antarctica Usnea antarctica 330e720 Kejimkujik Park, Nova Scotia, Canada Usnea spp. 66e660 Nova Scotia, Canada Usnea spp. 62e518

90 ± 10SE

60 ± 50SD 120 ± 80SD

470 (median) 178 (median) 160 ± 75SD

^te et al. (1992) Cre Landers et al. (1995) Riget et al. (2000) Sensen and Richardson (2002) Bargagli et al. (2005) Carignan and Sonke (2010) Monaci et al. (2012) ~o de Ferro et al. (2014) Ma Kłos et al. (2018) rina et al. (2018) Zve Rencz et al. (2003) This Study

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S.J. Klapstein et al. / Chemosphere 241 (2020) 125064

mining areas. Other trace PTEs showed different patterns, likely of a local mineralogical signature. This work highlights the use of lichens as biomonitors of both short and long range airborne PTEs in mainland Nova Scotia. The study methods have application to surrounding areas containing similar forest structure and therefore similar lichen communities. Results from this study will add to both local and global monitoring programs already using biomonitors (lichens, leaves, needles, bark, and tree rings) for air quality and to better understand and predict bioaccumulation in food webs and risk of PTE exposure. Further development of biomonitor work should focus on detection of ecological background concentrations in contrast to anthropogenic pollution, and lichen transplant studies should be used to validate the methods used. Acknowledgments Funding for this research was provided by: Arthur Irving Academy for the Environment Research Grant, Canada Foundation for Innovation (NJO grant #203477), Natural Sciences and Engineering Research Council of Canada (NJO grant # 341960-2013), and Canada Research Chairs Program (NJO grant # 950-203477). We would like to acknowledge Nova Scotia Department of Natural Resources Mineral Resources Brance for the Open File Map ME 2004-1 of Nova Scotia used in our graphical figure. Special thanks to the CARE Labs at Acadia University, Rachel Clarke and Haley Geizer for assisting with sample prep and analyses and to Ellen O’Driscoll, Jacob O’Driscoll, and Jake Walker for assistance with field work and sampling. References Bargagli, R., 2016. Moss and lichen biomonitoring of atmospheric mercury: a review. Sci. Total Environ. 572, 216e231. https://doi.org/10.1016/ j.scitotenv.2016.07.202. Bargagli, R., Agnorelli, C., Borghini, F., Monaci, F., 2005. Enhanced deposition and bioaccumulation of mercury in antarctic terrestrial ecosystems facing a coastal polynya. Environ. Sci. Technol. 39, 8150e8155. https://doi.org/10.1021/ es0507315. Bates, J.L.E., 1987. Gold in Nova Scotia. Nova Scotia Dept. of Mines and Energy, Halifax. Braaten, H.F.V., Åkerblom, S., Kahilainen, K.K., Rask, M., Vuorenmaa, J., Mannio, J., Malinen, T., Lydersen, E., Poste, A.E., Amundsen, P.-A., Kashulin, N., Kashulina, T., Terentyev, P., Christensen, G., de Wit, H.A., 2019. Improved environmental status: 50 Years of declining fish mercury levels in boreal and subarctic fennoscandia. Environ. Sci. Technol. https://doi.org/10.1021/acs.est.8b06399. Cameron, R.P., Neily, T., Richardson, D.H.S., 2007. Macrolichen indicators of air quality for Nova Scotia. Northeast. ON Nat. 14, 1e14. Carignan, J., Estrade, N., Sonke, J.E., Donard, O.F.X., 2009. Odd isotope deficits in atmospheric Hg measured in lichens. Environ. Sci. Technol. 43, 5660e5664. https://doi.org/10.1021/es900578v. Carignan, J., Sonke, J., 2010. The effect of atmospheric mercury depletion events on the net deposition flux around Hudson Bay, Canada. Atmos. Environ. 44, 4372e4379. https://doi.org/10.1016/j.atmosenv.2010.07.052. Castro, M.S., Sherwell, J., 2015. Effectiveness of emission controls to reduce the atmospheric concentrations of mercury. Environ. Sci. Technol. 49, 14000e14007. https://doi.org/10.1021/acs.est.5b03576. Chatterjee, A.K., 1983. Metallogenic Map of the Province of Nova Scotia | Novascotia ca. Cheng, I., Zhang, L., Blanchard, P., Dalziel, J., Tordon, R., 2013. Concentrationweighted trajectory approach to identifying potential sources of speciated atmospheric mercury at an urban coastal site in Nova Scotia, Canada. Atmos. Chem. Phys. 13, 6031e6048. https://doi.org/10.5194/acp-13-6031-2013. Chiarantini, L., Rimondi, V., Bardelli, F., Benvenuti, M., Cosio, C., Costagliola, P., Di Benedetto, F., Lattanzi, P., Sarret, G., 2017. Mercury speciation in Pinus nigra barks from Monte Amiata (Italy): an X-ray absorption spectroscopy study. Environ. Pollut. 227, 83e88. https://doi.org/10.1016/j.envpol.2017.04.038. Chiarantini, L., Rimondi, V., Benvenuti, M., Beutel, M.W., Costagliola, P., Gonnelli, C., Lattanzi, P., Paolieri, M., 2016. Black pine (Pinus nigra) barks as biomonitors of airborne mercury pollution. Sci. Total Environ. 569 (570), 105e113. https:// doi.org/10.1016/j.scitotenv.2016.06.029. Clayden, M.G., Kidd, K.A., Wyn, B., Kirk, J.L., Muir, D.C.G., O’Driscoll, N.J., 2013. Mercury biomagnification through food webs is affected by physical and chemical characteristics of lakes. Environ. Sci. Technol. 47, 12047e12053. https://doi.org/10.1021/es4022975.

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