Quantification of Spatial and Temporal Trends in Atmospheric Mercury Deposition across Canada over the Past 30 Years.

Mercury (Hg) is a pollutant of concern across Canada and transboundary anthropogenic Hg sources presently account for over 95% of national anthropogenic Hg deposition. This study applies novel statistical analyses of 82 high-resolution dated lake sediment cores collected from 19 regions across Canada, including nearby point sources and in remote regions and spanning a full west-east geographical range of ∼4900 km (south of 60°N and between 132 and 64°W) to quantify the recent (1990-2018) spatial and temporal trends in anthropogenic atmospheric Hg deposition. Temporal trend analysis shows significant synchronous decreasing trends in post-1990 anthropogenic Hg fluxes in western Canada in contrast to increasing trends in the east, with spatial patterns largely driven by longitude and proximity to known point source(s). Recent sediment-derived Hg fluxes agreed well with the available wet deposition monitoring. Sediment-derived atmospheric Hg deposition rates also compared well to the modeled values derived from the Hg model, when lake sites located nearby (<100 km) point sources were omitted due to difficulties in comparison between the sediment-derived and modeled values at deposition "hot spots". This highlights the applicability of multi-core approaches to quantify spatio-temporal changes in Hg deposition over broad geographic ranges and assess the effectiveness of regional and global Hg emission reductions to address global Hg pollution concerns.

Atmospheric trace metal deposition to remote Northwest Ontario, Canada: Anthropogenic fluxes and inventories from 1860 to 2010.

National and global inventories of anthropogenic trace element emissions to air is a comparatively recent phenomenon (post-1993 in Canada) as is the monitoring of atmospheric metal deposition, the latter being also very spatially limited. Paleo-reconstructive methods offer a contiguous record of environmental contamination providing a needed framework to establish locally relevant "pre-industrial" (~natural) conditions which can be compare with relative and quantitative deviations away from reference conditions. In this study, we reconstruct the history of the long-range, anthropogenic sourced atmospheric trace element deposition to the remote region of Northwestern Ontario Canada (Experimental Lakes Area (ELA)) using dated sediment records from five lakes. Several elements are shown to be highly enriched in lake sediments relative to pre-1860 sediments (Antimony, Lead, Tellurium, Tin, Arsenic, Bismuth, Cadmium and Mercury) and moderately (Zinc, Tungsten, Thallium, Copper, Silver, Selenium, Nickel and Vanadium). Mean decadal anthropogenic atmospheric fluxes (mg m-2 yr-1) are reconstructed for 1860-2010 and compare well with available local (ELA), regional (NW Ontario Canada, N Michigan USA) monitoring data, as well as global assessments of anthropogenic contribution to atmospheric trace metal burdens. Quantitative paleo reconstructions of atmospheric contamination history using the collective signal from multiple lakes provide a rigorous methodology to assess trends, uncertainties, evaluation with monitoring data and, provide an opportunity to explore landscape processes of contaminant transport and storage. Further study of the latter is recommended to understand the latency of legacy anthropogenic contamination of the environment.

Sources of atmospheric metal(loid) pollution recorded in Thompson Manitoba lake sediment cores within the Canadian boreal biome.

Global atmospheric emissions and subsequent deposition of numerous metal(loid)s has increased markedly since the industrial revolution. Due to a paucity of long-term metal(loid) flux measurements, the magnitude and timing of change are largely unknown, resulting in limited ability to predict time-scales of ecosystem recovery in response to emission decreases. In the absence of long-term data, palaeo-reconstructions provide continuous records of atmospheric metal(loid) deposition on an ecosystem, and landscape, scale. Here, we use high-resolution dated lake sediment cores to reconstruct the last c. 100 years of atmospheric anthropogenic deposition of a full suite (40) of metal(loid)s near a large nickel (Ni) and copper (Cu) smelter in an other-wise largely "pristine" region of northern Canada (Thompson, Manitoba). Anthropogenic depositional fluxes were compared to other regions of Canada including Kejimkujik National Park in Nova Scotia, Experimental Lakes Area in Ontario, as well as the Flin Flon, Manitoba Cu and zinc (Zn) smelter, located ~200 km southwest of Thompson. Deposition of 12 metal(loid)s were enriched above baseline (pre-1915) levels: antimony (Sb) > palladium (Pd) > bismuth (Bi) > mercury (Hg) > cadmium (Cd) > Ni > lead (Pb) > arsenic (As) > strontium (Sr) > Cu > platinum (Pt) > Zn. Spatio-temporal patterns in depositional fluxes and inventories demonstrate that 6 of these metal(loid)s were sourced primarily from the smelter, while As, Hg, Pb, Pt, Sb and Zn were sourced primarily from global and/or regional sources. Comparison of anthropogenic fluxes and inventories to available emissions data showed that Cu and Ni deposition has plateaued since the late 1970s despite dramatic smelter emission decreases between 2005 and 2014. We hypothesize that this discrepancy is due to releases of terrestrial metal(loid)s by climate-driven permafrost degradation, which is widespread across the region and will likely continue to drive increased metal(loid) fluxes to northern Canadian lakes for unknown time-scales.

Widespread Atmospheric Tellurium Contamination in Industrial and Remote Regions of Canada.

High tech applications, primarily photovoltaics, have greatly increased demand for the rare and versatile but toxic element tellurium (Te). Here we examine dated lake sediment Te concentration profiles collected near potential point sources (metal smelters, coal mining/combustion facilities, oil sands operations) and from rural regions and remote natural areas of Canada. Te contamination was most prevalent near a Cu/Zn smelter where observed deposition infers 21 g Te released per metric ton (t) of Cu processed. Globally, 9,500 t is predicted to have been atmospherically deposited near Cu smelters post-1900. In a remote area of central Canada (Experimental Lakes Area; ELA), preindustrial Te deposition rates were equivalent to the estimated average global mass flux supplied from natural sources; however more surprisingly, modern Te deposition rates were 6-fold higher and comparable with Te measurements in precipitation. We therefore suggest that sediment cores reliably record atmospheric Te deposition and that anthropogenic activities have significantly augmented atmospheric Te levels, making it an emerging contaminant of potential concern. Lake water residence time was found to influence lake sediment Te inventories among lakes within a region. The apparent settling rate for Te was comparable to macronutrients (C, N, P), likely indicative of significant biological processing of Te.

Atmospheric deposition of mercury and methylmercury to landscapes and waterbodies of the Athabasca oil sands region.

Atmospheric deposition of metals originating from a variety of sources, including bitumen upgrading facilities and blowing dusts from landscape disturbances, is of concern in the Athabasca oil sands region of northern Alberta, Canada. Mercury (Hg) is of particular interest as methylmercury (MeHg), a neurotoxin which bioaccumulates through foodwebs, can reach levels in fish and wildlife that may pose health risks to human consumers. We used spring-time sampling of the accumulated snowpack at sites located varying distances from the major developments to estimate winter 2012 Hg loadings to a ∼20 000 km(2) area of the Athabasca oil sands region. Total Hg (THg; all forms of Hg in a sample) loads were predominantly particulate-bound (79 ± 12%) and increased with proximity to major developments, reaching up to 1000 ng m(-2). MeHg loads increased in a similar fashion, reaching up to 19 ng m(-2) and suggesting that oil sands developments are a direct source of MeHg to local landscapes and water bodies. Deposition maps, created by interpolation of measured Hg loads using geostatistical software, demonstrated that deposition resembled a bullseye pattern on the landscape, with areas of maximum THg and MeHg loadings located primarily between the Muskeg and Steepbank rivers. Snowpack concentrations of THg and MeHg were significantly correlated (r = 0.45-0.88, p < 0.01) with numerous parameters, including total suspended solids (TSS), metals known to be emitted in high quantities from the upgraders (vanadium, nickel, and zinc), and crustal elements (aluminum, iron, and lanthanum), which were also elevated in this region. Our results suggest that at snowmelt, a complex mixture of chemicals enters aquatic ecosystems that could impact biological communities of the oil sands region.

Mercury in Arctic marine ecosystems: sources, pathways and exposure.

Mercury in the Arctic is an important environmental and human health issue. The reliance of Northern Peoples on traditional foods, such as marine mammals, for subsistence means that they are particularly at risk from mercury exposure. The cycling of mercury in Arctic marine systems is reviewed here, with emphasis placed on the key sources, pathways and processes which regulate mercury levels in marine food webs and ultimately the exposure of human populations to this contaminant. While many knowledge gaps exist limiting our ability to make strong conclusions, it appears that the long-range transport of mercury from Asian emissions is an important source of atmospheric Hg to the Arctic and that mercury methylation resulting in monomethylmercury production (an organic form of mercury which is both toxic and bioaccumulated) in Arctic marine waters is the principal source of mercury incorporated into food webs. Mercury concentrations in biological organisms have increased since the onset of the industrial age and are controlled by a combination of abiotic factors (e.g., monomethylmercury supply), food web dynamics and structure, and animal behavior (e.g., habitat selection and feeding behavior). Finally, although some Northern Peoples have high mercury concentrations of mercury in their blood and hair, harvesting and consuming traditional foods have many nutritional, social, cultural and physical health benefits which must be considered in risk management and communication.