Metals vs Minerals: Impacts of atmospheric dust deposition on the speciation of trace elements in snowmelt and peatland surface waters

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Open pit bitumen mining in northern Alberta generates considerable volumes of dust. The dusts are derived not only from the mines, but from wind erosion of dry tailings and gravel roads, construction activities, and quarries, in addition to natural sources such as river banks and sand bars. The dusts themselves consist mainly of mineral particles, some of which are chemically reactive (e.g. calcite, a calcium carbonate) whereas others are effectively insoluble (such as quartz, a silicate). There are also ongoing concerns about potentially toxic "heavy metals" being released to the atmosphere from bitumen mining and upgrading, but the extent of these emissions, and their ecological significance, is unclear. Most environmental impact studies to date have not clearly distinguished between heavy metals (such as cadmium and lead) from the combustion of fossil fuels needed for bitumen upgrading versus heavy metals which are hosted within the crystal lattice of the mineral particles themselves. Heavy metals which are emitted to the air during combustion at high temperatures tend to be very small (< 1 micron) and in soluble form (such as oxides), whereas mechanically-generated mineral dusts tend to be rather large (10 to 100 microns) and much less soluble (e.g. silicate minerals such as quartz and feldspar). Very small, soluble, metal-containing particles may represent a threat to biota, depending on the pH of soil and water, and other factors, but large, insoluble particles most likely do not. The main goal of this study is to clearly distinguish between these two sources of heavy metals to the air, using size-resolved analyses of snow and Sphagnum moss from bogs. The secondary objective is to understand what impact, if any, the two sources of heavy metals may have for the chemical composition of meltwater and peatland surface waters (from bogs, fens and swamps) which drain into the Athabasca River.