Trace metals in the dissolved fraction (<0.45μm) of the lower Athabasca River: Analytical challenges and environmental implications.

Water samples were collected on the Athabasca River (AR), upstream and downstream from bitumen mines and upgrading facilities, to identify changes in water quality due to industrial activities in this region of northern Alberta, Canada. Starting upstream of Fort McMurray and proceeding downstream ca. 100km, waters were collected in duplicate at 13 locations on the main stem of the river, as well as 5 tributary streams, using ultraclean sampling protocols developed for polar snow and ice. To estimate potential bioaccessibility, trace elements of concern (Ag, Cd, Pb, Sb, Tl) were determined in the dissolved fraction (<0.45μm) along with metals known for their enrichments in bitumen (V, Ni, Mo, Re) and those found mainly in ionic (Li, Sr) or colloidal forms (Al, Co, Cr, Fe, Ga, Mn, Th, Y). Analyses were performed in the metal-free, ultraclean SWAMP lab using quadrupole and sector-field ICP-MS. Concentrations of Ag, Cd, Pb, Sb and Tl were extremely low, not significantly more abundant downstream of industry and probably reflect "background" values. In contrast, V, Ni, Mo and Re concentrations were all significantly (p<0.05) greater downstream of industry. However, chloride also increased downstream, due to natural inputs of saline groundwaters and it is unclear whether the increases in V, Ni, Mo and Re are due to natural or anthropogenic inputs to the river. Although it had been claimed that the industrial development of the Athabasca Bituminous Sands (ABS) is a significant source of Ag, Cd, Pb, Sb and Tl to the river, our study failed to find any evidence to support this. Here we provide a first, robust (accurate and precise) description of baseline values for these trace elements in the AR, and suggest that V, Ni, Mo and Re are more valuable tracers for environmental monitoring and source assessment.