Fate of inorganic mercury and methyl mercury within the snow cover in the low arctic tundra on the shore of Hudson Bay (Québec, Canada)

Abstract

Snow samples were collected in the seasonal snow cover of the low arctic tundra (Whapmagoostui-Kuujjuarapik, Québec) during episodic atmospheric mercury depletion events (AMDEs) and in the snowmelt period, long after AMDEs had occurred. Total and methyl mercury analyses were done in order to investigate the critical factors influencing the fate of mercury once deposited in the snowpack. Following AMDEs, snow total mercury (THg) concentrations increased and were inversely proportional to the distance from Hudson Bay. The correlations between MeHg, sulfate (SO 4 2-), and chlorine (C1 -) snow concentrations implicated marine aerosols as a significant source of MeHg, independent of AMDEs. However, the newly deposited MeHg was unstable in the snow cover as 15-56% of the MeHg was demethylated or otherwise "lost" during the nighttime period. In contrast, during the snowmelt period, marine aerosols were not a significant source of MeHg. MeHg snow concentrations higher than 200 pg L -1 were observed when snow's heterotrophic plate counts, total suspended volatile solids, and total suspended solids were higher than 5.0 x 10 5 CFU L -1, 25 mg L -1, and 90 mg L -1, respectively. During the snowmelt, although the THg snow concentrations remained at 8-9 ng L -1, the proportion of MeHg increased from 2.7 to 7.6%. This is the first report suggestive of the presence of mercury methylation activities within the snow cover of the low arctic tundra.