Abstract: Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 + or - 10.6 SE ng cm(-2) yr(-1) for THg and 3.8 + or - 1.7 SE ng cm(-2) yr(-1) for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 + or - 30 SE ng cm(-2) yr(-1)). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations.
Abstract: Molecular hydrogen (H(2)) is an indirect greenhouse gas present at the trace level in the atmosphere. So far, the sum of its sources and sinks is close to equilibrium, but its large-scale utilization as an alternative energy carrier would alter its atmospheric burden. The magnitude of the emissions associated with a future H(2)-based economy is difficult to predict and remains a matter of debate. Previous attempts to predict the impact that a future H(2)-based economy would exert on tropospheric chemistry were realized by considering a steady rate of microbial-mediated soil uptake, which is currently responsible of ~80% of the tropospheric H(2) losses. Although soil uptake, also known as dry deposition is the most important sink for tropospheric H(2), microorganisms involved in the activity remain elusive. Given that microbial-mediated H(2) soil uptake is influenced by several environmental factors, global change should exert a significant effect on the activity and then, assuming a steady H(2) soil uptake rate for the future may be mistaken. Here, we present an overview of tropospheric H(2) sources and sinks with an emphasis on microbial-mediated soil uptake process. Future researches are proposed to investigate the influence that global change would exert on H(2) dry deposition and to identify microorganisms involved H(2) soil uptake activity.
Abstract: An open-bottom and a closed-bottom mesocosm were developed to investigate the release of mercury from sediments to the water column in a frozen freshwater lake. The mesoscosms were deployed in a hole in the ice and particulate mercury (Hg(P)) and total dissolved mercury (TDHg) were measured in sediments and in water column vertical profiles. In addition, dissolved gaseous mercury (DGM) in water and mercury water/airflux were quantified. Concentrations of TDHg, DGM, and mercury flux were all higher in the open-bottom mesocosm than in the closed-bottom mesocosm. In this paper we focus on the molecular diffusion of mercury from the sediment in comparison with the TDHg accumulation in the water column. We conclude that the molecular diffusion and sediment resuspension play a minor role in mercury release from sediments suggesting that solute release during ebullition is an important transport process for mercury in the lake.
Abstract: In situ mesocosm experiments were performed to examine dissolved gaseous mercury (DGM), mercury volatilization, and sediment interactions in a frozen freshwater fluvial lake (Lake St. Louis, Beauharnois, QC). Two large in situ mesocosm cylinders, one open-bottomed and one close-bottomed (no sediment diffusion), were used to isolate the water column and minimize advection. Mercury volatilization over the closed-bottom mesocosm did not display a diurnal pattern and was low (mean = -0.02 ng m(-2) h(-1), SD = 0.28, n=71). Mercury volatilization over the open-bottom mesocosm was also low (mean = 0.24 ng m(-2) h(-1), SD = 0.08, n=96) however a diurnal pattern was observed. Low and constant concentrations of DGM were observed in surface water in both the open-bottomed and close-bottomed mesocosms (combined mean = 27.6 pg L(-1), SD = 7.2, n=26). Mercury volatilization was significantly correlated with solar radiation in both the close-bottomed (Pearson correlation = 0.33, significance = 0.005) and open-bottomed (Pearson correlation = 0.52, significance = 0.001) mesocosms. However, DGM and mercury volatilization were not significantly correlated (at the 95% level) in either of the mesocosms (significance = 0.09 in the closed mesocosm and significance = 0.9 in the open mesocosm). DGM concentrations decreased with depth (from 62 to 30 pg L(-1)) in the close-bottomed mesocosm but increased with depth (from 30 to 70 pg L(-1)) in the open-bottomed mesocosm suggesting a sediment source. DGM concentrations were found to be high in samples of ice melt (mean 73.6 pg L(-1), SD = 18.9, n=6) and snowmelt (mean 368.2 pg L(-1), SD = 115.8, n=4). These results suggest that sediment diffusion of mercury and melting snow and ice are important to DGM dynamics in frozen Lake St. Louis. These processes may also explain the lack of significant correlations observed in the DGM and mercury volatilization data.
Abstract: Distribution of total mercury (THg), gaseous elemental Hg(0) (GEM), monomethyl Hg (MMHg), and dimethyl Hg (DMHg) was examined in marine waters of the Canadian Arctic Archipelago (CAA), Hudson Strait, and Hudson Bay. Concentrations of THg were low throughout the water column in all regions sampled (mean +/- standard deviation; 0.40 +/- 0.47 ng L(-1)). Concentrations of MMHg were also generally low atthe surface (23.8 +/- 9.9 pg L(-1)); however at mid- and bottom depths, MMHg was present at concentrations sufficient to initiate bioaccumulation of MMHg through Arctic marine foodwebs (maximum 178 pg L(-1); 70.3 +/- 37.3 pg L(-1)). In addition, at mid- and bottom depths, the % of THg that was MMHg was high (maximum 66%; 28 +/- 16%), suggesting that active methylation of inorganic Hg(II) occurs in deep Arctic marine waters. Interestingly, there was a constant, near 1:1, ratio between concentrations of MMHg and DMHg at all sites and depths, suggesting that methylated Hg species are in equilibrium with each other and/or are produced by similar processes throughout the water column. Our results also demonstrate that oceanographic processes, such as water regeneration and vertical mixing, affect Hg distribution in marine waters. Vertical mixing, for example, likely transported MMHg and DMHg upward from production zones at some sites, resulting in elevated concentrations of these species in surface waters (up to 68.0 pg L(-1)) where primary production and thus uptake of MMHg by biota is potentially highest. Finally, calculated instantaneous ocean-atmosphere fluxes of gaseous Hg species demonstrated that Arctic marine waters are a substantial source of DMHg and GEM to the atmosphere (27.3 +/- 47.8 and 130 +/- 138 ng m(-2) day(-1), respectively) during the ice-free season.
Abstract: The Canadian Atmospheric Network for Currently Used Pesticides (CANCUP) was the first comprehensive, nationwide air surveillance study of pesticides in Canada. This paper presentsthe atmospheric occurrence and distribution of pesticides including organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), acid herbicides (AHs), and neutral herbicides (NHs) during the spring to summer of 2004 and 2005 across agricultural regions in Canada. Atmospheric concentrations of pesticides varied within years and time periods, and regional characteristics were observed including the following: (i) highest air concentrations of several herbicides (e.g., mecoprop, triallate, and ethalfluralin) were found at Bratt's Lake, SK, a site in the Canadian Prairies; (ii) the west-coast site at Abbotsford, BC, had the maximum concentrations of diazinon; (iii) the fruit and vegetable growing region in Vineland, ON, showed highest levels for several insecticides including chlorpyrifos, endosulfan, and azinphos-methyl; (iv) high concentrations of atrazine and metolachlor were measured at St. Anicet, QC, a corn-growing region; (v) the Kensington site in PEI, Canada's largest potato-producing province, exhibited highest level of dimethoate. Analysis of particle- and gas-phase fractions of air samples revealed that most pesticides including OCPs, OPPs, and NHs exist mainly in the gas phase, while AHs exhibit more diversity in particle-gas partitioning behavior. This study also demonstrated that stirred up soil dust does not account for pesticides that are detected in the particle phase. The estimated dry and wet deposition fluxes indicate considerable atmospheric inputs for some current-use pesticides (CUPs). This data set represents the first measurements for many pesticides in the atmosphere, precipitation, and soil for given agricultural regions across Canada.
