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Lisbon, Portugal

Chatterjee M.,University of Calcutta | Canario J.,IPIMAR INRB IP | Sarkar S.K.,University of Calcutta | Branco V.,IPIMAR INRB IP | And 3 more authors.
Environmental Monitoring and Assessment

This study was performed to elucidate the distribution, concentration trend and possible sources of total mercury (Hg T) and methylmercury (MeHg) in sediment cores (<63 μm particle size; n=75) of Sundarban mangrove wetland, northeastern part of the Bay of Bengal, India. Total mercury was determined by atomic absorption spectrometry (AAS) in a Leco AMA 254 instrument and MeHg by gas chromatography- atomic fluorescence spectrometry (GC-AFS). A wide range of variation in Hg T (0.032-0.196 μg g -1 dry wt.) as well as MeHg (0.04-0.13 ng g -1 dry wt.) concentrations revealed a slight local contamination. The prevalent low Hg T levels in sediments could be explained by sediment transport by the tidal Hugli (Ganges) River that would dilute the Hg T values via sediment mixing processes. A broader variation of MeHg proportions (%) were also observed in samples suggesting that other environmental variables such as organic carbon and microbial activity may play a major role in the methylation process. An overall elevated concentration of Hg T in surface layers (0-4 cm) of the core is due to remobilization of mercury from deeper sediments. Based on the index of geoaccumulation (I geo) and low effects-range (ER-L) values, it is considered that the sediment is less polluted by Hg T and there is less ecotoxicological risk. The paper provides the first information of MeHg in sediments from this wetland environment and the authors strongly recommend further examination of Hg T fluxes for the development of a detailed coastal MeHg model. This could provide more refine estimates of a total flux into the water column. © Springer Science+Business Media B.V. 2011. Source

O'Driscoll N.J.,Acadia University | O'Driscoll N.J.,Kc Irving Environmental Science Center | Canario J.,IPIMAR INRB IP | Crowell N.,Applied Geomatics Research Group AGRG | Webster T.,Applied Geomatics Research Group AGRG
Water, Air, and Soil Pollution

Sediment cores were analysed from four coastal wetland sites within the Minas Basin, Bay of Fundy to compare mercury speciation and sediment characteristics. The coastal wetland sediments were low in total mercury (mean = 17.4 ± 9.9 ng g-1); however, MeHg concentration was 92 times higher (mean of 249 pg g-1) than intertidal mudflat sediment (mean of 2.7 pg g-1). Total mercury concentrations in intertidal mudflat cores were also low (0.5-23.7 ng g-1) and correlated (Pearson correlation = 0.98; p < 0.01) with % organic carbon; with low concentrations of MeHg present only below depths of 6 cm (mean = 2.7 ± 1.0 pg g -1). Total mercury concentrations were negatively correlated (correlation = 0.56, p < 0.05) with inorganic sulphur (acid volatile sulphides (AVS) and pyrite) while MeHg concentrations were inversely correlated (Pearson correlation = -0.68; p < 0.05) with the pyrite content but not with AVS. Methyl mercury concentrations were not significantly correlated with organic carbon content in the wetland sediments, and mercury-in-biomass enrichment factors were lower (total mercury mean 1.5 ± 1.9 and MeHg mean = 3.6 ± 4.8) than published measurements from mercury polluted sites. Modelling estimates found on average 4.4 times more total mercury mass in the intertidal mudflat sediments relative to vegetated wetlands. A negative relationship was observed between MeHg concentrations (below 20 cm depth) and modelled tidal inundation. The mineral fraction within wetland sediments contained 96.2% of the total mercury mass; however, the highest concentrations of mercury species were in root biomass. This research confirms that vegetated coastal wetlands are key areas for formation of bioavailable methyl mercury, and mercury distribution is tied to organic carbon and sulphur speciation. © 2011 Springer Science+Business Media B.V. Source

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