Mercury transfer from watersheds to aquatic environments following the erosion of agrarian soils: A molecular biomarker approach

Lake St. Pierre, an important freshwater location for sports and commercial fisheries in Canada, is composed of a 120 km2 stretchof the St. Lawrence River, located at the center of the St. Lawrence Lowlands. Receiving its waters from the St. Franc¸ ois, Yamaska, Ottawa, and St. Lawrence Rivers, it is subjected to important inputs of mercury (Hg) and suspended particles eroded from its watershed. This study aims at tracing back the origin of terrigenous Hg loadings to Lake St. Pierre. The specific phenol signatures yielded by a mild oxidation of the terrestrial organic matter (TOM) carried in the water column was used as a tracer to identify the different sources of terrigenous Hg to the lake. Our results demonstrate that most of the Hg bound to suspended particulate matter (SPM-bound Hg) found in Lake St. Pierre is associated withTOM. We were also able to distinguish the relative influence that forested soils, mainly drained by the Ottawa River, and agrarian soils, located on nearby watersheds, exert on the lake’s Hg burden. Our data strongly suggest that the erosion of vast areas of agrarian soils, drained by the Yamaska and St. Franc¸ois rivers to Lake St. Pierre, greatly facilitates the transfer of Hg from the watersheds to the lake. This study stresses the need to improve the management of agrarian soils and protect them from extensive erosion in order to preserve the integrity of the fish resources harvested in Lake St. Pierre

Terrestrial organic matter biomarkers as tracers of Hg sources in lake sediments

Terrestrial organic matter (TOM) plays a key role in mercury (Hg) dynamics between watersheds and lakes. In this study we attempts to determine the role of TOM source and quality and not only quantity, in the fate and transport of total Hg (T-Hg) to boreal lakes. Integrating the watershed complexity is a daunting task. Within the scope of this project, we characterized this organic matter at a molecular level in order to determine Hg transfer conditions to the sediments. We sampled ten lakes in the Quebec boreal forest. In each lake, we took a sediment core at the deepest point in addition to analyzing T-Hg and a set of terrigenous biomarkers in recent sediments. Our results show no relationship between TOM quantity and T-Hg concentration in lake sediments. However, [T-Hg] variation is well explained by the increase of 3,5Bd/V ratios (R2 = 0.84; p\0.0002) and the decrease of C/V ratios (R2 = 0.5; p\0.0227). Our study shows that TOM source and quality are determinant for Hg loadings in lake sediments. More precisely, increasing TOM derived from humified soil horizons explains most of Hg level variation within sediments

Mercury sources and bioavailability in lakes located in the mining district of Chibougamau, eastern Canada

The presence of Hg in the fish of the lakes from the Cu–Zn–Au mining region of Chibougamau (Canada) represents a serious source of concern for the health of local sports and subsistence fishers. This study focuses on identifying the origin of Hg present in the sediments of lakes with mine wastes stored in tailing facilities located on their shores. In addition to C/N ratios and determination of total Hg, Methyl Hg and other metals, a series of lignin biomarkers were used to contrast the history of the mining contamination with the nature and the intensity of terrigenous organic matter (TOM) inputs from the watersheds to the sampled lakes. It appears that sediments located nearest to mine tailings are as expected most enriched in total Hg and other metals (Cu, As, Al, Fe, Pb). Nevertheless, the presence of only small amounts of refractory TOM in these contaminated sediments could explain why only a very small fraction of Hg is found as Methyl Hg. In sediments with little or no impact by mining activities, a relationship was observed between logging activities in the lake watershed and increased TOM derived from inorganic gymnosperms soils horizons and increased Hg transport to the lakes. Nevertheless, it appears that the additional TOM transported to logged lakes is refractory enough not to promote high levels of Methyl Hg. The highest fractions of Methyl Hg relative to total Hg in lake sediments of the studied area were thus observed in relatively pristine environments where least degraded TOM is brought from the watersheds

Integrated transfers of terrigenous organic matter to lakes at their watershed level: A combined biomarker and GIS analysis

Terrigenous organic matter (TOM) transfer from a watershed to a lake plays a key role in contaminants fate and greenhouse gazes emission in these aquatic ecosystems. In this study, we linked physiographic and vegetation characteristics of a watershed with TOM nature deposited in lake sediments. TOM was characterized using lignin biomarkers as indicators of TOM sources and state of degradation. Geographical information system (GIS) also allowed us to integrate and describe the landscape morpho-edaphic characteristics of a defined drainage basin. Combining these tools we found a significant and positive relationship (R2 = 0.65, p < 0.002) between mean slope of the watershed and the terrigenous fraction estimated by Λ8 in recent sediments. The mean slope also correlated with the composition of TOM in recent sediments as P/(V + S) and 3,5Bd/V ratios significantly decreased with the steepness of the watersheds (R2 = 0.57, p < 0.021 and R2 = 0.71, p < 0.004, respectively). More precisely, areas with slopes comprised between 4° and 10° have a major influence on TOM inputs to lakes. The vegetation composition of each watershed influenced the composition of recent sediments of the sampled lakes. The increasing presence of angiosperm trees in the watershed influenced the export of TOM to the lake as Λ8 increased significantly with the presence of this type of vegetation (R2 = 0.44, p < 0.019). A similar relationship was also observed with S/V ratios, an indicator of angiosperm sources for TOM. The type of vegetation also greatly influenced the degradation state of OM. In this study, we were able to determine that low-sloped areas (0–2°) act as buffer zones for lignin inputs and by extension for TOM loading to sediments. The relative contribution of TOM from the soil organic horizons also increased in steeper watersheds. This study has significant implications in our understanding of the fate of TOM in lacustrine ecosystems

Mercury cycling and human health concerns in remote ecosystems in the Americas

Fish constitutes a praised—and sometimes irreplaceable—component of the daily diet for numerous communities throughout the Americas. These populations can be exposed to mercury (Hg)—ubiquitous in fish flesh—to levels potentially harmful to their health. Mercury is subjected to various chemical transformations once released to the environment. From diffuse loading on land and waters to accumulation in the aquatic food web, this paper draws a general picture of the main processes influencing the Hg cycle in different ecozones. Contrarily to other pollutants, the amount of Hg found in fish tissues is not clearly related to the extent of Hg loading in a given ecosystem. In the Arctic, the sudden stripping of gaseous elemental Hg from the atmosphere—known as the Hg depletion events—and its subsequent transformation into methylmercury (MeHg) seems to be one of the driving force behind Hg accumulation in freshwater aquatic organisms and marine mammals. In boreal environments, numerous watershed-based processes influence the transport and methylation of Hg deposited from atmospheric source and selectively control the amount of MeHg transferred from source to fish. In the tropics, small-scale gold mining operations have induced the release of considerable amount of Hg to the environment. However, the extensive deforestation of the tropical forest and the subsequent erosion and lixiviation of land-deposited Hg down to tropical rivers appears to have a greater impact on the observed wide-scale fish Hg contamination. Mercury accumulation in remote ecosystems do represent a significant and complex environmental issue, considering: (a) the high levels of Hg monitored in fish and marine mammals flesh; (b) the large-scale occurrence of such worrying Hg bioaccumulation patterns; (c) the extensive use of aquatic resources by numerous remote communities; (d) the fact that this issue shall persist at least on the mid-term, even if strong measures are taken to lessen Hg anthropogenic loadings to the global atmosphere. Although there are no simple answers to the potential threats to human health caused by Hg accumulation, several political actions to lessen human exposure to Hg are possible and are discussed here

Mercury cycling and human health concerns in remote ecosystems in the Americas

Fish constitutes a praised—and sometimes irreplaceable—component of the daily diet for numerous communities throughout the Americas. These populations can be exposed to mercury (Hg)—ubiquitous in fish flesh—to levels potentially harmful to their health. Mercury is subjected to various chemical transformations once released to the environment. From diffuse loading on land and waters to accumulation in the aquatic food web, this paper draws a general picture of the main processes influencing the Hg cycle in different ecozones. Contrarily to other pollutants, the amount of Hg found in fish tissues is not clearly related to the extent of Hg loading in a given ecosystem. In the Arctic, the sudden stripping of gaseous elemental Hg from the atmosphere—known as the Hg depletion events—and its subsequent transformation into methylmercury (MeHg) seems to be one of the driving force behind Hg accumulation in freshwater aquatic organisms and marine mammals. In boreal environments, numerous watershed-based processes influence the transport and methylation of Hg deposited from atmospheric source and selectively control the amount of MeHg transferred from source to fish. In the tropics, small-scale gold mining operations have induced the release of considerable amount of Hg to the environment. However, the extensive deforestation of the tropical forest and the subsequent erosion and lixiviation of land-deposited Hg down to tropical rivers appears to have a greater impact on the observed wide-scale fish Hg contamination. Mercury accumulation in remote ecosystems do represent a significant and complex environmental issue, considering: (a) the high levels of Hg monitored in fish and marine mammals flesh; (b) the large-scale occurrence of such worrying Hg bioaccumulation patterns; (c) the extensive use of aquatic resources by numerous remote communities; (d) the fact that this issue shall persist at least on the mid-term, even if strong measures are taken to lessen Hg anthropogenic loadings to the global atmosphere. Although there are no simple answers to the potential threats to human health caused by Hg accumulation, several political actions to lessen human exposure to Hg are possible and are discussed here

Représentations sociales chrétiennes, santé et environnement en Amazonie brésilienne

Cet article vise à mieux comprendre pourquoi certains groupes religieux s’impliquent plus que d’autres dans les questions qui connectent l’environnement et la santé. Nous analysons les représentations sociales des groupes catholiques et évangéliques de communautés riveraines en Amazonie brésilienne. À partir de verbatim d’entretiens semidirigés conduits avec des leaders religieux, nous avons réalisé une analyse qualitative à l’aide de catégories conceptualisantes. Les leaders de chacun des groupes ont des représentations similaires des principaux problèmes de santé et d’environnement. Toutefois, les résultats montrent que les catholiques accordent une grande importance à la conscientisation, à l’éducation, à l’implication et à la mobilisation sociale, tandis que les évangéliques misent fortement sur l’évangélisation et l’obéissance aux règles prescrites par la Bible. Nous concluons que les représentations sociales issues des traditions catholiques et évangéliques influent sur le type d’action sociale que les groupes préconisent pour améliorer les conditions de santé et la qualité de l’environnement.Este artigo visa entender melhor por que alguns grupos religiosos estão mais envolvidos do que outros em questões que conectam o meio ambiente e a saúde. Analisamos as representações sociais de grupos católicos e evangélicos de comunidades ribeirinhas na Amazônia brasileira. A partir de entrevistas semiestruturadas conduzidas com líderes religiosos, realizamos uma análise qualitativa utilizando categorias conceituais. Líderes de cada grupo têm representações semelhantes sobre as principais questões ambientais e de saúde. No entanto, os resultados mostram que os católicos atribuem grande importância à conscientização, educação, envolvimento e mobilização social, enquanto que os evangélicos confiam fortemente na evangelização e na obediência às regras prescritas pela Bíblia. Concluímos que as representações sociais dos grupos católicos e evangélicos influenciam o tipo de ação social desenvolvido para melhorar as condições de saúde e a qualidade do meio ambiente

Mercury and methylmercury concentrations in high altitude lakes and fish (Arctic charr) from the French Alps related to watershed characteristics

International audienceTotal mercury (THg) andmethylmercury (MeHg) concentrations were measured in the muscle of Arctic charr (Salvelinus alpinus) and in the water column of 4 lakes that are located in the French Alps. Watershed characteristics were determined (6 coverage classes) for each lake in order to evaluate the influence of watershed composition on mercury and methylmercury concentrations in fish muscle and in the water column. THg and MeHg concentrations in surface water were relatively low and similar among lakes and watershed characteristics play a major role in determining water column Hg and MeHg levels. THg muscle concentrations for fish with either a standardized length of 220 mm, a standardized age of 5 years or for individualuals did not exceed the 0.5 mg kg−1 fish consumption advisory limit established for Hg by the World Health Organization (WHO, 1990). These relatively low THg concentrations can be explained by watershed characteristics, which lead to short Hg residence time in the water column, and also by the short trophic chain that is characteristic of mountain lakes. Growth rate did not seem to influence THg concentrations in fish muscles of these lakes and we observed no relationship between fish Hg concentrations and altitude. This study shows that in the French Alps, high altitude lakes have relatively low THg and MeHg concentrations in both the water column and in Arctic charr populations. Therefore, Hg does not appear to present a danger for local populations and the fishermen of these lakes