Distribution Of Hg In Sediments Research Articles

Mercury Sources, Emissions, Distribution and Bioavailability along an Estuarine Gradient under Semiarid Conditions in Northeast Brazil

In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary's biological resources.

Mercury loss and isotope fractionation during thermal maturation of organic-rich mudrocks

Mercury (Hg) concentration and isotopic composition of organic-rich sedimentary rocks have been widely used as proxies to track ancient volcanism and associated environmental perturbations. However, interpretation of the Hg data is based on the assumption that the thermal maturity of the sedimentary rocks has limited effects on Hg abundance and isotopic composition, which is yet to be evaluated. Here we conduct closed-system anhydrous pyrolysis experiments to investigate the changes of Hg concentration and isotope composition during the thermal mature process, using both marine and lacustrine mudrocks. A siliceous shale section (Luocun, China) with heterogeneous thermal maturity caused by dike intrusion was also analyzed for Hg. Significant Hg loss (over 80%), with variations of δ202Hg (by 0.3 to 0.7‰) but small variations of Δ199Hg (by <0.1 to 0.36‰), were observed during the experiment. The Hg isotopic variation may be caused by the release of isotopically distinct Hg in different mineral phases at different temperatures. Samples from the Luocun section have anomalously low Hg and Hg/TOC values, due to thermal maturity. These findings suggest that (1) thermal maturation of organic-rich shales may be an important factor in distribution of Hg in sediments, and (2) the use of Hg, Hg/TOC and Hg isotopes proxies for paleoclimate and paleoceanography reconstruction should be applied in caution in substrates that may have experienced significant thermal alteration, especially if sill/dike intrusions were present that may cause large varieties of thermal maturity within sedimentary sections.

Mercury contamination of sediments in an open coastal area of the Hupo Basin, East Sea, Korea

Mercury (Hg) contamination in open coastal areas has attracted public concern regarding safe fish consumption and management of the coastal environment, especially in areas of accidental Hg spills on inland coasts. This study investigated the temporal and spatial distribution of Hg in sediments of Youngil Bay and the Hupo Basin, East Sea, Korea; it also discussed the sources and transport of anthropogenic Hg. Hg hot spots were found in the northern Hupo Basin (elevated by 2–3×) and the river mouth area in Youngil Bay (elevated by approximately 70×). The river mouth contamination resulted from the destruction of a dam impounding landfill waste, while the basin contamination was attributed to atmospheric deposition and Hg enrichment associated with increased organic carbon concentrations driven by high biological production in the coastal upwelling area. Spilled Hg was transported to open coastal areas up to 36.6°N.

From point source to diffuse source of contaminants: The example of mercury dispersion in the Paglia River (Central Italy)

Fluvial sediments of the Paglia River, a tributary of Tiber River (Central Italy), are contaminated by mercury (Hg) as a consequence of past mining activity (1846–1981, with main production 1900–1970) in the Monte Amiata district (the 3rd largest Hg producer worldwide). In this study, we combine a geomorphological analysis with geochemical data to try and understand the influence of fluvial dynamics on the spatial distribution of Hg in fluvial sediments over a 43 km segment of the river.By considering the evolution of the river course between 1883 and 2013, eight different geomorphic units (GUs) were recognised, including the active channel bed (baseflow channel and bar), the floodplain, and five orders of terraces. The distribution of Hg in sediments of these GUs reflects the timing of their formation with respect to evolution of the mining activity. In GUs formed before the main peak of mining activity, or after mine closure, sediments show mean Hg contents comparable to, or slightly higher than, the local background, estimated at 2–6 mg/kg; in GUs formed during the peak production, Hg mean contents are definitely higher (up to 26 mg/kg). The current floodplain also shows high contents (mean 19 mg/kg), because of continuous reworking and transport of older contaminated sediments during major flood events. Therefore, the point contaminant sources represented by mining centres evolved into a diffuse source spread over several tens of kilometres.By combining geochemical data with calculated sediment volumes, we estimate that not less than 63 tonnes of Hg are currently contained in the sediments of the investigated river stretch. Such amount of Hg will probably limit for the near future a full land use along the Paglia–Tiber course.

Distribution of mercury in coastal marine sediments of China: Sources and transport

A total of 220 surface sediments and eight sediment cores were analyzed to study the distribution and transport of Hg in Chinese marginal seas. Spatial distribution showed a general offshore decreasing trend towards the outer continental shelf. Vertical profiles of sediment cores displayed a general increasing trend from bottom to surface layers. Coastal land-based discharges and river-derived inputs are probably the main sources of Hg in coastal sediments of China seas, while TOC, pH, ocean currents and sediment characteristics could play important roles in the transport and spatial distribution of Hg in sediment. The influence of TOC on Hg concentration is more significant than that of pH. The mud deposits on the coastal shelves are main sinks of Hg in the region. The results showed that sedimentary Hg was affected by regional anthropogenic activities and riverine runoffs, and was also influenced by long-range atmospheric transport and ocean current circulations.

THE CORRELATIONS BETWEEN MERCURY SPECIATION AND DISSOLVED ORGANIC MATTER IN THE SEDIMENT OF THE RED SEA

This study addresses the correlations between Hg an d organic matter in recent sediment; samples were collected from the Gulf of Aqaba, Red Sea coasts (o ligotrophic regions) during 2010. In the present st udy TOC analyzer was used to determine Total Organic Carbon (TOC) and Total Nitrogen (TN) concentrations and the total amount of mercury (Hg T) in sediment samples were analyzed by Hydra-C mercury analyzer. The obtained results indicated that, mercury, TOC a nd TN average concentrations in the Red Sea were 85.42 ng g -1 , 5.10 and 4.45 mg L -1 , respectively. The results show that the Total Org anic Carbon (TOC) in sediment represents the sum of various organic comp ounds, which may play a completely different role i n the distribution and accumulation of Hg. slightly c orrelations between the TOC and the concentration o f Hg in the studied sediment arise mainly from the labil e portion of organic matter released. These compoun ds primarily consist of easily degradable algal-derive d lipids and various pigments, which are petrograph ically described as a soluble Organic Matter (OM). The preserved OM in sediment is commonly entrapped within the cell walls of phytoplankton and also appears as a surface coating on sediment particles. The stron g affinity between Hg and OM is due not only to its c hemical reactivity, but also to the physical charac teristic of these labile compounds, which plays the most imp ortant role in the distribution of Hg in sediment.

Relationship between organic matter and mercury in recent lake sediment: The physical–geochemical aspects

This study addresses the physical geochemical aspects of the relationship between Hg and organic matter in recent sediment from eutrophic lakes in central Alberta, Canada. The types of organic matter in the sediment are classified based on their degree of thermal degradation and their petrographical characteristics. This study uniquely applies the methods conventionally used in petroleum geosciences (Rock-Eval ® analyses and organic petrology) to investigate the relationship between various types of organic matter and the concentration of Hg in sediment. The results show that the total organic carbon (TOC) in sediment represents the sum of various organic compounds, which may play a completely different role in the distribution and accumulation of Hg. Strong correlations between TOC and the concentration of Hg in the studied sediment arise mainly from the thermally labile portion of organic matter released during pyrolysis under 300 °C. These compounds primarily consist of easily degradable algal-derived lipids and various pigments, which are petrographically described as soluble organic matter (SOM). The preserved SOM in sediment is commonly entrapped within the cell walls of phytoplankton and also appear as surface coating on sediment particles. The strong affinity between Hg and SOM is due not only to its chemical reactivity, but also to the physical characteristic of these labile compounds. The SOM may provide a substrate with enormous surface area by concentrating on the finer sediment size fractions and potentially acting as a “concentrator” for Hg and other organic-associated elements. Lastly, the quantity of the SOM has been calculated as an “elemental concentrator” portion of the TOC, which plays the most important role in the distribution of Hg in sediment.

Environmental fate of mercury discharged into the upper Wisconsin river

We studied the distribution of Hg in sediments, fish, and crayfish in a 60 km reach of the Upper Wisconsin River that formerly received Hg in discharges from pulp and paper mills. The most heavily contaminated strata of sediments were deposited during the 1950s and early 1960s and buried under subsequent deposits; however, surficial sediments remained substantially enriched at certain sites in 1981. Median concentrations of Hg in surficial sediments, adjusted for grain size, were at least 10-fold greater at the main study area than at an upstream reference site. Total concentrations exceeded 1.0 μg g−1 wet weight in axial muscle tissue in only 2 of 173 fish analyzed from the study area; however, historical comparisons revealed that Hg contamination of fish (common carp Cyprinus carpio and walleye Stizostedion vitreum vitreum) and crayfish (Orconectes) in the river had not decreased since the early 1970s. The availability of Hg to biota in this system may be enhanced by rapid methylation of the metal in surficial sediments, despite burial of the most heavily contaminated sediments. Management practices for this river should be designed to prevent conditions favoring mobilization and methylation of Hg in sediments.