Mercury distribution and transport in a contaminated river system in Kazakhstan and associated impacts on aquatic biota

The River Nura in Central Kazakhstan has been heavily polluted by Hg originating from an acetaldehyde plant. A number of studies were undertaken to investigate the transport, fate and bioavailability of Hg in this river system. The sediments within a 20 km section of the river downstream of the effluent outfall canal are highly polluted and are acting as a strong source of surface water contamination. Mercury transport in the river is dominated by the remobilization of contaminated bed sediments and river bank erosion during the annual spring flood. Peak Hg concentrations in unfiltered surface water samples during a larger than usual flood event in 2004 were in the order of 1600–4300 ng L⁻¹. The majority of the particulate-bound Hg appears to be sedimented in the shallow Intumak reservoir 75 km downstream of the source of the pollution, leading to a drop in aqueous Hg concentrations by an order of magnitude. Nevertheless, background concentrations of Hg in surface water are not reached until at least 200 km downstream, and during the flood period Hg is also detected in the terminal wetlands of the river.Mercury concentrations in sediment cores taken from the river bed in the most contaminated section of the Nura ranged from 9.95 to 306 mg kg⁻¹. Methylmercury (MeHg) levels in shallow sediment cores were highest in surface sediments and ranged between 4.9 and 39 μg kg⁻¹, but were generally less than 0.1% of total Hg (THg). A significant inverse relationship was found between THg concentrations and the percentage of MeHg formed in the sediments, irrespective of the sampling depth. The observed relationship was confirmed by comparison with results from a different river system, indicating that it may be true also for other highly contaminated aquatic systems. It is hypothesized that at high THg levels in severely contaminated sediments, the accumulation of MeHg may be limited by increasingly efficient demethylation processes, and that this underlying trend in sediments is the reason why MeHg levels in surface water are often found to be higher at less contaminated sites compared to upstream sites.Mercury concentrations in biota in the most contaminated section of the river were 15–20 times higher than background levels. Fish were found to be impacted for more than 125 km downstream from the source, indicating significant transport of dissolved MeHg to downstream areas and/or in-situ MeHg production in less contaminated downstream reaches. There were also indications that impoundments may increase the bioavailability of Hg.     

Seasonal Cycling and Transport of Mercury and Methylmercury in the Turbidity Maximum of the Delaware Estuary

The Delaware River Estuary (DRE) is a cornerstone of industrialization, shipping, and urban usage, and has a long history of human impact on pollution and recovery. Mercury (Hg) is a contaminant of concern in the DRE based upon concentrations in some fish samples that were found to exceed State and Federal fish tissue criteria. Methylation of Hg often follows a seasonal pattern as its production is biologically mediated. Surveys were conducted in November 2011, April 2012, and July 2012 to assess this effect. We sampled surface and bottom water at six sites spanning the estuarine turbidity maximum (ETM) in the main channel of the river, plus three sediment sites at shallow, subtidal locations. Our results indicate there is a clear seasonal increase in both water column and sediment methylmercury (MeHg) and %MeHg concentrations in the ETM during July. Water-column-filtered total mercury (HgT), suspended particle HgT, and MeHg concentrations were found to fluctuate little with location or season in the ETM. In contrast, sediment MeHg, water-column-filtered MeHg, and pore water HgT varied seasonally. Furthermore, pore water MeHg levels were elevated in concert with increased k _meth rates in July. Estimated river input and sediment and atmospheric depositional MeHg flux were compared seasonally. River flux was more than an order of magnitude higher than sediment flux in April, coinciding with higher fluvial transport. However, during July, river flux decreases and sediment flux becomes a larger relative source. This trend has potential implications for fish and other biota residing in the DRE during summer.     

Oxyanion Concentrations in Eastern Sierra Nevada Rivers – 3. Boron, Molybdenum, Vanadium, and Tungsten

Water samples were collected from 10 locations along the Truckee River system, 14 locations along the Walker River system, and 12 locations along the Carson River, and analyzed for B, Mo, V, W, Na, Cl, and pH. Boron concentrations ranged from approximately 2 mol/kg in the upper reaches of the Truckee River to almost 1,200 mol/kg in Pyramid Lake. Molybdenum, V, and W had concentrations in the nanomolal range; Mo varied from a low of about 12 nmol/kg to a high of 3,200 nmol/kg (Walker Lake); V ranged from 9 nmol/kg to approximately 470 nmol/kg; and W varied from a low value around 0.8 nmol/kg (West Walker River) to 1,030 nmol/kg. The high concentrations of these oxyanion-forming trace elements in the rivers reflects (1) the relative stability of these oxyanions (e.g., MoO₄ ^2-, HVO₄ ^2-, WO₄ ^2-, B(OH)₃, and/or B(OH)₄ ^-) in the alkaline, well oxygenated river and lake waters, (2) contributions of hydrothermal waters (especially for B), and (3) weathering of rocks/regolith with high concentrations of these elements. In the case of Mo, V, and W, each exhibited relatively conservative behavior in the upper, oxygenated reaches of all three rivers. During the study period the region experienced a prolonged drought such that the lower reaches of each river were typified by no flow or stagnant waters and probably low oxygen and/or anoxic conditions (although not measured). Reductive processes occurring in the low flow to stagnant reaches of each river could have led to removal of Mo, V, and W from solution as coprecipitates with Fe monosulfides, or via sorption to Fe oxides/oxyhydroxides and/or organic matter. Boron, however, exhibited essentially no or minor removal from these rivers, and instead was added to each river via B-rich hydrothermal waters (e.g., Steamboat Creek from Steamboat Hot Springs), or by B-rich groundwaters via base-flow during the extensive drought.     

Environmental quality evaluation of the Vacacaí River, Rio Grande do Sul, Brazil

The water quality of the Vacacaí River was assessed at different sites in the period between winter 2005 and autumn 2006. All samples were analyzed for 52 elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Li, Be, Mg, Al, Ca, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Ag, Cd, In, Cs, Ba, Tl, Pb, Bi, U, Na, K, Hg, B, Mo, Sn, Te, Ti), temperature, pH, ammonia, and alkalinity levels. Water from the Vacacaí River ranged from slightly acidic to alkaline. No difference was observed in the chemical composition at different sites of the Vacacaí River. Levels of Ba, Ca, Sr and Mg increase in the dry seasons and reach their highest concentrations in autumn; Be and U decrease in the dry season and reach their highest concentration in spring. Al, Fe, Cr, Ni, Th, U Mn, Ca and Mg are highly positively related, indicating a common origin. Se and Cu are probably from anthropogenic source, from the rice crops of the margins of the river. Waterborne Al and Fe levels were above the desirable level for drinking water at all sites during all seasons. These results demonstrate the need for constant monitoring of water parameters, which is crucial to ensure water quality for the population of this region.     

Methylmercury Bioaccumulation in an Urban Estuary: Delaware River,USA

Spatial variation in mercury (Hg) and methylmercury (MeHg) bioaccumulation in urban coastal watersheds reflects complex interactions between Hg sources, land use, and environmental gradients. We examined MeHg concentrations in fauna from the Delaware River estuary, and related these measurements to environmental parameters and human impacts on the waterway. The sampling sites followed a north to south gradient of increasing salinity, decreasing urban influence, and increasing marsh cover. Although mean total Hg in surface sediments (top 4 cm) peaked in the urban estuarine turbidity maximum and generally decreased downstream, surface sediment MeHg concentrations showed no spatial patterns consistent with the examined environmental gradients, indicating urban influence on Hg loading to the sediment but not subsequent methylation. Surface water particulate MeHg concentration showed a positive correlation with marsh cover whereas dissolved MeHg concentrations were slightly elevated in the estuarine turbidity maximum region. Spatial patterns of MeHg bioaccumulation in resident fauna varied across taxa. Small fish showed increased MeHg concentrations in the more urban/industrial sites upstream, with concentrations generally decreasing farther downstream. Invertebrates either showed no clear spatial patterns in MeHg concentrations (blue crabs, fiddler crabs) or increasing concentrations further downstream (grass shrimp). Best-supported linear mixed models relating tissue concentration to environmental variables reflected these complex patterns, with species specific model results dominated by random site effects with a combination of particulate MeHg and landscape variables influencing bioaccumulation in some species. The data strengthen accumulating evidence that bioaccumulation in estuaries can be decoupled from sediment MeHg concentration, and that drivers of MeHg production and fate may vary within a small region.     

Temporal and spatial patterns of trace elements in the Patuxent River: A whole watershed approach

Trace element distributions, partitioning, and speciation were examined at 15 sites in the Patuxent River watershed from May 1995 through October 1997 to determine possible sources of trace elements to the river and estuary, to examine the relationship of the trace element discharges to freshwater discharges as well as to land use and geographic region, to validate previous estimates of loadings to the river, and to provide baseline data for trace elements in the Patuxent River watershed and estuary. Six freshwater sites were examined, representing different basins and geographic provinces, and nine sites along the estuarine salinity gradient. Subregions within the watershed varied considerably in concentrations and areal yields for some elements. Concentrations of As, Cd, Ni, Pb, and Zn were elevated in the Coastal Plain sites compared to the Piedmont sites, while Cu and Hg were more evenly distributed. Cadmium, Cu, Hg, Ni, Pb, and Zn showed overall positive correlations with river flow while As and methylHg (meHg) showed negative correlations with river flow. Concentrations of trace elements in the estuarine portion of the river were generally low, and consistent with mixing between Patuxent River water with elevated concentrations and the lower concentrations of the Chesapeake Bay. Interesting features included a local Cd maximum in the low salinity region of the estuary, probably caused by desorption from suspended sediments, and a significant input of water containing high As concentrations from the Chesapeake Bay and from As being released from bottom sediments in summer. Comparisons between the estimated annual flux of trace elements and the estimates of suspected source terms (atmospheric deposition, urban runoff, and known point sources) suggest that, except for Hg, direct atmospheric deposition is small compared to fluvial loads. Current estimates of trace element inputs from point sources or from urban runoff are inadequate for comparison with other sources, because of inappropriate techniques and/or unacceptably high detection limits. A complete examination of trace element dynamics in the Patuxent River (and in other coastal systems) will require better data for these potential sources.     

Distribution,behavior, and transport of inorganic and methylmercury in a high gradient stream

Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14 km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1 N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg.     

The hydrochemical characteristics and evolution of groundwater and surface water in the western part of the River Nile, El Minia district, Upper Egypt

A combination of major and trace elements have been used to characterize surface- and groundwater in El Minia district, Egypt. Surface water versus groundwater chemistry data enabled geographical zonation and chemical types to be differentiated. The main target of this research is to investigate the groundwater quality and hydrochemical evaluation. The situation is further complicated by contamination with lithogenic and anthropogenic (agricultural and sewage wastewaters) sources and low plan exploitation techniques. The investigated Pleistocene aquifer is composed of sand and gravel of different sizes, with some clay intercalation. The semi-confined condition was around the River Nile shifted to unconfine outside the floodplain. The groundwater flow generally from south to north and locally diverts towards the western part from the River Nile. Fifty-six, 11, five, and two water samples were collected from the Pleistocene aquifer, River Nile, Ibrahimia canal, and Al Moheet drain, respectively. The collected water samples were analyzed for major and trace elements. The toxic metal concentrations of Al Moheet drain are higher than those in the River Nile and the Ibrahimia canal. Cr, Hg, As, and Cd concentrations in the River Nile and Ibrahimia canal are fluctuated above and below the WHO drinking standards. Se concentration in River Nile and Ibrahimia canal is below WHO drinking and irrigation guidelines. Total dissolved solid content in groundwater is generally low, but it is increased due to the western part of the study area. The geographic position of the River Nile, Ibrahimia canal, and Al Moheet drain impact on the groundwater quality. The PHREEQC confirm the high mixing proportions from the River Nile into the groundwater and decline away from it. In addition to the thicknesses of the Pleistocene, aquifer and aquitard layer enhance the River Nile and agricultural wastewaters intrusion into the aquifer system. The toxic metal concentrations (Pb, Cd, Cr, PO₄, Se, Mn, As, Hg, Ni, Al, Fe, and SIO₂) in groundwater were increased mainly in the northwestern and southeastern part (far from the River Nile). It is attributed to anthropogenic, high vulnerability rate (unconfined), and partially to lithogenic. In most localities, the groundwater are unsuitable for drinking and irrigation purposes with respect to Se concentration, while they are unsuitable for dinking according Mn, As, and Hg contents. There are some Cd and Pb anomalies concentrations, which cause severe restriction if used in irrigation. The results suggested that significant changes are urgently needed in water use strategy to achieve sustainable development.     

Evaluating natural and anthropogenic trace element inputs along an alpine to urban gradient in the Provo River,Utah, USA

Numerous natural and anthropogenic processes in a watershed produce the geochemical composition of a river, which can be altered over time by snowmelt and rainfall events and by built infrastructure (i.e., dams and diversions). Trace element concentrations coupled with isotopic ratios offer valuable insights to disentangle the effects of these processes on water quality. In this study, we measured a suite of 40+ trace and major elements (including As, Cd, Ce, Cr, Cs, Fe, La, Li, Mo, Pb, Rb, Sb, Se, Sr, Ti, Tl, U, and Zn), Sr isotopes (⁸⁷Sr/⁸⁶Sr), and stable isotopes of H and O (δD and δ¹⁸O) to investigate natural and anthropogenic processes impacting the Provo River in northern Utah, USA. The river starts as a pristine mountain stream and passes through agricultural and urban areas, with two major reservoirs and several major diversions to and from the river. We sampled the entire 120 km length of the Provo River at 13 locations from the Uinta Mountains to Utah Valley, as well as two important tributaries, across the range of hydrologic conditions from low flow to snowmelt runoff during the 2013 water year. We also sampled the furthest downstream site in the Utah Valley urban area during a major flood event. Trace element concentrations indicate that a variety of factors potentially influence Provo River chemistry, including inputs from weathering of carbonate/siliciclastic rocks (Sr) and black shales (Se and U), geothermal groundwater (As, Cs, Li, and Rb), soil erosion during snowmelt runoff (Ce, Cr, Fe, La, Pb, and Ti), legacy mining operations (Mo, Sb, and Tl), and urban runoff (Cr, Pb, and Zn). Although specific elements overlap between different groups, the combination of different elements together with isotopic measurements and streamflow observations may act as diagnostic tools to identify sources. ⁸⁷Sr/⁸⁶Sr ratios indicate a strong influence of siliciclastic bedrock in the headwaters with values exceeding 0.714 and carbonate bedrock in the lower reaches of the river with values approaching 0.709. δD and δ¹⁸O changed little throughout the year in the Provo River, suggesting that the river is primarily fed by snowmelt during spring runoff and snowmelt-fed groundwater during baseflow. Based on nonmetric multidimensional scaling (NMS) water chemistry was unique across the upper, middle, and lower portions of the river, with high temporal variability above the first reservoir but minimal temporal variability below the reservoir. Thus, the results show that dams alter water chemistry by allowing for settling of particle-associated elements and also by homogenizing inflows throughout the year to minimize dilution during snowmelt runoff. Taken together, trace element concentrations and isotopic measurements can be used to evaluate the complex geochemical patterns of rivers and their variability in space and time. These measurements are critical for identifying natural and anthropogenic impacts on river systems.     

Proton-induced X-ray emission measurements of trace elements in water samples collected from an Indiana coal mining locality

A new method of simultaneous multi-elemental analysis, Proton Induced X-ray Emission (PIXE), was used to detect trace elements in waters associated with a coal strip-mining operation in southern Indiana. Stream, pond, and ground water samples were collected and analyzed monthly from, or near, Sulphur Creek in Sullivan County. The concentrations of 26 major and trace elements were determined in samples from eleven locations: K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Mo, Cd, Sn, Sb, I, Ba, Hg, Pb, and U. Elemental concentrations fluctuated considerably throughout the 13-month sampling period and also among sampling sites. Nickel, Zn, As, Cd, Mn, Fe, and Ca were highest in the upstream water which was most acidic (pH = 2.9–4.0) because of old unreclaimed mining operations. The highest values recorded were Ni = 1662 ppb, Zn = 4953 ppb, As = 26 ppb, Cd = 93 ppb, Mn = 5063 ppb, Fe = 63 ppm, and Ca = 325 ppm. The concentrations of these elements decreased downstream as the pH of Sulphur Creek increased which was likely due to the influence of the calcareous glacial till cover in the area and the recent mining activity which disturbed overburden containing a high percentage of calcareous materials. Lead, I, Br, and Ti values were highest (661 ppb, 86 ppb, 70 ppb, and 45 ppb, respectively) in the ground water from the coal seam (pH approximately 7). Other elements which were relatively high in the pH 7 waters closest to the current mining operations (pond, stream, and groundwater) included K (17 ppm), Sr (3408 ppb), Ba (173 ppb), As (14 ppb), Rb (16 ppb), Sn (14 ppb), and Cu (3840 ppb). The highest Cu concentration was recorded at the point where drainage water from the mine entered Sulphur Creek. Gallium, U, Hg, and Mo were found in low (< 13 ppb for Ga and Hg; < 205 ppb for Mo and U) concentrations and only in the ponds within the mine.     

Behavior of mercury in an urban river and its accumulation in aquatic plants

The characteristics of mercury in the aquatic environment have been intensively studied in mining areas with heavy mercury pollution but little work has been conducted in urban areas, with no significant Hg source. This paper presents a study of the Haihe River, which flows through an urban area in North China. The concentrations of total mercury (THg) and methylmercury (MeHg) in the river water were 3.6–31.2 and 0.12–3.21 ng/l, and the corresponding values in river sediment were 22.9–374.8 and 0.03–0.46 μg/kg. These values are lower than the reported values from mining areas. The THg concentration in sediment samples collected from the urban areas was higher than that from the rural areas and the global background levels, indicating the influence of urbanization on mercury contamination. Samples of typical riparian and floating plants, reed and hornwort, were collected. Correlation analysis showed that sediment is the major source of THg and MeHg in reed and water is the major source of MeHg in hornwort. The higher bioaccumulation factor of reed indicates its higher potential to accumulate MeHg from the environment.     

成都市生态环境地球化学特点

成都平原多目标地球化学调查表明，成都市区土壤Hg、Ag、Pb、Cu、Zn、Sb、P、S、Se、C、Sr、Mo、Na2O等13种元素和河流水系沉积物P、Hg、S、Zn、Pb、Cu、Mo等有机质、N、Cd、Cr等11种高含量元素，土壤中主要污染元素Hg、Pb、Zn、Cu的含量，在浅层样中较高，其污染状况市区内及工厂区比城郊严重，府河，南河的污染比沙河严重，但其污泥可以综合利用，研究表明，东部龙泉山区深层样丰富的农业有益元素为水果生长提供了有利条件。     

Mercury mobility at the Carson River Superfund Site, west-central Nevada, USA: Interpretation of mercury speciation data in mill tailings, soils, and sediments

The Carson River Superfund Site in west-central Nevada is an area of Hg-contaminated soil, sediment, water, air, and biola resulting from the amalgamation milling of Ag-Au ores of the Comstock lode worked approximately a century ago. In order to develop an understanding of the behavior, transport, and fate of Hg at this site, a technique was developed to estimate the proportions of total, elemental, exchangeable, organic, and sulfide Hg in soils, sediments, and tailings.Results of this analysis performed on active Carson River sediments indicate that Hg is selectively dissolved out of Hg-Au amalgam particles and subsequently adsorbed to fine-grained sediments which are then deposited in downstream, low-energy reaches of the Carson River and Labontan Reservoir. In the relatively more-reducing environment of the reservoir Hg appears to be converted, in large part, to relatively-insoluble HgS.The original elemental form of Hg released to the environment is the chemical form which is still dominant in most highly-contaminated soils, sediments, and tailings. Deeper, more-reducing soil horizons, however, appear to fix a significant portion of the Hg as HgS, analogous to the Lahontan Reservoir example described above. This fixation as HgS is documented to be largely limited to higher-sulfur areas where sulfide minerals from the Comstock ores increase the total sulfur concentrations of contaminated soils, sediments, and tailings.     

四川省阿坝地区地表水地球化学特征

阿坝州位于四川西北部,与青海、甘肃交界,处于高海拔地区;该地区地表水资源丰富,长江与黄河上游水系均流经该区域。通过系统性采集区内河水(76件)、井水(7件)、溪水(8件)等样品,测试水体中D与¹⁸O的丰度与微量元素含量。结果表明:①受大气降水与流经地层的影响,阿坝地区河水中D与¹⁸O的丰度均显著高于溪水、井水与自来水等介质,线性相关性表明,河水中¹⁸O的富集与硫酸盐矿物的溶解密切相关;②阿坝地区井水、自来水、溪水之间存在明显的水力联系;③对于阿坝地区而言,黄河上游河流中δD与δ¹⁸O值均高于长江上游水系河流,但两者之间差别较小,这由于同一地区水系具有相同的大气降水来源;④河水、井水、溪水等表水中微量元素呈高Ba、Zn、Cr,低As、Pb、Cd的特点,与该地区岩石样品中微量元素特征基本一致,表明该地区表水中微量元素含量主要受地质背景因素控制。     

Benthic fluxes of mercury species in a lagoon environment (Grado Lagoon,Northern Adriatic Sea,Italy)

The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive fluxes from porewater and overlying water concentrations, (2) measurements of benthic fluxes using a deployed light benthic chamber in situ and (3) measurements of benthic fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g⁻¹, showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g⁻¹) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L⁻¹, 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive fluxes (up to 17 ng m⁻² day⁻¹) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and benthic flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive fluxes in the lagoon (up to 110 ng m⁻² day⁻¹) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg benthic fluxes were highest in summer at both sites (41,000 and 33,000 ng m⁻² day⁻¹ at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O₂ and inversely with DIC, suggesting an important influence of benthic photosynthetic activities on lagoon benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the benthic flux of MeHg was up to 15-fold higher in sediments overlain by O₂ depleted waters. In the anoxic phase, the MeHg fluxes proceeded in parallel with Fe fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column.     

The distribution of total mercury and methyl mercury in a shallow hypereutrophic lake (Lake Taihu) in two seasons

To understand the geochemical cycle of Hg in hypereutrophic freshwater lake, two sampling campaigns were conducted in Lake Taihu in China during May and September of 2009. The concentrations of unfiltered total Hg (unfTHg) were in the range of 6.8–83 ng L⁻¹ (28 ± 18 ng L⁻¹) in the lake water and total Hg in the sediment was 12–470 ng g⁻¹, both of which are higher than in other background lakes. The concentration of unfTHg in ∼11% of the lake water samples exceeded the second class of the Chinese environmental standards for surface water of 50 ng L⁻¹ (GB 3838-2002), indicating that a high ecological risk is posed by the Hg in Lake Taihu. However, the concentrations of unfiltered total MeHg (unfMeHg) were relatively low in the lake water (0.14 ± 0.05 ng L⁻¹, excluding two samples with 0.81 and 1.0 ng L⁻¹). Lake sediment MeHg varied from 0.2–0.96 ng g⁻¹, with generally low ratios of MeHg/THg of <1%. The low concentrations of TMeHg in the lake water may have resulted from a strong uptake by the high primary productivity and the demethylation of MeHg in oxic conditions. In addition, contrary to the results of previous research conducted in deep-water lakes and reservoirs, the low concentrations of MeHg and low ratio of MeHg/THg in the lake sediment indicates that the net methylation of Hg was not accelerated by the elevated organic matter load created by the eutrophication of Lake Taihu. The results also showed that sediments were a source of THg and MeHg in the water. Higher diffusion fluxes of THg and MeHg may be partly responsible for the higher concentrations of THg in the lake water in May, 2009.     

Dissolved rare earth elements in river waters draining karst terrains in Guizhou Province,China

Winter seasonal concentrations of dissolved rare earth elements (REE) of two major river systems (the Wujiang River system and the Yuanjiang River system) in karst-dominated regions in winter were measured by using a method involving solvent extraction and back-extraction and subsequent ICP-MS measurements. The dissolved REE concentrations in the rivers and their tributaries are lower than those in most of the large rivers in the world. High pH and high cation (i.e., Na⁺ + Ca²⁺) concentrations of the rivers are the most important factors controlling the concentrations of dissolved REE in the river water. The dissolved load (<0.22 μm) REE distribution patterns of high-pH river waters are very different from those of low-pH river waters. The shale (PAAS)-normalized REE patterns for the dissolved loads are characterized by light REE-enrichment and heavy REE-enrichment. Water in the upper reaches of the Wujiang River generally shows light REE-enriched patterns, while that in the middle and lower reaches generally shows heavy REE-enriched patterns. The Yuanjiang River is heavy REE enriched with respect to the light REE in the same samples. Water of the Wuyanghe River draining dolomite-dominated terrains has the highest heavy REE-enrichment. Most river water samples show the shale-normalized REE patterns with negative Ce and Eu anomalies, especially water from Wuyanghe River. Y/Ho ratios show that the water/particle interaction might have played an important role in fractionation between HREE and LREE.     

Fractionation,distribution and transport of mercury in rivers and tributaries around Wanshan Hg mining district,Guizhou Province,Southwestern China: Part 2 – Methylmercury

Water samples were collected during normal flow (2007) and during a drought period (2008) from five rivers and tributaries draining the Wanshan Hg mining district, Guizhou, China. Unfiltered methylmercury (MeHg) as well as particulate and dissolved fractions of MeHg (P-MeHg, D-MeHg) were measured to assess the spatial and temporal variation of MeHg contamination in the local river system. Most locations (about 80%) displayed higher MeHg concentrations during drought period than during normal discharge conditions. Concentrations of MeHg during the drought period ranged from <0.035 to 11 ng L⁻¹ (geometric mean: 0.43), while during normal flow the concentrations ranged from <0.035 to only 3.4 ng L⁻¹ (geometric mean: 0.21). Concentrations of MeHg were positively correlated with total Hg (THg) concentrations (R² = 0.20–0.58, P < 0.001) and inversely related to distance from the calcines, during both sampling periods (R² = 0.34 and 0.23, P < 0.001, for low and normal flow, respectively) indicating that calcines may be important sources of MeHg to the downstream environment. Approximately 39% of MeHg was bound to particulates and the rest was transported in the dissolved phase along stretches of the entire river, which was different from THg, as this was mainly transported bound to particulates (commonly more than 80%).     

Microbial mercury cycling in sediments of the San Francisco Bay-Delta

Microbial mercury (Hg) methylation and methylmercury (MeHg) degradation processes were examined using radiolabled model Hg compounds in San Francisco Bay-Delta surface sediments during three seasonal periods: late winter, spring, and fall. Strong seasonal and spatial differences were evident for both processes. MeHg production rates were positively correlated with microbial sulfate reduction rates during late winter only. MeHg production potential was also greatest during this period and decreased during spring and fall. This temporal trend was related both to an increase in gross MeHg degradation, driven by increasing temperature, and to a build-up in pore water sulfide and solid phase reduced sulfur driven by increased sulfate reduction during the warmer seasons. MeHg production decreased sharply with depth at two of three sites, both of which exhibited a corresponding increase in reduced sulfur compounds with depth. One site that was comparatively oxidized and alkaline exhibited little propensity for net MeHg production. These results support the hypothesis that net MeHg production is greatest when and where gross MeHg degradation rates are low and dissolved and solid phase reduced sulfur concentrations are low.     

Abundances and modes of occurrence of trace elements in the Çan coals (Miocene), Çanakkale-Turkey

This study presents the concentrations and modes of occurrence of trace elements in 81 coal samples from the Çan basin of northwestern Turkey. The concentration of trace elements in coal were determined by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectrometry. Additionally, traditional coal parameters were studied by proximate, ultimate, X-ray diffraction, and petrographic analyses. Twenty trace elements, including As, B, Ba, Be, Cd, Cu, Co, F, Hg, Mo, Ni, Pb, Sb, Se Sn, Th, Tl, U, V, and Zn, receive much attention due to their related environmental and human health concerns. The Çan coals investigated in this study are lignite to sub-bituminous coal, with a broad range of ash yields and sulphur contents. The trace element concentrations show variety within the coal seams in the basin, and the affinities vary among locations. The concentrations of B, Ba, Be, Cd, Cu, Co, F, Hg, Mo, Ni, Pb, Sb, Se, Sn, Tl, and Zn in Çan coals are within the Swaine's worldwide concentration range, with the exception of As, Th, U, and V. On the other hand, compared with world coals, the Çan basin coals have higher contents of As, B, Cu, Co, Mo, Pb, Th, U, V, and Zn. Based on statistical analyses, most of the trace elements, except for U, show an affinity to ash yield. Elements including As, Cd, Hg, Se, Cu, Mo, Ni, and Zn, show a possible association with pyrite; however, the elements Se, B, and Mo can be have both organic and inorganic associations.