Elevated Mercury Concentrations Research Articles

Marine anoxia and sedimentary mercury enrichments during the Late Cambrian SPICE event in northern Scotland

Elevated mercury concentrations in ancient sedimentary rocks are used as a fingerprint for large igneous province (LIP) volcanism because there is a tight association between known LIPs and coeval sedimentary Hg anomalies. While nonvolcanic processes of sedimentary Hg enrichment, including redox variations, have been demonstrated in modern settings, interpretations of ancient sedimentary Hg records have focused on LIP volcanism. Here, we document a link between sedimentary Hg enrichment and marine redox changes during the late Cambrian Steptoean positive isotopic carbon excursion (SPICE) event, a time with no known LIP. We report a new occurrence of the SPICE event from the Eilean Dubh Formation of northern Scotland, which preserves a series of coeval Hg enrichments. Abundant glauconite, a redox-sensitive iron-bearing mineral, co-occurs stratigraphically with the SPICE and Hg enrichments but is rare to absent from the rest of the section, and bioturbation is low in strata spanning the SPICE. We suggest that local Hg enrichments were driven by changing marine redox conditions during the SPICE event, rather than emplacement of a LIP. Redox oscillations should be considered as an additional control on Hg enrichments in the geologic record.

Mercury Isotopes Reveal Atmospheric Gaseous Mercury Deposition Directly to the Arctic Coastal Snowpack

Springtime atmospheric mercury depletion events (AMDEs) lead to snow with elevated mercury concentrations (>200 ng Hg/L) in the Arctic and Antarctic. During AMDEs gaseous elemental mercury (GEM) is...

Volcanoes, medicine, and monasticism: Investigating mercury exposure in medieval Iceland

AbstractThis study aimed to evaluate the possible use of mercury as a medical treatment at the medieval monastic hospital Skriðuklaustur (ad 1494–1554) in eastern Iceland. The individuals excavated from Skriðuklaustur exhibited a wide range of pathological conditions, including the only skeletal evidence of venereal syphilis in Iceland. Skeletal remains from the Skeljastaðir cemetery (ca. ad 1000–1104) in southern Iceland were also analysed in light of the site's proximity to the mercury emitting volcano Hekla. The eruption produced a severe toxic fallout resulting in the mass mortality of livestock and is believed to have caused the abandonment of Skeljastaðir and the other farms in the region. The skeletal analyses and sampling were conducted according to standard anthropological methods. Mercury concentrations were determined in human (n = 50), faunal (n = 23), and soil (n = 22) samples using inductively coupled plasma mass spectrometry. Individuals from both sites exhibited elevated mercury concentrations. At Skriðuklaustur, some individuals showed normal concentrations, but those with pathological conditions (e.g., hydatidosis, syphilis, tuberculosis, and other non‐specific infections) had the highest concentrations overall. On the other hand, all the individuals analysed from Skeljastaðir exhibited elevated mercury concentrations, some of which were remarkably high. A few of the individuals buried at Skeljastaðir post‐date the eruption, possibly indicating that some of them experienced heavy exposure to volcanic emissions. The less extreme concentrations at Skriðuklaustur may be a result of attention to dosage and the temporary nature of mercurial treatments. None of the faunal and soil samples presented with concentrations exceeding the normal limit, implying that diagenesis was not a concern in this research. The conclusion is that a variety of factors from medical treatment to scholarly work lead to mercury exposure at Skriðuklaustur, whereas at Skeljastaðir, volcanogenic emissions are implicated.

THE MERCURY CONTENT IN THE BLOOD OF INHABITANTS OF THE YAMALO-NENETS AUTONOMOUS DISTRICT

There are presented results of a study of the mercury content in the blood of 151 residents residing in the Yamalo-Nenets Autonomous district (YaNAO). Mercury is a toxic chemical of concern on a global scale. YaNAO is characterized by the presence of numerous sources of emissions of mercury - the enterprises of oil and gas production, develop the mineral deposits of the Polar Urals, housing and communal complex, gold mining, mercury ore occurrence. The study shows high levels of mercury in the blood of 41.7% of the surveyed residents of the Yamalo-Nenets Autonomous district, of which 35.6% are in the Taz district, 51.9% - in village Harsani, 60% - in the village Kutop’yugan. There were revealed high levels of mercury in the blood of the indigenous population of Yamal. The excessive accumulation of mercury was seen in 27.8% of indigenous males, in 18.2% of indigenous women (Tazovskiy district), in newly arriving men and women elevated levels of mercury in blood was not detected (Tazovskiy district). The absolute average values of mercury in blood from indigenous men (0.0112±0.0049 mg/ml) was almost five times higher than in migrant men (0.0023±0.0009 ág/ml); in indigenous women (0.0096±0.0063 mg/ml) the difference was almost three times in comparison with the migrant women (0.0038±0.0023 mg/ml). There is identified the possible damage to health from exposure to elevated concentrations of mercury for every third of the surveyed resident of Harshim settlement, village Kutop’yugan and 14.6% of the surveyed residents of the village Tazovskiy (the concentration of mercury in blood above 0.015 mg/ml). Elevated concentrations of mercury in the blood of residents of Nakhodka and Kutop tundra dictate the urgent necessity of the strengthening of control over the mercury contents in natural environments. It is necessary to conduct a surface gas-mercury survey on the territory of the Yamal and Gydan Peninsulas to identify a hidden source of mercury pollution. Research must be continued.

Tailings ponds of the Athabasca Oil Sands Region, Alberta, Canada, are likely not significant sources of total mercury and methylmercury to nearby ground and surface waters

Tailings ponds created during industrial bitumen extraction from the Athabasca Oil Sands Region (AOSR), Alberta, Canada, have been shown to contain numerous contaminants, such as polycyclic aromatic compounds and naphthenic acids, and to slowly leak into adjacent ground and surface waters. Despite elevated concentrations of total mercury (THg) in nearby Athabasca River waters downstream of the AOSR developments, to date there are no published studies of THg or methylmercury (MeHg; a potent neurotoxin) in the AOSR tailings ponds. Here we present concentrations of THg and MeHg, as well as various water chemistry parameters, within four AOSR tailings ponds. Concentrations of SO42−, NH3, Na, and Cl were elevated in tailings ponds relative to nearby freshwaters. Surface water concentrations of THg (filtered: 0.15–0.57 ng/L) and MeHg (unfiltered: <0.02–0.53 ng/L; filtered: <0.02–0.32 ng/L), though, were generally low in the tailings ponds, with the highest concentrations observed in the oldest pond. In the mature fine tailings that settle out in the ponds, concentrations of THg (37.0–197 ng/g) and MeHg (0.10–0.52 ng/g) were also low, with the highest concentrations again in the oldest pond. We calculated that if all the dissolved THg and MeHg potentially leaking annually from the tailings ponds entered the nearby Athabasca River, river THg and MeHg concentrations would increase by only 0.01% and 0.03%, respectively. Overall, these ponds are likely not significant sources of THg or MeHg to nearby ground and surface waters, although due to the potential for Hg methylation to occur in the ponds themselves, other tailings ponds in the AOSR should be monitored to ensure that concentrations of MeHg in them are also low.

Assessing mercury contamination patterns of fish communities in the Laurentian Great Lakes: A Bayesian perspective

We examine the spatio-temporal trends of mercury, a well-known global legacy contaminant, in eleven fish species across all of the Canadian Great Lakes. These particular fish species are selected based on their ecological, commercial, and recreational importance to the biodiversity and fishing industry of the Great Lakes. We present a two-pronged Bayesian methodological framework to rigorously assess mercury temporal trends across multiple fish species and locations. In the first part of our analysis, we develop dynamic linear models to delineate the total mercury levels and rates of change, while explicitly accounting for the covariance between fish length and mercury levels in fish tissues. We then use hierarchical modelling to evaluate the spatial variability of mercury contamination between nearshore and offshore locations, as well as to examine the hypothesis that invasive species have induced distinct shifts on fish mercury contamination trends. Our analysis suggests that the general pattern across the Great Lakes was that the elevated mercury concentrations during the 1970s had been subjected to a declining trend throughout the late 1980s/early 1990s, followed by a gradual stabilization after the late 1990s/early 2000s. The declining trend was more pronounced with top fish predators, whereas benthivorous fish species mainly underwent wax-and-wane cycles with a weaker evidence of a long-term declining trend. Historically contaminated regions, designated as Areas of Concern, and bays receiving riverine inputs are still characterized by mercury concentrations that can lead to consumption restrictions. Lake Erie displayed the lowest mercury levels across all the fish species examined. However, several species of commercial importance showed a reversing (increasing) trend in the 2000s, although their current levels do not pose any major concerns for consumption advisories. These recent trend reversals can be linked with systematic shifts in energy trophodynamics along with the food web alterations induced from the introduction of non-native species, and the potentially significant fluxes from the atmosphere.

Traditional Tibetan Medicine Induced High Methylmercury Exposure Level and Environmental Mercury Burden in Tibet, China.

Highly elevated concentrations of total mercury (THg) and methylmercury (MeHg) were found in the municipal sewage in Tibet. Material flow analysis supports the hypothesis that these elevated concentrations are related to regular ingestion of Hg-containing Traditional Tibetan Medicine (TTM). In Tibet in 2015, a total of 3600 kg of THg was released from human body into the terrestrial environment as a result of TTM ingestion, amounting to 45% of the total THg release into the terrestrial environment in Tibet, hence substantially enhancing the environmental Hg burden. Regular ingestion of TTM leads to chronic exposure of Tibetans to inorganic Hg (IHg) and MeHg, which is 34 to 3000-fold and 0-12-fold higher than from any other known dietary sources, respectively. Application of a human physiology model demonstrated that ingestion of TTM can induce high blood IHg and MeHg levels in the human body. Moreover, 180 days would be required for the MeHg to be cleared out of the human body and return to the initial concentration i.e. prior to the ingestion of 1 TTM pill. Our analysis suggests that high Hg level contained in TTM could be harmful to human health and elevate the environmental Hg burden in Tibet.

Fifty years after its discharge, methylation of legacy mercury trapped in the Penobscot Estuary sustains high mercury in biota

Fifty years ago, the Penobscot Estuary was contaminated by mercury discharged from the chlor-alkali plant located in Orrington, Maine, USA. Almost all of the mercury was discharged from the plant during the late 1960s and early 1970s. Despite the much lower mercury discharges in recent decades, present-day concentrations in surface sediment remain high (averaging 350–1100 ng/g dw) and are still high in blood of marsh birds (up to 10.5 μg/g), black duck muscle (0.8 μg/g), and lobster muscle (0.4 μg/g). Methyl mercury (MeHg) concentrations in marsh birds exceed levels that impair reproduction. There are health advisories for duck hunters and closures of shellfish fisheries. These continuing high mercury concentrations are caused by the trapping of legacy mercury in a mobile pool of sediment that is retained in the upper estuary above a tidally forced salinity front, which travels up and down the estuary each tidal cycle - slowing the transport of particulate mercury to Penobscot Bay. The trapped legacy mercury continues to be available for methylation 50 years after it first entered the estuary. This is demonstrated by the fact that rates of MeHg production are positively related to the inorganic mercury concentration in parts of the estuary with elevated concentrations of legacy mercury. Thus, remediation measures that would lower the THg concentration in surface sediment would lower the MeHg in birds, fish and shellfish. All of this new information leads us to recommend two remediation options. Addition of mercury binding agents may lower mercury concentrations in birds in some wetland areas. System-wide, we also recommend Enhanced Natural Recovery (ENR), a novel approach that involves the partial removal of the contaminated mobile sediment pool followed by replacement with clean-clay particulates to dilute inorganic mercury concentrations, which would lower methylation rates and mercury concentrations in biota.

Roles of rhizospheric organic acids and microorganisms in mercury accumulation and translocation to different winter wheat cultivars

Elevated mercury concentrations in wheat grains pose a potential health risk to human. In this study, we selected two low-mercury-accumulating wheat cultivars (Nongda-3163, Gaocheng-8901) and two high-mercury-accumulating wheat cultivars (Jimai-21, Taishan-21) to investigate the role of rhizospheric organic acids and microorganisms in mercury accumulation and translocation to different wheat plants. The wheat grew in greenhouse with three levels of mercury treatment: control (no added mercury), low treatment (1 mg kg−1 total mercury) and high treatment (5 mg kg−1 total mercury). Under low mercury treatment condition, Jimai-21 and Taishan 21 had significantly higher mercury concentrations in roots and secreted higher amounts of oxalic acid and citric acid in the rhizosphere soil than Nongda-3163 and Gaocheng-8901. Meanwhile, abundances of gram positive bacteria, gram negative bacteria and fungi in the rhizosphere soil of Jimai-21 were significantly higher than those of Nongda-3163 and Gaocheng-8901, while abundance of protozoa in the rhizosphere soil of Jimai-21 was significantly lower than those of Gaocheng-8901. These facts may lead to higher mercury concentrations in grains of Jimai-21 and Taishan-21 than those of Nongda-3163 and Gaocheng-8901. In the current study, the oxalic acid had the largest contribution on mercury accumulation and translocation (p = .002), followed by citric acid (p = .002) and protozoa (p = .038) under low mercury treatment condition. Under high mercury treatment condition, Jimai-21 and Taishan-21 had significantly higher translocation factors from roots to leaves, glumes and grains than Nongda-3163 and Gaocheng-8901, and the significant contribution sequentially were citric acid (p = .002), fungi (p = .02) and gram positive bacteria (p = .018). Improving the beneficial relationship among rhizospheric organic acids, microorganisms and wheat cultivars was a realizable strategy to ensure wheat safety for mercury.

Senegalese artisanal gold mining leads to elevated total mercury and methylmercury concentrations in soils, sediments, and rivers

The largest source of global mercury (Hg) anthropogenic inputs to the environment is derived from artisanal and small-scale gold mining (ASGM) activities in developing countries. While our understanding of global Hg emissions from ASGM is growing, there is limited empirical documentation about the levels of total mercury (THg) and methylmercury (MeHg) contamination near ASGM sites. We measured THg and MeHg concentrations in soil (n = 119), sediment (n = 22), and water (n = 25) from four active ASGM villages and one non-ASGM reference village in Senegal, West Africa. Nearly all samples had THg and MeHg concentrations that exceeded the reference village concentrations and USEPA regulatory standards. The highest median THg concentrations were found in huts where mercury-gold amalgams were burned (7.5 μg/g), while the highest median MeHg concentrations and percent Hg as MeHg were found in river sediments (4.2 ng/g, 0.41%). Median river water concentrations of THg and MeHg were also elevated compared to values at the reference site (22 ng THg/L, 0.037 ng MeHg/L in ASGM sites). This study provides direct evidence that Hg from ASGM is entering both the terrestrial and aquatic ecosystems where it is converted in soils, sediment, and water to the neurotoxic and bioavailable form of MeHg.

Effect of mercury on pollen germination and tube growth in Lilium longiflorum.

Pollen development and germination were adversely affected by the presence of mercury, whereas low-concentrations stimulated the whole procedure. Mercury caused morphological anomalies during the tube growth, characterized by irregularly increasing diameters and swelling tips. The main effect was the anomalous cell wall formation at the tip where a substantial number of organelles were found reducing the secretory vesicles. The dense organelle concentration caused a significant reduction of cytoplasmic movement integrity, and the cytosol streaming was gradually reduced or stopped completely. Electron dense, multilamellar myelin-like structures (MMS) of membranous material were frequently present, in close contact with plasmalemma or away from it. A loose network of fibrillar material and spherical aggregates mostly at the tip region were observed which progressively were loosened into the surrounding medium. Elevated mercury concentrations can affect plant reproduction, resulting in anomalies in gamete development and consequently loss of plant biodiversity.

1H NMR-based metabolomics investigation on the effects of petrochemical contamination in posterior adductor muscles of caged mussel Mytilus galloprovincialis

Environmental metabolomics is a high-throughout approach that provides a snapshot of the metabolic status of an organism. In order to elucidate the biological effects of petrochemical contamination on aquatic invertebrates, mussels Mytilus galloprovincialis were caged at the “Augusta-Melilli-Priolo” petrochemical area and Brucoli (Sicily, south Italy), chosen as the reference site. After confirming the elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) and mercury (Hg) in Augusta sediments in our previous work (Maisano et al., 2016a), herein an environmental metabolomics approach based on protonic nuclear magnetic resonance (1H NMR), coupled with chemometrics, was applied on the mussel posterior adductor muscle (PAM), the main muscular system in bivalve molluscs. Amino acids, osmolytes, energy storage compounds, tricarboxylic acid cycle intermediates, and nucleotides, were found in PAM NMR spectra. Principal Component Analysis (PCA) indicated that mussels caged at the polluted site clustered separately from mussels from the control area, suggesting a clear differentiation between their metabolic profiles. Specifically, disorders in energy metabolism, alterations in amino acids metabolism, and disturbance in the osmoregulatory processes were observed in mussel PAM. Overall, findings from this work demonstrated the usefulness of applying an active biomonitoring strategy for environmental risk assessment, and the effectiveness of metabolomics in elucidating changes in metabolic pathways of aquatic organisms caged at sites differentially contaminated, and thus its suitability to be applied in ecotoxicological studies.

Elevated mercury concentrations in the feathers of grey-faced petrels (Pterodroma gouldi) in New Zealand

Our objective was to measure the concentrations of Hg, As, Cd, Co, Cr, Cu, Pb, Sb, V and Zn in the body feathers of grey-faced petrel (Pterodroma gouldi), fluttering shearwater (Puffinus gavia), little shearwater (Puffinus assimilis) and common diving petrel (Pelecanoides urinatrix) from breeding colonies in New Zealand between 2006 and 2013. The mean Hg concentration (36.48ppm; SD=9.59) in grey-faced petrel feathers was approximately 8.5 to 14 times that detected in the other three species sampled. We detected no trend or differences in Hg concentrations in grey-faced petrels over the 8years of this study, but Hg concentrations varied between breeding colonies although there was no strong relationship with latitude. The elevated Hg concentrations detected in grey-faced petrels could pose a risk to the breeding performance of grey-faced petrels and the customary harvest of chicks by Māori (New Zealand's indigenous peoples).

Mercury exposure may influence fluctuating asymmetry in waterbirds.

Variation in avian bilateral symmetry can be an indicator of developmental instability in response to a variety of stressors, including environmental contaminants. The authors used composite measures of fluctuating asymmetry to examine the influence of mercury concentrations in 2 tissues on fluctuating asymmetry within 4 waterbird species. Fluctuating asymmetry increased with mercury concentrations in whole blood and breast feathers of Forster's terns (Sterna forsteri), a species with elevated mercury concentrations. Specifically, fluctuating asymmetry in rectrix feather 1 was the most strongly correlated structural variable of those tested (wing chord, tarsus, primary feather 10, rectrix feather 6) with mercury concentrations in Forster's terns. However, for American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), and Caspian terns (Hydroprogne caspia), the authors found no relationship between fluctuating asymmetry and either whole-blood or breast feather mercury concentrations, even though these species had moderate to elevated mercury exposure. The results indicate that mercury contamination may act as an environmental stressor during development and feather growth and contribute to fluctuating asymmetry of some species of highly contaminated waterbirds. Environ Toxicol Chem 2017;36:1599-1605. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Mercury enrichment in Brassica napus in response to elevated atmospheric mercury concentrations

Mercury enrichment in response to elevated atmospheric mercury concentrations in the organs of rape (Brassica napus) was investigated using an open top chamber fumigation experiment and a soil mercury enriched cultivation experiment. Results indicate that the mercury concentration in leaves and stems showed a significant variation under different concentrations of mercury in atmospheric and soil experiments while the concentration of mercury in roots, seeds and seed coats showed no significant variation under different atmospheric mercury concentrations. Using the function relation established by the experiment, results for atmospheric mercury sources in rape field biomass showed that atmospheric sources accounted for at least 81.81%of mercury in rape leaves and 32.29% of mercury in the stems. Therefore, mercury in the aboveground biomass predominantly derives from the absorption of atmospheric mercury.

Mercury Stoichiometric Relationships in a Subtropical Peatland

Spatially variable areas, or hotspots, of elevated mercury (Hg) concentrations in soil, water, and wildlife occur throughout the Everglades wetland ecosystem. This study investigates the stoichiometric controls of Hg relative to soil, water, and biotic components. Surface water, porewater, soil, periphyton, and Gambusia spp. (mosquitofish) were collected from hotspots and non-spot stations and analyzed for various parameters, including total mercury (THg), organic carbon (OC), total carbon (TC), total phosphorus (TP), and total nitrogen (TN) between late 2010 and early 2013. Soil nutrient ratios were significantly different between hotspot and non-hotspot stations, indicating a difference in trophic status and position along the decay continuum or differences in limiting nutrients. Overall, soil total Hg concentrations were negatively correlated with soil TC/TN, while soil TC/TP and soil TN/TP molar ratios and soil THg were negatively correlated at hotspot stations. Meanwhile, mosquitofish THg was negatively correlated with soil TC/TN molar ratio and positively correlated with soil TC/TP and TN/TP molar ratios, suggesting trophic truncation. Soil, surface water, and porewater THg, TC, and OC interactions resulted in significant differences between hotspot and non-hotspot stations and between molar ratios of C, N, and P. Periphyton-surface water THg/OC homeostasis and soil nutrient ratios significantly explained mosquitofish THg concentrations, further indicating a trophic influence on mosquitofish THg and potential hotspot dynamics. Several factors and processes including bottom-up trophic interaction and vegetation influence on Hg accumulation dynamics and food-chain length explain the development and persistence of Hg hotspot formation within the Everglades system.

Airborne mercury species at the Råö background monitoring site in Sweden: distribution of mercury as an effect of long-range transport

Abstract. Within the EU-funded project, Global Mercury Observation System (GMOS) airborne mercury has been monitored at the background Råö measurement site on the western coast of Sweden from mid-May 2012 to the beginning of July 2013 and from the beginning of February 2014 to the end of May 2015. The following mercury species/fractions were measured: gaseous elemental mercury (GEM), particulate bound mercury (PBM) and gaseous oxidised mercury (GOM) using the Tekran measurement system. The mercury concentrations measured at the Råö site were found to be low in comparison to other, comparable, European measurement sites. A back-trajectory analysis to study the origin of air masses reaching the Råö site was performed. Due to the remote location of the Råö measurement station it receives background air about 60 % of the time. However, elevated mercury concentrations arriving with air masses coming from the south-east are noticeable. GEM and PBM concentrations show a clear annual variation with the highest values occurring during winter, whereas the highest concentrations of GOM were obtained in spring and summer. An evaluation of the diurnal pattern of GOM, with peak concentrations at midday or in the early afternoon, which often is observed at remote places, shows that it is likely to be driven by local meteorology in a similar way to ozone. Evidence that a significant part of the GOM measured at the Råö site has been formed in free tropospheric air is presented.

Fracked ecology: Response of aquatic trophic structure and mercury biomagnification dynamics in the Marcellus Shale Formation.

Unconventional natural gas development and hydraulic fracturing practices (fracking) are increasing worldwide due to global energy demands. Research has only recently begun to assess fracking impacts to surrounding environments, and very little research is aimed at determining effects on aquatic biodiversity and contaminant biomagnification. Twenty-seven remotely-located streams in Pennsylvania's Marcellus Shale basin were sampled during June and July of 2012 and 2013. At each stream, stream physiochemical properties, trophic biodiversity, and structure and mercury levels were assessed. We used δ15N, δ13C, and methyl mercury to determine whether changes in methyl mercury biomagnification were related to the fracking occurring within the streams' watersheds. While we observed no difference in rates of biomagnificaion related to within-watershed fracking activities, we did observe elevated methyl mercury concentrations that were influenced by decreased stream pH, elevated dissolved stream water Hg values, decreased macroinvertebrate Index for Biotic Integrity scores, and lower Ephemeroptera, Plecoptera, and Trichoptera macroinvertebrate richness at stream sites where fracking had occurred within their watershed. We documented the loss of scrapers from streams with the highest well densities, and no fish or no fish diversity at streams with documented frackwater fluid spills. Our results suggest fracking has the potential to alter aquatic biodiversity and methyl mercury concentrations at the base of food webs.

Longitudinal occurrence of methylmercury in terrestrial ecosystems of the Tibetan Plateau

Methylmercury (MeHg), a neurotoxin, is a global concern because of its potential risk to human and ecological health. Elevated mercury (Hg) concentrations were recently reported in the Tibetan Plateau (TP) due to increasing Hg input from distant regions, yet little is known about MeHg production and distribution in the terrestrial ecosystems of the TP. Here, we report longitudinal occurrence of MeHg and the factors regulating net MeHg production in 23 grassland sites from eastern to western TP. The soil MeHg content varied from 0.002 to 0.058 ng g−1, with different distribution patterns between the eastern and western TP. There was a positive correlation between the MeHg concentration and the longitude after 90 °E, which is similar to the distribution patterns of the total mercury (THg), water and organic carbon in this region. Average MeHg concentration in topsoil is generally higher than that in subsoil. Our results show that MeHg concentration in soils of the TP is directly affected by soil water, potential microbial methylators and THg, while indirectly regulated by soil organic carbon through the microbial community and the longitude-dependent precipitation through soil water. Our study suggests that soil water is the most important driver regulating net MeHg production in the grasslands of the TP. These findings have important implications for unraveling the mechanism of net production of MeHg in high-altitude environments.

Groundwater Contamination by Uranium and Mercury at the Ridaura Aquifer (Girona, NE Spain).

Elevated concentrations of uranium and mercury have been detected in drinking water from public supply and agricultural wells in alluvial and granitic aquifers of the Ridaura basin located at Catalan Coastal Ranges (CCR). The samples showed high concentrations of U above the U.S. standards and the World Health Organization regulations which set a maximum value of 30 µg/L. Further, high mercury concentrations above the European Drinking Water Standards (1 μg/L) were found. Spatial distribution of U in groundwater and geochemical evolution of groundwater suggest that U levels appear to be highest in granitic areas where groundwater has long residence times and a significant salinity. The presence of high U concentrations in alluvial groundwater samples could be associated with hydraulic connection through fractures between the alluvial system and deep granite system. According to this model, oxidizing groundwater moving through fractures in the leucocratic/biotitic granite containing anomalous U contents are the most likely to acquire high levels of U. The distribution of Hg showed concentrations above 1 μg/L in 10 alluvial samples, mainly located near the limit of alluvial aquifer with igneous rocks, which suggests a possible migration of Hg from granitic materials. Also, some samples showed Hg concentrations comprised between 0.9 and 1.5 μg/L, from wells located in agricultural areas.