Total Hg Concentrations Research Articles

Geoecological features of mercury pressure on the south coast of the Republic of Crimea based on the study of needles

Abstract. The article presents the original data on the total Hg concentration in the needles of different tree species in the recreational zones of settlements on the south coast of the Republic of Crimea. Mean Hg concentrations were lower than in the Tomsk Region and the Republic of Sakha-Yakutia but higher than in Southern Siberia. Hg concentrations increased from west to east along the south coast of Crimea. Pine needles showed increased sorption properties relative to mercury, juniper needles had the least sorption. There was no dependence of the element input on height relative to sea level. Calculated indicators indicated elevated Hg concentrations in needles relative to the background, the temporary allowable concentration and the mean value for terrestrial plants.

Hg in waste from mining and processing enterprises in the Republic of Khakassia

Abstract. The article presents the original data on the total Hg concentration in the waste of enterprises for the extraction of iron ore, coal and marble located in the Republic of Khakassia. Hg concentrations in the rocks of the dumps and the material of the tailings depend on the electrical conductivity and magnetic susceptibility. The concentration of this element increases in more acidic environmental conditions, and its higher concentrations are associated with particles having a size of 0.04 mm. Geoecological indicators demonstrate the enrichment of Hg waste from all enterprises studied, as confirmed by the calculation data of the enrichment factor.

Exposure of Mercury from Gold Ming Area: A Case Study in Tendo and Aby Lagoon in Côte d’Ivoire

Lagoons of West African countries are seriously threatened by rapid artisanal and small-scale gold mining (ASGM) that exposes lagoons to mercury pollution. In this study, the mercury level in the sediments of the Tendo and Aby lagoons in Côte d’Ivoire had been evaluated. A total of 87 samples from 25 stations located on Tendo and Aby lagoons were analyzed by atomic fluorescence spectrometry. The mean Hg concentrations obtained in the sediments of Tendo and Aby lagoons were 0.89 ± 0.26 mg⋅kg-1 and 0.70 ± 0.18 mg⋅kg-1, respectively. Hg concentrations evaluated in the bays of Tendo and Aby during the dry season were 1.38 ± 0.45 mg⋅kg-1 and 1.07 ± 0.31 mg⋅kg-1, respectively. The minimum and maximum total Hg concentrations in the sediments from 25 stations were 0.04 and 3.56 mg⋅kg-1, respectively. Mercury contamination in lagoons during ASGM poses risks of pollution for the lagoon ecosystem and also poses health risks for the population living near these lagoons.

A novel simultaneous isotope dilution strategy as a powerful tool in the two-track certification process of trace metal mass fractions: a case study of mercury, cadmium and lead in soil and sediment materials.

An analytical methodology based on isotope dilution (ID) principles was developed to establish the reference procedure for the simultaneous assignation of aqua regia extractable and total mass fractions of Hg, Cd, and Pb in soil and sediment matrix samples. The 'twin sample-spike blends' were prepared under close to the exact matching conditions, resulting in almost identical mass ratios of the spike to the sample in the blends, which followed either the aqua regia extraction method or total digestion procedure. The isotope ratios in 'twin-blends' were measured by inductively coupled plasma mass spectrometry (ICP-MS). The two-track IDMS strategy proposed in this work was successfully applied to three certified reference materials (CRMs): ERM-CC141 loam soil, EnvCRM 03 soil, and MODAS-2 bottom sediment. This ensured an adequate method validation. For two CRMs (EnvCRM 03 and MODAS-2) it was found that the isotope ratio values in 'twin-blends' for Hg, Cd, and Pb were almost identical with a variability of less than 2.4%. This confirmed that there is no measurable difference between the aqua regia extractable and the total mass fractions within the uncertainty ranges. Therefore, aqua regia mass fractions assigned in this study were found to be equal to certified element contents. For ERM-CC141 loam soil, the Hg isotope ratio values measured in the 'twin-blends' were found to be identical within their measurement uncertainties, and thus, it was concluded that the aqua regia extractable Hg content is identical to the total Hg content. However, in the case of Cd and Pb isotope ratio values in 'twin-blends' varied around 24% or 16%, respectively and because this significant difference was noticed, for both elements it is necessary to calculate the aqua regia content and the total content separately. Because this significant difference was noticed for both elements, it is necessary to calculate the aqua regia content and the total content separately. A detailed comparison of the isotope ratio values between the 'twin-blends' provided unambiguous information about aqua regia extractability of metals and it is a strong indicator for making decisions related to the assignment of either a single mass fraction valid for both procedures or two separate element mass fraction values. To our knowledge and based on the relevant literature survey, this is a novel strategy based on IDMS, and such studies have not been undertaken and presented so far.

Methylmercury exposure during prenatal and postnatal neurodevelopment promotes oxidative stress associated with motor and cognitive damages in rats: an environmental-experimental toxicology study

The environmental contamination by methylmercury (MeHg) is a major concern for public health. The effects of MeHg in the central nervous system (CNS) of adult animals have been extensively investigated; however, little is known about the effects of MeHg exposure during intrauterine and lactation periods on motor and cognitive functions of adolescent rats. Therefore, this study aimed to investigate the effect of MeHg exposure during intrauterine life and lactation on both motor and cognitive functions of offspring rats. Ten female Wistar rats were exposed to 40 μg/kg/day of MeHg through cookie treats from the first day of pregnancy until the last day of breastfeeding. Both motor and cognitive functions of offspring male rats were assessed by open field, rotarod, and step-down inhibitory avoidance tests. Forty-one days after birth, the hippocampus and cerebellum were collected to determine total Hg content, antioxidant capacity against peroxyl radicals (ACAP), reduced glutathione (GSH) levels, lipid peroxidation (LPO), and nitrite levels. MeHg exposure during CNS development increased Hg levels in both hippocampal and cerebellar parenchymas, triggered oxidative stress throughout ACAP and GSH decrease, increased LPO and nitrite levels. These alterations resulted in reduced spontaneous and stimulated locomotion and short- and long-term memory deficits. Therefore, damages triggered by MeHg exposure during intrauterine life and lactation had detrimental effects on oxidative biochemistry and motor and cognitive functions of offspring rats.

Distribution of mercury and methylmercury in river water and sediment of typical manganese mining area

Manganese (Mn) ores contain substantial concentrations of mercury (Hg), and mining and smelting of Mn ores can bring Hg into the surrounding aquatic environment through atmospheric deposition, leaching of electrolytic Mn residue and Mn gangue dump. However, limited is known that how these processes influence the environmental behaviors of Hg in waterbody. Therefore, the seasonal distribution and existing form of Hg in water and sediment in one Mn ore area in Xiushan County, Chongqing were investigated. Our results showed that the mean Hg and methylmercury (MeHg) concentrations in water (n=35) were 5.8 ± 4.6 ng/L and 0.22 ± 0.14 ng/L, respectively. The mean Hg concentrations in retained riverbed and fluvial bank sediment (n=35) were 0.74 ± 0.26 mg/kg and 0.63 ± 0.27 mg/kg, respectively (the mean MeHg concentrations were 0.64 ± 0.40 µg/kg and 0.51 ± 0.30 µg/kg, respectively). It indicated that the mining and smelting of Mn ores were the main sources of anthropogenic Hg, and Mn may inhibit Hg methylation in rivers in Mn ore areas. Mercury in the bound to iron/ Mn (Fe/Mn) oxides of low crystallinity fraction (Hg-OX) accounted for 4.01% and 5.25% of the total Hg concentrations in the retained riverbed and fluvial bank sediment, respectively. The amount of Hg bound to Fe/Mn oxides in sediment increased significantly due to the manganese mining activities in the investigated area. Therefore, it could be hypothesized that high Hg concentrations in river sediment in Mn mining areas are closely related to high Mn concentration in sediment.

Significance of soil moisture on temperature dependence of Hg emission

Soil moisture is a key factor for mercury (Hg) emission from soil. Despite its significance for Hg emissions, the effect of soil moisture on Hg flux and fractions has not been thoroughly investigated. The objective of this study was to elucidate the influences of soil moisture and temperature on Hg fluxes from soils and Hg fractions. A kinetic study was performed to measure Hg emission fluxes of six soil samples under different temperature (T) (15 °C, 20 °C, 25 °C, 30 °C, and 35 °C) and moisture conditions (0%, 10%, and 20% added water). The results showed that the Hg fluxes increased with increases in T and soil moisture. A linear correlation was found between ln (Hg emission flux) and 1/T for the six soil samples at different moisture contents (R2 = 0.73–0.99). The range of activation energy (Ea) values was 25.31–57.86 kJ/mol. The Hg fractions in soils of different moisture content were determined by a sequential extraction method. The results demonstrated that soil moisture affected the Hg fractions in soils. The Ea values had different relationships with soil moisture in different soils. There were correlations between Ea and the elemental and mercuric sulfide fractions for air-dried soils. However, for moist soils, Ea was negatively correlated with the water-soluble and acid-soluble fractions. Collectively, the combination of the Hg emission kinetics and Hg fraction measurement of different moist soils indicated that Hg emission was affected by both total Hg concentration and Hg fractions.

Influence of Spartina alterniflora invasion on mercury storage and methylation in the sediments of Yangtze River estuarine wetlands

The influence of Spartina alterniflora invasion on mercury (Hg) cycling in the coastal wetlands of China and in other parts of the world is not well understood. By combining field sampling with laboratory-scale microcosm incubation experiments, we examined the effect of S. alterniflora invasion on mercury (Hg) storage and net methylmercury (MeHg) production in the sediments of the wetlands in the Yangtze River estuary. The results showed that (1) the estimated mean annual total Hg (THg) input to the wetlands from litterfall was 8.0–26.5 μg/m2 from S. alterniflora, Phragmites australis and Scirpus mariqueter, with the highest levels (26.5 ± 9.0 μg/m2) coming from S. alterniflora due to its high primary productivity. (2) The depth-integrated (<40 cm) mean concentrations of THg in vegetated sediments ranged from 47.5 to 109.1 ng/g, which showed significant positive correlations with the fraction of <16 μm particles and the loss-on-ignition content (P < 0.01). (3) The MeHg concentrations and MeHg/THg (%MeHg) spanned 0.14–1.30 ng/g and 0.2–1.7%, respectively, and showed similar decreasing patterns with depth across all the sites, thereby reflecting the higher rates of Hg methylation in the upper surface sediments. In addition, no significant differences in MeHg concentrations were observed among the sites vegetated by the three plants (P > 0.05). (4) During plant decomposition, net MeHg production was enhanced significantly, but it was inhibited in the presence of the sulfate reduction inhibitor molybdate; these results suggest that sulfate-reducing bacteria could be important methylation mediators in sediments. Moreover, a large fraction of reduced inorganic sulfur (S) species such as iron monosulfide formed during plant decomposition, as revealed by S K-edge XANES spectroscopy. All of these results suggest that S. alterniflora invasion facilitates Hg storage in wetland sediments and affects sulfur cycling but that its effects on MeHg production are similar to those of native plants in the Yangtze River estuarine wetlands.

Ant colonization increased total mercury but reduced methylmercury contents in boreal mires, Northeast China

Soil macroinvertebrates as ecosystem engineers play significant, but largely ignored, roles in affecting mercury (Hg) cycle by altering soil physical-chemical properties. Ant is likely expanded into boreal mires with climate warming, however, its impacts on Hg cycle remained poorly understood. We compared total Hg (THg) and methylmercury (MeHg) contents in soils from antmounds (Lasius flavus) and the nearby ambient in a boreal mire in Northeast China. The present work seeks to unravel factors that controlling MeHg levels in case of ant appearance or absence. The average THg was 179 µg/kg in the ant mound and was 106.1 µg/kg in nearby soils, respectively. The average MeHg was 10.9 µg/kg in the ant mound and was 12.9 µg/kg in nearby soils, respectively. The ratios of MeHg to THg (%MeHg) were 7.61% in ant mounds and 16.75% in nearby soils, respectively. Ant colonization caused THg enrichment and MeHg depletion, and this change was obvious in the 10-20 cm depth soil layer where ants mainly inhabited. Spectrometry characteristics of soil dissolved organic matter (DOM) exert a stronger control than microorganisms on MeHg variation in soils. A structural equation model revealed that the molecular weight of DOM inhibited MeHg irrespective of ant presence or absence, while humification conducive to MeHg significantly in ant mound soils. Microorganisms mainly affected Hg methylation by altering the molecular weight and humification of DOM. We propose that the effects of ant colonization on MeHg rested on DOM feature variations caused by microorganisms in boreal mires.

Responses of bacterial taxonomic attributes to mercury species in rhizosphere paddy soil under natural sulphur-rich biochar amendment

Biochar and sulphur (S) are important factors regulating the level, speciation and transformation of mercury (Hg), leading to alterations in the assemblage of the soil microbial community. However, variations in the taxonomic attributes of the rhizosphere soil bacterial community arising from the Hg speciation in paddy soil, amended with natural S-rich biochar (NSBC) derived from the pyrolysis of S-rich oilseed rape straw, remain unclear. Herein, a rice pot experiment was conducted. Hg-polluted paddy soils were amended with NSBC and low-S biochar (LSBC) to evaluate the role of Hg chemical form affected by NSBC in regulating the taxonomic attributes of rhizosphere soil, including microbial abundance, composition, and ecological clusters within the co-occurrence network of microbial communities. Results showed that microbial abundance was higher in soils with lower Hg levels, and mean increases of 149 observed operational taxonomic units (OTUs) and 238 predicted OTUs (Chao 1) were observed, with a 1 mg kg−1 decrease in the total Hg (T-Hg) content. Among the 13 predictor variables, the T-Hg content was the strongest and most consistent predictor of the bacterial taxonomic attributes. This finding may be attributed to the fact that the drastic reduction in T-Hg and Hg bioavailability induced by NSBC results in the decrease of Hg stress on the soil microbiome. Moreover, NSBC amendment shifted the ecological clusters toward the amelioration of Hg pollution.

Mercury concentrations and stable isotope ratios (δ13C and δ15N) in pelagic nekton assemblages of the south-western Indian Ocean

Mercury (Hg) concentrations and stable isotope values (δ13C and δ15N) were investigated in micronekton collected from La Pérouse and MAD-Ridge seamounts, Reunion Island and the southern Mozambique Channel. Organisms occupying epipelagic habitats showed lower Hg concentrations relative to deeper dwelling benthopelagic ones. Increasing Hg concentrations with increasing body size were recorded in the Mozambique Channel and Reunion Island. Positive relationships were observed between Hg levels and δ15N values in pelagic nekton assemblages collected at MAD-Ridge seamount and the southern Mozambique Channel, suggesting biomagnification of Hg. Concentrations of Hg in organisms across the south-western Indian Ocean were within the same range of values. Total Hg concentrations depend on a range of factors linked to habitat range, body size and trophic position of the individuals. To our knowledge, this is the first study investigating the patterns of Hg concentrations in pelagic nekton assemblages from the south-western Indian Ocean.

Subtidal benthic communities in Minamata Bay, Japan, approximately 30 years after mercury pollution remediation involving dredging disturbance

AbstractApproximately 30 years after mercury pollution remediation finished in Minamata Bay, we report here the present state of the subtidal benthic communities in Minamata Bay. The benthos was sampled at stations in Minamata Bay five times between July 2018 and 2019, capturing seasonal variations. Sediment characteristics were relatively stable across seasons. Sediments contained &gt;80% silt–clay and had total organic carbon (TOC), total nitrogen (TN), and residual total Hg content (THg) approximately 20 mg/g, 2.0 mg/g, and 2.5 mg/kg (dry‐weight basis), respectively, with a C/N ratio of ~11. THg was positively correlated with TOC, whereas TOC was negatively correlated with the C/N ratio, suggesting that TOC is a proxy for sediment microalgal matter (i.e., settling phytoplankton and/or microphytobenthos), a potential food for macrobenthos. Macrobenthos abundance was very low (approximately 100 individuals/m2) and the maximum effective number of species was three in all seasons. We detected effects of THg on species richness and composition of the community, but not on total macrobenthos abundance, biomass, species diversity, or relative species abundance. The TOC gradient was significantly related to both species composition and relative abundance of the community. However, the total variation explained by both TOC and THg for community composition was low (10% at most). These results suggests that other environmental factors, such as the alteration of hydrodynamic and physicochemical regimes caused by the reclamation for pollution mitigation, may also have had a long‐lasting effect on community assembly and the present poor macrofauna levels in Minamata Bay.

A High–Resolution Accumulation Record of Arsenic and Mercury after the First Industrial Revolution from a Peatland in Zoige, Qinghai–Tibet Plateau

The impacts of human activities on Zoige peatlands are poorly documented. We determined the concentrations and accumulation rates of As and Hg in a 210Pb-dated peat profile collected from this area and analyzed the correlations between accumulation rates of both As and Hg and other physicochemical properties. To reconstruct recent conditions of As and Hg, we analyzed peat sediments of Re’er Dam peatland in Zoige using 210Pb and 137Cs dating technologies. The concentrations of total As (86.38 to 174.21 μg kg−1) and Hg (7.30 to 32.13 μg kg−1) in the peat profile clearly increased after the first industrial revolution. From AD 1824 to AD 2010, the average accumulation rates were 129.77 μg m−2 yr−1 for As and 18.24 μg m−2 yr−1 for Hg. Based on our results, anthropogenic emissions significantly affected the atmospheric fluxes of As and Hg throughout the past 200 years, and As was also likely to be affected by other factors than atmospheric deposition, which needs further identification by future studies. The historical variations in As and Hg concentrations in Re’er Dam peatland in Zoige mirror the industrial development of China.

Investigation of the effects of pretreatment on the elemental composition of ash derived from selected Nigerian lignocellulosic biomass

Lignocellulosic biomass is an important source of renewable energy and a potential replacement for fossil fuels. In this work, the X-ray fluorescence (XRF) method was used to analyze the elemental composition of raw and pretreated lignocellulosic biomass of cassava peels, corn cobs, rice husks, sugarcane bagasse, yam peels, and mixtures of cassava peels and yam peels, corn cobs and rice husks and all five biomass samples combined. The influence of particle size on elemental properties was investigated by screening the selected biomass into two size fractions, of an average of 300 and 435 µm, respectively. The total concentration of Mg, Al, Si, P, S, Cl, Ca, Ti, Cr, Mn, Fe, Co, Cu, Zn, Sn, Ni, Br, Mo, Ba, Hg, and Pb were determined for each of the biomass samples before and after the different pretreatments adopted in this study. From the results of the analysis, there was a significant reduction in the concentration of calcium in all the analyzed biomass after the alkaline pretreatment with rice husks biomass having the lowest concentration of 66 ppm after the alkaline pretreatment. The sulfur content of the acid pretreated biomass increased considerably which is likely due to the sulfuric acid used for the acid pretreatment. The fact that a mixture of biomass feedstock affects the properties of the biomass after pretreatment was validated in the mixed biomass of cassava peels and yam peels biomass as an example. The concentration of Mg in the mixed biomass was 1441 ppm but was 200 ppm and 353 ppm in individual cassava peels and yam peels respectively. The results of this study demonstrated that pretreated mixtures of biomass have varied elemental compositions, which could be an important factor affecting downstream processes, especially if a hybrid feedstock is used in a large-scale application.

Shale weathering profiles show Hg sequestration along a New York-Tennessee transect.

Shale-derived soils have higher clay, organic matter, and secondary Fe oxide content than other bedrock types, all of which can sequester Hg. However, shales also can be Hg-rich due to their marine formation. The objectives of this study were to determine the concentration and phase partitioning of Hg in seven upland weathering profiles from New York to Tennessee USA and use geochemical normalization techniques to estimate the extent of Hg inheritance from weathering of shale bedrock or sequestration of atmospheric Hg. Total Hg concentrations in unweathered shale ranged from 3 to 94ng/g. Total Hg concentrations decreased with depth in the Ultisols and Alfisols, with total Hg concentrations ranging from 18 to 265ng/g. Across all shale soils and rocks, the oxidizable fraction of Hg (15% H2O2 extraction) comprised a large portion of the total Hg at 68% ± 8%. This fraction was dominated by organic matter as confirmed with positive correlations between Hg and %LOI, but could also be impacted by Hg sulfides. Across all sites, the reducible fraction of Hg (citrate-bicarbonate-dithionite extraction) was only 10% ± 4% of the total Hg on average. Thus, secondary Fe oxides did not contain a significant portion of Hg, as commonly observed in tropical soils. Although colder sites had a higher organic matter and sequestered more Hg, τ values for Hg indexed to Ti suggest that atmospheric deposition, such as pollution sources in Ohio River Valley, drove the highest enrichment of Hg along the transect. These results demonstrate that shale-derived soils have a net accumulation and retention of atmospheric Hg, primarily through stabilization by organic matter.

Lifelong mercury bioaccumulation in Atlantic horse mackerel (Trachurus trachurus) and the potential risks to human consumption

Atlantic horse mackerel is one of the most commercially important species in Europe. It can reach a longevity of 30 years, with potential implications in lifespan mercury contamination. This study conducted along the Portuguese coast aimed at evaluating the total Hg content and tissue distribution, to determine the annual mercury bioaccumulation patterns and the associated risk for consumption. The T-Hg accumulation patterns observed followed the order: muscle (0.34) > liver (0.28) > heart (0.19) > gills (0.11) > brain (0.041 mg kg−1). Significant differences between tissues reflect the role of the different tissues in storage and redistribution. Significant relationships observed between age and T-Hg for all tissues highlight the continuous nature of the bioaccumulation process. European food safety guidelines signalled significant risk of consumption in about 30% of the samples. Still, there was an overall low risk from the consumption of this species, which can be further minimized through consumer options to avoid health issues.

Temporal change and the influence of climate and weather factors on mercury concentrations in Hudson Bay polar bears, caribou, and seabird eggs

Temporal trends of mercury in Arctic wildlife are inconsistent within and between species and are often insignificant, which limits data interpretation. Recent multivariate analyses have shown that weather and climate factors (e.g. temperatures, sea ice conditions) are related to total Hg (THg) concentrations in wildlife tissues, though relatively few studies have explored these relationships. The present study compared time series of THg concentrations in liver of polar bear (Ursus maritimus, 2007/08–2015/16), eggs of thick-billed murres (Uria lomvia, 1993–2015) and kidney of caribou (Rangifer tarandus groenlandicus, 2006–2015) from the Hudson Bay region of Canada and statistically modelled THg over time with available climate and weather data. Significant temporal trends of THg concentrations were not detected in any species. However, in multivariate models that included time-lagged sea ice freeze up dates, THg concentrations increased 4.4% yr−1 in Qamanirjuaq caribou. Sea ice conditions were also related to THg levels in polar bear liver but not those in eggs of murres, though year was not a signifcant factor. Greater precipitation levels one to two years prior to sampling were associated with greater THg concentrations in polar bears and caribou, likely due to greater deposition, flooding and discharge from nearby wetlands and rivers. Time-lagged Arctic and/or North Atlantic Oscillation (AO/NAO) indices also generated significant, inverse models for all three species, agreeing with relationships in other time series of similar length. The magnitude and direction of many relationships were affected by season, duration of time-lags, and the length of the time series. Our findings support recent observations suggesting that temporal studies monitoring Hg in Arctic wildlife should consider including key climatic or weather factors to help identify consistent variables of influence and to improve temporal analyses of THg time series.

Phytoavailability and transfer of mercury in soil-pepper system: Influencing factors, fate, and predictive approach for effective management of metal-impacted spiked soils

Mercury (Hg) contamination and accumulation in food crops is a global threat posing potential health risk to humans. However, Hg phytoavailability in soil-pepper system and its influencing factors largely remain unknown. In this study, a greenhouse pot experiment was conducted to grow peppers using 21 Chinese agricultural soils with varied soil properties and aged Hg levels. Mercury concentration in pepper leaves and fruits ranged from 0.021 to 0.057 mg kg−1 and 0.005–0.022 mg kg−1 respectively, while fruit Hg content in three soils (Anhui, Hubei, Beijing) exceeded the safety limit. Fruit Hg concentration was better positively correlated with soil Mg(NO3)2-extractable Hg content (r = 0.7, P < 0.0001) than soil total Hg content (r = 0.45, P < 0.0001). Highest bioconcentration factor (BCF, ratio of Hg plant to Hg soil) yielded in acidic soils, while the lowest BCF occurred in alkaline soils. Path analysis indicated available-Hg (R2 = 0.40) and total-Hg (R2 = 0.40) had direct positive effects on the pepper fruit Hg concentration, while direct negative effects including pH (R2 = −0.86), organic matter (R2 = −0.7), crystalline-Fe (R2 = −0.68). Those agreed with the stepwise multiple linear regression analysis which yielded a regression predictive model (R2 = 0.73, P < 0.0001). Soil available-Hg, total-Hg, pH, organic matter and crystalline-Fe & Mn were the most influencing factors of Hg phytoavailability. These results provide new insights into the phytoavailability of Hg in soil-pepper system, thus facilitating the management of pepper cultivation in Hg-enriched soils.

Nutrient Inputs Stimulate Mercury Methylation by Syntrophs in a Subarctic Peatland

Climate change dramatically impacts Arctic and subarctic regions, inducing shifts in wetland nutrient regimes as a consequence of thawing permafrost. Altered hydrological regimes may drive changes in the dynamics of microbial mercury (Hg) methylation and bioavailability. Important knowledge gaps remain on the contribution of specific microbial groups to methylmercury (MeHg) production in wetlands of various trophic status. Here, we measured aqueous chemistry, potential methylation rates (kmeth), volatile fatty acid (VFA) dynamics in peat-soil incubations, and genetic potential for Hg methylation across a groundwater-driven nutrient gradient in an interior Alaskan fen. We tested the hypotheses that (1) nutrient inputs will result in increased methylation potentials, and (2) syntrophic interactions contribute to methylation in subarctic wetlands. We observed that concentrations of nutrients, total Hg, and MeHg, abundance of hgcA genes, and rates of methylation in peat incubations (kmeth) were highest near the groundwater input and declined downgradient. hgcA sequences near the input were closely related to those from sulfate-reducing bacteria (SRB), methanogens, and syntrophs. Hg methylation in peat incubations collected near the input source (FPF2) were impacted by the addition of sulfate and some metabolic inhibitors while those down-gradient (FPF5) were not. Sulfate amendment to FPF2 incubations had higher kmeth relative to unamended controls despite no effect on kmeth from addition of the sulfate reduction inhibitor molybdate. The addition of the methanogenic inhibitor BES (25 mM) led to the accumulation of VFAs, but unlike molybdate, it did not affect Hg methylation rates. Rather, the concurrent additions of BES and molybdate significantly decreased kmeth, suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in kmeth with combined addition of BES and molybdate, and accumulation of VFA in peat incubations containing BES, and a high abundance of syntroph-related hgcA sequences in peat metagenomes provide evidence for MeHg production by microorganisms growing in syntrophy. Collectively the results suggest that wetland nutrient regimes influence the activity of Hg methylating microorganisms and, consequently, Hg methylation rates. Our results provide key information about microbial Hg methylation and methylating communities under nutrient conditions that are expected to become more common as permafrost soils thaw.

Determination of the Elements Composition in Sempervivum tectorum L. from Bulgaria

Sempervivumtectorum L. is an evergreen plant with fleshy blue-green leaves forming a rosette. The plant is well-known in alternative medicine and has been used for thousands of years. Traditionally for medicinal purposes, the plant is used as a juice obtained by simple squeezing of fresh plants leaves. The total content of Ca, K, Na, Mg, Mn, Fe, Zn, Cu, Co, Al, V, Cr, Ni, Mo, Ba, Pb, Cd, Hg, As, and Tl in plant leaves of Sempervivum tectorum L. sampled from different habitats in Bulgaria was determined after microwave digestion and measurements by inductively coupled plasma mass spectrometry and flame atomic absorption spectrometry. Furthermore, the bioavailable fraction of essential elements Ca, Mg, Fe, Mn, and Zn was defined after extraction with a hydrochloric acid solution, mimicking stomach juice. The total element content showed a high bioavailability of essential human health elements, such as Ca, Mg, Fe, and Zn. Additionally, essential and toxic elements concentrations were quantified in a fresh juice, obtained by squeezing from plant leaves, as most frequently used in folk medicine. The results obtained demonstrated high concentrations of K, Mg, Ca, Zn, and Cu, which could be accepted as an explanation and a further confirmation of the anti-inflammatory action of this plant.