Total Hg Concentrations Research Articles

Dispatched microbial community assembly processes driving ecological succession during phytostabilization of mercury-rich tailings

Phytostabilization is an important way for the remediation of mine tailings, but the associated microbial processes and community succession remain largely unknown. In this study, we investigated the assembly mechanisms maintaining the core and satellite subcommunities diversity during phytostabilizaion of a mercury-rich mine tailings. The contents of total Hg and methylmercury decreased with a concomitant increase of total and available phosphorus content along the successive remediation stages. Microbial community composition, profiled by 16S rRNA gene sequencing, revealed amplicon sequence variants (ASVs) that were separated according to their abundance within either the core community or the satellite community. Community dynamics analysis showed that alpha diversity indices increased for the core community while decreased for the satellite community. Both satellite and core communities were mainly driven by stochastic drift process, and homogeneous selection was relatively higher in shaping the core community organization. The core community included ASVs affiliated to Proteobacteria, Crenarchaeota, Bacteroidota, Verrucomicrobiota, Acidobacteriota, and Myxococcota phyla, which were driven primarily by heterogeneous selection and drift. The satellite community included ASVs affiliated to Acidobacteriota, Ktedonobacteria, Anaerolineae and Verrucomicrobiota phyla, which were mainly influenced by heterogeneous selection. Nineteen taxa and one taxon were identified as keystone taxa for the satellite and core communities respectively. This study provides important insights on the assemble rules within the core and satellite communities, and theoretical guidance for further ecological restoration and management during microbial remediation of metal-mined derelict land.

Mercury speciation in environmental samples associated with artisanal small-scale gold mines using a novel solid-phase extraction approach to sample collection and preservation

In artisanal small-scale gold mines (ASGM), mercury (Hg) is known to pollute nearby river waters and sediments where it can be methylated to the highly bioavailable methylmercury (MeHg). The assessment of Hg speciation in water samples has been challenging for many years, with recommended procedures often not adequately allowing for analysis of samples in a suitable timeframe. Using a novel solid-phase extraction (SPE) method for sampling and preservation of Hg species, representative speciation data can be safely and easily collected and retained for up to 4-weeks (MeHg = 115 ± 8% refrigerated and 109 ± 13% unrefrigerated storage; Hg2+ = 100 ± 14% refrigerated and 94 ± 12% unrefrigerated storage). Concentrations of MeHg in environmental water samples and drinking water were below detection limit across two ASGM sites in western Kenya and concentrations of Hg2+ were below drinking water guidelines; however, drinking water sources contribute 20–30% of the tolerable weekly intake of Hg, indicating a need to minimise exposure of Hg from dietary sources to prevent Hg poisoning. Sediments from receiving rivers at ASGM sites showed total Hg concentrations above guideline limits (0.08–1.84 mg kg−1 total Hg) along the length of the river; however, MeHg concentrations fluctuated dependent on the stagnation of the river due to damns and ponds (5.9 ± 14.3 µg kg−1 MeHg). The findings show that SPE can be used as a robust sample collection and preservation approach for Hg speciation, which can better inform mitigation measures, understand ecological and human health implications, and improve environmental monitoring.

Concurrent measurements of atmospheric Hg in outdoor and indoor at a megacity in Southeast Asia: First insights from the region

Atmospheric mercury (Hg) is a critical indoor (ID) air pollutant and necessitates stringent monitoring. However, studies have primarily focused on Hg outdoors (OD) compared to ID, with no investigations conducted within the Southeast Asia (SEA) region. In this study, total gaseous Hg (TGM) concentrations and human exposure levels were investigated across various site characteristics in Ho Chi Minh City (HCMC), a megacity in SEA. The measured TGM concentrations for OD and ID were 5.12 ± 6.87 ng m−3 (1.20–48.7 ng m−3) and 34.5 ± 60.3 ng m−3 (1.26–271.9 ng m−3). The overall ID/OD ratio was 5.01 (0.77–9.3), signifying markedly elevated ID TGM concentrations. This ratio increases in the following order: shopping malls (1.50) < hospitals (3.21) < chemical laboratories (5.76) < households (11.7). Notably, sites associated with Hg incidents and the utilization of Hg-contained chemicals demonstrate notably high ID/OD levels, ranging from 8.0 to 40.1. The use of Hg-containing chemicals within the chemical laboratory serves as a significant contributor to heightened ID TGM levels. Non-combustion Hg sources, therefore, play an important role in inducing the ID TGM level. The hazard index (HQ) values observed for ID and OD were 0.1 and 0.01, respectively, indicating a negligible risk of exposure to TGM within the study area. However, HQ values recorded within laboratory environments employing Hg-associated chemicals and dental hospitals were 1–17 times greater compared to other sites. The present work provides new insight into the non-combustion ID source of TGM and was helpful for upcoming studies in exploring potential sources of TGM in megacities.

Spatial distribution and risk assessment of mercury in soils over the Tibetan Plateau

The Tibetan Plateau is one of the highest and most pristine plateaus in the world, and its ecological environment has a significant impact on global climate and the distribution of water resources. Mercury (Hg), as a toxic metal pollutant, can have a severe impact on the health of living organisms and the ecosystem due to its presence in the environment. This study collected 336 soil samples from 28 sites across four typical surface vegetation landscapes (meadow, grassland, desert, and forest) on the Tibetan Plateau to measure soil THg (Total Hg) concentrations. The research aimed to explore the factors influencing soil THg levels, analyze pollution and environmental risks of THg in the surface soil, and evaluate the associated health risks to the local population. The results indicate that the mean soil THg concentration (31.84 ± 32.58 ng·g−1) of this study is compared to the background value of THg in Tibetan Plateau soils (37.0 ng·g−1), but there are significant differences in THg concentration among soils with different surface vegetation landscapes. The mean THg concentration in soils of forest vegetation types (74.42 ± 41.19 ng·g−1) is approximately twice the background value of Tibetan Plateau soils. In the forested regions of the southeastern, eastern, and southern Tibetan Plateau, soil concentrations of total mercury are relatively high, whereas in the desert areas of the northern, northwestern, and northeastern Tibetan Plateau, the concentrations are lower. Organic matter (soil organic carbon) being an important factor influencing the soil THg. Based on existing surface soil THg data from this and previous research in Tibetan Plateau (n = 477), 34.2 % of the samples show Hg pollution and potential ecological risks. However, the health risks of soil Hg to both adults and children are not significant.

Organic matter is a predominant control on total mercury concentration of near-surface lake sediments across a boreal to low Arctic tundra transect in northern Canada

Mercury (Hg) is a bioavailable and toxic element with concentrations that are persistently high or rising in some Arctic and subarctic lakes despite reduced atmospheric emissions in North America. This is due to rising Hg emissions to the atmosphere outside of North America, enhanced sequestration of Hg to sediments by climate-mediated increases in primary production, and ongoing release of Hg from terrestrial reservoirs. To evaluate the influence of organic matter and other parameters on Hg accumulation in northern lakes, near-surface sediments were sampled from 60 lakes across a boreal to shrub tundra gradient in the central Northwest Territories, Canada. The organic matter of the lake sediments, assessed using programmed pyrolysis and petrology, is composed of a mixture of terrestrial, aquatic, and inert organic matter. The proportion of algal-derived organic matter is higher in sediments of lakes below treeline relative to shrub tundra sites. Total sedimentary Hg concentration is correlated to all organic matter constituents but is unrelated to latitude or lake position below or above treeline. The concentrations of Ag, Ca, P, S, U, Ti, Y, Cd, and Zn are also strong predictors of total sedimentary Hg concentration, indicating input from a common geogenic source and/or common sequestration pathways associated with organic matter. Catchment area is a strong negative predictor of total sedimentary Hg concentration, particularly in lakes above treeline, possibly due to retention capacity of Hg and other elements in local sinks. This research highlights the complexity of controls on Hg sequestration in sediment and shows that while organic matter is a strong predictor of total sedimentary Hg concentration on a landscape scale and across extreme gradients in climate and associated vegetation and permafrost, other factors such as catchment area and sources from mineralized bedrock are also important.

Co-analysis of total suspended particles and discharge reveals the dynamic of mercury input into glacier meltwater runoff in the northern Tibetan Plateau

Climate warming has accelerated glacier melting, releasing legacy pollutants such as mercury (Hg) into aquatic ecosystems. While the relationship between Hg in glacier meltwater runoff, total suspended particles (TSP), and runoff discharges has been established, the underlying inter-relationships and governing factors remain poorly understood. To address this knowledge gap, we conducted a continuous fixed-point sampling at Laohugou No. 12 Glacier in the northern Tibetan Plateau from June to September 2019 spanning the entire glacier ablation season. Our study analyzed the variations of Hg partition in the meltwater runoff and conducted a comprehensive co-analysis of Hg with TSP and discharge to uncover the dominant factors of Hg input into meltwater runoff. The concentration of total Hg (THg) in the meltwater runoff ranged from 0.7 to 112.6 ng/L, with an average concentration of 26.6 ± 25.1 ng/L. Particulate Hg (PHg) was found to be the predominant partition, while dissolved Hg (DHg) exhibited a notable increase in June and September. THg concentration significantly correlated with TSP concentration (r = 0.94, P < 0.01), exceeding the correlation with discharge (r = 0.76, P < 0.01) during the entire ablation period. However, further examination during varying hydrological periods revealed differing associations among Hg speciation concentrations, TSP concentration, and discharge. During the rising limb of the hydrograph, THg (r = 0.86, P < 0.01) and PHg concentrations (r = 0.87, P < 0.01) exhibited a significant correlation with TSP concentration, primarily driven by TSP, implying that Hg availability determines the Hg input into meltwater runoff. Conversely, during the recession limb of the hydrograph, THg concentration was primarily influenced by discharge (r = 0.85, P < 0.01). PHg (r = 0.84, P < 0.01) and TSP (r = 0.97, P < 0.01) concentrations were strongly influenced by discharge, indicating that hydraulic action is the dominant factor affecting Hg input. Our study elucidated the impact of glacier hydrological processes on Hg transport, revealing the dominant factors of Hg input during different hydrological periods. This contributes to a deeper understanding of Hg input into meltwater runoff and improves predictions of Hg export through glacier melt in high mountain regions.

Mercury isotope fractionation and mercury source analysis in coal

Understanding the sources of mercury (Hg) in coal is crucial for understanding the natural Hg cycle in the Earth's system, as coal is a natural Hg reservoir. We conducted analyses on the mass-dependent fractionation (MDF), reported as δ202Hg, and mass-independent fractionation (MIF), reported as Δ199Hg, of Hg isotopes among individual Hg species and total Hg (THg) in Chinese coal samples. This data, supplemented by a review of prior research, allowed us to discern the varying trend of THg isotope fractionation with coal THg content. The Hg isotopic composition among identified Hg species in coal manifests notable disparities, with species exhibiting higher thermal stability tending to have heavier δ202Hg values, whereas HgS species typically display the most negative Δ199Hg values. The sources of Hg in coal are predominantly attributed to Hg accumulation from the original plant material and subsequent input from hydrothermal activity. Hg infiltrates peat swamps via vegetation debris, thus acquiring a negative Δ199Hg isotopic signature. Large-scale lithospheric Hg recycling via plate tectonics facilitates the transfer of Hg with a positive Δ199Hg from marine reservoirs to the deep crust. The later-stage hydrothermal input of Hg with a positive Δ199Hg enhances coal Hg content. This process has resulted in an upward trend of Δ199Hg values corresponding with the increase in coal THg content, ultimately leading to near-zero Δ199Hg in high-Hg coals. Coal Hg reservoirs are affected by large-scale natural Hg cycling, which involves the exchange of Hg between continents and seas.

Atmospheric Mercury Concentrations and Isotopic Compositions Impacted by Typical Anthropogenic Mercury Emissions Sources.

Coal-fired power plants (CFPPs) and cement plants (CPs) are important anthropogenic mercury (Hg) emission sources. Mercury speciation profiles in flue gas are different among these sources, leading to significant variations in local atmospheric Hg deposition. To quantify the impacts of Hg emissions from CFPPs and CPs on local-scale atmospheric Hg deposition, this study determined concentrations and isotopes of ambient gaseous elemental mercury (GEM), particulate-bound mercury (PBM), and precipitation total Hg (THg) at multiple locations with different distances away from a CFPP and a CP. Higher concentrations of GEM and precipitation THg in the CFPP area in summer were caused by higher Hg emission from the CFPP, resulting from higher electricity demand. Higher concentrations of GEM, PBM, and precipitation THg in the CP area in winter compared to those in summer were related to the higher output of cement. Atmospheric Hg concentration peaked near the CFPP and CP and decreased with distance from the plants. Elevated GEM concentration in the CFPP area was due to flue gas Hg0 emissions, and high PBM and precipitation Hg concentrations in the CP area were attributed to divalent Hg emissions. It was estimated that Hg emissions from the CFPP contributed 58.3 ± 20.9 and 52.3 ± 25.9% to local GEM and PBM, respectively, and those from the CP contributed 47.0 ± 16.7 and 60.0 ± 25.9% to local GEM and PBM, respectively. This study demonstrates that speciated Hg from anthropogenic emissions posed distinct impacts on the local atmospheric Hg cycle, indicating that Hg speciation profiles from these sources should be considered for evaluating the effectiveness of emission reduction policies. This study also highlights the Hg isotope as a useful tool for monitoring environmental Hg emissions.

Impacts of oyster farms on sediment-associated mercury and methylmercury concentrations and health risks in an estuarine, mangrove forest, Zhanjiang Bay, China

Estuarine sediments serve as significant reservoirs for mercury (Hg) and methylmercury(MeHg), which can also interconvert in the external environment. The release of Hg in response to human activities raises concerns about its potential ecological and human health effects. Sediment samples were collected in December 2021 from four locations (sites), and Hg cycling by measuring the concentrations of, and controls on, the spatial distribution of total Hg (THg) and methylmercury (MeHg) in high-tidal zone (HTZ) and mid-tidal zone (MTZ) sediments of a mangrove forest (MF) and oyster farm (OF) was examined in northwestern Zhanjiang Bay, including simultaneous determination of sediment particle size, oxidation-reduction potential (Eh), pH, total organic carbon (TOC), sulfide concentration (S2-), and sulfate reducing bacteria (SRB). The research results indicated that concentrations of both THg and MeHg ranged between 20.0–104.0 ng/g and 0.011–0.277 ng/g in the sediments, respectively. The highest methylation potentials within the MF and OF were in sediments located approximately 10–15 cm below the surface. MeHg in the HTZ of the OF was likely derived from exogenous inputs as Hg methylation appears limited, and the formation of MeHg depended not only on the amount of inorganic mercury available for methylation in SRB, but also on the TOC, pH, Eh and S2- content in the sediment. A risk assessment of MeHg during the anthropogenic disturbance of this estuaries conducted on individuals eating oysters demonstrated that health risks are low.

Comparative study of the sequential extraction methodologies for fractionation analysis of mercury in coal of Thar coalfield.

The primary objective of this study was to evaluate the bound fractions of mercury (Hg), physicochemical parameters, and mineral composition of coal. Coal samples were collected from various depths within Block-VII of the Thar coalfield in Pakistan. The Hg associated with different chemical fractions of coal was extracted using a sequential extraction scheme as per the community bureau of reference (BCR) protocol. This study utilized both the BCR-sequential extraction method (BCR-SEM) and a single-step sequential extraction based on an ultrasonic-assisted method (SSE-UAM) for the fractionation analysis of Hg in coal. The extraction methodologies, BCR-SEM and SSE-UAM, were specifically designed for analyzing Hg fractionation in coal samples. The SSE-UAM offers an operational advantage, requiring only 2h compared to the 51h needed for BCR-SEM. The analyses were validated using standard reference material (SRM-1635a) and the spiking addition method, achieving a recovery percentage of 97.1% for total Hg concentrations using the pseudo-extraction method in SRM-1635A. Total Hg content in the coal samples ranged from 0.60 to 2.34µgg-1 across four different coal seams from Block-VII of the Thar coalfield. Additionally, Hg concentration was observed to decrease with increasing depth, attributed to changes in mineralogical composition. The highest concentration of Hg was detected at a depth of 200-203m, while the lowest concentration was at a depth of 152-154m. The concentration of Hg in various fractions was 32-60% in the acid-soluble fraction, 1.72-4.92% in the reducible fraction, and 9.58-50.8% in the oxidizable fractions. The coal sample characteristics were analyzed using an elemental analyzer and scanning electron microscopy with energy-dispersive spectroscopy. Cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the extracted fractional concentration of Hg in coal.

Utilizing biochars to stabilize mercury in contaminated floodplain sediment: Implications on mercury remediation.

Major weather events contribute to the mobility and remobilization of legacy mercury (Hg) contamination and sequestration within sediments. Remediation using biochar as a soil amendment is a useful technique to immobilize and decrease Hg toxicity. This study explored whether biochar application is effective at stabilizing labile mercury (LaHg) from floodplain sediment. Controlled mesocosms simulating contamination events and flooding conditions were conducted. Floodplain sediment, which experiences annual periodic flooding, was collected. Sediment was spiked with inorganic Hg, applied with different types of biochar, and experienced simulated flooding events. Four types of biochar, pure rice husk (RH), pure peanut hull (PH), sulfur-modified rice husk (SMRH), and sulfur-modified peanut hull (SMPH), were applied at 10 and 40g/kg rates (i.e., RH 10, RH 40; PH 10, PH 40, SMRH 10, SMRH 40, SMPH 10, SMPH 40). Total Hg, methylmercury, and LaHg concentrations were analyzed by coupling with redox potential measurements. Results indicate that SMRH 10, PH 10, PH 40, SMPH 10, and SMPH 40 successfully remediate Hg by stabilizing and reducing LaHg species from floodplain sediment. However, a high Hg methylation potential was observed with unsulfated and sulfated peanut hulls (PH 10, PH 40, SMPH 10, and SMPH 40), as they tend to create a reducing microenvironment that favors sulfate reduction reactions. Additionally, sulfur-modified biochar tends to promote Hg methylation potential at high application rates (i.e., 40g/kg). We thus recommend using SMRH at a relatively low application rate (SMRH 10) for the remediation of Hg from floodplain sediment.

Wildfires Influence Mercury Transport, Methylation, and Bioaccumulation in Headwater Streams of the Pacific Northwest.

The increasing frequency and severity of wildfires are among the most visible impacts of climate change. However, the effects of wildfires on mercury (Hg) transformations and bioaccumulation in stream ecosystems are poorly understood. We sampled soils, water, sediment, in-stream leaf litter, periphyton, and aquatic invertebrates in 36 burned (one-year post fire) and 21 reference headwater streams across the northwestern U.S. to evaluate the effects of wildfire occurrence and severity on total Hg (THg) and methylmercury (MeHg) transport and bioaccumulation. Suspended particulate THg and MeHg concentrations were 89 and 178% greater in burned watersheds compared to unburned watersheds and increased with burn severity, likely associated with increased soil erosion. Concentrations of filter-passing THg were similar in burned and unburned watersheds, but filter-passing MeHg was 51% greater in burned watersheds, and suspended particles in burned watersheds were enriched in MeHg but not THg, suggesting higher MeHg production in burned watersheds. Among invertebrates, MeHg in grazers, filter-feeders, and collectors was 33, 48, and 251% greater in burned watersheds, respectively, but did not differ in shredders or predators. Thus, increasing wildfire frequency and severity may yield increased MeHg production, mobilization, and bioaccumulation in headwaters and increased transport of particulate THg and MeHg to downstream environments.

Total mercury concentrations in Tasman Sea mesopelagic fish: Exploring biotic and abiotic drivers

Understanding mercury (Hg) concentrations in mesopelagic and mid-trophic fishes is important for assessing Hg accumulation in oceanic ecosystems and higher-order predators. This study measured total Hg (THg) concentrations in the whole body of 16 abundant mesopelagic fish species sampled in two distinct sites within the Tasman Sea. Across all species, total Hg concentrations ranged from 0.02 to 0.48 μg g−1 dry weight (0.01 to 0.15 μg g−1 wet weight). Total Hg concentrations varied with vertical migration patterns, with shallower migrators exhibiting higher THg. Females typically had statistically higher THg concentrations than males. Positive correlations between THg concentration and standard length were observed for some but not all species. At the community level, THg concentrations correlated positively with estimated trophic position and foraging habitat, as inferred by stable isotope values. These findings contribute to our understanding of Hg cycling in oceanic ecosystems and the potential for biomagnification in oceanic top-order predators.

Inter- and intraspecific variability of total mercury concentrations in bats of Texas (USA)

Exposure to mercury (Hg) may cause deleterious health effects in wildlife, including bats. Texas produces more Hg pollution than any other state in the United States, yet only one study has examined Hg accumulation in bats. This study measured the concentration of total Hg (THg) in fur (n = 411) collected from ten bat species across 32 sites in eastern and central Texas, USA. Fur THg concentrations were compared among species, and when samples sizes were large enough, between sex and life stage within a species, and the proximity to coal-fired power plants. For all sites combined and species with a sample size ≥8, mean THg concentrations (μg/g dry weight) were greatest in tri-colored bats (Perimyotis subflavus; 6.04), followed by evening bats (Nycticeius humeralis; 5.89), cave myotis (Myotis velifer; 2.11), northern yellow bats (Lasiurus intermedius; 1.85), Brazilian free-tailed bats (Tadarida brasiliensis; 1.03), and red bats (Lasiurus borealis/blossevillii; 0.974), and lowest in hoary bats (Lasiurus cinereus; 0.809). Within a species, fur THg concentrations did not significantly vary between sex for the five examined species (red bat, northern yellow bat, cave myotis, evening bat, Brazilian free-tailed bat) and only between life stage in evening bats. Site variations in fur THg concentrations were observed for evening bats, tri-colored bats, and Brazilian free-tailed bats. Evening bats sampled closer to point sources of Hg pollution had greater fur THg concentrations than individuals sampled further away. Sixteen percent of evening bats and 8.7% of tri-colored bats had a fur THg concentration exceeding the 10 μg/g toxicity threshold level, suggesting that THg exposure may pose a risk to the health of bats in Texas, particularly those residing in east Texas and on the upper Gulf coast. The results of this study can be incorporated into future management and recovery plans for bats in Texas.

Synchronous influence of soil amendments on alkylmercury and methane emissions in mercury-contaminated paddy soil

Mercury (Hg) alkylation and methane (CH4) emissions pose significant global concerns. Paddy soil, due to its long-term anaerobic conditions and abundant organic matter, is hotspots for soil Hg alkylation and CH4 emissions. However, the relevance between Hg alkylation and CH4 emissions, especially their simultaneous reduction strategies, remains poorly understood. Here, we investigated the effects of biochar (BC), selenium (Se) and rice straw (RS) amendments on Hg alkylation and CH4 emissions in paddy soil, and the accumulation of Hg speciation. Results found that both BC and RS amendments significantly increased the levels of soil organic carbon (SOC) and humification index (HIX). Furthermore, BC decreased the concentrations of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by 63.1%, 53.6% and 100% in rice grains. However, RS increased Hg(II) concentration but decreased the total Hg (THg), MeHg and EtHg concentrations in rice grains. Compared to the CK, RS significantly increased CH4 emissions, while BC decreased CH4 emissions, and Se showed no significant difference. Se amendment increased the Hg(II) and EtHg concentrations by 20.3% and 17.0% respectively, and decreased the MeHg concentration in grains by 58.3%. Both BC and RS impacted the abundance of methanogens by enhancing SOC and HIX, subsequently modulating the relevance between Hg alkylation and CH4 emissions. These findings provide insights into the relevance between Hg alkylation and CH4 emissions and propose potential mitigation mechanisms in Hg-contaminated paddy soil.

Mercury from Icelandic geothermal activity: High enrichments in soils, low emissions to the atmosphere

Geothermal activity is a natural source of mercury (Hg) to surface environments, but its contributions as part of the larger geogenic flux to the global Hg budget are poorly understood, in part due to large geographic gaps in emissions data where no measurements have been made. In this study we report the results of a field campaign over 2021 and 2022 on the highly active volcanic island country of Iceland. Six geothermal sites across the country were investigated for soil gaseous elemental mercury (GEM) and total Hg (THg) concentrations through a series of measurements made across the diffuse degassing surface. At 10 cm depth, soil GEM concentrations were often hundreds and in some cases thousands of times higher than ambient surface air concentrations. Geothermal soils were also highly enriched in THg due to the sorption of hydrothermal Hg on the characteristically fine, thermally-altered clays and silts. Soil “hotspots” displayed THg concentrations exceeding 100 µg g−1 comparable to levels in areas heavily contaminated by anthropogenic activity and in Hg-rich mineral soils. Strong correlations were observed between soil GEM, THg and soil temperature, and intensive measurements made at small spatial scales (∼1 m2) demonstrated the representativeness of individual sampling points. By adapting an active sampling gradient method for determining soil–air gas fluxes, we estimate an Icelandic geothermal GEM flux of 1.8 kg a−1 and a total Icelandic GEM flux, including non-geothermal areas, of ∼18 kg a−1. This work shows that Icelandic geothermal activity can generate high GEM and THg concentrations in the local soil environment, but its contribution to global Hg cycling appears to be minor.

Influencing Factors and Prediction Models of Mercury Phytoavailability and Transference in a Soil–Lettuce System under Chinese Agricultural Soils

Mercury (Hg) is a highly toxic contaminant posing serious ecological and human health risks. This study investigates the Hg transfer characteristics and prediction models in a soil–lettuce system, employing bioconcentration factors (BCF), path analysis (PA), and Freundlich-type functions. A pot experiment was conducted in a greenhouse, where lettuce was grown in a range of Chinese agricultural soils (n = 21) and deliberately spiked with Hg using Hg(NO3)2 solution. The results indicated that lettuce grown in Hg-spiked acidic soils (pH &lt; 6.5) accumulated total Hg (THg) levels up to 14.01 µg kg−1, surpassing the safe consumption limit of 10 µg kg−1. The BCF for lettuce THg was less than 1.0, suggesting a low transfer of Hg from soil to lettuce. Notably, BCF values were significantly higher in acidic soils (0.02) compared to alkaline soils (0.005). Path analysis accounted for 82% of the variation in lettuce THg content, identifying soil THg, pH, and amorphous (Amo) Al and Fe oxides as primary direct factors. Additionally, soil-available Hg (AvHg), exchangeable Hg (ExHg), clay, and organic matter (OM) were significant indirect factors affecting lettuce THg content. To validate the findings of the path analysis, an extended Freundlich-type equation was developed using stepwise multiple linear regression (SMLR). This model exhibited high predictive accuracy (R2 = 0.82, p ≤ 0.001), with soil pH, THg, and amorphous Al and Fe oxides being the key variables for predicting Hg transfer in the soil–lettuce system. The insights from this study can guide the management of safe lettuce production in Hg-contaminated soils, ensuring the mitigation of Hg exposure through agricultural produce.

Mercury speciation in pilot whale from Faroe Islands, 1977–2015

Mercury (Hg) is a naturally occurring heavy metal, but human activities and natural processes have led to increased pollution with Hg in the environment. Organic mercury, such as methyl mercury (MeHg), is considered more toxic than most inorganic mercury compounds. MeHg is rapidly taken up by aquatic organisms and bioaccumulates through the aquatic food web. The bioaccumulation causes high levels of MeHg in apex predators, such as pilot whales. Pilot whale meat is a traditional food source on the Faroe Islands; thus the consumption of pilot whale meat can lead to high Hg exposures in humans. The majority of the total Hg in pilot whale and fish is generally assumed to be MeHg. However, the relative amount of MeHg to total Hg can be highly variable. For risk assessment, it is relevant to know both the MeHg and the total Hg content. This study summarizes the knowledge of muscle MeHg concentrations relative to total Hg concentrations in pilot whales in the Faroe Islands. The pilot whale tissue was sampled during 1977–78, 1986–87, 2009–2010, and 2015. The 2015 samples included two pairs of fetuses/mothers. The results showed that the 1977–78 pilot whale muscle samples had lower relative concentrations of MeHg to total Hg compared to samples from the subsequent years. This discrepancy between early and later years could not solely be explained by increased demethylation related to concentration differences. Instead, the difference is more likely explained by variations in relative amounts of MeHg in prey of the pilot whales. In the fetuses the total Hg concentration was 20% of the Hg concentration in the mother. The relative MeHg concentrations in the fetuses were also lower (∼20%–30%) than in the mother. However, the MeHg to total Hg fraction in the fetus was similar or higher than in the mother.

“Hg distribution and accumulation in soil and vegetation in areas impacted by artisanal gold mining in the Southern Amazonian region of Madre de Dios, Peru.”

Artisanal and small-scale gold mining (ASGM) is the primary global source of anthropogenic mercury (Hg) emissions. It has impacted the Amazon rainforest in the Peruvian region of Madre de Dios. However, few studies have investigated Hg's distribution in terrestrial ecosystems in this region. We studied Hg's distribution and its predictors in soil and native plant species from artisanal mining sites. Total Hg concentrations were determined in soil samples collected at different depths (0–5 cm and 5–30 cm) and plant samples (roots, shoots, leaves) from 19 native plant species collected in different land cover categories: naked soil (L1), gravel piles (L2), natural regeneration (L3), reforestation (L4), and primary forest (L5) in the mining sites. Hg levels in air were also studied using passive air samplers. The highest Hg concentrations in soil (average 0.276 and 0.210 mg kg−1 dw.) were found in the intact primary forest (L5) at 0–5 cm depth and in the plant rooting zones at 5–30 cm depth, respectively.Moreover, the highest Hg levels in plants (average 0.64 mg kg−1 dw) were found in foliage of intact primary forest (L5). The results suggest that the forest in these sites receives Hg from the atmosphere through leaf deposition and that Hg accumulates in the soil surrounding the roots. The Hg levels found in the plant leaves of the primary forest are the highest ever recorded in this region, exceeding values found in forests impacted by Hg pollution worldwide and raising concerns about the extent of the ASGM impact in this ecosystem. Correlations between Hg concentrations in soil, bioaccumulation in plant roots, and soil physical-chemical characteristics were determined. Linear regression models showed that the soil organic matter content (SOM), pH, and electrical conductivity (EC) predict the Hg distribution and accumulation in soil and bioaccumulation in root plants.

BIOGENIC AND RISK ELEMENTS IN GRAPE POMACE OF DIFFERENT CULTIVARS

The contents of biogenic and risk elements in the pomace of 6 grape cultivars (Blaufränkisch, Cabernet Franc, Cabernet Sauvignon, Devín, Dunaj, and Merlot) were analyzed in this study. Content of K, Ca, P, Mg, and Na was 11 750 – 19 070, 2 400 – 3 908, 1 678 – 2 684, 336 – 760, and 1.43 - 59.3 mg.kg-1 DM respectively. Content of Fe, Cu, Mn, Zn, Ni, Cr, and Co was 79.5 – 245, 6.18 – 48.4, 10.3 – 22.6, 4.19 – 17.0, 0.66 – 1.36, 0.058 – 2.33, and 0.42 – 0.63 mg.kg-1 DM respectively. Pb and Cd were detected in the grape pomace of Merlot (0.94 and 0.03 mg.kg-1 DM, respectively) and Cabernet Sauvignon (0.36 and 0.08 mg.kg-1 DM, respectively). The total content of Hg ranged from 0.0055 to 0.0080 mg.kg-1 DM. Analysis of variance showed that there are differences in the content of elements among cultivars. Grape pomace of cultivars Blaufränkisch and Cabernet Sauvignon could be characterized by the higher Fe, Mn, Zn, Ni, and Cr content, while grape pomace of cultivar Merlot by higher Mg content. With relatively low content of risk elements, grape pomace can serve as a good source of essential minerals in the human diet.