Mercury Cycling Research Articles

Simultaneous Reduction and Methylation of Nanoparticulate Mercury: The Critical Role of Extracellular Electron Transfer.

Mercury nanoparticles are abundant in natural environments. Yet, understanding their contribution to global biogeochemical cycling of mercury remains elusive. Here, we show that microbial transformation of nanoparticulate divalent mercury can be an important source of elemental and methylmercury.Geobacter sulfurreducensPCA, a model bacterium predominant in anoxic environments (e.g., paddy soils), simultaneously reduces and methylates nanoparticulate Hg(II). Moreover, the relative prevalence of these two competing processes and the dominant transformation pathways differ markedly between nanoparticulate Hg(II) and its dissolved and bulk-sized counterparts. Notably, even when intracellular reduction of Hg(II) nanoparticles is constrained by cross-membrane transport (a rate-limiting step that also regulates methylation), the overall Hg(0) formation remains substantial due to extracellular electron transfer. With multiple lines of evidence based on microscopic and electrochemical analyses, gene knockout experiments, and theoretical calculations, we show that nanoparticulate Hg(II) is preferentially associated with c-type cytochromes on cell membranes and has a higher propensity for accepting electrons from the heme groups than adsorbed ionic Hg(II), which explains the surprisingly larger extent of reduction of nanoparticles than dissolved Hg(II) at relatively high mercury loadings. These findings have important implications for the assessment of global mercury budgets as well as the bioavailability of nanominerals and mineral nanoparticles.

Dissolved elemental mercury accumulation by freshwater phytoplankton species: A pilot study

Bioaccumulation of dissolved elemental mercury (DGM) by various organisms has been demonstrated, but no study has shown its uptake and sequestration by phytoplankton species. The present study aims to investigate the accumulation of mercury by phytoplankton species exposed to DGM. Diatoms (Cyclotella meneghiniana and Navicula pelliculosa) and green algae (Chlamydomonas reinhardtii and Haematococcus pluvialis) were exposed to constant high level of atmospheric gaseous Hg (∼7.7 µg m−3). Total mercury concentrations (THg) in the medium (dissolved fraction) and algae cells (cellular fraction) were determined using cold vapor atomic fluorescence spectroscopy. Results revealed a partitioning of Hg(0) between the atmosphere and phytoplankton cultures, with THg predominantly found in the algae cells. THg in the algae cultures decreased in the order: C. reinhardtii >H. pluvialis >N. pelliculosa >C. meneghiniana. However, the cellular concentration (mol cell−1) decreased in the order: H. pluvialis >C. reinhardtii >C. meneghiniana >N. pelliculosa. These results highlight species specificity in Hg accumulation upon exposure to DGM, further linked to the phytoplankton surface area. Our findings reveal for the first time that phytoplankton species significantly influence the partitioning of atmospheric Hg(0) in aquatic environments, with important implications for the understanding of the aquatic mercury cycle.

Overview of Methylation and Demethylation Mechanisms and Influencing Factors of Mercury in Water.

Mercury, particularly in its methylated form, poses a significant environmental and health risk in aquatic ecosystems. While the toxicity and bioaccumulation of mercury are well documented, there remains a critical gap in our understanding of the mechanisms governing mercury methylation and demethylation in aquatic environments. This review systematically examines the complex interplay of chemical, biological, and physical factors that influence mercury speciation and transformation in natural water systems. We provide a comprehensive analysis of methylation and demethylation processes, specifically focusing on the dominant role of methanogenic bacteria. Our study highlights the crucial function of hgcAB genes in facilitating mercury methylation by anaerobic microorganisms, an area that represents a frontier in current research. By synthesizing the existing knowledge and identifying key research priorities, this review offers novel insights into the intricate dynamics of mercury cycling in aquatic ecosystems. Our findings provide a theoretical framework to inform future studies and guide pollution management strategies for mercury and its compounds in aquatic environments.

Unraveling atmospheric mercury dynamics at Mauna Loa through the isotopic analysis of total gaseous mercury

Our investigation seeks to uncover the intricate nature of mercury dynamics in the free troposphere through analysis of the isotopic composition of total gaseous elemental mercury (TGM) at the high altitude Mauna Loa Observatory (MLO, 3397 m) in Hawaii, USA. By focusing on this unique site, we aim to provide essential insights into the behavior and cycling of mercury, contributing valuable data to a deeper understanding of its global distribution and environmental impacts. Forty-eight hours of TGM sampling from January to September 2022 revealed significant variations in δ202Hg (−1.86 % to −0.32 %; mean = −1.17 ± 0.65 %, 2 SD, n = 34) and small variations in Δ199Hg (−0.27 % to 0.04 %; mean = −0.13 ± 0.14 %, 2 SD, n = 34) and Δ200Hg (−0.20 % to 0.06 %; mean = −0.05 ± 0.13 %, 2 SD, n = 34). During the sampling period, GEM was negatively correlated with gaseous oxidized mercury (GOM). However, the GOM/GEM ratio was not −1, suggesting that GEM oxidation and subsequent scavenging occurred previously. The δ202Hg isotopic compositions of TGM at MLO were different from those of reported values of high-altitude mountains; the δ202Hg of TGM at MLO was lower than the isotopic ratios that were obtained from other mountain regions. The unique atmospheric conditions at Mauna Loa, with (upslope winds during the day and downslope winds at night, likely result in the) possibly mixing of GEMs from terrestrial (and possibly oceanic GEM emission) sources with and tropospheric sources, influencing and affect the isotopic composition. During the late summer to early fall (September 14–28), negative correlations were found between relative humidity and GOM and between particle number concentrations and Δ199Hg, indicating the gas-to-particle partitioning of the atmospheric mercury during this period. This study will improve our understanding on mercury dynamics of marine origin and high altitudes and shed light on its complex interactions with environmental factors.

A Study on Total Mercury Content in Surface Water and Backwater Fishes of Periyar

Aquatic systems are extensively contaminated with heavy metals released due to anthropogenic activities. Mercury is one of toxic elements and its toxicity to humans has been established. The concern about mercuric pollution in the environments started with the incident of ‘Minamata’ in Japan in 1950’s. During the study period, flowing mercury electrode was used for the preparation of caustic at Travancore Cochin Chemicals Ltd (TCC), Eloor and effluents of small industries at Edayar were the sources of mercuric pollution. Surface water samples were collected from 1Km apart from TCC, near to Indian Rare Earth Ltd (IRE), Muttinakam and Mannamthuruth and fishes (male and female) were collected from this region with the help of local fishermen. This study implies the amount of mercury in aquatic system and its influence in different body components of three fishes. Total mercury content in both the samples analysed using cold vapour atomic absorption using Mercury Analyser MA-5840 and loss on mercury on heating processes (fishes) was decreased by the use of Bethge Apparatus. Fishes were Oreochromis mossambicus (Thilapia), Mugil cephalus (Mullet) and Arius arius (Cat fish) which were living in surface to near shore, middle of the river and bottom. The proximate composition (AOAC, 2000) of fishes showed that they were low fat (0.57-4.24%) with high protein content (18.4-21.96%). The total mercury content in surface water varied from 1.667- 3.334ng/ml and it was above tolerance level (1ng/ml) while in fishes followed the order A. arius> M. cephalus> O. mossambicus. Relatively higher concentrations of mercury were noticed in gut and liver than muscle, and also male fishes predominated over female. This study shows that mercury cycle in the habitat water did not influence to any hazardous level in these three fishes.

Atmospheric mercury species at Nam Co (4730m a.s.l.), a highland background site in the inland Tibetan Plateau: implications of mercury potential sources.

A field survey was conducted in the central Tibetan Plateau (Nam Co) in China for high-time resolution measurements of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM). Average concentrations (± 1 SD) of GEM, PBM, and GOM from November 2014 to March 2015 were 1.11 ± 0.20ngm-3, 50.8 ± 26.5pgm-3, and 3.6 ± 3.2pgm-3, respectively. During the monitoring period, both GEM and GOM exhibited relative stability in their monthly variations, whereas PBM concentrations were significantly higher in winter compared to those in later autumn and early spring. In terms of diurnal variations, the maximum concentration of GEM was typically observed after sunrise, while PBM reached its peak before sunrise, and the highest concentration of GOM was recorded in the afternoon. Vertical convection conditions, photochemical production, and gas-particle partitioning were responsible for the diurnal cycle of atmospheric mercury. Based on modeling results, it was determined that the air mass transported from South Asia significantly impacted atmospheric mercury levels at Nam Co Station. The regions of western and central Nepal, central and eastern Pakistan, and northern India were identified as potential sources of atmospheric mercury at Nam Co.

Temporal Evolution of Gaseous Mercury Across the Sea Ice‐Seawater Interface: A Mesocosm Study

AbstractIn the marine cryosphere, seasonal sea ice dynamics affect the behavior of gaseous mercury, yet the mechanism remains poorly understood. By carrying out an outdoor sea ice mesocosm study, we examine primarily the abiotic factors influencing mercury dynamics and show distinct behaviors of gaseous mercury across the sea ice‐seawater interface over the full growth‐melt cycle. The distribution of gaseous mercury in sea ice is influenced by entrapment of gaseous mercury from different sources into sea ice of different textures, transport schemes within sea ice, and in situ cryo‐processes that affect mercury speciation. In the growing sea ice sections where solar radiation penetrated, production of gaseous mercury was observed, supporting the occurrence of in‐ice cryo‐photoreduction of divalent mercury. In under‐ice seawater, concentrations of dissolved gaseous mercury decreased gradually during ice growth and increased rapidly to pre‐freezing levels as ice started to melt, suggesting that the atmosphere‐sea ice‐seawater exchange pathway of gaseous mercury could be re‐established through melting first‐year sea ice. Our results from this unique mesocosm study provide new insights on the dynamics of gaseous mercury in and around sea ice that are primarily driven by abiotic processes, assisting model parameterizations for mercury cycling in polar regions.

Particulate mercury export in the Central Pacific Ocean using 234Th[sbnd]238U disequilibria

Mercury (Hg) is a potent neurotoxin that enters the food web and may contaminate commercial, recreational, subsistence, and ceremonial fish stocks. Understanding the pathways by which this contamination occurs in marine systems is thus an essential component of minimizing consumer health risk. Our knowledge of the biogeochemical cycling of mercury, however, is relatively limited. Temporal changes in sinking particulate mercury (PHg) fluxes throughout the upper 400 m were examined at Station ALOHA (22°N, 158°W) in the North Pacific Subtropical Gyre (NPSG) and spatially along a north-south transect to the Equator (17.5°N to 5°N x 155°W) using a combination of in situ pumps and Uranium-238/Thorium-234 disequilibria as a tracer of particle export. Our results indicate that Station ALOHA is characterized by seasonally variable export fluxes of PHg, with highest fluxes occurring in May (175 m, 346 pmol m−2 day−1), with the advent of summer zooplankton growth, and in September (400 m, 356 pmol m−2 day−1), coinciding with a diazotroph mediated summer export pulse. PHg fluxes in May and September were higher than those previously measured in the equatorial Pacific at 150 m and continued to be high (> 100 pmol Hg m−2 d−1) down to 400 m, thereby providing a significant source of Hg to the mesopelagic food web. In contrast to Station ALOHA, at 8 and 5°N, PHg fluxes attenuated rapidly with depth, and fluxes were generally lower, with a maximum flux of 86 pmol m−2 d−1 (5°N). Depth profiles at 8 and 5°N were significantly different from one another, with PHg fluxes higher throughout the water column at 5°N and characterized by a subsurface peak in Hg flux 3 times higher than at 8°N (86 vs. 29 pmol Hg m−2 d−1). Monomethylmercury (MeHg) fluxes (max = 1.09 ± 0.57 pmol m−2 d−1) and concentrations (max = 0.14 fmol L−1) comprised only a small percentage of the total PHg pool. These results suggest that PHg cycling significantly differed between the NPSG and near the equator at least during an El Niño year. At Station ALOHA, microbial reworking of small particles below the deep chlorophyll maximum coupled with changes in zooplankton grazing drive seasonal export variability. In contrast near the equator, low fluxes associated with low biological productivity result in significantly lower PHg transport to depth during an El Niño year.

Mercury cycling in contaminated coastal environments: modeling the benthic-pelagic coupling and microbial resistance in the Venice Lagoon

Anthropogenic activities have been releasing mercury for centuries, and despite global efforts to control emissions, concentrations in environmental media remain high. Coastal sediments can be a long-term repository for mercury, but also a secondary source, and competing processes in marine ecosystems can lead to the conversion of mercury into the toxic and bioaccumulative species methylmercury, which threatens ecosystem and human health. We investigate the fate and transport of three mercury species in a coastal lagoon affected by historical pollution using a novel high-resolution finite element model that integrates mercury biogeochemistry, sediment dynamics and hydrodynamics. The model resolves mercury dynamics in the seawater and the seabed taking into account partitioning, transport driven by water and sediment, and photochemical and microbial transformations. We simulated three years (early 2000s, 2019, and 2020) to assess the spatio-temporal distribution of mercury species concentrations and performed a sensitivity analysis to account for uncertainties. The modeled mercury species concentrations show high temporal and spatial variability, with water concentrations in some areas of the lagoon exceeding those of the open Mediterranean Sea by two orders of magnitude, consistent with available observations from the early 2000s. The results support conclusions about the importance of different processes in shaping the environmental gradients of mercury species. Due to the past accumulation of mercury in the lagoon sediments, inorganic mercury in the water is closely related to the resuspension of contaminated sediments, which is significantly reduced by the presence of benthic vegetation. The gradients of methylmercury depend on the combination of several factors, of which sediment resuspension and mercury methylation are the most relevant. The results add insights into mercury dynamics at coastal sites characterized by a combination of past pollution (i.e. sediment enrichment) and erosive processes, and suggest possible nature-based mitigation strategies such as the preservation of the integrity of benthic vegetation and morphology.

Deep sea cold seeps are a sink for mercury and source for methylmercury

The effect of seafloor cold seeps on the biogeochemical cycling of mercury (Hg) remains enigmatic. Here we demonstrate substantial enrichments of mercury and methylmercury, along with the presence of microbes capable of metabolizing mercury in sediments of the Haima cold seep, South China Sea, by analyzing mercury and methylmercury concentrations, mercury isotopic composition analyses and metagenomic analyses of sediment cores. Compared to the reference area, the sediments in the upper sediment column of the active-seep area were 2.4 times enriched in Hg and 10.5 times in methylmercury. The slope of the capital delta ratio of mercury 199 to mercury 201 (Δ199Hg/Δ201Hg) with 1.23 ± 0.10 in the active-seep area indicate the occurrence of dark redox reactions. Genes related to mercury methylation (hgcA), demethylation (merB) and reduction (merA) were phylogenetically associated with several bacterial and archaeal linages. We roughly estimated an additional 2,835 Mg mercury and 9 Mg methylmercury are stored in cold seep globally. In summary, we propose that cold seeps globally function as a previously unrecognized sink for mercury and source for methylmercury in the deep ocean.

Low mercury concentrations in a Greenland glacial fjord attributed to oceanic sources

As the role of the Greenland Ice Sheet in the Arctic mercury (Hg) budget draws scrutiny, it is crucial to understand mercury cycling in glacial fjords, which control exchanges with the ocean. We present full water column measurements of total mercury (THg) and methylmercury (MeHg) in Sermilik Fjord, a large fjord in southeast Greenland fed by multiple marine-terminating glaciers, whose circulation and water mass transformations have been extensively studied. We show that THg (0.23-1.1 pM) and MeHg (0.02-0.17 pM) concentrations are similar to those in nearby coastal waters, while the exported glacially-modified waters are relatively depleted in inorganic mercury (Hg(II)), suggesting that inflowing ocean waters from the continental shelf are the dominant source of mercury species to the fjord. We propose that sediments initially suspended in glacier meltwaters scavenge particle-reactive Hg(II) and are subsequently buried, making the fjord a net sink of oceanic mercury.

Cumulative Effects of Watershed Disturbances and Run-of-river Dams on Mercury Cycling: Case Study and Recommendations for Environmental Managers.

Run-of-river power plants (ROR) represent the majority of hydroelectric plants worldwide. Their environmental impacts are not well documented and are believed to be limited, particularly regarding the contamination of food webs by methylmercury (MeHg), a neurotoxin. RORs are typically installed in small rivers where combined effects of watershed disturbances with dam construction can complicate environmental management. We report a multi-year case study on the Saint-Maurice River (Canada) where an unpredicted temporary increase in MeHg accumulation in predator fish was observed after the construction of two ROR plants. The associated pondages acted as sedimentation basins for mercury (Hg) and organic matter from a watershed disturbed by a forest fire and by logging. This fresh organic carbon likely fueled microbial MeHg production. Hg methylation was more associated with environmental conditions than to the presence of Hg, and main methylating microbial groups were identified. A constructed wetland was a site of significant Hg methylation but was not the main source of the fish Hg increase. Organic carbon degradation was the main driver of MeHg accumulation at the base of the food chain whereas trophic levels explained the variations at the top of the food chain. Overall, carbon cycling was a key driver of Hg dynamics in this system, and ROR plants can cause temporary (ca. 12 years) Hg increase in food webs when developed in disturbed watersheds, although this increase is smaller than for large reservoirs. Recommendations for future ROR construction are to establish a good environmental monitoring plan with initial high temporal resolution and to consider recent and potential watershed disturbances in the plan.

Sources, Fates, and Geochemical Cycling of Mercury in Geothermal Fields: Insights From Mercury Isotopes

AbstractGeothermal fields emit remarkable amounts of mercury (Hg) to the environment. To address the source, fate and geochemical cycling of Hg in geothermal fields, we investigated Hg concentrations and isotopic compositions of hot spring water and fumarole gases from Rehai and Dagejia in SW‐China. Elevated Hg concentrations in fumarole gases (10.0–167 ng m−3) and hot spring water (3.44–84.5 ng L−1) were observed, suggesting that both geothermal fields are of environmental concern. The variation in Δ199Hg (−0.06 to 0.23‰) and Δ200Hg (−0.09 to 0.19‰) in hot spring water supports Hg likely originating from endogenous volcanic degassing and/or rainwater. Negative and nearly zero Δ199Hg in fumarole gases (−0.32 to 0.03‰) supports volcanic degassing and background atmosphere origin. The ranges of δ202Hg in fumarole gases (−0.74 to 0.59‰) and hot spring water (−1.29 to 0.52‰) could reflect limited fluids boiling in geothermal fields. This study, thus, fills an important knowledge gap regarding Hg global cycling.

Atmospheric gaseous mercury and associated health risk assessment in the economic capital of India.

Mercury cycling in coastal metropolitan areas on the west coast of India becomes complex due to the combined effects of both intensive domestic anthropogenic emissions and marine air masses. The present study is based on yearlong data of continuous measurements of gaseous elemental mercury (GEM) concentration concurrent with meteorological parameters and some air pollutants at a coastal urban site in Mumbai, on the west coast of India, for the first time. The concentration of GEM was found in a range between 2.2 and 12.3ng/m3, with a mean of 3.1 ± 1.1ng/m3, which was significantly higher than the continental background values in the Northern Hemisphere (~ 1.5ng/m3). Unlike particulates, GEM starts increasing post-winter to peak during the monsoon and decrease towards winter. July had the highest concentration of GEM followed by October, and a minimum in January. GEM exhibited a distinct diurnal cycle, mainly with a broad peak in the early morning, a narrow one by nightfall, and a minimum in the afternoon. The peaks and their timing suggest the origin of urban mobility and the start of local activities. A positive correlation between SO2, PM2.5, temperature, relative humidity, and GEM indicates that emissions from local industrial plants in the Mumbai coastal area. Principal component analysis (PCA) and cluster analysis (CA) confirm this fact. Monthly back trajectory analysis showed that air mass flows are predominantly from the Arabian Sea and local human activities. Assessment of human health risks by USEPA model reveals that the hazardous quotient, HQ < 1, implies negligible carcinogenic risk. GEM observations in Mumbai during the study period are below the World Health Organization's (WHO) safe limit (200ng/m3) for long-term inhalation.

Hydrology and oxygen addition drive nutrients, metals, and methylmercury cycling in a hypereutrophic water supply reservoir

Impaired water quality in Mediterranean climate reservoirs is mainly associated with eutrophication and internal nutrient loading. To improve water quality in hypereutrophic Hodges Reservoir, California, United States, a hypolimnetic oxygenation system (HOS), using pure oxygen gas, was implemented in 2020. This study encompasses 3 years of pre-oxygenation data (2017–2019) and 2 years of post-oxygenation data (2020–2021) to understand the cycling of nutrients, metals, and mercury in the reservoir. During the wet year of 2017, mildly reduced conditions lasted until mid-summer in the enlarged reservoir. Nutrients and metals were seen in the hypolimnion including ammonia (~2 mg-N/L), manganese (~0.5 mg/L), phosphate (~0.5 mg-P/L), and sulfide (~10 mg/L). Production of methylmercury (MeHg), an important bioaccumulative toxin, was favored from April to June with a hypolimnetic accumulation rate of around 200 ng/m2·d. In contrast, the dry year of 2018 exhibited higher hypolimnetic concentrations of ammonia (~4 mg-N/L), manganese (~1 mg/L), phosphate (&amp;gt;0.5 mg-P/L), and sulfide (&amp;gt;15 mg/L). The rapid onset of highly reduced conditions in 2018 corresponded with low MeHg hypolimnetic accumulation (~50 ng/m2·d). It seems that mildly reduced conditions were associated with higher MeHg accumulation, while sulfidic, reduced conditions impaired inorganic mercury bioavailability for MeHg production and/or promoted microbial demethylation. Sulfide also appeared to act as a sink for iron via FeS precipitation, and potentially for manganese via MnS precipitation or manganese coprecipitation with FeS. Mass flux estimates for 2017–2019 indicate that much of the nutrients that accumulated in the hypolimnion moved via turbulent diffusion into the epilimnion at loading rates far exceeding thresholds predicting eutrophic conditions. After oxygenation in 2020–2021, the reservoir water column was highly oxidized but showed a lack of thermal stratification, suggesting reservoir operations in combination with HOS implementation inadvertently mixed the water column in this relatively shallow reservoir. Post-oxygenation, concentrations of ammonia, phosphate, manganese, and mercury in bottom waters all decreased, likely in response to oxidized conditions. Oxygenated bottom waters exhibited elevated nitrate, a byproduct of ammonia nitrification, and iron, a byproduct of FeS oxidation, indicating a lake-wide response to oxygenation.

Assessment of total mercury in urban particulate matter by filter fiber assisted matrix solid-phase dispersion coupling with microplasma assisted-cold vapor generation

BackgroundThe evaluation of particle-bound mercury (PBM) exposure is a crucial aspect of assessing the global cycle of mercury (Hg) and its adverse effects on human health and ecosystems. Nevertheless, the precise and reliable measurement of PBM remains a formidable task because of the costly and cumbersome equipment required, as well as the inadequate sensitivities exhibited by current analytical techniques. In this study, we provided a unique and straightforward approach utilising filter fiber-assisted matrix solid-phase dispersion (FF-MSPD) in conjunction with single-drop solution electrode discharge-induced cold vapor generation atomic fluorescence spectrometry (SD-SEGD-CVG-AFS) for the precise quantification of PBM. The PBM contained in a small filter was efficiently extracted with 200 μL of eluent (0.2 % L-cysteine and 4 % HCOOH) by FF-MSPD and subsequently converted to Hg0 using SD-SEGD-CVG, before being subjected to examination using AFS. ResultsThe resulted limit of detection (LOD, 3σ) was 0.17 pg m−3, obtained with a sample volume of 12 m3, which was much higher than that of the techniques published in the literatures. The aforementioned technique was effectively utilised for the detection of mercury in 19 samples of PM2.5 and PM10 which were collected over a span of several months. SigniffcanceContrast to conventional methods, the proposed method offers a range of distinct advantages, including simplified operation, absence of memory effects, enhanced sensitivity, substantial reduction in reagent usage, and decreased secondary pollution. These advantages are particularly valuable for advancing research on the fate, transport, and exposure routes of environmental mercury.

Review of the Influence of Climate Change on the Hydrologic Cycling and Gaseous Fluxes of Mercury in Boreal Peatlands: Implications for Restoration

Review of the Influence of Climate Change on the Hydrologic Cycling and Gaseous Fluxes of Mercury in Boreal Peatlands: Implications for Restoration

Biotic transformation of methylmercury at the onset of the Arctic spring bloom

Despite the lack of local anthropogenic mercury sources, methylated mercury (MeHg) concentrations in Arctic biota are higher than in biota from lower latitudes. The main entry route occurs during the bioconcentration of seawater monomethylmercury (MMHg) into phytoplankton. Despite the known seasonal changes in biological activity in the region, little is known about the seasonal cycling of total mercury (THg) and MeHg in the Arctic Ocean. Here, we report the concentrations of THg and MeHg in seawater sampled from the northwestern Barents Sea water column during late winter and spring. In the upper 500 m, the THg concentrations are significantly higher in spring (0.64 ± 0.09 pmol L-1) compared to late winter (0.53 ± 0.07 pmol L-1), driven by seasonal inputs to surface waters from atmospheric deposition and the dynamics of changing sea ice conditions. Contrastingly, the MeHg concentrations in spring were significantly lower (41 ± 39 fmol L-1) compared to late winter (85 ± 42 fmol L-1). We suggest that most MeHg is biotically demethylated by both phytoplankton and bacteria, with additional losses from photodemethylation and evasion. Our observations highlight the importance of demethylation during potential uptake of methylmercury coinciding with the Arctic spring bloom. Lastly, we use our new data together with previously published seasonal data in the region to construct a simplified seasonal mercury cycle in an Arctic marginal ice zone.

Biomimetic mercury immobilization by selenium functionalized polyphenylene sulfide fabric

Highly efficient decontamination of elemental mercury (Hg0) remains an enormous challenge for public health and ecosystem protection. The artificial conversion of Hg0 into mercury chalcogenides could achieve Hg0 detoxification and close the global mercury cycle. Herein, taking inspiration from the bio-detoxification of mercury, in which selenium preferentially converts mercury from sulfoproteins to HgSe, we propose a biomimetic approach to enhance the conversion of Hg0 into mercury chalcogenides. In this proof-of-concept design, we use sulfur-rich polyphenylene sulfide (PPS) as the Hg0 transporter. The relatively stable, sulfur-linked aromatic rings result in weak adsorption of Hg0 on the PPS rather than the formation of metastable HgS. The weakly adsorbed mercury subsequently migrates to the adjacent selenium sites for permanent immobilization. The sulfur-selenium pair affords an unprecedented Hg0 adsorption capacity and uptake rate of 1621.9 mg g−1 and 1005.6 μg g−1 min−1, respectively, which are the highest recorded values among various benchmark materials. This work presents an intriguing concept for preparing Hg0 adsorbents and could pave the way for the biomimetic remediation of diverse pollutants.

Assessment of mercury accumulation in various tissues of rice plant (Oryza sativa L.) from a Ramsar site in India

Dietary exposure to mercury through rice consumption is an issue of solemn global concern. The favourable bio-geochemical environment of paddy fields often makes them potential mercury cycling hotspots. India is one of the largest producers and consumers of rice globally. To date, studies focusing on mercury bioaccumulation in rice during the different stages of its growth cycle have not been studied in Indian agro-ecosystems.This inturn resulted in a knowledge gap in the global mercury assessment. Being a party to the Minamata Convention, there is an urgent need to unravel the scenario of mercury contamination in rice, one of the staple food crops across the world. In the present study, total mercury (THg) in the rhizosphere soil as well as its accumulation in different tissues of the rice plant were examined by a field investigation in Kuttanad – a unique Ramsar site in Kerala, India. For the purpose of the study five permanent plots were selected and monitored for the entire rice-growing season (from the 30th to the 120th day). Direct Mercury Analyzer (DMA – 80, Milestone, USA) was used for analyzing THg in rhizosphere soil and plant tissues. Mercury concentration in soils varied from 0.037 mg/kg to 0.117 mg/kg with a mean concentration of 0.088 mg/kg. The THg accumulation pattern in plant tissues followed the order: root > leaf > grain > husk > stem. The mean THg concentration in rice grains was 0.22 mg/kg. The low values for bioaccumulation factor (0.616) and translocation factor (0.425) revealed that a major portion of mercury accumulated by the plant is stored in the roots.