Mercury Accumulation Research Articles

Influence of global warming and human activity on mercury accumulation patterns in wetlands across the Qinghai-Tibet Plateau

Abstract Wetlands in the Qinghai-Tibet Plateau (QTP) are a unique and fragile ecosystem undergoing rapid changes. We show two unique patterns of mercury (Hg, a global pollutant) accumulation in wetland sediments. One is the ‘Surface Peak’ in monsoon-controlled regions, and the other is the ‘Subsurface Peak’ in westerly-controlled regions. The former is attributed to the combined effects of increasing anthropogenic emissions and climate-induced changes in the cryosphere and wetland hydrology in the last 100 − 150 years. The climate changes in westerly-controlled regions in the last 50 − 70 years led to a fluctuation of hydrology and an Hg peak in the sediment subsurface. The increase of legacy Hg input from soil erosion largely enhanced the Hg accumulation rate in wetlands since the 1950s, especially in the proglacial wetlands. We highlight that accelerated glacier melting and permafrost thawing caused by global warming have altered geomorphology and hydrology and affected Hg transport and accumulation in wetlands.

Phytoremediation of Mercury and Cyanide Contaminated Soils by Physic Nut (Jatropha curcas L.) and Citronella Grass (Cymbopogon nardus)

Mercury and cyanide are compounds that have the potential to pollute the environment, both of which are found in the tailing waste of artisanal and small-scale gold mining (ASGM). The purpose of this study was to determine the ability of physic nut (Jatropha curcas L.) and citronella grass (Cymbopogon nardus) to absorb mercury and cyanide in soils polluted with tailings waste based on the value of transfer factors. During this research stage, the remediation of soil polluted with amalgamation tailings and cyanide tailings was carried out for 28 days. Soil sampling was carried out every seven days for 28 days, while root and leaf sampling was carried out on day 28, analysis of mercury and cyanide content in soil and plants using atomic absorption spectroscopy (AAS) and UV-visible spectrophotometer. After 28 days of remediation, mercury and cyanide levels may decrease in soil by 93.7% for mercury and 81.8% for cyanide. The decrease can be caused by absorption and accumulation in plants, where mercury and cyanide accumulate more in physic nut than citronella grass. Physic nut and citronella grass have a transfer factor value of <1 for mercury and cyanide, so they are an excluder plant, except for the accumulation of mercury in physic nut from cyanide tailings soil, which has a transfer factor value of >1, which is an accumulator plant.

Mitigating Mercury Accumulation and Enhancing Methylmercury Degradation in Rice: Insights from Zinc-Mercury Antagonism at Molecular Levels.

Zn as an essential element has the potential to protect against mercury (Hg) toxicity in rice. However, the antagonistic effects between Zn and Hg in rice and their mechanisms remain unknown. This study proposed a promising strategy for Zn application to mitigate Hg accumulation and toxicity in rice and revealed the underlying molecular mechanisms. The findings revealed that Zn supplementation significantly reduced the uptake and transportation of both IHg and MeHg in rice, thereby alleviating Hg phytotoxicity. In particular, Zn profoundly mitigated Hg-induced oxidative damage to rice, which was attributed to the redistribution of Hg and Zn in the root and Zn competing for binding sites on glutathione. The co-binding of Zn2+ and HgCH3+ within the same active sites of Zn transporters can promote the transfer of regions with a high charge density distribution at the highest occupied molecular orbital (HOMO) level. This process facilitates proton attack on the Hg-C bond, thereby enhancing MeHg demethylation in rice. By elucidating the molecular mechanisms of Zn, IHg, and MeHg interactions in rice, this study offers new insights for developing efficient strategies to mitigate Hg risks while boosting the Zn content in crops, thereby fortifying food safety.

Effects of mercury and magnetic fields on the activity of proteinases and glycosidases in the intestine of common carp Cyprinus carpio.

Aquatic ecosystems are increasingly affected by anthropogenic pollution, including heavy metals like mercury, which accumulate in organisms and cause harmful effects. At the same time, human activities such as industrial operations and the use of electric power lines also alter the magnetic background in natural water bodies. However, the interaction between mercury exposure and magnetic fields remains poorly understood. This study aimed to investigate the combined effects of mercury and magnetic fields on the digestive enzyme activity of common carp (Cyprinus carpio), focusing on the relevance of magnetic fields due to their increasing presence in industrialized environments. Two groups of fish were fed diets with low (0.02mg/kg) or high (0.27mg/kg) mercury content for 6months and exposed to extremely low-frequency magnetic fields or hypomagnetic conditions. Results showed significant differences in mercury accumulation between groups, with higher levels in carps fed with high-mercury content diets. These fish also exhibited increased body length and weight compared to those on a low-mercury diet. The amylolytic activity (total activity of enzymes hydrolyzing starch: α-amylase, glucoamylase, and maltase) and proteolytic activity (total activity of serine proteinases) in the fish intestine were assessed. Magnetic exposure had contrasting effects on enzyme activity, depending on mercury levels in the diet. Fish fed the low-mercury diet exhibited decreased amylolytic activity following magnetic field exposure, while fish on the high-mercury diet showed increased activity. Proteolytic activity followed a similar pattern, with opposite effects observed between the two dietary groups. These findings suggest that mercury accumulation alters the biological response to magnetic fields, possibly through compensatory biochemical mechanisms. Understanding the interactions between toxic substances and magnetic fields is critical for improving environmental risk assessments.

Relationship of mercury bioaccumulation with seasonality and feeding habits of fish species caught upstream and downstream of the Curuá-Una hydroelectric dam in the Brazilian Amazon.

Hydroelectric plants impact the dynamics of mercury accumulation and transfer to aquatic ecosystems and organisms. This study aimed to determine total mercury (THg) concentration in filtered water, aquatic macrophytes, and fish and assess the influence of fluvial regime (low-water, rising-water, and high-water) and the feeding habits of fish species caught upstream and downstream of the Curuá-Una hydroelectric dam in the Brazilian Amazon. THg levels were determined by cold-vapor atomic fluorescence spectrometry. THg concentration in filtered water was higher (5.3-11.2 ng L-1) during the low-water period. THg concentration in fish ranged from 0.075 to 1.160 µg g-1 in specimens caught downstream and from 0.014 to 1.036 µg g-1 in specimens caught upstream of the dam. The highest THg concentrations were detected in specimens of the piscivorous species Acestrorhynchus falcirostris (1.161 µg g-1) caught at downstream sites. There were significant correlations of THg concentration with the trophic level (Analysis of Variance; p ≤ 0.001) of fish species and fluvial regime (Analysis of Variance; p ≤ 0.001). The macrophyte Utricularia foliosa contained the highest THg levels in leaf tissues in the low-water period (71.4 µg g-1). It is concluded that THg concentration varies between fish trophic levels and fluvial regimes. Macrophytes contribute to enhancing mercury transfer and availability along the aquatic trophic chain.

Organic-rich Shales Reveal Local Controls That Enhanced Mercury Accumulation During a non-LIP Interval of the Miocene: Implications for the Mercury Paleoproxy

Organic-rich Shales Reveal Local Controls That Enhanced Mercury Accumulation During a non-LIP Interval of the Miocene: Implications for the Mercury Paleoproxy

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.

Investigating how H2S can alter the interactions between Hg0 and corroded steel surfaces to guide future decommissioning projects

Many oil and gas developments will soon be decommissioned and, knowledge on the accumulation of mercury (Hg), throughout offshore infrastructure is limited. Any release of Hg could have a detrimental impact on marine ecosystems. To bridge this knowledge gap, a fractionation approach was taken on steel samples exposed to Hg0 and H2S, separating Hg compounds removed from the surface into polar, non-polar and insoluble fractions. Hg0 reacted on corroded surfaces to form several compounds, over 50 % of which were removed by seawater. This suggests that pipelines on the seabed could release a dramatic amount of Hg into the sea if they are left in place. Furthermore, a Cu-Hg amalgam, was identified to be a dominant species, by a combination of XFM, XANES and LA-ICP-TOFMS. Seawater-soluble and amalgam-bound Hg were present regardless of co-exposure to H2S. When H2S was present Hg nanoparticles accounted for up to 1 % of the total Hg on the steel. This investigation has shown that the Hg speciation on the surfaces of pipelines is complex and future decommissioning strategies should consider a range of Hg species beyond only Hg0 and metacinnabar (β-HgS), all of which could interact with biota and impact Hg biomagnification through the marine the food web.

Application of biochar and selenium together at low dose efficiently reduces mercury and methylmercury accumulation in rice grains

Irrespective of cost and ecological risk, literatures have reported that both biochar and selenium (Se) alone at high application rate exhibited positive effects on decreasing rice mercury (Hg) uptake in high Hg contaminated paddy soil. In this study, we investigated whether biochar and Se together at low dose could efficiently reduce the rice grain Hg and MeHg accumulation in the slight Hg-contaminated soil. Compared with control (CK), the Hg concentration of grains in the BC3, Se0.5, and BC3 + Se0.5 treatments decreased by 5.4 %, 38.3 %, and 48.5 %, respectively. Co-application of biochar and Se also decreased the methylmercury (MeHg) concentration in rice grains by 29.1–91.6 %. The decrease of Hg and MeHg level in rice grains for biochar and Se treatments could be attributed to the following mechanisms: (1) high Hg (primarily inorganic Hg) adsorption on biochar through its high hydroxyl groups and large specific surface area; (2) Increased dissolved organic carbon and cysteine contents in pore water after biochar application, which reduced the availability of soil Hg through complexation; (3) Decreased bioavailability of Hg in soil due to the formation of HgSe precipitation which inhibited Hg uptake and translation by rice plant; (4) Both biochar and Se facilitated the reduction of MeHg in soil. Our results indicate that co-application of biochar and Se at low dose is a promising method to effectively mitigate Hg accumulation in rice grains from the slight Hg-contaminated soil.

A discovery in traditional Chinese medicine compatibility: Cinnabaris suppresses the Strychni Semen-induced neurotoxicity in Shang-Ke-Jie-Gu tablet

BackgroundCinnabaris, as a commonly used mineral drugs, is a classic sedative medicine. Shang-Ke-Jie-Gu tablet is a famous Chinese patent medicine with Cinnabaris, However, the function of Cin in the prescription hasn't been clarified. PurposeOur study evaluated the toxicity of Shang-Ke-Jie-Gu tablet (SK) with or without Cinnabaris, and illuminate the related mechanisms that why cinnabaris is necessary. MethodsThe toxicity of SK and Cin free Shang-Ke-Jie-Gu tablet (CFSK) was evaluated by physical and behavioral tests and histological examinations. The detoxificaion mechanism of Cin on Strychni Semen (SS)-induced neurotoxicity in SK was performed based on the analysis of intestinal absorption, liver metabolism, serum metabolomics, and gut microbiota. The mercury accumulation of SK was assayed using human hair by ICP-MS. ResultsCin was found to inhibit the neurotoxicity of SS in SK. Our study shows that Cin could inhibit SS's absorption in small intestine and promote its metabolism in the liver. A serum metabolomics study showed that taurine and hypotaurine metabolism and retrograde endocannabinoid signaling pathway were associated with Cin attenuation. Association analysis with gut microbiota suggested that Cin could downregulate four key metabolites, including 12‑hydroxy arachidonic acid, GM4(d18:1/18:0), C16 sphinganine, and LysoPC(18:1(11Z)/0:0), by downregulating Lachnospiraceae_NK4A136 and upregulating Prevotella to inhibit the toxic effects of SS. In addition, the danger of mercury poisoning in a longer time administration of SK was evaluated using human hair, and no visible increase in mercury was observed. ConclusionAs a new discovery in compatibility, Cin was proved to be capable of inhibiting the neurotoxicity not only in SK but also in Cin-SS combination, displaying vital roles in Traditional Chinese Medicines.

Mitigating the Accumulation of Mercury (Hg) and Lead (Pb) through Humic Acid Application under Aquaponic Conditions Using Watercress (Nasturtium officinale R. Br.) as a Model Plant.

In aquaponic farming, there is a potential risk that heavy metals will contaminate the water, which can lead to heavy metal accumulation in the plants. Our research investigated the accumulation of mercury (Hg) and lead (Pb) under aquaponic conditions and the effect of their increased presence on the uptake of other macro- and micronutrients using watercress (Nasturtium officinale) as a model plant. The potential modifying effect of humic acid on heavy metal accumulation was also investigated. Adding Hg and Pb increased the mercury and lead levels of the watercress plants to over 300 µg kg-1, while the addition of humic acid significantly reduced the concentration of both mercury and lead in the plants compared to plants treated with heavy metals alone, from 310.647 µg kg-1 to 196.320 µg kg-1 for Hg and from 313.962 µg kg-1 to 203.508 µg kg-1 for Pb. For Fe and Mn, higher values were obtained for the Hg + humic acid treatments (188.13 mg kg-1 and 6423.92 µg kg-1, respectively) and for the Pb + humic acid treatments (198.26 mg kg-1 and 6454.31 µg kg-1, respectively). Conversely, the Na, K, Cu levels were lower compared to those in plants treated with heavy metals alone. Our results demonstrated that watercress can accumulate mercury, leading to high levels, even above food safety standards, highlighting the importance of water quality control in aquaponic systems. Furthermore, these results suggest that watercress could be used as a natural filter in recirculation systems. The addition of humic acid significantly reduced the accumulation of heavy metals and altered the element content in the plant.

Application of selenium to reduce heavy metal(loid)s in plants based on meta-analysis

Agricultural soils are currently at risk of pollution from toxic heavy metal(loid)s (HMs) due to human activities, resulting in the excessive accumulation of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), lead (Pb) and zinc (Zn) in food plants. This poses significant risks to human health. Exogenous selenium (Se) has been proposed as a potential solution to reduce HMs accumulation in plants. However, there is currently a lack of comprehensive quantitative overview regarding its influence on the accumulation of HMs in plants. This study utilized meta-analysis to consolidate the existing knowledge on the impact of Se amendments on plant HMs accumulation from contaminated soil media. The present study conducted a comprehensive meta-analysis on literature published prior to December 2023, investigating the effects of different factors on HMs accumulation by meta-subgroup analysis and meta-regression model. Se application showed an inhibitory effect on plant uptake of Hg (28.9%), Cr (25.5%), Cd (25.2%), Pb (22.0%), As (18.3%) and Cu (6.00%) concentration. There was a significant difference in the levels of HMs between treatments with Se application and those without Se application in various plant organs. The percentage changes in the HMs contents of the organs varied from −13.0% to −22.0%. Compared with alkaline soil (pH > 8), Se application can reduce more HMs contents in plants in acidic soil (pH < 5.5) and neutral soil (pH = 5.5–8). For daily food plants(e.g. rice, wheat and corn), Se application can reduce HMs contents in Oryza sp., Triticum sp. and Zea sp., ranging from 14.0–20.0%. Our study emphasizes that the impact of Se on reducing HMs depends on the single or combined effects of Se concentration, plant organs, plant genera and soil pH condition.

Assessment of mercury methylation and methylmercury demethylation potentials in water and sediments along the Wabigoon River system

Monomethylmercury (MMHg) plays a crucial role in the accumulation of mercury (Hg) within aquatic food chains. Since ambient levels of methylmercury are governed by the balance of simultaneous methylation and demethylation processes, determining in situ methylation and demethylation rates is critically important to understand the dynamics of methylmercury in the environment. This is especially important in the Wabigoon River system in Ontario, Canada, which is severely contaminated with Hg by a chlor-alkali facility operating in the 1960s, and still exhibits some of the highest recorded fish mercury concentrations in Canada. This work used a simultaneous addition of isotope enriched Hg and MMHg tracers to ascertain Hg methylation and MMHg demethylation potentials. At the locations investigated for this study, the most favourable conditions for Hg methylation were found at the Hydroelectric dam, being able to transform 4.2 % and 4.4 % of added Hg in water and sediments per day, respectively, to MMHg. This could correspond to 1.9 ng/L and 29 ng/g of new MMHg being produced from current ambient Hg. Clay Lake, which is considered a sink for mercury and exhibiting a seasonal anoxic environment at its bottom waters, also demonstrated significant MMHg generation, being able to produce 2.7 ng/L and 13 ng/g of MMHg per day, respectively. Demethylation rates in sediments of riverbed and wetland locations showed an average half-life for methylmercury of 2.1 days, indicating a rapid turnover of MMHg in the Wabigoon River. However, significantly lower demethylation rates were also measured near the inflow of Clay Lake, where it took up to 144 days for MMHg to decrease by 50 %. Generally, most of the investigated locations downstream of the pollution source displayed the potential to generate methylmercury, which could be distributed throughout the Wabigoon River system and therefore require attention with respect to future remediation activities.

Influence of migration range and foraging ecology on mercury accumulation in Southern Ocean penguins

In order to evaluate mercury (Hg) accumulation patterns in Southern Ocean penguins, we measured Hg concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in body feathers of adult Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins living near Anvers Island, West Antarctic Peninsula (WAP) collected in the 2010/2011 austral summer. With these and data from Pygoscelis and other penguin genera (Eudyptes and Aptenodytes) throughout the Southern Ocean, we modelled Hg variation using δ13C and δ15N values. Mean concentrations of Hg in feathers of Adélie (0.09 ± 0.05 μg g−1) and gentoo (0.16 ± 0.08 μg g−1) penguins from Anvers Island were among the lowest ever reported for the Southern Ocean. However, Hg concentrations in chinstrap penguins (0.80 ± 0.20 μg g−1), which undertake relatively broad longitudinal winter migrations north of expanding sea ice, were significantly higher (P < 0.001) than those in gentoo or Adélie penguins. δ13C and δ15N values for feathers from all three Anvers Island populations were also the lowest among those previously reported for Southern Ocean penguins foraging within Antarctic and subantarctic waters. These observations, along with size distributions of WAP krill, suggest foraging during non-breeding seasons as a primary contributor to higher Hg accumulation in chinstraps relative to other sympatric Pygoscelis along the WAP. δ13C values for all Southern Ocean penguin populations, alone best explained feather Hg concentrations among possible generalized linear models (GLMs) for populations grouped by either breeding site (AICc = 36.9, wi = 0.0590) or Antarctic Frontal Zone (AICc = 36.9, wi = 0.0537). Although Hg feather concentrations can vary locally by species, there was an insignificant species-level effect (wi < 0.001) across the full latitudinal range examined. Therefore, feeding ecology at breeding locations, as tracked by δ13C, control Hg accumulation in penguin populations across the Southern Ocean.

Converting flooded rice to dry farming can alleviate MeHg accumulation in grains

The study explored the impact of water management on rice cultivation in mercury-contaminated paddy soil. The objective was to analyze the characteristics of mercury translocation by converting flooded soils to dry farming (non-flooded) to alleviate mercury accumulation in rice grains. The experiment was conducted over three consecutive rice-growing seasons, employing two distinct water management models: a continuously flooded rice cultivation mode and a flooded rice planting mode in the first season, followed by a non-flooded rice farming mode in the second and third seasons. The results showed that the change from flooded to non-flooded rice cultivation patterns presented extremely excellent environmental potential for inhibiting the uptake of both methylmercury and total mercury in rice. When transitioning from flooded cultivation to dry farming, the concentration of methylmercury and total mercury in the grains of non-flooded rice decreased by 87.15 % and 9.57 %, respectively, compared to that in the grains of flooded rice. In the third season, the methylmercury and total mercury in the grains of non-flooded rice decreased further by 95.03 % and 69.45 %, respectively. This study verified that the conversion of rice cultivation from flooded to non-flooded is an efficient strategy for suppressing the accumulation of methylmercury in rice grains, and it might offer a promising solution for managing soil mercury risks and ensuring the safety of rice for human consumption.

Dietary protein affects tissue accumulation of mercury and induces hepatic Phase I and Phase II enzyme expression after co-exposure with methylmercury in mice

Methylmercury (MeHg) is a ubiquitous environmental contaminant, well known for its neurotoxic effects. MeHg can interact with several nutrients in the diet and affect nutrient metabolism, however the interaction between MeHg and dietary proteins has not been thoroughly investigated. Male BALB/c mice were fed diets based on either casein, cod or chicken as protein sources, which were or were not spiked with MeHg (3.5 mg Hg kg−1). Following 13 weeks of dietary exposure to MeHg, the animals accumulated mercury in a varying degree depending on the diet, where the levels of mercury were highest in the mice fed casein and MeHg, lower in mice fed cod and MeHg, and lowest in mice fed chicken and MeHg in all tissues assessed. Assessment of gut microbiota revealed differences in microbiota composition based on the different protein sources. However, the introduction of MeHg eliminated this difference. Proteomic profiling of liver tissue uncovered the influence of the dietary protein sources on a range of enzymes related to Phase I and Phase II detoxification mechanisms, suggesting an impact of the diet on MeHg metabolism and excretion. Also, enzymes linked to pathways including methionine and glycine betaine cycling, which in turn impact the production of glutathione, an important MeHg conjugation molecule, were up-regulated in mice fed chicken as dietary protein. Our findings indicate that dietary proteins can affect expression of hepatic enzymes that potentially influence MeHg metabolism and excretion, highlighting the relevance of considering the dietary composition in risk assessment of MeHg through dietary exposure.

Quantifying soil accumulation of atmospheric mercury using fallout radionuclide chronometry

Soils are a principal global reservoir of mercury (Hg), a neurotoxic pollutant that is accumulating through anthropogenic emissions to the atmosphere and subsequent deposition to terrestrial ecosystems. The fate of Hg in global soils remains uncertain, however, particularly to what degree Hg is re-emitted back to the atmosphere as gaseous elemental mercury (GEM). Here we use fallout radionuclide (FRN) chronometry to directly measure Hg accumulation rates in soils. By comparing these rates with measured atmospheric fluxes in a mass balance approach, we show that representative Arctic, boreal, temperate, and tropical soils are quantitatively efficient at retaining anthropogenic Hg. Potential for significant GEM re-emission appears limited to a minority of coniferous soils, calling into question global models that assume strong re-emission of legacy Hg from soils. FRN chronometry poses a powerful tool to reconstruct terrestrial Hg accumulation across larger spatial scales than previously possible, while offering insights into the susceptibility of Hg mobilization from different soil environments.

Effects of legacy mining on mercury concentrations in conifer needles and mushrooms in northern Palatinate, Germany

Due to integrated pollution prevention and control measures and the reduced burning of coal, air concentrations of mercury (Hg0) are currently levelling off. In the future, however, evasion from land surfaces will probably reverse this trend. Reasons are the rising temperatures and the loss of forest cover caused by calamities, droughts, storms and wildfires. Plant leaves constitute an important matrix for the accumulation of gaseous mercury and uptake and re-volatilisation by plants depends on the species, the vitality and the age and morphology of leaf organs. It has been shown that older conifer needles show higher concentrations than young needles and Hg accumulation is increasing throughout the season.In present study, we collected branches from Norway Spruce (Picea abies) in a former cinnabar mining region in Northern Palatinate, where artisanal and small-scale mining left innumerable waste dumps. While mining, smelting and processing of the ores were terminated during WWII, high total mercury concentrations remained in the top soils locally, with presumably only small fractions being plant available. In the lab, up to seven needle age classes were analysed. 1000 needle weights increased with age and as expected, also the Hg concentrations were elevated in the older needles. Needle concentrations were higher than those reported from other national biomonitoring programs confirming the regional imprint from legacy mercury. To complement our biomonitoring study, we collected edible mushrooms in former mining areas. Hg concentrations in most samples exceeded the EU maximum residue levels (MRL), while only a few broke the existing cadmium and lead limits. Tolerable weekly intake (TWI) for inorganic mercury would be surpassed with the consumption of a small portion of mushrooms. Further studies should be performed on the outgassing of Hg from mine wastes and the incorporation of Hg in the local food web, including its methylation and biomagnification.

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.

Mercury Accumulation Pathways in a Model Marine Microalgae: Sorption, Uptake, and Partition Kinetics.

The accumulation of dissolved mercury (Hg) by phytoplankton is the largest concentration step along aquatic food chains. However, the cell uptake mechanisms remain unclear. In this study, the marine haptophyteTisochrysis lutea, a model phytoplankton species, was examined for its interactions with picomolar levels of dissolved inorganic divalent Hg (iHg) and monomethyl Hg (MMHg). For both these Hg species, the study observed their successive sorption and internalization over time, yielding Hg partition coefficients as well as sorption, uptake, and release rates. These results were integrated into a time-dependent, three-compartment model for marine cellular Hg accumulation that included exposure medium, phycosphere, and internalized mercury. Assuming equilibria and pseudo-first-order kinetics between compartments, this study obtained transfer rates of Hg between compartments. The results provide insight into the phycosphere as an intermediate compartment for Hg species accumulation and quantify its role in the internalization of Hg. Ultimately, the new model and its parametrization were successfully applied to literature data showing Hg cellular accumulation in different groups of marine phytoplankton, lending confidence in its robustness and potential contributions to help model the uptake of Hg in the aquatic food web.