Dietary intake of methylmercury by 0-5 years children using the duplicate diet method in Japan.

BACKGROUND: The developing brains are sensitive to methylmercury (MeHg). However, the exposure to MeHg in baby foods and toddler meals remains unknown. This study aimed to determine MeHg intake from baby food or toddler meals, and to investigate the relationship with child hair total mercury (THg). METHODS: A total of 3 days of 24-hour dietary diet and hair samples were collected from 260 consenting children aged 0-5 years. We measured the concentrations of THg and MeHg in the diet and THg in the hair. RESULTS: The results of measuring THg were below both the method detection and method quantification limits or either of both in powdered milk (93.8%), 5-6 months (53.3%), and 7-8 months (39.5%). The median daily THg intake was 20.3 (95% confidence interval 0.72-232.5) ng/kgbw. MeHg was not detected in 213 samples with dietary THg concentrations below 1 ng/g. The MeHg concentration with THg concentrations of 1 ng/g or higher was 1.70 (0.87-6.21) ng/g, and MeHg percentage in THg was 90.0%. To estimate MeHg intake, we multiplied the THg concentration by 90.0%, resulting in an estimated MeHg intake of 18.3 (0.65-209.2) ng/kgbw/day. The THg in children's hair was 1.05 (0.31-3.96) ppm, and a weak positive correlation was observed between hair THg and dietary MeHg (r = 0.170). CONCLUSIONS: This study highlights the accurate estimation of MeHg intake in children using a duplicate method. Japanese children consume fish, the MeHg intakes exceeded the reference dose and/or provisional tolerable weekly intake in several children. Further discussion based on epidemiological data is required.

Understanding mercury accumulation in mosses of two subalpine forests in China.

The role of forest ecosystems in the global mercury (Hg) biogeochemical cycle is widely recognized; however, using litterfall as a surrogate to assess the Hg sink function of forests encounters limitations. We investigated the accumulation characteristics and influencing factors of Hg in mosses from two remote subalpine forests in southwestern China. The results indicated that there was high Hg accumulation in subalpine forest mosses, with average concentrations of 82 ± 49 ng g-1 for total mercury (THg) and 1.3 ± 0.8 ng g-1 for methylmercury (MeHg). We demonstrated that the accumulation capacity of Hg in mosses was significantly dependent on species and substrates (micro-habitats), the mosses on tree trunks exhibited significantly elevated Hg accumulation levels (THg 132 ± 56 ng g-1, MeHg 1.6 ± 0.2 ng g-1) compared to mosses in other substrates. The surface morphologies and biochemical components of leaf (phyllidia), such as cation exchange capacity (CEC), pectin, uronic acid, and metallothionein, play a crucial role in the accumulation of Hg by mosses. These findings provide valuable insights into Hg accumulation in forest mosses. Suggesting that the contribution of mosses Hg accumulation should be considered when assessing atmospheric Hg sinks of forests.

Mercury supply limits methylmercury production in paddy soils.

The neurotoxic methylmercury (MeHg) is a product of inorganic mercury (IHg) after microbial transformation. Yet it remains unclear whether microbial activity or IHg supply dominates Hg methylation in paddies, hotspots of MeHg formation. Here, we quantified the response of MeHg production to changes in microbial activity and Hg supply using 63 paddy soils under the common scenario of straw amendment, a globally prevalent agricultural practice. We demonstrate that the IHg supply is the limiting factor for Hg methylation in paddies. This is because IHg supply is generally low in soils and can largely be facilitated (by 336-747 %) by straw amendment. The generally high activities of sulfate-reducing bacteria (SRB) do not limit Hg methylation, even though SRB have been validated as the predominant microbial Hg methylators in paddies in this study. These findings caution against the mobilization of legacy Hg triggered by human activities and climate change, resulting in increased MeHg production and the subsequent flux of this potent neurotoxin to our dining tables.

Light-induced degradation of dimethylmercury in different natural waters.

Photo-induced degradation of dimethylmercury (DMHg) is considered to be an important source for the generation of methylmercury (MMHg). However, studies on DMHg photodegradation are scarce, and it is even debatable about whether DMHg can be degraded in natural waters. Herein, we found that both DMHg and MMHg could be photodegraded in three natural waters collected from the Yellow River Delta, while in pure water only DMHg photodegradation occurred under visible light irradiation. The effects of different environmental factors on DMHg photodegradation were investigated, and the underlying mechanisms were elucidated by density functional theory calculations and a series of control experiments. Our findings revealed that the DMHg degradation rate was higher in the tidal creek water compared to Yellow River, Yan Lake, and purified water. NO3-, NO2-, and DOM could promote the photodegradation with DOM and NO3- showing particularly strong positive effects. Different light sources were employed, and UV light was found to be more effective in DMHg photodegradation. Moreover, MMHg was detected during the photodegradation of DMHg, confirming that the photochemical demethylation of DMHg is a source of MMHg in sunlit water. This work may provide a novel mechanistic insight into the DMHg photodegradation in natural waters and enrich the study of the global biogeochemical cycle of Hg.

Soil Geobacteraceae are the key predictors of neurotoxic methylmercury bioaccumulation in rice.

Contamination of rice by the potent neurotoxin methylmercury (MeHg) originates from microbe-mediated Hg methylation in soils. However, the high diversity of Hg methylating microorganisms in soils hinders the prediction of MeHg formation and challenges the mitigation of MeHg bioaccumulation via regulating soil microbiomes. Here we explored the roles of various cropland microbial communities in MeHg formation in the potentials leading to MeHg accumulation in rice and reveal that Geobacteraceae are the key predictors of MeHg bioaccumulation in paddy soil systems. We characterized Hg methylating microorganisms from 67 cropland ecosystems across 3,600 latitudinal kilometres. The simulations of a rice-paddy biogeochemical model show that MeHg accumulation in rice is 1.3-1.7-fold more sensitive to changes in the relative abundance of Geobacteraceae compared to Hg input, which is recognized as the primary parameter in controlling MeHg exposure. These findings open up a window to predict MeHg formation and accumulation in human food webs, enabling more efficient mitigation of risks to human health through regulations of key soil microbiomes.

Characterizing the risk related to the exposure to methylmercury over a lifetime: A global approach using population internal exposure.

Seafood products accumulate methylmercury throughout the food chain and are the main source of methylmercury exposure. Methylmercury may trigger a number of adverse health effects, such as neurodevelopmental or nephrotoxic effects, the risk of which cannot be ruled out for the French high consumers of seafood. The characterisation of methylmercury-related risks is generally based on short-term dietary exposure without considering changes in consumption and exposure over the lifetime. Additionally, focusing on short-term dietary exposure, the fate of methylmercury (especially its accumulation) in the organism is not considered. The present study proposes a methodology basing risk characterization on estimates of body burden over a lifetime. First, trajectories of dietary exposures throughout lifetime were constructed based on the actual concentrations of total diet studies for a fictive representative French population, taking into account the social, economic and demographic parameters of individuals. Next, the fate of methylmercury in the body was estimated, based on these trajectories, using a specific physiologically-based kinetic (PBK) model that generated a representative pool of body burden trajectories. Simulated hair mercury concentrations were closed to previously reported French representative human biomonitoring data. Results showed that at certain stages of life, concentrations of methylmercury in hair were higher than the human biomonitoring guidance value set at 2.5 µg/g of hair by JECFA. This study showed the added value, in the case of substances accumulating in the body, of estimating dietary exposure over a lifetime and using exposure biomarkers estimated by a PBK model characterize the risk.

Human health risk assessment based on a total diet study of daily mercury intake in Chengdu, China.

To assess the total daily mercury intake and main exposure sources of residents, six food groups, including marine fish, freshwater fish, poultry, livestock, vegetables, and cereals, were collected from five districts of Chengdu, China. The median concentrations of total mercury (THg) and methylmercury (MeHg) were 12.8 and 6.94 µg kg-1 ww, respectively. Cereals (32.2%), vegetables (30.5%), and livestock (16.2%) contributed to a much larger extent to the total consumption for the participants in Chengdu. All food categories that contributed the most of THg (2.16 µg day-1) and MeHg 1.44 (µg day-1) to the daily intake in Chengdu were cereals and marine fish, respectively. The total Hazard Ratios values below 1 in this study indicate that there is no health risk associated with Hg ingestion from the consumption of these foods for the residents in Chengdu.

Influence of irrigation water and soil on annual mercury dynamics in Sacramento Valley rice fields.

Methylmercury (MeHg) is a human and environmental toxin produced in flooded soils. Little is known about MeHg in rice (Oryza Sativa L.) fields in Sacramento Valley, California. The objectives of this study were to quantify mercury fractions in irrigation water and within rice fields and to determine their mercury pools in surface water, soil, and grain. Soil, grain, and surface water (dissolved and particulate) MeHg and total mercury (THg) were monitored in six commercial rice fields throughout a winter fallow season and subsequent growing season. Both dissolved and particulate mercury fractions were higher in fallow season rice field water. Total suspended solids and particulate mercury concentrations were positively correlated (r = 0.99 and 0.98 for THg and MeHg, respectively), suggesting that soil MeHg was suspended in the water column and potentially exported. Dissolved THg and MeHg concentrations were positively correlated with absorbance at 254 nm (r = 0.47 and 0.58, respectively) in fallow season field water. In the growing season, fields with higher irrigation water MeHg concentrations (due to recycled water use) had elevated field-water MeHg (r = 0.86) and grain MeHg concentrations (r = 0.96). Based on a mass balance analysis, soil mercury pools were orders of magnitude larger than surface water or grain mercury pools; however, fallow season drainage and grain harvest were the primary pathways for MeHg export. Based on these findings, reducing (1) discharge when water is turbid, (2) straw inputs, and (3) use of recycled irrigation water could help reduce mercury exports in rice field drainage water.

Accumulation and risk assessment of mercury in soil as influenced by mercury mining/smelting in Tongren, Southwest China.

To investigate the influence of mercury (Hg) mining/smelting on the surrounding soil environment, ninety soil samples were collected around Hg mining/smelting areas in Tongren city, Guizhou Province, Southwest China. The total mercury (THg), methylmercury (MeHg), bioavailability and fractions of Hg in the soil and their potential risk were evaluated. The results showed that Hg mining/smelting significantly increased the soil pH and decreased the soil organic matter content (p < 0.05). The THg content in the surrounding soil was much higher than that at the control site, with almost all the samples exceeding the national standard in China (3.4 mg/kg, GB15618-2018). Similarly, the concentrations of MeHg (0.09-2.74 µg/kg) and bioavailable Hg (0.64-62.94 µg/kg) in these soil samples were also significantly higher than those in the control site. However, the MeHg/THg ratio was significantly lower in mining/smelting influenced soils (0.01-0.68%) than in control soils (0.60-3.72%). Fraction analysis revealed that residual (RES-Hg) and organic matter-bounded (OM-Hg) Hg accounted for more than 50% of the THg. Ecological risk assessment revealed that the potential ecological risk for most of the Hg mining/smelting-influenced soils (30.16 ≤ Er ≤ 2280.02) were higher than those at the control site (15.12 ≤ Er ≤ 27.1). In addition, these Hg mining/smelting-influenced soils posed acceptable noncarcinogenic risks to adults (except for two soil samples), with hazard indices (HIs) ranging from 0.04 to 1.11 and a mean HI of 0.44. However, children suffer serious noncarcinogenic risks, with HIs ranging from 0.34 to 7.43 and a mean HI of 3.10.

Non-mercury methylating microbial taxa are integral to understanding links between mercury methylation and elemental cycles in marine and freshwater sediments.

The goal of this study was to explore the role of non-mercury (Hg) methylating taxa in mercury methylation and to identify potential links between elemental cycles and Hg methylation. Statistical approaches were utilized to investigate the microbial community and biochemical functions in relation to methylmercury (MeHg) concentrations in marine and freshwater sediments. Sediments were collected from the methylation zone (top 15 cm) in four Hg-contaminated sites. Both abiotic (e.g., sulfate, sulfide, iron, salinity, total organic matter, etc.) and biotic factors (e.g., hgcA, abundances of methylating and non-methylating taxa) were quantified. Random forest and stepwise regression were performed to assess whether non-methylating taxa were significantly associated with MeHg concentration. Co-occurrence and functional network analyses were constructed to explore associations between taxa by examining microbial community structure, composition, and biochemical functions across sites. Regression analysis showed that approximately 80% of the variability in sediment MeHg concentration was predicted by total mercury concentration, the abundances of Hg methylating taxa, and the abundances of the non-Hg methylating taxa. The co-occurrence networks identified Paludibacteraceae and Syntrophorhabdaceae as keystone non Hg methylating taxa in multiple sites, indicating the potential for syntrophic interactions with Hg methylators. Strong associations were also observed between methanogens and sulfate-reducing bacteria, which were likely symbiotic associations. The functional network results suggested that non-Hg methylating taxa play important roles in sulfur respiration, nitrogen respiration, and the carbon metabolism-related functions methylotrophy, methanotrophy, and chemoheterotrophy. Interestingly, keystone functions varied by site and did not involve carbon- and sulfur-related functions only. Our findings highlight associations between methylating and non-methylating taxa and sulfur, carbon, and nitrogen cycles in sediment methylation zones, with implications for predicting and understanding the impact of climate and land/sea use changes on Hg methylation.

Rapid, easy and catalyst-free preparation of magnetic thiourea-based covalent organic frameworks at room temperature for enrichment and speciation of mercury with HPLC-ICP-MS.

The complex and cumbersome preparation of magnetic covalent organic frameworks (COFs) nanocomposites on a small scale limits their application. Herein, a rapid and easy route was employed for the preparation of magnetic thiourea-based COFs nanocomposites. COFs were coated on Fe3O4 nanoparticles at room temperature without a catalyst within approximately 30 min. This method is suitable for the large-scale preparation of magnetic adsorbent. Using the as-prepared magnetic adsorbent (Fe3O4@COF-TpTU), we developed a simple, efficient, and sensitive magnetic solid-phase extraction-high performance liquid chromatography-inductively coupled plasma-mass spectrometry (MSPE-HPLC-ICP-MS) for the enrichment and determination of mercury species, including Hg2+, methylmercury (MeHg), and ethylmercury (EtHg). The effects of the experimental parameters on the extraction efficiency, including solution pH, adsorption and desorption time, composition and volume of the elution solvent, salinity, coexisting ions, and dissolved organic matter, were comprehensively investigated. Under optimised conditions, the limits of detection in the developed method were 0.56, 0.34, and 0.47 ng L-1 with enrichment factors of 190, 195, and 180-fold for Hg2+, MeHg, and EtHg, respectively. The satisfactory spiked recoveries (97.0-103%) in real water samples and high consistency between the certified and determined values in a certified reference material demonstrate the high accuracy and reproducibility of the developed method. The as-proposed method with simple operation, high sensitivity, and excellent anti-matrix interference performance was successfully applied to the enrichment and determination of trace levels of mercury species in the natural samples with complicated matrices, such as underground water, surface water, seawater and biological samples.

A high-throughput, straightforward procedure for biomonitoring organomercury species in human hair.

Mercury is a pervasive and concerning pollutant due to its toxicity, mobility, and tendency to biomagnify in aquatic and terrestrial ecosystems. Speciation analysis is crucial to assess exposure and risks associated with mercury, as different mercury species exhibit varying properties and toxicities. This study aimed at developing a selective detection method for organic mercury species in a non-invasive biomonitoring matrix like human hair. The method is based on frontal chromatography (FC) in combination with inductively coupled plasma mass spectrometry (ICP-MS), using a low pressure, homemade, anion exchange column inserted in a standard ICP-MS introduction system, without requiring high-performance liquid chromatography (HPLC) hyphenation. In addition to the extreme simplification and cost reduction of the chromatographic equipment, the proposed protocol involves a fast, streamlined and fully integrated sample preparation process (in contrast to existing methods): the optimized procedure features a 15-min ultrasonic assisted extraction procedure and 5 min analysis time. Consequently, up to 100 samples could be analyzed daily, making the method highly productive and suitable for large-scale screening programs in public and environmental health. Moreover, the optimized procedure enables a limit of detection (LOD) of 5.5 µg/kg for a 10 mg hair microsample. All these features undeniably demonstrate a significant advancement in routine biomonitoring practices. To provide additional evidence, the method was applied to forty-nine human hair samples from individuals with varying dietary habits successfully finding a clear correlation between methylmercury levels (ranging from 0.02 to 3.2 mg/kg) in hair and fish consumption, in line with previous literature data.

Replacing manual operation with bio-automation: A high-throughput evolution strategy to construct an integrated whole-cell biosensor for the simultaneous detection of methylmercury and mercury ions without manual sample digestion.

Methylmercury is primarily responsible for most food mercury pollution cases. However, most biosensors developed for mercury pollution analysis can only detect mercury ions. Although oxidative strong-acid digestion or microwave-assisted digestion can convert methylmercury into mercury ions, it is unsuitable for on-site detection. This study designed a bio-digestion gene circuit and integrated it into a mercury ion whole-cell biosensor，creating a novel on-site methylmercury detection method. Five alkyl mercury lyases from different bacterial genomes were screened via bioinformatics analysis, of which goMerB from Gordonia otitis showed the highest catalytic biological digestion efficiency. The goMerB site-specific saturation and random mutation libraries were constructed. After two rounds of high-throughput visualization screening, the catalytic activity of the mutant increased 2.5-fold. The distance between the three crucial amino acid sites and methylmercury changed in the mutant, which likely contributed to the enhanced catalytic efficiency. The optimized whole-cell biosensor showed a linear dynamic concentration range of 100 nM to 100 µM (R2 =0.991), satisfactory specificity, and interference resistance. The detection limit of the goMerBt6-MerR-RFP biosensor was 0.015 µM, while the limit of quantitation was 0.049 µM. This study demonstrated the application of synthetic biology for food safety detection and highlighted the future potential of "Lab in a Cell" for hazard analysis.

Increased Contribution of Circumpolar Deep Water Upwelling to Methylmercury in the Upper Ocean around Antarctica: Evidence from Mercury Isotopes in the Ornithogenic Sediments.

Upwelling plays a pivotal role in supplying methylmercury (MeHg) to the upper oceans, contributing to the bioaccumulation of MeHg in the marine food web. However, the influence of the upwelling of Circumpolar Deep Water (CDW), the most voluminous water mass in the Southern Ocean, on the MeHg cycle in the surrounding oceans and marine biota of Antarctica remains unclear. Here, we study the mercury (Hg) isotopes in an ornithogenic sedimentary profile strongly influenced by penguin activity on Ross Island, Antarctica. Results indicate that penguin guano is the primary source of Hg in the sediments, and the mass-independent isotope fractionation of Hg (represented by Δ199Hg) can provide insights on the source of marine MeHg accumulated by penguin. The Δ199Hg in the sediments shows a significant decrease at ∼1550 CE, which is primarily attributed to the enhanced upwelling of CDW that brought more MeHg with lower Δ199Hg from the deeper seawater to the upper ocean. We estimate that the contribution of MeHg from the deeper seawater may reach more than 38% in order to explain the decline in Δ199Hg at ∼1550 CE. Moreover, we found that the intensified upwelling may have increased the MeHg exposure for marine organisms, highlighting the importance of CDW upwelling on the MeHg cycle in Antarctic coastal ecosystems.

Cross-shelf processes of terrigenous organic matter drive mercury speciation on the east siberian shelf in the Arctic Ocean.

The cross-shelf distributions of total mercury (THg), methylmercury (MeHg) and organic and inorganic matter, as well as the presence of the hgcA gene were investigated on the East Siberian Shelf (ESS) to understand the processes underlying the speciation of sedimentary Hg. Samples were collected from 12 stations grouped into four zones based on water depth: inner shelf (5 stations), mid-shelf (3 stations), outer shelf (2 stations), and slope (2 stations). The THg concentration in the surface sediment increased from the inner shelf (0.25 ± 0.023 nmol g-1) toward the slope (0.52 nmol g-1), and, when normalized to total organic carbon content, the THg showed a positive correlation with the clay-to-sand ratio (r2 = 0.48, p = 0.012) and degree of chemical weathering (r2 = 0.79, p = 0.0001). The highest MeHg concentrations (3.0 ± 1.8 pmol g-1), as well as peaks in the S/C ratio (0.012 ± 0.002) of sediment-leached organic matter, were found on the mid-shelf, suggesting that the activities of sulfate reducers control the net Hg(II) methylation rates in the sediment. This was supported by results from a principal component analysis (PCA) performed with Hg species concentrations and sediment-leached organic matter compositions. The site-specific variation in MeHg showed the highest similarity with that of CHONS compounds in the PCA, where Deltaproteobacteria were projected to be putative Hg(II) methylators in the gene analysis. In summary, the hydrodynamic sorting of lithogenic particles appears to govern the cross-shelf distribution of THg, and in situ methylation is considered a major source of MeHg in the ESS sediment.

Distribution and Homogenization of Multiple Mercury Species Inputs to Freshwater Wetland Mesocosms.

Mercury (Hg)-impaired aquatic ecosystems often receive multiple inputs of different Hg species with varying potentials for transformation and bioaccumulation. Over time, these distinct input pools of Hg homogenize in their relative distributions and bioaccumulation potentials as a result of biogeochemical processes and other aging processes within the ecosystem. This study sought to evaluate the relative time scale for homogenization of multiple Hg inputs to wetlands, information that is relevant for ecosystem management strategies that consider Hg source apportionment. We performed experiments in simulated freshwater wetland mesocosms that were dosed with four isotopically labeled mercury forms: two dissolved forms (Hg2+ and Hg-humic acid) and two particulate forms (nano-HgS and Hg adsorbed to FeS). Over the course of one year, we monitored the four Hg isotope endmembers for their relative distribution between surface water, sediment, and fish in the mesocosms, partitioning between soluble and particulate forms, and conversion to methylated mercury (MeHg). We also evaluated the reactivity and mobility of Hg through sequential selective extractions of sediment and the uptake flux of aqueous Hg in a diffusive gradient in thin-film (DGT) passive samplers. We observed that the four isotope spikes were relatively similar in surface water concentration (ca. 3000 ng/L) immediately after spike addition. At 1-3 months after dosing, Hg concentrations were 1-50 ng/L and were greater for the initially dissolved isotope endmembers than the initially particulate endmembers. In contrast, the Hg isotope endmembers in surface sediments were similar in relative concentration within 2 months after spike addition. However, the uptake fluxes of Hg in DGT samplers, deployed in both the water column and surface sediment, were generally greater for initially dissolved Hg endmembers and lower for initially particulate endmembers. At one year postdosing, the DGT-uptake fluxes were converging toward similar values between the Hg isotope endmembers. However, the relative distribution of isotope endmembers was still significantly different in both the water column and sediment (p < 0.01 according to one-way ANOVA analysis). In contrast, selective sequential extractions resulted in a homogeneous distribution, with >90% of each endmember extracted in the KOH fraction, suggesting that Hg species were associated with sediment organic matter. For MeHg concentrations in surface sediment and fish, the relative contributions from each endmember were significantly different at all sampling time points. Altogether, these results provide insights into the time scales of distribution for different Hg species that enter a wetland ecosystem. While these inputs attain homogeneity in concentration in primary storage compartments (i.e., sediments) within weeks after addition, these input pools remain differentiated for more than one year in terms of reactivity for passive samplers, MeHg concentration, and bioaccumulation.

Single-cell ICP-MS for evaluating the Se-protective effect against MeHg+-induced neurotoxicity in human neuroblastoma cell line (SH-SY5Y).

The protective effect of selenium (Se) against Hg-induced neurotoxicity has been widely investigated; however, the mechanisms behind this interaction have not been fully elucidated yet. In the current work, the role of Se against MeHg+-induced cytotoxicity in the human neuroblastoma cell line (SH-SY5Y) is reported for the first time by tracking Hg uptake and accumulation at the single-cell level by inductively coupled plasma-mass spectrometry in single-cell mode (SC-ICP-MS). The influence of different Se species (SeMet, SeMeSeCys, citrate-SeNPs, and chitosan-SeNPs) on MeHg+ cytotoxicity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. SeMet and SeMeSeCys exhibited protective effects against MeHg+-induced cell death, particularly at high MeHg+ concentrations (LC50). In addition, chitosan-SeNPs showed greater protection compared to citrate-SeNPs when co-exposed with MeHg+. Interestingly, SC-ICP-MS unveiled the heterogeneous distribution of Hg uptake by SH-SY5Y cells. Co-exposure of SeMet and SeMeSeCys with MeHg+ led to a reduction of the amount of Hg accumulated per individual cell, which decreased the maximum level of Hg per cell by half (from 60 fg Hg cell-1 to 30 fg Hg cell-1) when SeMet was present, along with a decrease in the percentage of cells that accumulated the highest quantity of MeHg+. All these data corroborate the protective role of Se against Hg toxicity at the cellular level.

High resolution visualisation of tiemannite microparticles, essential in the detoxification process of mercury in marine mammals.

The North Sea is an ecologically rich habitat for marine wildlife which has also been impacted by industrial developments and anthropogenic emissions of contaminants such as mercury. Marine mammals are particularly susceptible to mercury exposure, due to their trophic position, long lifespan, and dependence on (increasingly contaminated) aquatic prey species. To mitigate impact, marine mammals can detoxify methylmercury by binding it to selenium-containing biomolecules, creating insoluble mercury selenide granules. Here, liver, kidney, muscle, and brain samples from an adult male bottlenose dolphin (Tursiops truncatus) with known elevated mercury concentrations were analysed through scanning electron microscopy (SEM). Tiemannite (HgSe) deposits were identified in all organs, ranging from 400 nm to 5 µm in diameter, with particle size being organ-dependent. Although reported in other studies, this is the first time that the three-dimensional nature of tiemannite is captured in marine mammal tissue.

Selenium- and chitosan-modified biochars reduce methylmercury contents in rice seeds with recruiting Bacillus to inhibit methylmercury production.

Biochar could reshape microbial communities, thereby altering methylmercury (MeHg) concentrations in rice rhizosphere and seeds. However, it remains unclear whether and how biochar amendment perturbs microbe-mediated MeHg production in mercury (Hg) contaminated paddy soil. Here, we used pinecone-derived biochar and its six modified biochars to reveal the disturbance. Results showed that selenium- and chitosan-modified biochar significantly reduced MeHg concentrations in the rhizosphere by 85.83% and 63.90%, thereby decreasing MeHg contents in seeds by 86.37% and 75.50%. The two modified bicohars increased the abundance of putative Hg-resistant microorganisms Bacillus, the dominant microbe in rhizosphere. These reductions about MeHg could be facilitated by biochar sensitive microbes such as Oxalobacteraceae and Subgroup_7. Pinecone-derived biochar increased MeHg concentration in rhizosphere but unimpacted MeHg content in seeds was observed. This biochar decreased the abundance in Bacillus but enhanced in putative Hg methylator Desulfovibrio. The increasing MeHg concentration in rhizosphere could be improved by biochar sensitive microbes such as Saccharimonadales and Clostridia. Network analysis showed that Saccharimonadales and Clostridia were the most prominent keystone taxa in rhizosphere, and the three biochars manipulated abundances of the microbes related to MeHg production in rhizosphere by those biochar sensitive microbes. Therefore, selenium- and chitosan-modified biochar could reduce soil MeHg production by these microorganisms, and is helpful in controlling MeHg contamination in rice.