Methylmercury (MeHg) is a potent neurotoxin and can lead to neurodegeneration in animals and humans. Fecal microbiota transplantation has been found to regulate the neurotoxicity of MeHg in rats. This study investigated the therapeutic potential of orally-given commercially-available probiotics (primarily Bifidobacterium and Lactobacillus acidophilus) against MeHg-poisoning in rats. It was found that probiotics intervention promoted the demethylation of MeHg in the liver and intestines, accompanied by upregulation of demethylating bacteria such as Desulfovibrionaceae and Geobacteraceae. It also reshaped the gut microbiota, significantly increasing beneficial short-chain fatty acids(SCFA)-producing bacteria like Ruminococcaceae and Lachnospiraceae. SCFA, amino acids and bile acids were found increased in feces. The expression of pro-inflammatory cytokines TNF-α and IL-6, and up-regulated IL-10 in the gut, serum and brain was found reduced, showing the decreased inflammation. Besides, the capability of spatial learning, memory, and motor coordination of MeHg-poisoned rats was improved as showed through Morris water maze test. Histologically, H&E staining revealed neatly arranged neurons with reduced nuclear condensation, while Nissl staining showed increased Nissl bodies and restored neuronal activity. In all, this study provides a simple and potentially translational strategy for MeHg-poisoning and sheds lights for the treatment of neurodegenerative diseases.

Vegetation in mountains offers specific habitats for endemic wildlife while serving as a sink for long-range transported pollutants such as mercury (Hg). Over half of the atmospheric Hg is absorbed by vegetation, making it a major pathway for Hg transfer into terrestrial ecosystems. As one of the world's 22 biodiversity hotspots and situated between the major Hg emitters in Asia, the Himalayas host numerous endemic and endangered species, including large herbivores that play vital ecological roles. We investigated total Hg (THg) in vegetation across five vegetation zones along the longest elevational gradient (1800 ∼ 5400 m) in the Central Himalayas. Mean vegetation THg was 20.2 ± 10.7 ng g-1 (6.0 ∼ 62.9 ng g-1, 60 sampling sites). Overall, vegetation THg decreased significantly with elevation (y = (-0.004 ± 0.001) x + (33.5 ± 4.8), R2 = 0.13, p = 0.005), with soil THg explaining the variation most. We found 6 herbivore species inhabiting evergreen broad-leaved forest and 10 species inhabiting subalpine coniferous forest, could be facing potential Hg exposure risk in those vegetation zones. When we combine this with captive daily intake estimation of vegetation, we identified endangered high-altitude species, such as Himalayan tahr (Hemitragus jemlahicus) and kiang (Equus kiang), which could be more at Hg exposure risk under climate change due to potential habitat shrinkage. Our findings highlight that, in addition to predators, large herbivores may also face elevated Hg exposure risk due to their substantial consumption of vegetation, which is important when evaluating the Minamata Convention's effectiveness.

BackgroundMercury, as a global heavy metal pollutant, poses a serious threat to human health. The toxicity of mercury depends on its chemical form. Distinguishing the forms of mercury in the environment is of great significance for mercury management and reducing human mercury exposure risks. ObjectiveTo establish a non-targeted metallomics method based on synchrotron radiation X-ray fluorescence (SRXRF) spectroscopy combined with machine learning to screen inorganic mercury (IHg) or methylmercury (MeHg) exposed rice plants. MethodsRice seeds were exposed to ultra-pure water (control group), 0.1 mg·L−1 IHg (IHg group) or MeHg (MeHg group) solutions, respectively. After germination, the seedlings were cultured for 21 d, and rice leaves were collected, dried, weighed, and pressed. The content of metallome in rice leaves was determined by SRXRF. Machine learning models including soft independent modeling cluster analysis (SIMCA), partial least squares discriminant analysis (PLS-DA), and logistic regression (LR) were used to classify the SRXRF full spectra of different groups and find the best model to distinguish rice exposed to IHg or MeHg. Besides, characteristic elements were selected as input parameters to optimize the model by improving computing speed and reducing model calculation. ResultsThe SRXRF spectral intensities of the control group, IHg group, and MeHg group were different, indicating that exposure to IHg and MeHg can interfere the homeostasis of metallome in rice leaves. The results of principal component analysis (PCA) of SRXRF spectra showed that the control group could be well distinguished from the mercury exposed groups, but the IHg group and the MeHg group were mostly overlapped. The accuracy rates of the three models (PLS-DA, SIMCA, and LR) were higher than 98% for the training set, higher than 95% for the validation set, and higher than 94% for the cross-validation set. Besides, the accuracy of the LR model was higher than that of the PLS-DA model and the SIMCA model. Furthermore, the accuracy was 92.05% when using characteristic elements K, Ca, Mn, Fe, and Zn selected by LR to distinguish the IHg group and the MeHg group. Compared with the full spectra model, although the prediction accuracy of the characteristic spectral model decreased, the input parameters of the model decreased by 99.51%, and precision, recall, and F1 score were above 84.48%, indicating that the model could distinguish rice exposed to different mercury forms. ConclusionNon-targeted metallomics method based on SRXRF and machine learning can be applied for high-throughput screening of rice exposed to different forms of mercury and thus decrease the risks of people being exposed to mercury.

Exposure to pollutants is a potentially crucial but overlooked driver of population declines in shorebirds along the East Asian-Australasian Flyway. We combined knowledge of moult strategy and life history with a standardised sampling protocol to assess mercury (Hg) contamination in 984 individuals across 33 migratory shorebird species on an intercontinental scale. Over one-third of the samples exceeded toxicity benchmarks. Feather Hg was best explained by moulting region, while habitat preference (coastal obligate vs. non-coastal obligate), the proportion of invertebrates in the diet and foraging stratum (foraging mostly on the surface vs. at depth) also contributed, but were less pronounced. Feather Hg was substantially higher in South China (Mai Po and Leizhou), Australia and the Yellow Sea than in temperate and Arctic breeding ranges. Non-coastal obligate species (Tringa genus) frequently encountered in freshwater habitats were at the highest risk. It is important to continue and expand biomonitoring research to assess how other pollutants might impact shorebirds. Over one-third of the sampled shorebirds along the East Asian-Australasian Flyway are facing Hg risk. Tringa genus in South China was at the highest risk. Feather Hg was best explained by feathers' moulting region, while habitat preference, diet, and foraging stratum were less important.

Environmental pollution is widespread and poses significant risks to both human populations and diverse animal species. As part of conservation initiatives, many endangered animals are housed in zoos and breeding centers close to human activities, potentially exposing them to health threats arising from envrionmental contamination. By analyzing non-invasive fecal samples from 13 Chinese zoos, we assessed total mercury (THg) and methylmercury (MeHg) exposure in two non-human primate species: the endangered species golden snub-nosed monkey (Rhinopithecus roxellana), and the most widely distributed rhesus macaque (Macaca mulatta). The concentration of THg in golden snub-nosed monkeys (median: 71.8ng/g, range: 11.2 to 200.0ng/g, n = 71) was significantly higher than that in rhesus macaques (median: 17.5ng/g, range: 7.4 to 409.0ng/g, n = 98). No significant differences were observed in both MeHg and MeHg% between these two species. Age and sex did not predict fecal mercury. Among adults, Approximately 85% of sampled individuals exhibited hazard quotient (HQ) values exceeding 1, indicating mercury poses a health risk to captive primate populations. The average HQ for golden snub-nosed monkeys was 2.98 ± 1.68 (range: 0.46 – 8.21, n = 43), while for rhesus macaques was 1.84 ± 1.64 (range: 0.61 – 12.49, n = 71). Our finding suggest that conservation efforts for captive primates may be compromised by Hg pollution, particularly in golden snub-nosed monkeys. Further investigation and ongoing biomonitoring from an ecotoxicological perspective, are crucial to ensuring the health of captive primate populations.

AbstractThe 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.

As a global pollutant, mercury (Hg), especially methylmercury (MeHg) has strong neurotoxicity and poses a great threat to human health. Accumulating evidence suggests that the gut microbiota plays an important role in mediating the neurotoxicity of Hg. For example, Hg in the gut can undergo biotransformation by gut microbiota, including the demethylation of MeHg and the methylation of elemental mercury (Hg0) and inorganic mercury(iHg) to MeHg. On the other hand, MeHg can disrupt the interaction between the gut and the brain by changing the community structure and function of the gut microbiota and the metabolites related to neurological activities. Therefore, understanding the interaction between gut microbiota in the mediating of the neurotoxicity of different mercury species will help further understand the mechanism of the neurotoxicity of Hg. In this chapter, a systematic summary of the mediating effects of gut microbiota on the neurotoxicity of Hg, especially MeHg was presented. The future aspect on the study of gut microbiota against the neurotoxicity of Hg was also put forward.

Abstract Background Methylmercury (MeHg) can bring devastating neurotoxicity to animals and human beings. Gut microbiota has been found to demethylate MeHg while MeHg exposure was found to destroy the diversity and abundance of gut microbiota. Besides, some neurotransmitters such as GABA, glutamate and other metabolites were altered due to MeHg exposure. Fecal microbiota transplantation (FMT) has been successfully applied to treat a series of diseases like Tourette syndrome, irritable bowel syndrome, necrotizing enterocolitis and to treat ulcerative coliti. The objective of this study was to investigate the effects of FMT in treating MeHg-poisoned rats. Results: It was found that FMT for 14 days promoted body weight gain, enhanced demethylation of MeHg and increased fecal excretion of Hg in MeHg-poisoned rats. Furthermore, the gut microbial bacteria associated with demethylation, such as sulfate-reducing bacteria were restored and some metabolites related to neuroactivity through gut-brain axis were increased after FMT, there is also repair of brain derived neurotrophic factor(BDNF)-related factor levels in the intestine, brain and serum. Conclusions: In all, it was showed that FMT can be a effective way in treating MeHg-poisoned rats through the reconstruction of gut microbiota, especially the bacteria that are associated with the demethylation of MeHg. Furthermore, the modulation of metabolites that are related to gut-brain axis after FMT also contributed to the treating of MeHg-poisoning. This study provides a novel way to treat MeHg-poisoning, which may contribute to the health promotion of mercury exposed population and shed lights on the treatment of other neurological diseases like Parkinson’s disease.

Due to toxicities, capacities for long-range transportation, bioaccumulation, and biomagnification, mercury (Hg) presents a unique concern to wildlife in remote ecosystems, including “the roof of the world”. Large carnivorous predators are thought to be exposed to elevated Hg due to their high trophic positions, but the direct assessment for Hg contamination is a challenge. Given the poorly understood Hg exposure in these carnivores, establishing a reliable and straightforward assessment would be essential to identify targeted species at Hg exposure risk for effective conservation, particularly in fragile biodiversity hotspots. Small mammals are abundant and serve as prey for large top predators. Combined with local observations, we provided an assessment to estimate the daily Hg exposure via consumption of small mammals for large carnivorous mammals recorded in the Hengduan Mountains, a world biodiversity hotspot, China. Within an altitude span from 2043 to 4251 m a.s.l., the average topsoil total mercury concentration (hereafter [THg]) was 44.65 ± 25.80 μg/kg (mean ± sd; 10.54 – 135.15 μg/kg, n = 41), while the hair [THg] in small mammals was 104.66 ± 91.96 μg/kg (mean ± sd; 7.73 to 385.70 μg/kg, n = 13). Furthermore, the daily intake of Hg was calculated among the 22 investigated/historical-recorded carnivore mammals belonging to 5 families. We found a large variance in daily intake of Hg via small mammals: Felidae (median: 205.93 μg/day) > Ursidae (135.02 μg/day) > Canidae (92.92 μg/day) > Viverridae (19.88 μg/day) > Mustelidae (7.18 μg/day). Specifically, Tiger Panthera tigris was found with the highest Hg daily intake (1701.39 μg/day) via consuming small mammals, while species belonging to Mustelidae generally have low Hg daily intake (<3 μg/day). This study provides a feasible approach to identifying species at environmental Hg risk in this fragile remote high-elevation region. The limitations and future improvements were discussed.

Water safety concerning Barium (Ba) has become a public issue worldwide. As the "Asian water tower", Tibetan Plateau is the birthplace of many rivers. However, the distribution, source, and output flux of Ba are largely unknown. In this study, surface water samples were collected from different catchments in the Sanjiangyuan Region (SJY) and the Qilian Mountain Region (QLM) in Tibetan Plateau. The concentration of Ba was determined by inductively coupled plasma optical emission spectroscopy, the source of Ba was discussed by a Gibbs diagram, and the output flux of Ba was estimated using the observation data from different hydrological stations. The results showed that the Ba concentrations were less than 160 µg/L, which is much lower than the guideline value of 700 µg/L for surface waters. The main sources of Ba were rock weathering and evaporation concentration. The total Ba output flux from SJY and QLM to downstream waters was 1,240 t/yr, which accounts for about 0.01% of the global freshwater Ba output flux to the ocean. The Ba production rate in Tibetan Plateau was comparable with that in the Arctic rivers. Under the scenario of global warming, water safety issues concerning Ba will be more serious since the output flux of Ba to downstream waters will be increased by intensified rock weathering, evaporation concentration, glacial retreat, and permafrost thawing. This study reveals the Ba flux and production rate in Tibetan Plateau, which will provide important information for evaluating the environmental impact of global warming on public health.

In order to comprehend the transfer of inorganic mercury (IHg) and methylmercury (MeHg) within food chains in terrestrial pine forests, we collected samples of Great Tit nestlings, common invertebrates, plants, and soil in a subtropical pine forest and used Bayesian isotope mixing model analysis, Hg daily intake, and stable Hg isotopes to elucidate the flow of MeHg and IHg in these food chains. Results indicate that caterpillars and cockroaches are the predominant prey items for nestlings, accounting for a combined contribution of 81.5%. Furthermore, caterpillars, cockroaches, and spiders were found to contribute the most (∼80%) of both IHg and MeHg that dietary accumulated in nestlings. The provisoned invertebrates tend to supply more IHg and diluting the proportion of MeHg as total Hg (MeHg%). Notably, nestling feathers displayed the highest Δ199Hg values but a relatively lower MeHg%, suggesting an imbalanced incorporation of Hg from maternal transfer and dietary accumulation during the nestling stage. This study highlights the efficacy of nestlings as indicators for identifying Hg sources and transfers in avian species and food chains. However, caution must be exercised when using Hg isotope compositions in growing feathers, and the contribution of maternally transferred Hg should not be ignored.

Mercury (Hg) is a persistent and toxic metal while mercury selenide (HgSe) is generally considered as the environmental sink of Hg in its biogeochemical cycle. Recent studies found nano-sized HgSe (nano-HgSe) could be transformed by certain bacteria. This raises safety concerns about the application of selenium (Se) to curb Hg contamination in farmlands. Therefore, hydroponic experiments were performed in which rice plants were cultured with different concentrations of nano-HgSe and micro-sized HgSe (micro-HgSe) to explore their bioavailability and toxicity. It was found that both nano-HgSe and micro-HgSe did not affect the germination of rice seeds but affected the growth of rice seedlings. However, nano-HgSe could be more readily absorbed by roots and transferred to the aboveground parts compared to micro-HgSe. The highest Hg and Se levels were found to be 5255.67 ± 2496.14 μg/g and 1743.75 ± 61.87 μg/g, respectively in roots when exposed to 5000 mg/L nano-HgSe. Besides, small portion (1.2%) of methylmercury (MeHg) to total Hg was found accumulated in rice stem when exposed to 100 mg/L nano-HgSe, suggesting that nano-HgSe could be decomposed. Furthermore, nano-HgSe exposure brought oxidative damage to rice with decreased chlorophyll content and GSH-Px activity. In all, nano-HgSe was found to be more absorbable, transportable and methylated in rice plant compared to micro-HgSe. This suggests that although Se application in Hg contaminated farmland is an effective way to reduce the bioavailability of Hg, the risk of the possible remobilization of HgSe should not be neglected. Besides, the finding that nano-HgSe can act as an environmental source of Hg for plants deepens the understanding of biogeochemical cycle of Hg. More works are required to study the factors affecting the formation of nano-HgSe in the environment and the mechanisms of Hg methylation in rice plants after exposure to nano-HgSe.

Effective biomarkers are necessary to better understand the human mercury (Hg) exposure levels. However, mismatched biomarker sampling method causes extra uncertainty in assessing the risk of Hg exposure. To compare the differences between hair and fingernail, and further understand the excretion rates of methylmercury (MeHg) and inorganic mercury (IHg) via hair and fingernails, the total mercury (THg), MeHg, and IHg concentrations in paired hair and fingernail samples were investigated through paired samples collected from two typical mining areas, Wanshan mercury mine area (WMMA) and Hezhang zinc smelting area (HZSA). The positive correlation in THg, MeHg, and IHg concentrations (p <0.01) between hair and fingernail samples indicated that those two biomarkers can be corrected in application of assessing human Hg exposure. Compared to fingernails, the hair was suggested to be a more sensitive biomarker as the concentration of THg, MeHg and IHg were 2 ∼ 4 times higher than those in fingernails. Furthermore, the amounts of THg, MeHg, and IHg excreted via hair were 70 ∼ 226 times higher than that excreted via fingernails, and the hair plays a more important role than fingernails in the excretion of Hg from human bodies. Present study therefore provides some new insights to better understand the fate of human assimilated Hg.

The Karst Plateau is characterized by elevated heavy metals (HM), the farmland soils in the Karst Plateau area is especially vulnerable to HM pollution. To cope with soil HM pollution and conduct precaution in Karst Plateau, the key bottleneck is to understand the pollution levels, sources, and priority‐control of HM. Hence, geochemical baselines of HM in farmland soils were established to accurately evaluate the pollution characteristics. Pollution sources were identified with multivariate statistics, geostatistical methods, and receptor models. Priority‐control of HM were distinguished via health assessments with a Monte Carlo simulation. A remarkable accumulation of Pb, Sb, Zn, As, and Cd was observed. Hotspots of As, Cd, Pb, Sb, and Zn clustered in the southwestern region of Hezhang. Pb–Zn related activities, cement product activities, coal mining, and coal combustion were dominant sources. Both noncarcinogenic risk and carcinogenic risk followed the order: children>adult females>adult males. As, Cd, and Pb were found to be priority contaminants in farmland soils in Hezhang.

The constituents and content of dissolved organic matter (DOM) in the Qilian Mountain watershed were characterized with a spectroscopic technique, especially 3-DEEM fluorescence assisted by parallel factor (PARAFAC) analysis. The level of DOM in the surrounding area of Qinghai lake (thereafter the lake in this article specifically refers to Qinghai Lake)was highest at 9.45 mg C·L−1 and about 3 times less (3.09 mg C·L−1) in a cropland aquatic regime (the lowest value). In general, DOM was freshly autochthonously generated by plankton and plant debris, microorganisms and diagenetic effects in the aquatic environment (FI > 1.8). Component 1 (humic acid-like) and 3 (fulvic acid-like) determined the humification degree of chromophoric dissolved organic matter (CDOM). The spatial variation of sulfate and nitrate in the surrounding water regime of the lake revealed that organic molecules were mainly influenced by bacterial mediation. Mineral disintegration was an important and necessary process for fluorescent fraction formation in the cropland water regime. Exceptionally, organic moiety in the unused land area was affected by anespecially aridclimate in addition to microbial metabolic experience. Salinity became the critical factor determining the distribution of DOM, and the total normalized fluorescent intensity and CDOM level were lower in low-salinity circumstances (0.2–0.5 g·L−1) with 32.06 QSU and 1.38 m−1 in the grassland area, and higher salinity (0.6~0.8 g·L−1) resulted in abnormally high fluorescence of 150.62 QSU and absorption of 7.83 m−1 in the cropland water regime. Climatic conditions and microbial reactivity controlled by salinity were found to induce the above results. Our findings demonstrated that autochthonous inputs regulated DOM dynamics in the Qilian Mountains watershed of high altitude.

AbstractMercury (Hg) is an important element in seafloor cold seeps that might govern methane emission. However, so far, the knowledge of biogeochemical Hg cycle in it remains poorly understood. In this study, Hg geochemical characteristics and microorganisms involved in Hg biogeochemical cycling were examined in three (active, inactive seep vs reference) different types of sediments sampled from the Haima cold seep in the South China Sea. Sediments in the active seep area were significantly enriched in mercury and methylmercury (MeHg) compared to the reference. Accordingly, abundant genes related to Hg methylation (hgcAB), demethylation (merB) and reduction (merA) were detected in the active seep sediments, phylogenetically associated with various bacterial and archaeal linages (e.g.Desulfobacterota, GammaproteobacteriaandHalobacteriota). Hg odd-mass number isotopes (Δ199Hg and Δ201Hg) pointed to their source from the upper ocean and the occurrence of abiotic dark oxidation. The δ202Hg values indicate Hg mass fractionation, migration and transformation in the active seep sediments. These geochemical and microbial data highlight active Hg biogeochemical cycles in seafloor cold seeps, functioning as important Hg-sinks and MeHg sources in the deep ocean.

In agricultural lands with selenium (Se) deficiency, bioavailability of Se in plants is low. Residents from large-scale agricultural production areas with Se deficiency often suffer from endemic diseases because of consumption of agricultural products lacking in Se. One such area in Northeast China where Keshan disease and Kashin–Beck disease originated, was selected for investigating the geochemistry, influencing factors, and risks of Se in the agroecosystems. Analysis of field samples indicates that the Se deficiency in soil is significantly reduced compared with that of several decades ago, and 62.6% of soils are now Se-sufficient in the southern Songnen Plain. However, Se in crop products remains low due to weak soil-plant transfer, resulting in high risks of Se deficiency related diseases in the rural population of this area. Structural equation modeling, principal component analysis, and other statistical analyses revealed that climate conditions and soil physical and chemical properties are the key factors influencing the spatial distribution of soil Se. Extensive use of agricultural fertilizers may indirectly inhibit the migration of Se from soil to plants. Ensuring sufficient Se contents in agricultural products to meet the minimum daily requirements of residents remains a challenge in Se-deficient areas, especially in the increased agricultural production environment in China.

Mercury (Hg), as a global pollutant, its contamination has been documented in environmental compartments of the Himalayan region. However, little research exists regarding to Hg accumulation in terrestrial wildlife, as well as its driving factors. In this study, surface soil and small mammals were collected in the Lebu Valley, East Himalayas of China, in order to measure the uptake of the long-distance transported Hg along an elevational gradient approximately from 2300 to 5000 m a.s.l. The soil Hg concentrations were measured and predicted mostly by vegetation type as well as soil organic matter, while the Hg in hair of small mammals (Muridae and Cricetidae) showed deeply influenced by soil Hg. Notably, combined with the field survey data, soil and hair Hg were both enhanced in low and mid-elevations, which overlapped the distribution ranges of a majority of mammals. Overall, this indicates that Hg contamination in low-and mid-elevations poses a potential threat to the top predators that consuming small mammals directly or indirectly. Furthermore, our data advances the understanding of Hg dynamics in remote, high mountain ecosystems and provides baseline data for biomonitoring for reduction of Hg emission globally.