BACKGROUND: Mercury (Hg), especially methylmercury (MeHg) as a most toxic format of Hg in the environment, has been paid widely concern due to its high bioaccumulative capability and great risk to humans. Great efforts have been made to develop ethylation-purge and trap-gas chromatography-inductively coupled plasma mass spectrometry system for MeHg analysis and Hg biogeochemical cycling investigation. However, the generally manual operation limits the analytical efficiency, and the lack of applications in the real environmental samples restricts the future study. There is a great need for a rapid and accurate method to determine MeHg and Hg methylation/demethylation processes in environmental samples.
RESULTS: Herein, an automatic ethylation-purge and trap-GC-ICP-MS system based on isotope dilution method for MeHg analysis was developed. The results showed that the limit of detection of the developed method was 0.01 ng L-1, the MeHg can be analyzed within 6 min with a relative standard deviation of 4.3 %. The accuracy of this proposed method was verified by the satisfying recoveries of certified reference materials (99.0 ± 0.35 % in ECM-CC580, sediment; 98.0 ± 0.67 % in DORM-4, Fish protein). In addition, comparable concentrations of MeHg in natural water were measured using both of the developed and classical distillation methods. Subsequently, the developed method was adapted for measuring concentrations of MeHg in the water, sediment, and fish muscle collected from the coastal and freshwater systems. Finally, the photic demethylation and biotic methylation/demethylation rate constants in natural surface water and sediment were determined using isotope dilution/tracing methods by automatic ethylation-purge and trap-GC-ICP-MS.
UNASSIGNED: The developed automatic ethylation-purge and trap-GC-ICP-MS system is promising for accurate and convenient MeHg analysis and Hg biogeochemical cycling investigation in real environmental samples with isotope dilution and tracing methods.

The Cree Peoples of the Eeyou Istchee territory (northern Québec, Canada) rely on fish as a part of their traditional and contemporary diet. Fish is a culturally significant food and a source of nutrients, but it is also the main pathway of methylmercury (MeHg) exposure for humans. Significant hydroelectric developments in this territory are responsible for increasing the concentrations of MeHg found in fish and thus increase the human exposure to this neurotoxic compound. As this is an ongoing issue, our study assessed the current MeHg fish-tissue concentrations in Eeyou Istchee and the spatial distribution of MeHg hot spots using Geographic Information Systems (GIS) to compare our results to those found in previous studies from the same region. We also performed a probabilistic hazard assessment of the exposure to MeHg from fish consumption. The GIS models indicated significant clustering of increased MeHg fish-tissue concentrations around hydroelectric reservoirs and showed higher MeHg fish-tissue concentrations around newer hydroelectric reservoirs, but a decrease in older reservoirs. Similar to past studies, we found that fish consumption continues to pose an MeHg exposure hazard for men who consume large piscivore species (i.e., lake trout, walleye, and pike), while for women, lake trout and walleye consumption constitute a hazard (any size), and pike should be consumed with caution. The hazard of exposure was mainly associated with intake rate in all cases. Lastly, we recommend monitoring MeHg fish-tissue concentrations in this region, as the MeHg tissue concentrations remain elevated, and updated consumption guidelines where and when necessitated.

Prior research into the association between prenatal mercury (Hg) exposure and the secondary sex ratio has yielded inconclusive and conflicting results. Notably, no study has used cord blood Hg measurement in this context. Also, the differences in Hg species and the potential modifying role of selenium (Se) on this association remain unexplored. Using data from the Japan Environment and Children\'s Study, we analyzed mother-child pairs with available data for concentrations of total mercury (THg) and Se in maternal blood during late pregnancy, and THg, inorganic mercury (IHg), methylmercury (MeHg), and Se in cord blood. Logistic regression models were employed to examine the association between Hg and Se biomarkers and the secondary sex ratio. Out of the total sample of 3698 children, 1877 (50.8 %) were male, corresponding to an overall secondary sex ratio of 1.03. After adjusting for maternal age and parity, no significant associations were observed between THg concentrations of maternal blood and the secondary sex ratio. Nevertheless, we identified that two-fold increases in THg, IHg, and MeHg concentrations in cord blood were positively associated with increased odds of having a male child, yielding adjusted odds ratios of 1.13 (95 %CI: 1.04, 1.22), 1.12 (1.03, 1.21), and 1.12 (1.03, 1.22), respectively. When stratified by the median Se concentrations, no apparent differences were detected in the associations between Hg concentrations and the secondary sex ratio. In summary, elevated Hg concentrations in cord blood, but not maternal blood, were associated with an increased probability of male births.

Wolverines are facultative scavengers that feed near the top of terrestrial food chains. We characterized concentrations of mercury and other trace elements in tissues of wolverine from a broad geographic area, representing much of their contemporary distribution in northwestern North America. We obtained tissues from 504 wolverines, from which mercury was measured on muscle (n = 448), kidney (n = 222), liver (n = 148), hair (n = 130), and brain (n = 52). In addition, methylmercury, seven trace elements (arsenic, cadmium, chromium, cobalt, lead, nickel, selenium), and arsenic compounds were measured on a subset of samples. Concentrations of mercury and other trace elements varied between tissues and were generally highest in kidney compared to brain, liver and muscle. Mercury was predominately as methylmercury in brain and muscle, but largely as inorganic mercury in liver and kidney. Mercury concentrations of hair were moderately correlated with those of internal tissues (Pearson r = 0.51-0.75, p ≤ 0.004), making hair a good non-lethal indicator of broad spatial or temporal differences in mercury exposure to wolverine. Arsenobetaine was the dominant arsenic compound identified in tissues, and arsenite, arsenocholine and dimethylarsinic acid were also detected. A preliminary risk assessment suggested the cadmium, lead, mercury, and selenium concentrations in our sample of wolverines were not likely to pose a risk of overt toxicological effects. This study generated a comprehensive dataset on mercury and other trace elements in wolverine, which will support future contaminants study of this northern terrestrial carnivore.

Mercury (Hg), especially methylmercury (MeHg), accumulation in rice grain due to rice paddy possessing conditions conducive to Hg methylation has led to human Hg exposure through consumption of rice-based daily meals. In addition to being a food staple, rice is widely used as a raw material to produce a vast variety of processed food products. Little is known about Hg levels in snacking rice-food products and potential Hg exposure from consumption of them, besides previous studies on infant rice cereals. Aiming to provide complementary information for a more complete assessment on Hg exposure risk originated from Hg-containing rice, this study determined total Hg (THg) and MeHg levels in 195 rice-containing and rice-free processed food products covering all major types of snack foods marketed in China and the estimated daily intake (EDI) of dietary Hg from the consumption of these foods. The results clearly showed THg and MeHg contents in rice-containing foods were significantly higher than rice-free products, suggesting the transfer of Hg and MeHg from the rice to the end products, even after manufacturing processes. Moreover, significant positive correlations were observed between THg, MeHg, or MeHg/THg ratio and rice content for samples containing multiple grains as ingredients, further indicating the deciding role of rice for Hg levels in the end food products. Although the EDI of THg and MeHg via rice-based food products were relatively low compared to the reference dose, it should be considered these snacking food products would contribute additive Hg intake outside of the daily regular meals.

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.

OBJECTIVE: This cross-sectional study aimed to explore the association between methyl mercury (MeHg) level and latent tuberculosis infection (LTBI) risk based on the data from National Health and Nutrition Examination Survey (NHANES 2011-2012).
METHODS: A total of 5243 participants with 20 variables were enrolled. The importance of these variables on TB infection was first ranked by XGBoost and Random Forest methods. Then the association between MeHg level and infection risk was evaluated by restricted cubic spline, threshold effect, and generalized linear regression analyses. We also explored the factors correlated with the difference in MeHg level and finally conducted a mediation analysis to assess the mediating effect of MeHg in LTBI.
RESULTS: 521 participants were experiencing the LTBI, and 12 variables showed the differences between infection and non-infection groups (all P < 0.05). Of them, MeHg presented the highest importance on the LTBI. Restricted cubic spline (RCS) next revealed a significant non-linear correlation of MeHg with LTBI (all P < 0.05). Adjusted regression models further indicated their independent association (all P < 0.05), and infection risk increased with the increase of MeHg (P for trend < 0.05). We also found a significant turning point, and their association was significantly observed when MeHg > 5.75 µg/L (P < 0.05). In addition, asthma history was related to the difference in MeHg levels between LTBI and non-LTBI groups. Mediation analysis found that MeHg level partially mediated the association of asthma and LTBI risk (all P < 0.05).
CONCLUSIONS: Our study identified MeHg as an independent risk factor for LTBI risk. Their causal relationship needs more investigation to verify.

The main route of human exposure to toxic contaminants is through the consumption of contaminated food. To protect against potential negative health effects of rice consumption, the concentration of total mercury (THg) in rice and rice products sold in Poland was determined, and a consumer risk assessment was carried out. In this study, the concentration of THg in selected types of rice and rice products was determined and assessed. The determinations were carried out using atomic absorption spectroscopy (AAS) in a DMA-1 mercury analyzer. Based on the estimated daily intake (EDI), target hazard quotient values (THQ), and tolerable weekly intake (TWI), the toxicological risk associated with the intake of total mercury and methylmercury (MeHg) from the products tested was also estimated. The analysis indicated that the highest Hg content was in rice cakes and the lowest in white rice and rice noodles. Total mercury content was found to be below the maximum permitted level. The estimated daily intake (EDI) and target hazard quotient (THQ) values for THg and MeHg in rice and rice products were lower than 1. These findings suggest that the food items examined pose no health risk.

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.

Complexes with low-molecular-weight thiols are crucial species of methylmercury (MeHg) excreted by anaerobic Hg-methylating microbes, notably, MeHg-cysteine (MeHg-Cys). As MeHg-Cys diffuses into surface water, it would undergo a ligand exchange process with dissolved organic matter (DOM) under nonsulfidic conditions, inevitably altering MeHg speciation and bioavailability to phytoplankton. In this study, we investigated the competitive binding kinetics between MeHg-Cys and Suwannee River natural organic matter, and their influence on the adsorption and uptake of MeHg by the cyanobacterium, Synechocystis sp. PCC6803. Liquid chromatography-inductively coupled plasma mass spectrometry was employed to monitor the kinetics processes involving competition of DOM with Cys for MeHg binding, which revealed that competitive binding kinetics were dictated by the abundance of thiol moieties in DOM. Thiol concentrations of 0.97 and 49.34 μmol of thiol (g C)-1 resulted in competitive binding rate constant (k values) of 0.30 and 3.47 h-1, respectively. Furthermore, the time-dependent competitive binding of DOM toward MeHg-Cys significantly inhibited MeHg adsorption and uptake by cyanobacteria, an effect that was amplified by an increased thiol abundance in DOM. These findings offer valuable insights into the kinetic characteristics of MeHg\'s fate and transport, as well as their impact on bioconcentration in aquatic organisms within natural aquatic ecosystems.