Uncovering the Role of Methylmercury on DNA Lesions at Cytotoxic Concentrations in Glutathione-Depleted Cells: Insights from Experimental and Computational Studies.

Organomercurials (RHg+), especially methylmercury (MeHg+) and ethylmercury (EtHg+), are considered to be more neurotoxic than the inorganic counterpart (Hg2+). They cause massive DNA damage in cells, especially in neurons, where cellular glutathione (GSH) levels are significantly low. However, the mechanism by which RHg+ exerts massive DNA damage at cytotoxic concentrations in brain cells remains obscure. In this study, we investigated the effect of RHg+ on the structural and electronic properties of nucleosides and its effects on DNA damage. The direct interaction of RHg+ with the nucleoside significantly weakens N-glycosidic bonds, decreases the C-H bond energy of sugar moieties, and increases the electrophilicity of the C8-center of purine bases. As a consequence, RHg+-conjugated DNA molecules are extremely labile and highly sensitive to any nucleophiles/radicals present in GSH-depleted cells and, thus, undergo enhanced oxidative and unusual alkylative DNA damage. We also report a functional model of organomercurial lyase, which showed excellent cytoprotective effect against RHg+-induced cytotoxicity; this reverses the activity of glutathione reductase inhibited by MeHgCl and ceases oxidative and alkylating DNA damage. This intriguing finding provides new mechanistic insight into the mode of action of organomercurials in GSH-depleted cells and their adverse effects on individuals with neurodegenerative disorders associated with oxidative stress.

Degradation of methylmercury into Hg(0) by the oxidation of iron(II) minerals.

Mercury contamination is a global concern, and the degradation and detoxification of methylmercury have gained significant attention due to its neurotoxicity and biomagnification within the food chain. However, the currently known pathways of abiotic demethylation are limited to light-induced photodegradation process and little is known about light-independent abiotic demethylation of methylmercury. In this study, we reported a novel abiotic pathway for the degradation of methylmercury through the oxidation of both mineral structural iron(II) and surface-adsorbed iron(II) in the absence of light. Our findings reveal that methylmercury can be oxidatively degraded by reactive oxygen species, specifically hydroxyl and superoxide radicals, which are generated from the oxidation of iron(II) minerals under dark conditions. Surprisingly, Hg(0) trapping experiments demonstrated that inorganic Hg(II) resulting from the oxidative degradation of methylmercury was rapidly reduced to gaseous Hg(0) by iron(II) minerals. The demethylation of methylmercury, coupled with the generation of Hg(0), suggests a potential natural attenuation process for methylmercury. Our results highlight the underappreciated roles of iron(II) minerals in the abiotic degradation of methylmercury and the release of gaseous Hg(0) into the atmosphere.

New Insights into MeHg Accumulation in Rice (Oryza sativa L.): Evidence from Cysteine.

The intake of methylmercury (MeHg)-contaminated rice poses immense health risks to rice consumers. However, the mechanisms of MeHg accumulation in rice plants are not entirely understood. The knowledge that the MeHg-Cysteine complex was dominant in polished rice proposed a hypothesis of co-transportation of MeHg and cysteine inside rice plants. This study was therefore designed to explore the MeHg accumulation processes in rice plants by investigating biogeochemical associations between MeHg and amino acids. Rice plants and underlying soils were collected from different Hg-contaminated sites in the Wanshan Hg mining area. The concentrations of both MeHg and cysteine in polished rice were higher than those in other rice tissues. A significant positive correlation between MeHg and cysteine in rice plants was found, especially in polished rice, indicating a close geochemical association between cysteine and MeHg. The translocation factor (TF) of cysteine showed behavior similar to that of the TF of MeHg, demonstrating that these two chemical species might share a similar transportation mechanism in rice plants. The accumulation of MeHg in rice plants may vary due to differences in the molar ratios of MeHg to cysteine and the presence of specific amino acid transporters. Our results suggest that cysteine plays a vital role in MeHg accumulation and transportation inside rice plants.

Adherence to the EAT-Lancet diet in relation to mortality and exposure to food contaminants in population-based cohorts of Swedish men and women.

BACKGROUND: The EAT-Lancet diet was created to support dietary transition towards sustainable diets. Current evidence indicates that adherence to the EAT-Lancet diet may reduce mortality risk, yet how adherence may impact dietary exposure to food contaminants remains unexplored. We aimed to estimate the association between adherence to the EAT-Lancet diet and i) all-cause, cardiovascular-, and cancer-mortality and ii) predicted dietary exposure to the following food contaminants: cadmium, methylmercury, polychlorinated biphenyls (PCBs), and pesticide residues. METHODS: We used self-reported dietary data from a 96-item food frequency questionnaire of two population-based cohorts - the Cohort of Swedish Men (n = 35,687) and the Swedish Mammography Cohort (n = 32,488). The EAT-Lancet Adherence Index (EAI) was created by scoring consumption of the 14 dietary components included in the EAT-Lancet diet (totalling 0-14 points). Cox proportional hazards regression models were applied to assess the association between EAI and mortality outcomes, presented as multivariable-adjusted hazard ratios (HR) and 95 % confidence intervals (CI). Descriptive statistics were used to characterise predicted exposure to food contaminants, and the correlations between EAI and food contaminants assessed using Spearman's rank correlation. RESULTS: Increased adherence to the EAT-Lancet diet was associated with a lower risk of all-cause mortality (per 3-point increase in EAI: HR = 0.93; CI:0.90,0.97 and HR = 0.91; CI:0.87,0.95 for men and women, respectively) and cardiovascular-mortality (corresponding HR = 0.94; CI:0.88,1.00 and HR = 0.93; CI:0.87,1.00). No clear association was found with cancer-mortality. Increasing EAI was correlated with increased predicted dietary exposure to cadmium, methylmercury, PCBs, and pesticide residues and their median predicted dietary exposures were greater in the high adherence group, compared to the low adherence group. CONCLUSION: High adherence to the EAT-Lancet diet is associated with a reduction in risk of all-cause and cardiovascular-mortality, but also increased dietary exposure to food contaminants.

[The Role of Supersulfide in Methylmercury Detoxification].

Methylmercury is a ubiquitous neurotoxic substance present in the environment, and health concerns, especially through the consumption of seafood, remain. Glutathione (GSH)-mediated detoxification and the excretion of methylmercury are known metabolic detoxification pathways. We have also discovered a mechanism by which endogenous super-sulfides convert methylmercury to nontoxic metabolites such as bis-methylmercury sulfide. However, these metabolites are present in very small quantities, and the significance of the detoxification of methylmercury by super-sulfides is not well understood. Methylmercury binds to thiol groups in vivo but can also react with highly reactive selenols (selenocysteine residues). Such covalent bonds (S-mercuration and Se-mercuration) are broken by nucleophilic substitution reactions with other thiol and selenols, however, the contribution of super-sulfides to this substitution reaction is not well understood. Interestingly, a recent study suggested that selenoprotein P, the major selenium transport protein in plasma, binds to methylmercury, however, Se-mercuration was not determined. In this review, we introduce these series of reactions and discuss their involvement with super-sulfides in methylmercury toxicity.

N-acetylcysteine protects against neurodevelopmental injuries induced by methylmercury exposure during pregnancy and lactation.

As an extremely dangerous environmental contaminant, methylmercury (MeHg) results in detrimental health effects in human brain nervous system, one of its main targets. However, as a developmental toxicant, the brain of offspring is vulnerable to MeHg during pregnancy and lactation exposure. Unfortunately, mechanisms of neurodevelopmental injuries induced by MeHg have not been fully elucidated. N-acetylcysteine (NAC) has been used for several decades as an antioxidant to antagonize oxidative stress. However, the molecular mechanisms of NAC alleviating MeHg-induced neurodevelopmental toxicity are not clear. Here, for evaluation of the dose-dependent effects of MeHg exposure on neurodevelopmental injuries of offspring, and the possible protective effects of NAC, the pregnant female mice were exposed to MeHg (4, 8, 12 mg/L, respectively) and NAC (50, 100, 150 mg/kg, respectively) from gestational day 1 (GD1) to postnatal day 21 (PND21). Our results indicated that administering MeHg caused behavioral impairment and neuronal injuries in the cerebral cortex of newborn mice. MeHg dose-dependently caused reactive oxygen species (ROS) overproduction and oxidative stress aggravation, together with expression of Nrf2, HO-1, Notch1, and p21 up-regulation, and CDK2 inhibition. NAC treatment dose-dependently antagonized MeHg-induced oxidative stress that may contribute to alleviating neurobehavioral and neurodevelopmental impairments. These results give insight into that NAC can protect against MeHg-induced neurodevelopmental toxicity by its antioxidation capacity.

Levels and Health Risk Assessment of Inorganic Arsenic, Methylmercury, and Heavy Metals in Edible Mushrooms Collected from Online Supermarket in China.

Chromium (Cr), total arsenic (As), inorganic arsenic (iAs), cadmium (Cd), mercury (Hg), methylmercury (MeHg), and lead (Pb) were analyzed in in Agaricus blazei, Tricholoma matsutake, Pholiota nameko, agrocybe aegirit, Boletus edulis, Auricularia auricula, and Lentinus edodes collected from online supermarket in China from 2015 to 2017. The order of mean concentrations for the five heavy metals in edible mushrooms was As > Cd > Cr > Pb > Hg. No positive correlation was found between total As and iAs, nor between total Hg and MeHg. The contents of iAs were at a low level except for A. blazei samples. The contents of MeHg were at a low level in all test mushroom samples. And Cr, Cd, and Pb pollution were common problems in the test mushroom samples. The comprehensive factor pollution index was between 0.569 (A. auricula) and 3.056 (B. edulis). The THQ values for the five heavy metals from P. nameko, A. auricula, A. aegirit, and L. edodes samples were less than 1. The hazard index (HI) values of A. blazei, T. matsutake, and B. edulis samples for adults and children were greater than 1, indicating significant health hazard to the adults and children consumers. The cancer risk (CR) values for iAs ranged from 3.82 × 10- 6 (T. matsutake) to 8.61 × 10- 5 (A. blazei), indicating no potential carcinogenic risk to the consumers. The order for carcinogenic risk of each edible mushroom species was A. blazei > L. edodes > P. nameko > A. aegirit > A. auricula > B. edulis > T. matsutake.

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.

Dietary selenium and mercury intakes from fish consumption during pregnancy: Seychelles Child Development Study Nutrition Cohort 2.

Some health agencies have issued precautionary principle fish advisories to pregnant women based on the presence of methylmercury (MeHg) in fish that could possibly be harmful to the developing fetus. Fish, however, is a rich source of selenium (Se) and other nutrients essential for normal brain development. Selenium is also thought to have a key role in alleviating MeHg toxicity. We estimated the dietary Se and MeHg intakes and dietary Se:Hg molar ratios from the fish consumed in a high fish-eating pregnant cohort where no adverse associations of fish consumption and outcomes has been reported. We used dietary data collected as part of the Seychelles Child Development Study Nutrition Cohort 2 (n = 1419). In this cohort 98% of participants consumed fish, with an average intake of 106.2 g per day. Daily Se intakes from fish consumption were 61.6 µg/ d, within the range recommended during pregnancy. The mean dietary Se:Hg molar ratios was 6. These findings demonstrate that fish consumption exposes pregnant Seychellois women to Se in excess of MeHg. Based on these findings, fish consumption, especially fish with Se:Hg ratios above 1, may help pregnant women achieve optimum dietary Se intakes, which may protect against MeHg toxicity.

Fish consumption and omega-3 polyunsaturated fatty acids from diet are positively associated with cognitive function in older adults even in the presence of exposure to lead, cadmium, selenium, and methylmercury: a cross-sectional study using NHANES 2011-2014 data.

BACKGROUND: Long-chain omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are reported to be beneficial for cognition, but limited consumption of some fish is recommended due to high concentrations of heavy metals and persistent organics. OBJECTIVE: We aimed to determine whether dietary ω-3 PUFAs from fish consumption are associated with higher cognitive scores in older adults and explored the associations of mixtures of ω-3 PUFAs and blood concentrations of lead, cadmium, selenium, and methylmercury on cognitive performance. METHODS: We conducted a cross-sectional study with data from the NHANES 2011-2014, assessing cognitive scores of immediate recall, delayed recall, and executive function in adults ≥60 y (n = 3123). We performed multivariate linear regressions and mixture models utilizing the quantile-based g-computation method to identify associations between monthly fish consumption or dietary ω-3 PUFAs with blood concentrations of lead, cadmium, methyl mercury, and selenium on cognitive scores. RESULTS: Fish consumption had significant positive associations with all 3 cognitive scores, whereas dietary ω-3 PUFAs were only significantly associated with the Digit Symbol Substitution Test (DSST) scores. Mixture analysis showed significant positive associations with DSST scores for fish consumption (ß: 0.88; 95% CI: 0.48, 1.29) and dietary ω-3 PUFAs (ß: 0.41; 95% CI: 0.03, 0.78) with positive component weights for fish consumption, dietary ω-3 PUFAs, and blood selenium and negative component weight for blood cadmium concentrations. CONCLUSIONS: Our findings support dietary recommendations for older adults to consume fish to maintain cognitive function, likely due to biomolecular actions of ω-3 PUFAs that increase neuronal membrane fluidity, have antioxidation activity, and restore cell damage. The combination of selenium and fish consumption or ω-3 PUFAs was associated with reduced decline in cognitive scores and less negative associations from exposures to lead, cadmium, and mercury compounds.

An improved method for rapid and safe preparation and measurement of dimethylmercury using gas chromatography-atomic fluorescence spectrometry.

Transformations between dimethylmercury (DMHg) and other mercury (Hg) species have been one of the critical knowledge gaps in the Hg global biogeochemical cycle due to the lack of detailed studies. The preparation and measurement of DMHg are challenging due to the high toxicity and volatility of DMHg. In this work, we invented a new DMHg generator for successfully preparing high-purity DMHg in a highly controllable and safe way. The DMHg could be spontaneously volatilized and diffused from the original preparation solution to the solution to be studied. The parameters for generating DMHg were optimized to be the pH value of 4.0 with a MeCo/Hg2+ molar ratio of 10 at 20 °C. The following measurement method of DMHg in the presence of various species of Hg was also investigated and optimized. Hg0 and DMHg could be separated effectively with the carrier gas flow rate of 15 mL min-1 and the gas chromatography column temperature of 30 °C. The interferences of Hg0, monomethylmercury and other species were excluded by systematic control experiments. A sensitive and reliable approach for quantifying trace DMHg in water was developed. Under the optimal conditions, the limits of detection for Hg0, MMHg and DMHg were 0.03, 0.002 and 0.024 ng L-1, respectively, with the relative standard deviation below 8.2%. The developed method was validated by the determination Hg species of different natural water samples. This work is expected to provide a new and safe strategy for DMHg preparation and a verified method for DMHg measurement.

N-Acetylcysteine Displaces Glutathionyl-Moieties from Hg2+ and MeHg+ to Form More Hydrophobic Complexes at Near-Physiological Conditions.

The anthropogenic release of Hg is associated with an increased human exposure risk. Since Hg2+ and MeHg+ have a high affinity for thiols, their interaction with L-glutathione (GSH) within mammalian cells is fundamentally involved in their toxicological chemistry and excretion. To gain insight into the interaction of these mercurials with multiple small molecular weight thiols, we have investigated their competitive interactions with GSH and N-acetylcysteine (NAC) at near-physiological conditions, using a liquid chromatographic approach. This approach involved the injection of each mercurial onto a reversed-phase (RP)-HPLC column (37 °C) using a PBS buffer mobile phase containing 5.0 mM GSH to simulate cytosolic conditions with Hg being detected in the column effluent by an inductively coupled plasma atomic emission spectrometer (ICP-AES). When the 5.0 mM GSH mobile phase was amended with up to 10 mM NAC, gradually increasing retention times of both mercurials were observed. To explain this behavior, the experiment with 5.0 mM NAC and 5.0 mM GSH was replicated using 50 mM Tris buffer (pH 7.4), and the Hg-containing fractions were analyzed by electrospray ionization mass spectrometry. The results revealed the presence of Hg(GS)(NAC) and Hg(NAC)2 for Hg2+ and MeHg(GS) and MeHg(NAC) for MeHg+, which suggests that the coordination/displacement of GS-moieties from each mercurial by the more hydrophobic NAC can explain their retention behavior. Since the biotransformations of both mercurials were observed at near-physiological conditions, they are of toxicological relevance as they provide a biomolecular explanation for some results that were obtained when animals were administered with each mercurial and NAC.

Inhibition of p38 Mitogen-Activated Protein Kinases Attenuates Methylmercury Toxicity in SH-SY5Y Neuroblastoma Cells.

Methylmercury (MeHg) is a toxic metal that causes irreversible damage to the nervous system, making it a risk factor for neuronal degeneration and diseases. MeHg activates various cell signaling pathways, particularly the mitogen-activated protein kinase (MAPK) cascades, which are believed to be important determinants of stress-induced cell fate. However, little is known about the signaling pathways that mitigate the neurotoxic effects of MeHg. Herein, we showed that pretreatment with a p38 MAPK-specific inhibitor, SB203580, attenuates MeHg toxicity in human neuroblastoma SH-SY5Y cells, whereas pretreatment with the extracellular signaling-regulated kinase inhibitor U0126 and the c-Jun N-terminal kinase inhibitor SP600125 does not. Specifically, we quantified the levels of intracellular mercury (Hg) and found that pretreatment with SB203580 reduced Hg levels compared to MeHg treatment alone. Further analysis showed that pretreatment with SB203580 increased multidrug resistance-associated protein 2 (MRP2) mRNA levels after MeHg treatment. These results indicate that detoxification of MeHg by p38 MAPK inhibitors may involve an efflux function of MeHg by inducing MRP2 expression.

Disclosing the Preferential Mercury Chelation by SeCys Containing Peptides over Their Cys Analogues.

Methylmercury, mercury (II), and mercury (I) chlorides were found to react with vasopressin, a nonapeptide hormone cyclized by two cysteine residues, and its mono- and diselenium analogues to form several mercury-peptide adducts. The replacement of Cys by SeCys in vasopressin increased the reactivity toward methylmercury, with the predominant formation of -Se/S-Hg-Se-bridged structures and the consequent demethylation of methylmercury. In competitive experiments, CH3HgCl reacted preferentially with the diselenium analogue rather than with vasopressin. The diselenium peptide also showed the capability to displace the CH3Hg moiety bound to S in vasopressin. These results open a promising perspective for the use of selenopeptides for methylmercury chelation and detoxification strategies.

Methylmercury induced ferroptosis by interference of iron homeostasis and glutathione metabolism in CTX cells.

Environmental methylmercury (MeHg) exposure has gained global attention owing to its serious health hazards, especially neurotoxicity. Ferroptosis is a novel form of programmed cell death characterized by lipid peroxidation and iron overload. However, the occurrence of ferroptosis and its underlying mechanisms have not been fully elucidated in the methylmercury-induced neurotoxicity and the role of Nrf2 in MeHg-induced ferroptosis remains unexplored. In this study, we verified that MeHg decreased cell viability in a dose- and time-dependent manner in the Rat Brain Astrocytes cells (CTX cells). MeHg (3.5 µmol/L) exposure induced CTX cells to undergo ferroptosis, as evidenced by glutathione (GSH) depletion, lipid peroxidation, and iron overload, which was significantly rescued by the ferroptosis-specific inhibitors Ferrostatin-1 and Deferoxamine. MeHg directly disrupted the process of GSH metabolism by downregulating of SLC7A11 and GPX4 and interfered with intracellular iron homeostasis through inhibition of iron storage and export. Simultaneously, the expression of Nrf2 was upregulated by MeHg in CTX cells. Hence, the inhibition of Nrf2 activity further downregulated the levels of GPX4, SLC7A11, FTH1, and SLC40A1, which aggravated MeHg-induced ferroptosis to a greater extent. Overall, our findings provided evidence that ferroptosis played a critical role in MeHg-induced neurotoxicity, and suppressing Nrf2 activity further exacerbated MeHg-induced ferroptosis in CTX cells.

Pathogenesis of selective damage of granule cell layer in cerebellum of rats exposed to methylmercury.

Granule cell-selective toxicity of methylmercury in the cerebellum is one of the main unresolved issues in the pathogenesis of Minamata disease. Rats were orally administered methylmercury chloride (10 mg/kg/day) for 5 consecutive days, and their brains were harvested on days 1, 7, 14, 21, or 28 after the last administration for histological examination of the cerebellum. It was found that methylmercury caused a marked degenerative change to the granule cell layers but not to the Purkinje cell layers. The generative change of the granule cell layer was due to cell death, including apoptosis, which occurred at day 21 and beyond after the methylmercury administration. Meanwhile, cytotoxic T-lymphocytes and macrophages had infiltrated the granule cell layer. Additionally, granule cells are shown to be a cell type susceptible to TNF-α. Taken together, these results suggest that methylmercury causes small-scale damage to granule cells, triggering the infiltration of cytotoxic T-lymphocytes and macrophages into the granule cell layer, which secrete tumor necrosis factor-α (TNF-α) to induce apoptosis in granule cells. This chain is established based on the susceptibility of granule cells to methylmercury, the ability of cytotoxic T lymphocytes and macrophages to synthesize and secrete TNF-α, and the sensitivity of granule cells to TNF-α and methylmercury. We propose to call the pathology of methylmercury-induced cerebellar damage the "inflammation hypothesis."

MeHg production in eutrophic lakes: Focusing on the roles of algal organic matter and iron-sulfur-phosphorus dynamics.

The mechanisms by which eutrophication affects methylmercury (MeHg) production have not been comprehensively summarized, which hinders accurately predicting the MeHg risk in eutrophic lakes. In this review, we first discussed the effects of eutrophication on biogeochemical cycle of mercury (Hg). Special attentions were paid to the roles of algal organic matter (AOM) and iron (Fe)-sulfur (S)-phosphorus (P) dynamics in MeHg production. Finally, the suggestions for risk control of MeHg in eutrophic lakes were proposed. AOM can affect in situ Hg methylation by stimulating the abundance and activities of Hg methylating microorganisms and regulating Hg bioavailability, which are dependent on bacteria-strain and algae species, the molecular weight and composition of AOM as well as environmental conditions (e.g., light). Fe-S-P dynamics under eutrophication including sulfate reduction, FeS formation and P release could also play crucial but complicated roles in MeHg production, in which AOM may participate through influencing the dissolution and aggregation processes, structural order and surface properties of HgS nanoparticles (HgSNP). Future studies should pay more attention to the dynamics of AOM in responses to the changing environmental conditions (e.g., light penetration and redox fluctuations) and how such variations will subsequently affect MeHg production. The effects of Fe-S-P dynamics on MeHg production under eutrophication also deserve further investigations, especially the interactions between AOM and HgSNP. Remediation strategies with lower disturbance, greater stability and less cost like the technology of interfacial O2 nanobubbles are urgent to be explored. This review will deepen our understanding of the mechanisms of MeHg production in eutrophic lakes and provide theoretical guidance for its risk control.

Total mercury and methylmercury in garfish (Belone belone) of different body weights, sizes, ages, and sexes.

BACKGROUND: Garfish, (Belone belone) is a migratory pelagic fish that inhabits the waters of coastal Europe, North Africa, the North Sea, the Mediterranean Sea. Little information about garfish has been disseminated mainly because of its low abundance and its brief occurrence in various water bodies. Data is lacking on mercury compounds, particularly dangerous the toxic organic form of methylmercury (MeHg), which endangers the health of fish and their consumers. METHODS: The research material was garfish caught off the southern Baltic Sea coast in Puck Bay during the spawning period. Total mercury (THg) content was assayed with the cold vapour atomic absorption method in an AMA 254 mercury analyser. The MeHg extraction procedure was based on three-step sequential extraction method: hydrolysis using of hydrochloric acid, extract by toluene, bind the MeHg by L-cysteine. RESULTS: The concentrations of THg and MeHg was determined in the muscle of garfish. The highest concentrations of THg (0.210 mg kg-1) and MeHg (0154 mg kg-1) were detected in the longest specimens (80 cm). The THg and MeHg concentrations in garfish muscles increased with specimens length, weight and age, which was confirmed by positive correlations. Differences were also noted depending on sex. Males accumulated more THg and MeHg than did females. The mercury in garfish from the southern Baltic Sea occurred mainly in its organic form MeHg and accounted for 84.7% of the THg. CONCLUSION: Significant differences were noted in mercury concentrations depends on length, weight, age and sex. Concentration of MeHg in garfish must be done by length class, and fish sex when selecting this fish for contamination studies and risk assessment. The toxic MeHg in garfish tissues did not pose a threat to the health of consumers, as indicated by the low values of EDI, TWI and THQ indices.

Mercury and methylmercury in Hg-contaminated paddy soil and their uptake in rice as regulated by DOM from different agricultural sources.

In this study, from the perspectives of structural and compositional variations of soil-dissolved organic matter (DOM), we explored the effects of agricultural DOM inputs on methylmercury (MeHg) accumulation in the soil and mercury (Hg) bioaccumulation in rice grains. Pot experiments with the addition of DOMs from maize straw (MaS), rape straw (RaS), rice straw (RiS), composted rice straw (CRiS), cow dung (CD), and composted cow dung (CCD) were then conducted. Results showed that, relative to the control, the DOM amendment from each agricultural source elevated MeHg concentrations in the soil, with an increase of 18-227%, but only parts of DOMs elevated total dissolved Hg (DHg) and MeHg (DMeHg) concentrations in pore water. Among all DOM species, RiS, CRiS, and CCD significantly increased total Hg (THg) and MeHg contents in rice grains by 34-64% and 32-118%, respectively. Compared with RiS, THg and MeHg contents in rice grains in the CRiS treatment decreased slightly, which was consistent with the distributions of DHg and DMeHg concentrations in pore water and the aromaticity variation of soil DOM. In contrast, the CCD input significantly enhanced the enrichment of THg and MeHg in rice grains relative to CD because it significantly reduced the humification of soil DOM at all rice-growing stages while increasing the low-molecular-weight fractions in soil DOM. The THg and MeHg contents in the rice grains were significantly lower treated by RaS than those by MaS and RiS, which may be related to the higher sulfur-containing compounds such as sulfate and cysteine in rape straw or its DOM solution. Overall, DOM amendment from different agricultural sources resulted in significantly discriminative effects on the MeHg accumulation in soil and Hg enrichment in rice in the Hg-contaminated paddy field by shaping soil DOM properties.

Evaluation of mRNA markers in differentiating human SH-SY5Y cells for estimation of developmental neurotoxicity.

Current guidelines for developmental neurotoxicity (DNT) evaluation are based on animal models. These have limitations so more relevant, efficient and robust approaches for DNT assessment are needed. We have used the human SH-SY5Y neuroblastoma cell model to evaluate a panel of 93 mRNA markers that are frequent in Neuronal diseases and functional annotations and also differentially expressed during retinoic acid-induced differentiation in the cell model. Rotenone, valproic acid (VPA), acrylamide (ACR) and methylmercury chloride (MeHg) were used as DNT positive compounds. Tolbutamide, D-mannitol and clofibrate were used as DNT negative compounds. To determine concentrations for exposure for gene expression analysis, we developed a pipeline for neurite outgrowth assessment by live-cell imaging. In addition, cell viability was measured by the resazurin assay. Gene expression was analyzed by RT-qPCR after 6 days of exposure during differentiation to concentrations of the DNT positive compounds that affected neurite outgrowth, but with no or minimal effect on cell viability. Methylmercury affected cell viability at lower concentrations than neurite outgrowth, hence the cells were exposed with the highest non-cytotoxic concentration. Rotenone (7.3 nM) induced 32 differentially expressed genes (DEGs), ACR (70 µM) 8 DEGs, and VPA (75 µM) 16 DEGs. No individual genes were significantly dysregulated by all 3 DNT positive compounds (p < 0.05), but 9 genes were differentially expressed by 2 of them. Methylmercury (0.8 nM) was used to validate the 9 DEGs. The expression of SEMA5A (encoding semaphorin 5A) and CHRNA7 (encoding nicotinic acetylcholine receptor subunit α7) was downregulated by all 4 DNT positive compounds. None of the DNT negative compounds dysregulated any of the 9 DEGs in common for the DNT positive compounds. We suggest that SEMA5A or CHRNA7 should be further evaluated as biomarkers for DNT studies in vitro since they also are involved in neurodevelopmental adverse outcomes in humans.