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Ecotoxicology (London, England) Oct 2023Mercury contamination is a widespread phenomenon that impacts ecosystems worldwide. Artisanal Small Scale Gold Mining (ASGM) activities are responsible for more than a... (Review)
Review
Mercury contamination is a widespread phenomenon that impacts ecosystems worldwide. Artisanal Small Scale Gold Mining (ASGM) activities are responsible for more than a third of atmospheric Hg emission. Due to Hg toxicity and its broad and elevated prevalence in the environment resulting from ASGM activities in the tropics, its biomonitoring is essential to better understand the availability of its methylmercury (MeHg) form in the environment. The Minamata Convention was ratified with the objective to "protect human health and the environment from anthropogenic emissions and releases of mercury compounds". Biomagnification of MeHg occurs through the trophic food web, where it biomagnifies and bioaccumulates in top predators. To monitor environmental MeHg contamination, studies have evaluated the use of living organisms; however, reptiles are among the least documented vertebrates regarding MeHg exposure. In this review we evaluate the use of crocodylians for Hg biomonitoring in tropical ecosystems. We found that out of the 28 crocodiles species, only 10 have been evaluated regarding Hg contamination. The remaining challenges when using this taxon for Hg biomonitoring are inconsistencies in the applied methodology (e.g., wet versus dry weight, tissues used, quantification method). However, due to their life history traits, crocodylians are particularly relevant for monitoring MeHg contamination in regions where ASGM activities occur. In conclusion and given their ecological and socio-economic importance, crocodylians are at great risk of MeHg contamination and are excellent bioindicators for tropical ecosystems.
Topics: Animals; Humans; Mercury; Ecosystem; Environmental Monitoring; Methylmercury Compounds; Vertebrates; Gold; Fishes
PubMed: 37815690
DOI: 10.1007/s10646-023-02703-1 -
Biochimica Et Biophysica Acta. General... Dec 2019Methylmercury is a neurotoxicant that is found in fish and rice. MeHg's toxicity is mediated by blockage of -SH and -SeH groups of proteins. However, the identification... (Review)
Review
Methylmercury is a neurotoxicant that is found in fish and rice. MeHg's toxicity is mediated by blockage of -SH and -SeH groups of proteins. However, the identification of MeHg's targets is elusive. Here we focus on the chemistry of MeHg in the abiotic and biotic environment. The toxicological chemistry of MeHg is complex in metazoans, but at the atomic level it can be explained by exchange reactions of MeHg bound to -S(e)H with another free -S(e)H group (RS(e)-HgMe + R-S(e)H ↔ RS(e)H + R-S(e)-HgMe). This reaction was first studied by professor Rabenstein and here it is referred as the "Rabenstein's Reaction". The absorption, distribution, and excretion of MeHg in the environment and in the body of animals will be dictated by Rabenstein's reactions. The affinity of MeHg by thiol and selenol groups and the exchange of MeHg by Rabenstein's Reaction (which is a diffusion controlled reaction) dictates MeHg's neurotoxicity. However, it is important to emphasize that the MeHg exchange reaction velocity with different types of thiol- and selenol-containing proteins will also depend on protein-specific structural and thermodynamical factors. New experimental approaches and detailed studies about the Rabenstein's reaction between MeHg with low molecular mass thiol (LMM-SH) molecules (cysteine, GSH, acetyl-CoA, lipoate, homocysteine) with abundant high molecular mass thiol (HMM-SH) molecules (albumin, hemoglobin) and HMM-SeH (GPxs, Selenoprotein P, TrxR1-3) are needed. The study of MeHg migration from -S(e)-Hg- bonds to free -S(e)H groups (Rabenstein's Reaction) in pure chemical systems and neural cells (with special emphasis to the LMM-SH and HMM-S(e)H molecules cited above) will be critical to developing realistic constants to be used in silico models that will predict the distribution of MeHg in humans.
Topics: Animals; Brain; Cysteine; Environmental Pollutants; Humans; Methylmercury Compounds; Nerve Tissue Proteins; Neurons; Selenoproteins
PubMed: 30659885
DOI: 10.1016/j.bbagen.2019.01.006 -
Current Environmental Health Reports Jun 2021Our comparative analysis sought to understand the factors which drive differences in fish consumption advisories across the USA - including exposure scenarios (acute and... (Review)
Review
PURPOSE OF REVIEW
Our comparative analysis sought to understand the factors which drive differences in fish consumption advisories across the USA - including exposure scenarios (acute and chronic health risk, non-cancer and cancer health endpoints), toxicity values (reference dose, cancer slope factor, acute tolerance level), and meal size and bodyweight assumptions.
RECENT FINDINGS
Fish consumption provides essential nutrients but also results in exposure to contaminants such as PCBs and methylmercury. To protect consumers from the risks of fish contaminants, fish consumption advisories are established, most often by state jurisdictions, to estimate the amount of a certain fish species a person could consume throughout their lifetime without harm. However, inconsistencies in advisories across the USA confuse consumers and undermine the public health goals of fish advisory programs. To date, no rigorous comparison of state and national fish consumption advisories has been reported. Our work identifies discrepancies in key assumptions used to derive risk-based advisories between US states, reflecting differences in the interpretation of toxicity science. We also address the implications for these differences by reviewing advisories issued by contiguous states bordering two waterbodies: Lake Michigan and the Lower Mississippi River. Our findings highlight the importance of regional collaboration when issuing advisories, so that consumers of self-caught fish are equipped with clear knowledge to make decisions to protect their health.
Topics: Animals; Fishes; Food Contamination; Humans; Methylmercury Compounds; Polychlorinated Biphenyls
PubMed: 33934293
DOI: 10.1007/s40572-021-00312-w -
RSC Advances Jun 2020Mercury (Hg) is a natural element and its compounds are found as inorganic and organic forms in the environment. The different Hg forms (, methylmercury (MeHg)), are... (Review)
Review
Mercury (Hg) is a natural element and its compounds are found as inorganic and organic forms in the environment. The different Hg forms (, methylmercury (MeHg)), are responsible for many adverse health effects, such as neurological and cardiovascular effects. The main source of Hg is from natural release. Nevertheless, with the development of industrialization and urbanization, Hg-contaminated soil mainly influenced by human activities (especially near mercury mining areas) has become a problem. Therefore, much more attention has been paid to the development and selection of various treatment methods to remediate Hg-contaminated soils. This paper presented a systematical review of the recent developments for the remediation of Hg-contaminated soils. Firstly, we briefly introduced the Hg chemistry, toxicity and the main human activity-related sources of mercury in soil. Then the advances in remediation technologies for removing Hg pollution from the soil were summarized. Usually, the remediation technology includes physical, chemical and biological remediation technology. Depending on this, we further classified these remediation technologies into six techniques, including thermal desorption, electrokinetic extraction, soil washing, chemical stabilization, phytoremediation and microbial technology. Finally, we also discussed the challenges and future perspectives of remediating Hg-contaminated soils.
PubMed: 35520308
DOI: 10.1039/d0ra01507e -
Biochimica Et Biophysica Acta. General... Dec 2019Methylmercury (MeHg) is a toxic chemical compound naturally produced mainly in the aquatic environment through the methylation of inorganic mercury catalyzed by aquatic... (Review)
Review
Methylmercury (MeHg) is a toxic chemical compound naturally produced mainly in the aquatic environment through the methylation of inorganic mercury catalyzed by aquatic microorganisms. MeHg is biomagnified in the aquatic food chain and, consequently, piscivorous fish at the top of the food chain possess huge amounts of MeHg (at the ppm level). Some populations that have fish as main protein's source can be exposed to exceedingly high levels of MeHg and develop signs of toxicity. MeHg is toxic to several organs, but the central nervous system (CNS) represents a preferential target, especially during development (prenatal and early postnatal periods). Though the biochemical events involved in MeHg-(neuro)toxicity are not yet entirely comprehended, a vast literature indicates that its pro-oxidative properties explain, at least partially, several of its neurotoxic effects. As result of its electrophilicity, MeHg interacts with (and oxidize) nucleophilic groups, such as thiols and selenols, present in proteins or low-molecular weight molecules. It is noteworthy that such interactions modify the redox state of these groups and, therefore, lead to oxidative stress and impaired function of several molecules, culminating in neurotoxicity. Among these molecules, glutathione (GSH; a major thiol antioxidant) and thiol- or selenol-containing enzymes belonging to the GSH antioxidant system represent key molecular targets involved in MeHg-neurotoxicity. In this review, we firstly present a general overview concerning the neurotoxicity of MeHg. Then, we present fundamental aspects of the GSH-antioxidant system, as well as the effects of MeHg on this system.
Topics: Animals; Antioxidants; Glutathione; Humans; Methylmercury Compounds; Neurotoxicity Syndromes; Neurotoxins; Oxidative Stress
PubMed: 30659883
DOI: 10.1016/j.bbagen.2019.01.007 -
Biological Trace Element Research Aug 2022Many studies evaluating methylmercury (MeHg) toxicity rely on whole blood total mercury (THg) measurements to estimate MeHg exposure. However, whole blood THg includes...
Many studies evaluating methylmercury (MeHg) toxicity rely on whole blood total mercury (THg) measurements to estimate MeHg exposure. However, whole blood THg includes other forms of mercury (Hg), such as inorganic Hg, which have different exposure sources and toxicological effects than MeHg. Therefore, estimating the whole blood MeHg/THg ratio is critical to predicting MeHg exposure and, subsequently, efforts to establish an exposure-response relationship for use in risk assessment. A large, representative dataset (National Health and Nutrition Examination Survey (NHANES) 2011-2016) was used to determine the whole blood MeHg/THg ratio among (a) self-reported fish and shellfish consumers, ≥ 15 years of age (the "full adult" population (N = 5268 training dataset; N = 2336 test dataset)) and (b) female fish and shellfish consumers, 15-44 years of age (the "women of reproductive age" population (N = 1285 training dataset; N = 560 test dataset)). Unadjusted and adjusted linear and spline models with direct measurements for both THg and MeHg were evaluated. The mean whole blood MeHg/THg ratio was 0.75 (95% confidence interval (CI): 0.74, 0.75). This ratio was significantly higher among those with higher THg concentrations. All models exhibited excellent fit (adjusted R from 0.957 to 0.982). Performance was slightly improved in spline versus linear models. For the full adult population and women of reproductive age, the unadjusted spline model predicted whole blood MeHg concentrations of 5.65 µg/L and 5.55 µg/L, respectively, when the THg concentration was 5.80 µg/L. These results suggest that whole blood THg is a good predictor of whole blood MeHg among fish and shellfish consumers.
Topics: Animals; Environmental Monitoring; Female; Fishes; Humans; Mercury; Methylmercury Compounds; Nutrition Surveys; Seafood; Shellfish; Water Pollutants, Chemical
PubMed: 34686996
DOI: 10.1007/s12011-021-02968-9 -
Yakugaku Zasshi : Journal of the... 2024Methylmercury is a ubiquitous neurotoxic substance present in the environment, and health concerns, especially through the consumption of seafood, remain. Glutathione... (Review)
Review
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.
Topics: Methylmercury Compounds; Selenium; Glutathione; Sulfhydryl Compounds; Sulfides
PubMed: 38171793
DOI: 10.1248/yakushi.23-00162-1 -
Proceedings of the National Academy of... Nov 2022Fungi are central to every terrestrial and many aquatic ecosystems, but the mechanisms underlying fungal tolerance to mercury, a global pollutant, remain unknown. Here,...
Fungi are central to every terrestrial and many aquatic ecosystems, but the mechanisms underlying fungal tolerance to mercury, a global pollutant, remain unknown. Here, we show that the plant symbiotic fungus degrades methylmercury and reduces divalent mercury, decreasing mercury accumulation in plants and greatly increasing their growth in contaminated soils. does this by demethylating methylmercury via a methylmercury demethylase (MMD) and using a mercury ion reductase (MIR) to reduce divalent mercury to volatile elemental mercury. can also remove methylmercury and divalent mercury from fresh and sea water even in the absence of added nutrients. Overexpression of MMD and MIR significantly improved the ability of to bioremediate soil and water contaminated with methylmercury and divalent mercury. MIR homologs, and thereby divalent mercury tolerance, are widespread in fungi. In contrast, MMD homologs were patchily distributed among the few plant associates and soil fungi that were also able to demethylate methylmercury. Phylogenetic analysis suggests that fungi could have acquired methylmercury demethylase genes from bacteria via two independent horizontal gene transfer events. Heterologous expression of MMD in fungi that lack MMD homologs enabled them to demethylate methylmercury. Our work reveals the mechanisms underlying mercury tolerance in fungi, and may provide a cheap and environmentally friendly means of cleaning up mercury pollution.
Topics: Biodegradation, Environmental; Water; Mercury; Methylmercury Compounds; Phylogeny; Ecosystem; Metarhizium; Soil
PubMed: 36375055
DOI: 10.1073/pnas.2214513119 -
Environmental Science & Technology Mar 2022Microbial reduction of inorganic divalent mercury (Hg) and methylmercury (MeHg) demethylation is performed by the operon, specifically by and genes, respectively, but...
Microbial reduction of inorganic divalent mercury (Hg) and methylmercury (MeHg) demethylation is performed by the operon, specifically by and genes, respectively, but little is known about the mercury tolerance capacity of marine microorganisms and its prevalence in the ocean. Here, combining culture-dependent analyses with metagenomic and metatranscriptomic data, we show that marine bacteria that encode genes are widespread and active in the global ocean. We explored the distribution of these genes in 290 marine heterotrophic bacteria ( and spp.) isolated from different oceanographic regions and depths, and assessed their tolerance to diverse concentrations of Hg and MeHg. In particular, the sp. ISS312 strain presented the highest tolerance capacity and a degradation efficiency for MeHg of 98.2% in 24 h. Fragment recruitment analyses of sp. genomes (ISS312 strain and its associated reconstructed metagenome assembled genome MAG-0289) against microbial bathypelagic metagenomes confirm their prevalence in the deep ocean. Moreover, we retrieved 54 and 6 genes variants related to the sp. ISS312 strain from global metagenomes and metatranscriptomes from Oceans. Our findings highlight the biological reductive MeHg degradation as a relevant pathway of the ocean Hg biogeochemical cycle.
Topics: Bacteria; Mercury; Methylmercury Compounds; Oceans and Seas; Prevalence
PubMed: 35245029
DOI: 10.1021/acs.est.1c05635 -
Environmental Science & Technology Sep 2021Mercury concentrations in the Laurentian Great Lakes waters are among the lowest reported in the literature, while game fish concentrations approach consumption advisory...
Mercury concentrations in the Laurentian Great Lakes waters are among the lowest reported in the literature, while game fish concentrations approach consumption advisory limits, particularly in Lakes Superior, Huron, and Michigan, indicating efficient methylmercury transfer from water to game fish. To determine if increased transfer efficiency is evident within the lower food web, we measured (2010-2018) mercury and dissolved organic carbon (DOC) in water, and in size-sieved seston, dietary tracers (carbon and nitrogen isotope ratios), phytoplankton methylmercury bioaccumulation, and methylmercury biomagnification between increasing seston size fractions. We observed consistently low filter-passing methylmercury (<0.010 ng L) and comparatively variable DOC (1.1 to 3.4 mg L) concentrations. Methylmercury biomagnification factors between size-sieved seston were similar between lakes. Bioaccumulation factors in phytoplankton were among the highest in the literature (log 5.5 to 6.1), exceeding those in oceans, smaller lakes, and streams, and was influenced by DOC. Higher bioaccumulation rates increase the susceptibility of methylmercury accumulation into the food web. Because mercury is dominantly delivered to the Great Lakes through the atmosphere and the biota therein is highly susceptible to methylmercury uptake, we propose that the Laurentian Great Lakes are excellent sentinels to trace the success of efforts to decrease global mercury emissions (e.g., Minamata Treaty) in the future.
Topics: Animals; Bioaccumulation; Environmental Monitoring; Fishes; Food Chain; Lakes; Mercury; Methylmercury Compounds; Water Pollutants, Chemical
PubMed: 34460225
DOI: 10.1021/acs.est.1c02319