Degradation of methylmercury by selenium

When methylmercury was incubated in the presence of selenite and reduced glutathione (GSH), the mercury which was extracted into benzene under acidic condition decreased gradually with the elapse of time. This decrease was due to the cleavage of mercury-carbon bond of methylmercury. The reaction did not proceed when selenite or GSH was singly added to the reaction mixture. L-Cysteine, 2-mercaptoethanol and sodium sulfide in place of GSH also were effective for decomposition of methylmercury in combination with selenite, but oxidized glutathione (GSSG) and L-cystine were not. This suggests that reduction of selenite is needed for the degradation of methylmercury. Thus, the effect of reduced metabolites of selenite produced by GSH was investigated. Glutathione selenotrisulfide (GSSeSG) requierd GSH for the degradation of methylmercury, whereas H₂Se possessed a strong activity even in the absence of GSH. This may indicate that H₂Se is involved directly in the conversion of methylmercury to inorganic mercury. This phenomenon found in $\text{in vitro}$ experiments is discussed in relation to the biotransformation of methylmercury.     

Mercury-selenium interactions in relation to histochemical staining of mercury in the rat liver

Summary Selenium has been suggested to enhance the histochemical staining of mercury when sections of tissue are subjected to the silver-enhancement method. In the present study, histochemical staining patterns of mercury in tissue sections of rat livers were compared with the actual content of organic and inorganic Hg in the livers, in both the presence and the absence of Se. Rats were injected intravenously with 5g of Hgg^–1 body weight as methyl [²⁰³Hg] mercury chloride (MeHg) or as [²⁰³Hg]mercuric chloride (Hg²⁺). After 2h, half the rats received an additional intraperitoneal injection of 2g of Se g^–1 body weight as sodium [⁷⁵Se]selenite. All the rats were killed 1h later. Homogenized liver samples were prepared for mercury analysis by two different methods: alkaline digestion and ultrasonic disintegration. Quantitative chemical analysis based on benzene extrction of the radioactively labelled Hg compounds showed that the chemical form of mercury, either organic or inorganic, was preserved from its administration to its deposition in the liver. Light and electron microscopy demonstrated that no silver enhancement of Hg occurred when MeHg alone was present in the sections of tissue, whereas MeHg accompanied by Se induced a moderate deposition of silver grains. In contrast, sections containing Hg²⁺ alone yielded some staining, and the addition of Se increased the staining dramatically. The results of the present study show that acute selenite pretreatment is a prerequisite for the histochemical demonstration of methyl mercury, and greatly increases the staining of inorganic mercury when applying the silver-enhancement method.     

Influence of sodium selenite on203Hg absorption,distribution, and elimination in male mice exposed to methyl203Hg

To study the effects of long-term selenium supplementation on absorption, distribution, and elimination of methylmercury (MeHg) in mice, three groups of male mice (Balb/c CA) were exposed for 7 wk to 0, 0.6, and 3 ppm sodium selenite in tap water. They were then given a single oral dose of Me²⁰³Hg (2 μmol/kg) by gastric intubation, and elimination of²⁰³Hg was followed by whole-body counting for 49 d at the same Se exposure as previously. Twenty-four hours and 49 d after dosage, 6–7 animals/group were sampled for analysis of²⁰³Hg distribution in the body. Glutathione peroxidase (GSH-PX) activity in blood and selenium levels in the liver were used as measures of selenium status. Gastrointestinal absorption of Me²⁰³Hg was not influenced by the Se status of the animals. Selenium supplementation of MeHg-exposed mice caused an enhanced whole-body elimination of Hg, but selenium-supplemented animals did not have lower Hg levels in the brain and kidney than nonsupplemented animals. The effect of selenium on the accumulation, of Hg in the brain was dose-dependent, a high dose (3 ppm Se) causing a higher initial accumulation of Hg. The intracellular distribution of²⁰³Hg in the liver and kidney was not affected by Se. The results indicate that selenium treatment of MeHg-exposed mice may have a positive effection the health of the animals by decreasing the total body burden of MeHg.     

Interactions between selenium and methylmercury in rat brain

The interaction of selenium with methylmercury was investigated in brain of animals labeled with ⁷⁵SeO₃^2? and CH₃²⁰³Hg⁺. Brains were fractionated into subcellular components and the cytosol was further fractionated by chromatography on Sephadex G-150 and G-200. The main result of these studies was evidence suggesting a shift of ⁷⁵Se from the cytosol to the mitochondrial fraction in brain when CH₃Hg⁺ was given. Concurrent equimolar (10 μmoles/kg) selenite injections increased the uptake of Hg but did not alter ²⁰³Hg distribution in brain. Changing the dose of CH₃Hg⁺ from 1 to 38 μmoles/kg had little effect on Hg uptake (% of dose per g). Gel filtrations on Sephadex G-150 and G-200 revealed that ²⁰³Hg in cytosol followed a pattern more closely related to protein (A₂₈₀) than to ⁷⁵Se, although a considerable portion of both isotopes eluted with proteins in the void volume. Assays of whole brain homogenates revealed a slight reduction in glutathione peroxidase activity in CH₃Hg⁺-treated rats which was not seen when equimolar selenite was injected with the CH₃Hg⁺.     

Selenite metabolism in rat and human blood

The binding of selenite, the form of selenium used in the treatment of Keshan disease, to plasma proteins and the role of erythrocytes in this process have been studied. The experiments were carried out by incubating⁷⁵Se as selenite with plasma and whole bloodin vitro (human and rat) andin vivo (rat) and subsequent fractionation by Sephadex G-150 gel filtration. Human and rat plasma proteins were unable to incorporate selenium from selenite, as shown by the negligible amount present in proteins after incubation of plasma with selenite. The incorporation can be carried out after internalization of selenite by the erythrocytes in a fast, temperature dependent process. Hemoglobin, being the major binding protein for the newly reduced selenium in the erythrocyte, might have a role in the uptake of selenite by erythrocytes. The greater affinity of plasma proteins for the final selenium compound resulting from reduction could be the cause of the efflux. However, this is minimal in the absence of plasma, as is evident from the results obtained from blood reconstituted with saline solution instead of plasma. At least two proteins, one albumin like, probably albumin itself and the other of molecular weight close to or greater than 200,000 in the plasma, are involved in the binding and efflux processes.     

Incorporation of selenium from selenite and selenocystine into glutathione peroxidase in the isolated perfused rat liver

The erythrocyte-free, isolated perfused rat liver was used to study the incorporation of selenium into glutathione peroxidase. Gel filtration and ion exchange chromatography of liver supernatant demonstrated ⁷⁵Se incorporation into glutathione peroxidase. A 9-fold excess of unlabelled selenium as selenite or selenide very effectively reduced ⁷⁵Se incorporation from L[⁷⁵Se]-selenocystine, but a 100-fold excess of unlabelled selenium as selenocystine was relatively ineffective as compared to selenite or selenide in diluting ⁷⁵Se incorporation from [⁷⁵Se]selenite. These results indicate that selenide and selenite are more readily metabolized than is selenocysteine to the immediate selenium precursor used for glutathione peroxidase synthesis, and suggest a posttranslational modification at another amino acid residue, rather than direct incorporation of selenocysteine, as the mechanism for formation of the presumed selenocysteine moiety of the enzyme.     

Exploring the structural basis for selenium/mercury antagonism in Allium fistulosum

While continuing efforts are devoted to studying the mutually protective effect of mercury and selenium in mammals, few studies have investigated the mercury-selenium antagonism in plants. In this study, we report the metabolic fate of mercury and selenium in Allium fistulosum (green onion) after supplementation with sodium selenite and mercuric chloride. Analysis of homogenized root extracts via capillary reversed phase chromatography coupled with inductively coupled plasma mass spectrometry (capRPLC-ICP-MS) suggests the formation of a mercury-selenium containing compound. Micro-focused synchrotron X-ray fluorescence mapping of freshly excised roots show Hg sequestered on the root surface and outlining individual root cells, while Se is more evenly distributed throughout the root. There are also discrete Hg-only, Se-only regions and an overall strong correlation between Hg and Se throughout the root. Analysis of the X-ray absorption near edge structure (XANES) spectra show a "background" of methylselenocysteine within the root with discrete spots of SeO(3)(2-), Se(0) and solid HgSe on the root surface. Mercury outlining individual root cells is possibly binding to sulfhydryl groups or plasma membrane or cell wall proteins, and in some places reacting with reduced selenium in the rhizosphere to form a mercury(ii) selenide species. Together with the formation of the root-bound mercury(ii) selenide species, we also report on the formation of cinnabar (HgS) and Hg(0) in the rhizosphere. The results presented herein shed light on the intricate chemical and biological processes occurring within the rhizosphere that influence Hg and Se bioavailability and will be instrumental in predicting the fate and assisting in the remediation of these metals in the environment and informing whether or not fruit and vegetable food selection from aerial plant compartments or roots from plants grown in Hg contaminated soils, are safe for consumption.     

Elevated mercury bound to serum proteins in methylmercury poisoned rats after selenium treatment

Methylmercury is a toxic pollutant and is generated by microbial methylation of elemental or inorganic mercury in the environment. Previous study found decreased hepatic MDA levels and urinary mercury levels in methylmercury poisoned rats after sodium selenite treatment. This study further found increased mercury levels in serum samples from methylmercury poisoned rats after selenium treatment. By using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry, three Hg- binding protein fractions and two Se-binding protein fractions were identified with the molecular weight of approximately 21, 40, and 75 kDa and of 40 and 75 kDa, respectively. Elevated mercury level in the 75 kDa protein fraction was found binding with both Hg and Se, which may explain the decreased urinary Hg excretion in MeHg poisoned rats after Se treatment. MALDI-TOF-MS analysis of the serum found that the 75 kDa protein fractions were albumin binding with both Hg and Se and the 21 kDa fraction was Hg- binding metallothionein.     

Milk transfer of inorganic mercury to suckling rats

The transport of mercury into rat milk, and uptake in the suckling offspring was studied after peroral administration of inorganic mercury to lactating control rats, and to rats fed selenite in the diet. On day 8, 9, 10, or 11 of lactation, dams were administered a single oral dose of 0.1, 0.4, 0.7, 1.3, or 5.8 mg Hg/kg bw labeled with 203mercuric acetate. There was a linear relationship between mercury concentrations in dam's plasma and milk. The level of mercury in milk was approximately 25% of the level in plasma. After 3 d, milk levels were reduced to half the levels at 24 h. In the suckling offspring, exposed to mercury via milk during 3 d, the mercury level in blood was approximately 1% of the level in maternal blood. Mercury concentration in milk was linearly correlated to the levels in kidney, liver, and brain in the suckling offspring after 3 d exposure to mercury via milk. Selenite treatment of rats, 1.3 micrograms Se/g diet for 5 mo, resulted in increased transport of mercury to milk, probably because of increased plasma levels of mercury. However, selenite treatment of the dams did not cause any increased tissue levels of mercury in the suckling offspring.     

Changed Clinical Chemistry Pattern in Blood After Removal of Dental Amalgam and other Metal Alloys Supported by Antioxidant Therapy

This study aimed to investigate a possible connection between removal of dental amalgam restorations supported by antioxidant therapy and indicative changes of clinical chemistry parameters. A group of 24 patients, referred for complaints related to amalgam restorations, underwent a removal of their amalgams. All patients were treated with antioxidants (vitamin B-complex, vitamin C, vitamin E, and sodium selenite). An age- and sex-matched control group of 22 individuals was also included. The mercury (Hg) and selenium (Se) concentration in plasma, Hg concentration in erythrocytes, and 17 clinical chemistry variables were examined in three groups: patients before amalgam removal (Before), patients after amalgam removal (After), and control individuals (Control). The Hg and Se values decreased (p < 0.05) in plasma, and the Hg concentration decreased (p < 0.05) in erythrocytes after amalgam removal. The variables serum lactate dehydrogenase (serum LDH) and serum sodium differed significantly both when comparing Control with Before (p < 0.01) and Before with After (p < 0.01). The variables white blood cell count (WBC), blood neutrophil count, blood eosinophil count, blood basophil count, blood lymphocyte count, blood monocyte count, serum potassium, and serum creatinine differed in the Before/After test (p < 0.05). Multivariate statistics (discriminant function analysis) could separate the groups Before and After with only one misclassification.     

The metabolism of selenite and selenomethionine in mouse fibroblasts grown in tissue culture

Recent reports have provided evidence that selenium is an essential growth factor for cells grown in tissue culture. The aim of the work reported in this paper was to evaluate mouse fibroblasts as a model for the study of selenium metabolism in mammalian cells. The results showed that transformed mouse lung fibroblasts grown in media containing 9.1% bovine serum did not show a growth response to added selenium as selenite over the range of 10–1000 ng/mL. Uptake of selenium by cells was a direct function of the selenium concentration in the medium. The rate of uptake varied with the time of exposure of the cells to the selenium, and to the form of selenium in the medium. Experiments using radioactive selenium showed that⁷⁵Se from selenite was rapidly absorbed into the cell wall, but slowly incorporated into the soluble protein fraction.⁷⁵Se from selenomethionine was more slowly absorbed into the cells, but once inside, it became rapidly incorporated into soluble cytoplasmic proteins. Cell fractionation and gel filtration procedures established that⁷⁵Se from selenite was rapidly incorporated into glutathione peroxidase (GSHpx), whereas⁷⁵Se from selenomethionine was initially incorporated into a wide spectrum of proteins and only after a longer period did the⁷⁵Se peak become associated with GSHpx. These findings suggest fundamental differences exist in the manner in which mammalian cells initially absorb and metabolize different selenium compounds.     

A proton nuclear magnetic resonance study of the interaction of mercury with intact human erythrocytes

The binding of mercuric ion (Hg(II)) by small molecules in the intracellular region of intact human erythrocytes has been studied by ¹H-NMR spectroscopy. HgCl₂ added to intact erythrocytes in saline-glucose suspension is found to cross the membrane and reach an equilibrium distribution among the molecules of the erythrocyte within 4 min. In the intracellular region Hg(II) reacts with GSH and hemoglobin to form the ternary mixed-ligand complex GSH-Hg(II)-hemoglobin. The analogous complex with ergothioneine is formed after all the GSH is complexed. ¹H-NMR spectra show that the GSH-Hg(II)-hemoglobin complex also forms in simpler solutions containing HgCl₂, GSH and hemoglobin, whereas the complex Hg(GSH)₂ predominates in solutions of GSH and HgCl₂. The lifetime of the GSH in the GSH-Hg(II)-hemoglobin complex is shown to be less than 30 s, which provides direct evidence for the first time that Hg(II) complexes in biological systems are quite labile, even though their thermodynamic stability is large. The effectiveness of eight sulfhydryl-containing ligands, some of which have been used as antidotes for Hg(II) poisoning, for releasing GSH from its Hg(II) complex in hemolyzed erythrocytes was also studied. Dithiol ligands were found to be more effective than monothiols, with dithioerythritol the most effective of the dithiols.     

Selenium-mediated biochemical changes in Japanese quails

The tissue uptake and distribution of injected [⁷⁵Se]-sodium selenite as a variance with time and as influenced by dietary selenium status was followed in the tissues of Japanese quails,Coturnix coturnix japonica. Quails maintained on a low selenium semipurified (basal) diet and basal diets supplemented with 0.2 and 2.0 ppm selenium as sodium selenite were injected intraperitonially with⁷⁵Se as sodium selenite (2.8 microcuries). The injected⁷⁵Se was monitored in blood, liver, kidney, heart, and testis at 24, 72, and 144 h after injection. Maximal uptake of the injected⁷⁵Se was observed in tissues of quails maintained on basal diet. The uptake of⁷⁵Se in tissues in general was determined by the dietary Se status. Among the organs studied, kidney had the maximal level of⁷⁵Se, 0.2 ppm (μg/g wet tissue) followed by liver, testis, and heart, but testis had the maximal level when the level per milligram of protein was considered, about 3.0 ng/mg protein, followed by liver, kidney, and heart. About 10–20% of the tissue⁷⁵Se was located in the mitochondria and 50–60% in the post-mitochondrial supernatant fractions in all dietary Se levels. Significant incorporation of⁷⁵Se in the mitochondrial membrane was observed. The percent distribution ratio between the membrane and matrix fractions of the mitochondria remained constant at all dietary Se levels which, in liver was 65∶35, in kidney 55∶45, and in testis 75∶25. However, in heart mitochondria, the distribution of⁷⁵Se between membrane and matrix varied with dietary Se status, the ratio being 82∶18 in the basal group, and 72∶28 and 41∶59 in the 0.2 and 2.0 ppm Se-supplemented groups, respectively. This is indicative of a preferential uptake of⁷⁵Se in the mitochondrial membrane in conditions of deficiency. About 40–60% of the mitochondrial membrane-associated⁷⁵Se was released upon Triton treatment in all the organs. Of the membrane-bound⁷⁵Se, about 10–15% was acid-labile in liver and kidney and 25% in the heart tissue. Possibilities of tissue specific roles, especially in the heart mitochondrial membrane-related processes, are indicated for selenium.     

Effects of glutathione and of cysteine on intestinal absorption of selenium from selenite

The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of⁷⁵Se-labeled selenite (10 μmol/L) was investigated in rat jejunum. For comparison, the effect ofl-cysteine (1 mmol/L) on in vivo absorption of⁷⁵Se-labeled selenite was also studied. In the in vitro, uptake experiments, only the mucosal surface was exposed to the incubation medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal Se uptake, whereas absorption in vivo was stimulated by GSH.l-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlikel-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of the reaction of selenite with GSH occuring more efficiently under in vivo than in vitro conditions may be a prerequisite for the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since, GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from selenite.     

Selenium–Mercury Interactions in Man and Animals

Selenium–mercury interactions were most extensively studied in relation to alleviation of Hg toxicity by added selenium. This presentation considers the influence of mercury on endogenous selenium, on its tissue and cellular “status” after lifelong or acute exposure to mercury vapor (Hg^o). Discussed are data obtained from (1) humans living near or working in a mercury mine, and (2) rats experimentally exposed in the mine. Mercury vapor is unique—or similar to methylmercury—because of its ability to penetrate cell membranes and so invade all cells, where it is oxidized in the biologically active form (Hg⁺⁺) by catalase. Such in situ-generated ions can react with endogenously generated highly reactive Se metabolites, like HSe−, and render a part of the selenium unavailable for selenoprotein synthesis. Data on human populations indicate that in moderate Hg exposure combined with an adequate selenium supply through diet, Se bioavailability can be preserved. On the other hand, the results of an acute exposure study emphasize the dual role of selenium in mercury detoxification. Besides the well-known Se coaccumulation through formation of nontoxic Hg–Se complexes, we observed noticeable Se (co)excretion, at least at the beginning of exposure. The higher Hg accumulation rate in the group of animals with lower basal selenium levels can also point to selenium involvement in mercury excretion. In such conditions there is a higher probability for decreased selenoprotein levels (synthesis) in some tissues or organs, depending on the synthesis hierarchy.     

Interactive effects of organic and inorganic selenium with cadmium and mercury on spermatozoal oxygen consumption and motility in vitro

The effects of cadmium (Cd), mercury (Hg), and three different chemical forms of selenium (Se) (selenite, selenocystine, and selenomethionine) on ram spermatozoal motility and oxygen consumption in vitro were studied over a 4-mo period. Concentrations of 10(-6) to 10(-2) M Cd and Hg were injurious to spermatozoa as indicated by depressed motility and reduced oxygen uptake. Equimolar concentrations of Se as selenite, selenocystine, or selenomethionine counteracted the toxicity of Cd and Hg at low concentrations (10(-5) and 10(-6) M) but not at higher concentrations (10(-4) to 10(-2) M). Gel filtration (Sephadex G-75) of seminal plasma and solubilized sperm prepared from semen incubated with Cd or Hg with or without the Se compounds revealed that Cd or Hg eluted with the void volume proteins in all treatments. Incubation of ram spermatozoa with any of the three chemical forms of Se ranging from 10(-6) to 2.5 X 10(-5) M significantly improved sperm motility and oxygen consumption.     

The bioavailability of various selenium compounds to a marine wading bird

The uptake of dietary selenium (about 3.5 mg/kg AF dry wt) as selenomethionine, selenocystine, selenite, selenate, and fish selenium in the plasma and red blood cells (RBC) of the oystercatcher has been investigated. The birds received the various selenium compounds subsequently, for at least 9 wk. After dietary supplementation of selenocystine, selenite, and selenate, plasma selenium was about 350 μg/L and RBC selenium 2.1 mg/kg dry wt. After supplementation of selenomethionine, the plasma concentration increased to 630 μg/L, and the RBC concentration to 4.1 mg/kg dry wt. When the fodder contained 3.1 mg/kg fish Se, an average plasma and RBC concentration of 415 μg/L and 14.4 mg/kg dry wt, respectively, was measured. The maximal increase of the selenium concentration in the plasma was attained at first sampling, 14 d after a change in dietary selenium (selenomethione or fish Se); the uptake seemed to be a concentration-regulated process. RBC concentrations (γ in mg/kg dry wt) increased with time (X in d) according toY=a?be^?cX . Fifty percent of the total increase was attained within 17d, suggesting that diffusion into the RBC played a role. The selenium concentration in the plasma was positively correlated with the (fish) Se concentration in the fodder; the RBC concentration (60 d after the change in diet) was positively correlated with the plasma concentration. When the diet contained fish Se, the blood selenium concentrations of the captive birds were similar to the concentrations measured in field birds. Fish Se is a yet undetermined selenium compound. The present experiment showed that fish Se differed from selenomethionine, selenocystine, selenite, or selenate in uptake from the food and uptake in the RBC.     

Influence of dietary selenium on metabolism of cadmium and mercury in reproductive tissues of rats

Dietary selenium supplementation for rats resulted in a greater deposition of ¹⁰⁹Cd in testis, but caused decreased deposition of the isotope in seminal vesicles, epididymis and prostate gland. In contrast, dietary selenium caused increased deposition of ²⁰³Hg in seminal vesicles and prostate gland but drastically reduced the levels of this radioisotope in testis and epididymis. Selenium diverted the binding of ¹⁰⁹Cd in cytosols in testis, seminal vesicles, epididymis and prostate gland, but had minimal effects on the binding of ²⁰³Hg in these reproductive organs. Selenium deficiency caused increased excretion of ¹⁰⁹Cd in feces and urine, and increased excretion of ²⁰³Hg in urine of rats. The biological half-lives of the two radioisotopes in the −Se and +Se rats were calculated to be, respectively, 202 and 219 days for ¹⁰⁹Cd, and 2 and 6 days for ²⁰³Hg.     

Fish eating and variations in selenium and mercury levels in plasma and erythrocytes in free-living healthy Japanese men

The levels and its interindividual and intraindividual variations of selenium (Se) and mercury (Hg) in erythrocytes and plasma were investigated in seven healthy young men during a period of 10 wk, with emphasis on the relationship to the dietary intake of several defined food items. The intraindividual variation, estimated by coefficients of variation (CVs), was 9.9% for plasma Se (PSe), 9.5% for erythrocyte Se (ESe), 42.4% for PHg, and 11.7% for EHg on the average. Significant correlations were found for mean ESe levels in each subject and his fish-eating frequency during this study (r=0.752, p<0.01). Weekly PHg levels were also correlated with average fish-eating frequency in the corresponding week of blood collection (r=0.367, p<0.05). Fish intake within 24 h before blood collection influenced PHg levels significantly.     

The relationships of Hg(II) volatilization from a freshwater pond to the abundance ofmer genes in the gene pool of the indigenous microbial community

The role of biological activities in the reduction and volatilization of Hg(II) from a polluted pond was investigated. Elemental mercury was evolved from pond water immediately following spiking with²⁰³Hg(NO₃)₂, whereas an acclimation period of 36 hours was required in control samples collected from a nearby, unpolluted river before onset of volatilization. Genes encoding the bacterial mercuric reductase enzyme (mer genes) were abundant in DNA fractions extracted from biomass of the pond microbial community, but not in samples extracted from control communities. Thus, evolution of Hg⁰ was probably due to activities mediated by the bacterial mercuric reductase. Of four characterizedmer operons, the system encoded by transposon 501 (mer(Tn501)) dominated and likely contributed to the majority of the observed Hg(II) volatilization. Thus,mer-mediated reduction and volatilization could be used to reduce Hg(II) concentrations in polluted waters, in turn decreasing rates of methylmercury formation by limiting substrate availability.