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Results for “Methylmercury Compounds”

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At least 19 recordsLinked to original sources
PubMed1990

Interaction of methylmercury compounds with albumin.

The nature of interaction between bovine serum albumin (BSA) and methylmercurial compounds has been investigated by ultrafiltration analysis. Four types of BSA samples, mercaptalbumin, its mixed disulfides with glutathione (GSH) and L-cysteine (CySH), and S-carbamidomethylated derivative, were used for binding assays with methylmercury (MM) chloride (MMC) and three kinds of MM mercaptides of low molecular weight thiols, GSH (GS-MM), CySH (CyS-MM) and cysteinylglycine (CG-MM). Among various ligands tested, MMC showed the highest affinity for all BSA species, and the BSA-bound fraction of the ligand did not change with ligand/protein ratio. MMC strongly and stoichiometrically bound to mercaptalbumin even at a molar ratio of 1:1. In contrast, the albumin bound fractions of three other MM ligands increased with concomitant decrease in ligand/protein ratio and with time except for the alkylated albumin, the highest binding being shown by mercaptalbumin. Binding of S-2-nitrophenyl-glutathione, a GSH analog with a hydrophobic S-substituent, to albumin species occurred similarly to that of GS-MM. However, GSH and oxidized glutathione (GSSG) interacted differently with albumin; mercaptalbumin showed the lowest affinity for GSH, and GSSG scarcely interacted with all BSA species. These results suggest that the sulfhydryl group at Cys-34 is not the only site of BSA that interacts with MM compounds and that albumin interacts preferentially with the hydrophobic domains of a mercurial ligand rather than its hydrophilic peptide moiety.

Animals↗
PubMed1983

A review of the toxicity of methylmercury compounds with application to occupational exposures associated with laboratory uses.

The toxicological and physicochemical properties of methylmercury compounds are reviewed together in an attempt to foster a conceptual synthesis between the biochemistry and toxicity of these compounds. Where insights from chemical analysis bear on conclusions derivable from earlier toxicology studies, these studies have in some instances been reinterpreted. Physical and toxicity data alike are relevant to evaluating risk, and an application of these principles is made to assess occupational exposures in the particular setting of the laboratory. Information is presented from which hazard evaluation may be extrapolated to include a wide range of other exposure environments.

Carcinogens↗
PubMed1990

Absorption of methylmercury compounds from rat intestine.

Intestinal absorption of methylmercury complexed with non-protein sulfhydryl compounds (NPSHs) as occurs in bile was studied by means of direct injection of mercury compounds into ligated intestinal segments of rats. The extent of absorption of methylmercury-cysteinylglycine (MM-CysGly) was similar to that of methylmercury-cysteine (MM-Cys) and 1.5 times larger than that of methylmercury-glutathione (MM-GSH). This results suggested that MM-CysGly, which is recognized as a major component of methylmercury in rat bile, can be easily reabsorbed from the intestine. These results indicate that not only MM-GSH and MM-Cys but also MM-CysGly may play important roles in the intestinal reabsorption of methylmercury during its enterohepatic circulation. When the ligated intestine was pretreated with probenecid and acivicin, the intestinal absorption of MM-GSH was depressed much more than in the case of treatment with acivicin alone. This indicates the possibility that there are at least two systems for intestinal transport of MM-GSH, i.e. gamma-glutamyltranspeptidase (GGT)-dependent and -independent systems.

Animals↗
PubMedDate not supplied

Biosynthesis of methylmercury compounds by the intestinal flora of the rat.

The contents of the rat cecum and, to a lesser extent, those of the small intestine, synthesized methylmercury from mercuric chloride labeled with Hg 203 in vitro under aerobic or anaerobic conditions. The rate of formation was approximately 18 ng/g cecal contents/20 hr. The synthesis of methylmercury was inhibited by antibiotics and by filtration of the cecal contents through membrane filters, indicating that the bacterial flora of the gut participates in the reaction. Pure cultures of bacteria, isolated from the intestinal tract of the rat, could methylate mercuric chloride. It was estimated that the total amount of methylmercury synthesized from ingested inorganic mercury in man in approximately 400 ng/day.

Anaerobiosis↗
PubMed1999

Current status and future needs for biological and environmental reference materials certified for methylmercury compounds.

A good quality control/quality assurance programme should be implemented in all environmental or health related studies on mercury and its organic compounds, particularly, for monomethylmercury (MeHg) which is the most toxic mercury compound. This can be achieved initially by analysing suitable certified reference materials (CRMs), which are available from various producers such as the National Institute of Standards and Technology (NIST) from USA, National Institute of Environmental Studies (NIES), National Research Council of Canada (NRCC), Standards, Measurements and Testing programme (SM&T) of the European Commission, and the International Atomic Energy Agency (IAEA). It is well understood that these materials are not covering present needs, as most of them are of the marine origin, while many laboratories are conducting research and monitoring in terrestrial ecosystems and fresh water environment. In addition, CRMs for human exposure assessment, such as blood, urine, and hair at several levels of concentrations are still lacking. Therefore, many other actions should be undertaken to achieve, improve and/or maintain quality of data, including participation in interlaboratory studies, proficiency testing and production of laboratory reference materials. A review of these actions has shown that MeHg compounds determination in samples such as soil, sediment and water is rather difficult and the results are also method dependent. In addition, it has been shown that some of the most frequently employed analytical methods may be a subject to spurious MeHg formation in the presence of high concentrations of inorganic mercury and organic matter. These findings have put a number of previous data on MeHg in question and consequently prompt actions were undertaken by a number of well experienced laboratories and producers of CRMs. So far, it is shown that the results obtained by various laboratories using different analytical techniques agree well with certified values in all RMs certified for MeHg. This suggests that comparability of data can be achieved, which however is not a guarantee of the true values.

Animals↗
PubMed2002

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters.

The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg(2+)) and monomethylmercury compounds (MeHg) in natural water samples at the pg L(-1) level. The method is based on the simultaneous extraction of MeHg and Hg(2+)dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na(2)S, removal of H(2)S by purging with N(2), subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L(-1) for MeHg and 0.06 ng L(-1) for Hg(2+)when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg(2+). Recoveries were 90-110% for both species.

Chromatography, Gas↗
PubMed1993

Carcinogenicity of trace elements with reference to evaluations made by the International Agency for Research on Cancer.

The monograph program of the International Agency for Research of on Cancer has evaluated many trace elements for their carcinogenicity to humans. Five groups of compounds were considered human carcinogens: arsenic and arsenic compounds, beryllium and beryllium compounds, cadmium and cadmium compounds, hexavalent chromium compounds, and nickel compounds. Antimony trioxide, cobalt and cobalt compounds, lead and inorganic lead compounds, methylmercury compounds, and metallic nickel were considered possibly carcinogenic to humans. Antimony trisulfide, trivalent chromium compounds, metallic chromium, ferric oxide, organolead compounds, metallic mercury, inorganic mercury compounds, selenium and selenium compounds, and titanium dioxide were not classifiable. Trace elements studied to a limited extent include copper, manganese, tin, vanadium, and zinc. Among the problems are the lack of relevant data, the definition of active species, the extrapolation of the results of experimental studies to humans, the methodological problems of epidemiologic studies, and the possible anticarcinogenic activity of some trace elements.

Humans↗
PubMed1995

Environmental contaminants in the food chain.

Both terrestrial and aquatic food chains are capable of accumulating certain environmental contaminants to toxic concentrations. This article focuses on the aquatic food chain because we have less control over contaminant entry into this chain than we have for the terrestrial chain. In general, at least three special properties are required for a contaminant to bioaccumulate in an aquatic food chain: 1) a high octanol-water partition coefficient, 2) chemical and metabolic stability in water and in organisms in the food chain, and 3) a low toxicity to organisms in the chain so that the chain is not broken by loss of an intermediate species. Few of the thousands of chemicals produced by human industry meet these requirements. In terms of organic chemicals, the best known examples of bioaccumulation in aquatic food chains are the polychlorinated biphenyls (PCBs), dioxins, and organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT). Few examples exist of bioaccumulation of metal compounds. Methylmercury is arguably the most dramatic and best documented example of high bioaccumulation.

Animals↗