RESUMO
The compounds of mercury can be more toxic than those of any other non-radioactive heavy element. Despite this, environmental mercury pollution and human exposure to mercury are widespread, and are increasing. While the unusual ability of selenium to cancel the toxicity of mercury compounds has been known for nearly five decades, only recently have some aspects of the molecular mechanisms begun to be understood. We report herein a study of the interaction of mercury and selenium in the larval stage zebrafish, a model vertebrate system, using X-ray fluorescence imaging. Exposure of larval zebrafish to inorganic mercury shows nano-scale structures containing co-localized mercury and selenium. No such co-localization is seen with methylmercury exposure under similar conditions. Micro X-ray absorption spectra support the hypothesis that the co-localized deposits are most likely comprised of highly insoluble mixed chalcogenide HgSxSe(1-x) where x is 0.4-0.9, probably with the cubic zincblende structure.
Assuntos
Poluentes Ambientais/metabolismo , Mercúrio/metabolismo , Compostos de Metilmercúrio/metabolismo , Selênio/metabolismo , Peixe-Zebra/metabolismo , Animais , Poluentes Ambientais/análise , Larva/metabolismo , Larva/ultraestrutura , Mercúrio/análise , Compostos de Metilmercúrio/análise , Modelos Moleculares , Imagem Óptica , Selênio/análiseRESUMO
Human exposure to potentially neurotoxic methylmercury species is a public-health concern for many populations worldwide. Both fish and whale are known to contain varying amounts of methylmercury species. However studies of populations that consume large quantities of fish or whale have provided no clear consensus as to the extent of the risk. The toxicological profile of an element depends strongly on its chemical form. We have used X-ray absorption spectroscopy to investigate the comparative chemical forms of mercury and selenium in fish and whale skeletal muscle. The predominant chemical form of mercury in whale is found to closely resemble that found in fish. In the samples of skeletal muscle studied, no involvement of selenium in coordination of mercury is indicated in either whale or fish, with no significant inorganic HgSe or HgS type phases being detected. The selenium speciation in fish and whale shows that similar chemical types are present in each, but in significantly different proportions. Our results suggest that for equal amounts of Hg in skeletal muscle, the direct detrimental effects arising from the mercury content from consuming skeletal muscle from whale and fish should be similar if the effects of interactions with other components in the meat are not considered.
Assuntos
Mercúrio/química , Músculo Esquelético/química , Selênio/química , Poluentes Químicos da Água/química , Baleias/anatomia & histologia , Animais , Feminino , Peixes , Humanos , Análise dos Mínimos Quadrados , Mercúrio/toxicidade , Selênio/toxicidade , Espectroscopia por Absorção de Raios XRESUMO
Methylmercury is among the most potentially toxic species to which human populations are exposed, both at high levels through poisonings and at lower levels through consumption of fish and other seafood. However, the molecular mechanisms of methylmercury toxicity in humans remain poorly understood. We used synchrotron X-ray absorption spectroscopy (XAS) to study mercury chemical forms in human brain tissue. Individuals poisoned with high levels of methylmercury species showed elevated cortical selenium with significant proportions of nanoparticulate mercuric selenide plus some inorganic mercury and methylmercury bound to organic sulfur. Individuals with a lifetime of high fish consumption showed much lower levels of mercuric selenide and methylmercury cysteineate. Mercury exposure did not perturb organic selenium levels. These results elucidate a key detoxification pathway in the central nervous system and provide new insights into the appropriate methods for biological monitoring.
Assuntos
Química Encefálica , Poluentes Ambientais/intoxicação , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Mercúrio/análise , Compostos de Metilmercúrio/intoxicação , Absorciometria de Fóton , Acidentes de Trabalho , Idoso , Animais , Criança , Cisteína/análogos & derivados , Cisteína/análise , Exposição Ambiental , Poluentes Ambientais/farmacocinética , Feminino , Peixes , Contaminação de Alimentos , Humanos , Inativação Metabólica , Masculino , Carne/análise , Mercúrio/química , Compostos de Mercúrio/análise , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Compostos de Metilmercúrio/análise , Compostos de Metilmercúrio/farmacocinética , Pessoa de Meia-Idade , Modelos Moleculares , Estrutura Molecular , Nanopartículas , New York , Imagem Óptica , Selênio/análise , Compostos de Selênio/análise , Seicheles , SuínosRESUMO
Using a combination of As and Se K-edge and Hg L(III)-edge X-ray absorption spectroscopy, 77Se nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry and molecular modeling, we have structurally characterized the novel species methylmercury(II) seleno bis(S-glutathionyl) arsenic(III). This species is formed in aqueous solution from CH3HgOH and the seleno bis(S-glutathionyl) arsinium ion and constitutes an important first step towards characterizing the observed toxicologically relevant interaction between arsenite, selenite and methylmercury which has been previously reported in mammals.