Arsenic methylation biological

Del Razo, L.M., Styblo, M., Cullen, W.R. and Thomas, D.J. (2001b) Determination of trivalent methylated arsenicals in biological matrices. Toxicology and Applied Pharmacology, 174(3), 282-93. 

Frost DV (1967) Arsenicals in biology. Retrospect and prospect. Fed Proc 26 194-208 Fuentes N, Zambrano F, Rosenmann M (1981) Arsenic contamination metabolic effects and localization in rats. Comp Biochem Physiol 70C 269-272 Gadd GM (1993) Microbial formation and transformation of organometallic and organometalloid compounds. FEMS Microbiol Rev 11 297-316 Georis B, Cardenas A, Buchet JP, Lauwerys R (1990) Inorganic arsenic methylation by rat tissue slices. Toxicology 63 73-84... 

From a practical point of view, saturation of elimination has important consequences. If the metabolism becomes saturated, the duration of the action of the compound is prolonged. In such a case, correct timing for collection of biological monitoring samples also becomes difficult to assess. Furthermore, saturation of metabolism may also have qualitative effects. For example, it has been argued (but not yet proved) that arsenic compounds cause cancer at high doses at which methylation of inorganic arsenic becomes saturated. ... 

The biological cycle of arsenic in the surface ocean involves the uptake of arsenate by plankton, the conversion of arsenate to a number of as yet unidentified organic compounds, and the release of arsenite and methylated species into the seawater. Biological demethylation of the methyl-arsenicals and the oxidation of arsenite by as yet... 

It is now well established that organometallic compounds are formed in the environment from mercury, arsenic, selenium, tellurium and tin and hence were also deduced on the basis of analytical evidence for lead, germanium, antimony and thallium. Biological methylation of tin has been demonstrated by the use of experimental organisms. Methylgermanium and methyllead were widely found in the environment but it is debatable whether germanium and lead are directly methylated by biological activity in natural environment. 

The classic studies by Challenger (127-129) on microbial methyla-tion of arsenic still provide the basis of our understanding of these processes. Although Challenger s work focused on mycological methyla-tions (he mistakenly believed that bacteria did not methylate arsenic), the scheme he proposed is applicable to other biological systems as well. It is briefly discussed here, together with the confirmatory studies of Cullen and co-workers. 

On the basis of chemical profile, Wood (38) predicted that arsenic, selenium, and tellurium will be methylated in the environment, and lead, cadmium, and zinc will not. Elemental concentration in the aquatic food chain has been reported for As (39), Hg (40), Cd (41), Pb (42), and Cu (43). The biological half-life of methylmercury in fish, for example, is one to two years (44). Pillay et al. (40) implicated heavy coal burning in the mercurial contamination of plankton and fish populations of Lake Erie. Other metals, notably cadmium, have been shown to be incorporated into the grazing grasses surrounding a coal burning source (27). Trace element contamination, therefore, can enter the food chain at various points. Disposal of solid wastes in the form of ash and slag is yet another environmental consideration (45). 

Historically, the investigations into biological methylation have followed two separate and distinct lines of research whose relationships have only recently become apparent and which remain to be fully developed. The first and older line had its origin in the arsenic rooms of the... 

In natural waters, arsenic may exist as one or more dissolved species, whose chemistry would depend on the chemistry of the waters. Over time, arsenic species dissolved in water may (1) interact with biological organisms and possibly methylate or demethylate (Chapter 4), (2) undergo abiotic or biotic oxidation, reduction, or other reactions, (3) sorb onto solids, often through ion exchange, (4) precipitate, or (5) coprecipitate. This section discusses the dissolution of solid arsenic compounds in water, the chemistry of dissolved arsenic species in aqueous solutions, and how the chemistry of the dissolved species varies with water chemistry and, in particular, pH, redox conditions, and the presence of dissolved sulfides. Discussions also include introductions to sorption, ion exchange, precipitation, and coprecipitation, which have important applications with arsenic in natural environments (Chapters 3 and 6) and water treatment technologies (Chapter 7). 

Bentley, R. and Chasteen, T.G. (2002) Microbial methylation of metalloids arsenic, antimony, and bismuth. Microbiology and Molecular Biology Reviews, 66(2), 250-71. 

Marafante, E., Vahter, M. and Envall, J. (1985) The role of the methylation in the detoxication of arsenate in the rabbit. Chemico-Biological Interactions, 56(2-3), 225-38. 

Henry and Thorpe [14] separated monomethylarsonic acid, dimethylarsenic acid, As(III) and As(IV) on an ion exchange column from samples of pond water receiving fly ash from a coal-fired power station. They then determined these substances by differential pulse polarography. The above four arsenic species were present in non saline water systems. Moreover, a dynamic relationship exists whereby oxidation-reduction and biological methylation-dimethylation reactions provide the pathways for the intercoversions of the arsenicals. 

Biological methylation of arsenic is effected via the transfer of a carbocation, a process known as oxidative... 

The leaching of arsenic forms is usually performed from soil or from tissues of plants or marine animals. The extraction of materials of biological origin typically involves methanol or mixtures of methanol and water. Solutions obtained by centrifugation and filtration are diluted with water and then loaded into an ion-exchange column. The method is applied for assay of arsenic acid salts and arsenosugars, even though they are more easily soluble in water than in methanol. This method of extraction into a solution involves transfer of a smaller quantity of toxic As(III) and As(V) salts than methylated derivatives and AsB or AsC, which are of markedly lower toxicity [88]. 

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