Mercury elemental, ionic

The renal effects of mercury vapor are also considered to result from the conversion of mercury to ionic mercury by the oxidation of elemental mercury. 

In electrogravimetry, also called electrodeposition, an element, e.g., a metal such as copper, is completely precipitated from its ionic solution on an inert cathode, e.g., platinum gauze, via electrolysis and the amount of precipitate is established gravimetrically in the newer and more selective methods one applies slow electrolysis (without stirring) or rapid electrolysis (with stirring), both procedures either with a controlled potential or with a constant current. Often such a method is preceded by an electrolytic separation using a stirred cathodic mercury pool, by means of which elements such as Fe, Ni, Co, Cu, Zn and Cd are quantitatively taken up from an acidic solution whilst other elements remain in solution. 

Mercury (Hg) can occur in a large number of physical and chemical forms with a variety of properties, thus determining complex distribution, bioavailability, and toxicity patterns [1]. The most important chemical forms are elemental Hg (Hg°), ionic Hg (Hg2+ and Hg22+), and alkylmercury compounds. Because of their capability to permeate through biological membranes and to bioaccumulate and to biomagnificate through the trophic chain, alkylmercury compounds are the most toxic mercury species found in the aquatic environment [2]. 

Complexation of metals with organic compounds can also increase the toxicity of metals. This is the case with mercury, in which the organo-Hg species, methyl- and dimethylmercury, are fer more toxic than elemental or ionic mercury (Hg (aq)). The enhanced toxicity is caused by the increased tendency of the organo species to be retained, and therefore concentrated within, organisms. As discussed in Chapter 28.6.8, mercury is naturally biomethylated by bacteria under conditions of low pH and low... 

Mercury may be present in air in different chemical states such as the elemental form (as a vapour or adsorbed on particular matter) or in the form of volatile mercury compounds (mercury chloride, methyl-mercuric chloride, and dimethyl mercury). Although elemental mercury is only one of the mercury forms which is not as toxic as its organic or ionic forms, analytical determination of elemental mercury is of special importance. Such analysis is used not only for determination of elemental mercury in environment, but also as a method for determination of other forms of mercury after reductive treatment. 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

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