Arsenic and Selenium

After rising at copper and zinc, the curve of metallic radii approaches those of the normal covalent radii and tetrahedral covalent radii (which themselves differ for arsenic, selenium, and bromine because of the difference in character of the bond orbitals, which approximate p orbitals for normal covalent bonds and sp3 orbitals for tetrahedral bonds). The bond orbitals for gallium are expected to be composed of 0.22 d orbital, one s orbital, and 2.22 p orbitals, and hence to be only slightly stronger than tetrahedral bonds, as is indicated by the fact that R(l) is smaller than the tetrahedral radius. 

The term metallo-organic is used somewhat loosely in CVD parlance, since it includes compounds of elements, such as silicon, phosphorus, arsenic, selenium, and tellurium, that are not considered metallic. To conform to what appears to be a well-established tradition, such nonmetal compounds will be included here as metallo-organics. 

Mason RP, Laporte J, Andres S. 2000. Factors controlling the bioaccumulation of mercury, methyhnercury, arsenic, selenium, and cadmium by freshwater invertebrates and fish. Arch Environ Contam Toxicol 38 283-297. 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

About 100 gal of process wastewater is typically generated from 1 t of coke produced.15 These wastewaters from byproduct coke making contain high levels of oil and grease, ammonia nitrogen, sulfides, cyanides, thiocyanates, phenols, benzenes, toluene, xylene, other aromatic volatile components, and polynuclear aromatic compounds. They may also contain toxic metals such as antimony, arsenic, selenium, and zinc. Water-to-air transfer of pollutants may take place due to the escape of volatile pollutants from open equalization and storage tanks and other wastewater treatment systems in the plant. 

Electrolyte preparation (arsenic, selenium, and zinc) pH is slightly alkaline... 

Arsenic, selenium and tellurium all react with incandescence on heating [1], Interaction on heating powdered zinc and sulfur is considered to be too violent for use as a school experiment [2],... 

Kuroda and Tarui [498] developed a spectrophotometric method for molybdenum based on the fact that MoVI catalyses the reduction of ferric iron by divalent tin ions. The plot of initial reaction rate constant versus molybdenum concentration is rectilinear in the range 0.01-0.3 mg/1 molybdenum. Several elements interfere, namely, titanium, rhenium, palladium, platinum, gold, arsenic, selenium, and tellurium. 

Hoffman, D.J., C.J. Sanderson, L.J. LeCaptain, E. Cromartie, and G.W. Pendleton. 1992. Interactive effects of arsenate, selenium, and dietary protein on survival, growth, and physiology in mallard ducklings. Arch. Environ. Contam. Toxicol. 22 55-62. 

Glover, J.W. 1979. Concentrations of arsenic, selenium and ten heavy metals in school shark, Galeorhinus australis (Macleay), and gummy shark, Mustelus antarcticus Gunt, in south-eastern Australian waters. Austral. Jour. Mar. Freshwater Res. 30 505-510. 

PerSniemi S., Hannonen S., Mustalathi H., Ahlgren M., Zirconium-loaded activated charcoal as an adsorbent for arsenic, selenium and mercury, Fresenius J. Anal. Chem. 349, 1994,510-515. 

Some of the polymers containing phosphorous, arsenic, selenium and tellurium are shown below ... 

Silver is a white, ductile metal occurring naturally in its pure form and in ores (USEPA 1980). Silver has the highest electrical and thermal conductivity of all metals. Some silver compounds are extremely photosensitive and are stable in air and water, except for tarnishing readily when exposed to sulfur compounds (Heyl et al. 1973). Metallic silver is insoluble in water, but many silver salts, such as silver nitrate, are soluble in water to more than 1220 g/L (Table 7.3). In natural environments, silver occurs primarily in the form of the sulfide or is intimately associated with other metal sulfides, especially fhose of lead, copper, iron, and gold, which are all essentially insoluble (USEPA 1980 USPHS 1990). Silver readily forms compounds with antimony, arsenic, selenium, and tellurium (Smith and Carson 1977). Silver has two stable isotopes ( ° Ag and ° Ag) and 20 radioisotopes none of the radioisotopes of silver occurs naturally, and the radioisotope with the longest physical half-life (253 days) is "° Ag. Several compounds of silver are potential explosion hazards silver oxalate decomposes explosively when heated silver acetylide (Ag2C2) is sensitive to detonation on contact and silver azide (AgN3) detonates spontaneously under certain conditions (Smith and Carson 1977). 

The compounds of Group V elements are often volatile, and loss of, for example, arsenic, selenium and tellurium during ashing of the sample can be reduced by the addition of nickel, to form nickel arsenide. Such stabilization procedures are called matrix modification (see Section 3.6.4). 

Gaseous and volatilised analytes can also be easily determined by FAAS and ETAAS. For example, the determination of several elements by the formation of covalent volatile hydrides e.g. arsenic, selenium) and cold vapour generation (mercury and cadmium) is feasible with good analytical sensitivity (see Section 1.4.1.1). 

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). 

Zinc(ll). gallium(lll), and germanium(IV) are the most stable oxidation states for these elements, but the later nonmetals (arsenic, selenium, and bromine) show a reluctance to assume their highest possible oxidation state. 

Another important group of methyl transfer reactions are those from methyl corrinoids to mercury, tin, arsenic, selenium, and tellurium. For example, Eq. 16-44 describes the methylation of Hg2+. These reactions are of special interest because of the generation of toxic methyl and dimethyl mercury and dimethylarsine. 

Gonz lez, A.Z.I., Krachler, M., Cheburkin, A.K. and Shotyk, W. (2006) Spatial distribution of natural enrichments of arsenic, selenium, and uranium in a minerotrophic peatland, Gola di Lago, Canton Ticino, Switzerland. Environmental Science and Technology, 40(21), 6568-74. 

Seames, W.S. and Wendt, J.O.L. (2000) Partitioning of arsenic, selenium, and cadmium during the combustion of Pittsburgh and Illinois 6 coals in a self-sustained combustor. Fuel Processing Technology, 63(2), 179-96. 

Strawn, D Doner, H Zavarin, M. and McHugo, S. (2002) Microscale investigation into the geochemistry of arsenic, selenium, and iron in soil developed in pyritic shale materials. Geoderma, 108(3-4), 237-57. 

In this chapter, the factors influencing the distribution of metal- and metalloid-containing species are discussed, and more recent developments in understanding the behaviour of antimony, arsenic, selenium and tin in biological systems are reviewed. 

Techniques and approaches to the study of the distribution of chemical species of metals and metalloids in biological materials after sample preparation are similar to those already described for other matrices in this book, and in a recent review by Lobinski (1997). The application of these methods has led to a greater understanding of the role of metals and metalloids in biological systems. Some of the new developments in understanding the environmental behaviour of antimony, arsenic, selenium and tin are reviewed. 

Tkeshelashvili LK, Shearman CW, Zakour RA, et al. 1980. Effects of arsenic, selenium, and chromium on the fidelity of DNA synthesis. Cancer Res 40 2455-2460. 

As might be anticipated, the reduction in flame temperature has a deleterious effect upon the incidence and extent of matrix interferences when such boat techniques are used. As a consequence, precise matrix matching is necessary for accurate results, or the standard additions method may be employed.6 If the user is in any doubt as to whether matrix matching alone is sufficient, the adequacy of this approach may be confirmed by the analysis of certified reference materials and/or by applying the standard additions technique as well to a selection of samples to make sure that both techniques give the same results. For bismuth, cadmium, lead, silver, and thallium, detection limits by AAS are a few ng ml -1 or better.6 For arsenic, selenium, and tellurium they tend to lie in the range 10-30 ng ml-1, depending upon the source used. 

B. Welz, M. Melcher, Decomposition of marine biological tissues for determination of arsenic, selenium and mercury using hydride-generation and cold vapour atomic absorption spectrometeries, Anal. Chem., 57 (1985), 427-431. 

Fluoride, arsenic, selenium and, in certain circumstances, nitrate should be given high priority. As noted in Chapter 2, the presence of these chemicals in drinking-water has been shown to cause health effects. The natural occurrence of these chemicals is relatively common in water supplies around the world in both developing and developed countries therefore, they should be assumed to be potentially present, and consideration should be given as to whether they are actually present in concentrations of concern. 

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