Arsenic chemical species

Carbonell-Barrachina AA, Burlo E, Valero D, Lopez E, Marti nez-Romero D and Marti nez-Sanchez E (1999) Arsenic toxicity and accumulation in turnip as affected by arsenic chemical speci-ation. J Agric Eood Chem 47 2288 - 2294. 

In the environment, metals are common as a chemical species, and as usual the metal-organic species are more toxic. For example, the inorganic lead and mercury species are less toxic for living organisms than the organic ones (methyl mercury, tetraethyl lead). However inorganic arsenic compounds are more toxic than organic... 

The most useful chemical species in the analysis of arsenic is the volatile hydride, namely arsine (AsH3, bp -55°C). Analytical methods based on the formation of volatile arsines are generally referred to as hydride, or arsine, generation techniques. Arsenite is readily reduced to arsine, which is easily separated from complex sample matrices before its detection, usually by atomic absorption spectrometry (33). A solution of sodium borohydride is the most commonly used reductant. Because arsenate does not form a hydride directly, arsenite can be analyzed selectively in its presence (34). Specific analysis of As(III) in the presence of As(V) can also be effected by selective extraction methods (35). 

Most of the studies on the uptake and transformation of arsenic in water have dealt with arsenate it is the predominant arsenic component in seawater, and radiolabeling experiments are most easily carried out with this chemical species. Generally, the results have shown that uptake of arsenate from water is a slow process and is unlikely to be significant in natural environments (160-163). 

Absorption is the assimilation of a chemical species into the interior of a solid substance. Absorption may include the migration of solutes into the internal pores of a solid material (Fetter, 1993), 117 or the migration or exchange of atoms within the crystalline structure of a mineral (Krauskopf and Bird, 1995), 150. Some researchers use the generic term sorption to refer to a treatment method where both adsorption and absorption may be involved or if adsorption and absorption cannot be distinguished. Sorption and ion exchange have many important roles in immobilizing arsenic in natural environments (Chapter 3). They... 

Adsorption in Reactions 2.47-2.52 also involves ion exchange (Eby, 2004), 345. During the formation of inner-sphere complexes, adsorbing arsenic commonly replaces hydroxides or other chemical species on the surface of the adsorbent. Complexes in Stern outer-sphere and Gouy layers are also susceptible to ion exchange, especially because they are weakly adsorbed (Krauskopf and Bird, 1995), 150. 

Interferences with arsenic adsorption and ion exchange Dissolved organics and anions may interfere with arsenic adsorption and ion exchange in both natural environments and water treatment systems. In some cases, chemical species directly compete with arsenic for adsorption sites. They may also desorb and replace arsenic. Vanadium is one element that could interfere with the adsorption of arsenic onto mineral surfaces. In most cases, vanadium is not abundant in water. However, alkaline (pH 7.0-8.8) groundwaters in the loess aquifers of La Pampa, Argentina contain up to 12mgL 1 of vanadium (Smedley et al., 2005). The vanadium readily hinders the sorption of As(V) onto iron (III) (oxy)(hydr)oxides (Chapter 3). 

Yamauchi, H. and Yamamura, Y. (1983) Concentration and chemical species of arsenic in human tissue. Bulletin of Environmental Contamination and Toxicology, 31(3), 267-77. 

Methylthioarsenate A chemical species containing pentavalent arsenic, sulfide, and methyl groups, as examples (CH3)As02S2-, (CH3)AsOS22, (CEE AsOS-, and (CH3)2AsS2- (compare with thioarsenic, thioarsenate, and thioarsenite). 

Speciation (chemistry) The chemical species in a sample, which includes information on its valence state and specific chemistry. For example, the speciation of arsenic in a groundwater sample may include arsenic fluoride species, such as AsCbF2-. Also, an analytical method that identifies the valence state of a chemical species in a sample. 

Andreae, M.O., 1983. The determination of the chemical species of some of the "hydride elements" (arsenic, antimony, tin and germanium) in seawater methology and results. In C.S. Wong, E. Boyle, K.W. Bruland, 3.D. Burton and E.D. Goldberg (eds). Trace Metals in Seawater. Plenum, New York, pp. 1-19. 

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. 

Arsenic, chromium, mercury, selenium, and tin have been the object of numerous investigations. Because some of them are classified as probable human carcinogens23-25 (strictly speaking, some of their species), the accurate assessment of concentration and speciation in environmental matrices is enormously important. Unfortunately, such factors as chemical reactions between species, low concentration, microbial activity, redox conditions, as well as the presence of other dissolved metal ions, may cause the amounts and distributions of chemical species in a sample to vary. In response to these problems, analytical research efforts have focused on developing techniques enabling the original valence state of the metals to be preserved. Table 2.3 lists some of these stabilization methods. 

Finally, particular chemical species can be determined in some cases, as when arsenic content is separated into As(III), As(V), monomethyl arsonic acid, and dimethyl arsinic acid using ion-exchange chromatography. Chemical speciation is sometimes possible but is often very difficult. If the metals... 

Recognizing the applicability of XRD to occupational health chemistry, Lennox and Leroux (1) suggested a number of chemical species which would be suitable for XRD analysis arsenic trioxide, beryllium oxide, mica, vanadium oxides, calcium fluoride in ceramic materials, as well as a number of organics such as DDT, lindane and chlordane. Unfortunately, the general application of XRD to the quantitation of industrial hygiene samples has not been realized and the majority of these analyses are restricted to free silica and to a lesser extent asbestos and talc. 

The presence of specific chemical species in the corrosive environment poisons or retards the rate of the Hads atom combination reaction, thereby permitting a higher fraction of the H atoms generated by corrosion to become absorbed by (enter into) the steel. Bisulfide ions (HS ), formed when H2S molecules are dissolved in water, are very effective H atom combination poisons. Other effective H atom combination poisons are cyanide ions (CN ) and arsenic ions (As3+). 

Aziznr Rahman, M., Hasegawa, H., Ueda, K., Maki, T., and Rahman, M.M. 2008. Influence of EDTA and chemical species on arsenic accumulation in Spirodela polyrhiza L. (dnckweed). Ecotoxicology and Environmental Safety, 70(2) 311-18. 

Arsenic pollution can be originated in anthropic activities (mining, use of biocides, wood preservers). However, most pollution is natural, coming from mineral dissolution in surface or groundwaters (Bundschuh et al., 2000, 2004 Litter, 2002). Predominant As forms in natural ground and surfacewaters (neutral pH) are arsenate (As(V), as H2AsO and HAsO ) and arsenite (As(III), as neutral H3ASO3). The mobility of arsenical forms in waters is very dependent on pH, Eh conditions, and presence of different chemical species (Smedley et al., 2002). Consequently, removal methods... 

Mixed valent arsenic selenide compounds are known, and they are related to the arsenic sulfide species. For example, As4Se4 is isomorphous with realgar AS4S4 and As4Se3 is isomorphous with AS4S3. However, chemical reactivity is different due to the larger size of the selenium atom. ... 

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