Arsenate reduction

The dichromate ion oxidises iron(II) to iron(III), sulphite to sulphate ion, iodide ion to iodine and arsenic(III) to arsenic(V) (arsenate). Reduction of dichromate by sulphite can be used to prepare chrome alum, since, if sulphur dioxide is passed into potassium dichromate acidified with sulphuric acid, potassium and chromium(III) ions formed are in the correct ratio to form the alum, which appears on crystallisation ... 

Fig. 33.2. Factors controlling reaction rate (expressed per kg water, as r/nw) in the simulation of bacterial arsenic reduction, including kinetic factors FD and Fa, thermodynamic potential factor FT, and biomass concentration [X], Biomass concentration determines the rate early in the simulation, but later the thermodynamic drive exerts the dominant control.

Johnson, D.L. and R.M. Burke. 1978. Biological mediation of chemical speciation. II. Arsenate reduction during marine phytoplankton blooms. Chemosphere 8 645-648. 

Arsenic recoveries from the zinc column in the range 0.1-5pg ml-1 arsenic exceeded 97%. The concentrations at which certain elements interfere are shown in Table 12.16. Various other elements [A1 m, B m, Ca II, Cd II, Co II, Cr VI, Fe III, K I, Li I, Mg II, Mn H, Na I, Ni II, Pb II, S VI, Sn II and Zn II] showed no significant interference at the 500pg level. Only low senium concentrations in extracts can be tolerated. However, few environmental samples contain appreciable amounts of selenium. As selenium is not reduced to hydrogen selenide on the column, selenium will not interfere in the final determination step, but probably suppresses either arsenic reduction or arsine formation. Selenium appears to suppress arsine generation at high arsenic concentrations but causes a slight enhancement at low arsenic concentrations (around O.lpg), which could not be traced to arsenic impurities in the selenium standard used. 

Macy JM, Santini JM, Pauling BV, et al. 2000. Two new arsenate/sulfate-reducing bacteria mechanism of arsenate reduction. Arch Microbiol 173 49-57. 

Newman DK, Ahmann D, Morel EMM. 1998. A brief review of microbial arsenate reduction. Geomicrobiology 15 255-68. 

When potassium iodide is added to a strongly acid solution of an arsenate, reduction to arsenite occurs with liberation of iodine ... 

Chesapeake Bay, USA, is the largest estuary on Earth and almost all of the arsenic entering the headwaters is As(V). Although inorganic As(V) is consistently the most abundant arsenic species in the estuary, extensive arsenic reduction and methylation occur during warm months (Sanders, Riedel and Osman, 1994), 295 (Millward et al., 1997), 53. The appearance of As(III) and methylarsenic species correlates well with phytoplankton production. Similar seasonal patterns involving arsenic reduction and methylation are seen in other estuaries (Sanders, Riedel and Osman, 1994), 295. 

Nemeti, B. and Gregus, Z. (2005) Reduction of arsenate to arsenite by human erythrocyte lysate and rat liver cytosol -Characterization of a glutathione-and NAD-dependent arsenate reduction linked to glycolysis. Toxicological Sciences, 85(2), 847-58. 

Nemeti, B., Csanaky, I. and Gregus, Z. (2003) Arsenate reduction in human erythrocytes and rats — Testing the role of purine nucleoside phosphorylase. Toxicological Sciences, 74(1), 22-31. 

Reductive Dissolution. Many substances in nature contain the same metal or metalloid, but under different oxidation states. For example, the metalloid arsenic may exist as arsenite (AsIII, As03) or arsenate (AsIV, As04) in the forms of ferrous-arsenite or ferric-arsenate, respectively. Ferrous-arsenite is more soluble than ferric-arsenate for this reason, one may be interested in studying the kinetics of arsenate reduction to arsenite. Similar chemistry applies to all elements present in soil-water systems with more than one oxidation state (e.g., iron, manganese, selenium, and chromium). 

Basu, A., Kumar, S., and Mukhijee, S. 2003. Arsenic reduction from aqueous enviromnent by water lettuce (Pistia stratiotes L.). Indian Journal of Environmental Health, 45 143-50. 

Bleeker, P.M., HakvoorL H.W., Bliek, M., Souer, E., and Schat, H. 2006. Enhanced arsenate reduction by aCDC25-like tyrosine phosphatase explains increased phytochelatin accumulation in arsenate-tolerant Holcus lanatus. Plant Journal, 45 917-29. 

Even as little as 20 years ago, arsenic compounds were mainly analyzed by LLE. Organic and inorganic forms were separated by arsenic reduction in its inorganic combinations, leading to formation of halogen metal acids or heteropoly acids extracted with toluene or trichloromethane. Organic arsenic was assayed as the difference between the total quantity and the quantity extracted by performing the... 

Hoeft, S.E., Lucas, F., Hollibaugh, J.T., Oremland, R.S. (2002). Characterization of microbial arsenate reduction in the anoxic bottom waters of Mono Lake, California. Geomicrobiol. J. 19 23-40. 

The authors thank Kirk Nordstrom for an early copy of his review of the thermodynamics of the As-O-S system and also an anonymous reviewer for constmctive comments about the microbiology of arsenate reduction. This chapter is published with the permission of the Executive Director of the British Geological Survey (NERC). 

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