Arsenic anoxic waters

In sulfide-rich and anoxic waters, dissolved thioarsenic species commonly occur. Thioarsenic species form when sulfur substitutes for one or more of the oxygens in the dissolved forms of arsenious or arsenic acids (e.g. fbAsCbS-). Traditionally, aqueous thioarsenic species have been identified as thioarsenites... 

Abdullah, M.I., Shiyu, Z. and Mosgren, K. (1995) Arsenic and selenium species in the oxic and anoxic waters of the Oslofjord, Norway. Marine Pollution Bulletin, 31(1-3), 116-26. 

The relative proportions of arsenic species in estuarine waters are more variable because of changes in redox, salinity, and terrestrial inputs (Abdullah et al., 1995 Howard et al., 1988). Arsenic(V) tends to dominate, although M. O. Andreae and T. W. Andreae (1989) found increased proportions of As(III) in the Schelde Estuary of Belgium. The highest values occur in anoxic zones near sources of industrial effluent. Increased proportions of As(III) also occur near sources of mine effluent (M. O. Andreae and T. W. Andreae, 1989). Seasonal variations in concentration and speciation have been reported in seasonally anoxic waters (Riedel, 1993). Peterson and Carpenter (1983) reported a clear crossover in the proportions of the two species with increasing depth in the Saanich Inlet of British Columbia. Arsenic(III) represented only 5% (0.10 p,g L ) of the dissolved arsenic above the redox front but 87% (1.58p,gL ) below it. In marine and estuarine waters, organic forms of arsenic are... 

Anoxic water samples, because they contain little in the way of particles, are far easier than aquifer materials to develop radioassays for the measurement of arsenate reduction. Arsenic speciation quantitatively changes from arsenate to arsenite with vertical transition from the surface oxic waters to the anoxic bottom depths of stratified lakes and fjords (55,56). This also occurs in Mono Lake, California (57), a transiently meromictic, alkaline (pH = 9.8), and hypersaline (salinity = 70-90 g/L) soda lake located in eastern California (Fig. 11). The combined effects of hydrothermal sources coupled with evaporative concentration have resulted in exceptionally high ( 200 fiM) dissolved arsenate concentrations in its surface waters. Haloalkaliphilic arsenate-respiring bacteria have been isolated from the lake sediments (26), and sulfate reduction, achieved with... 

This chapter discusses the chemical mechanisms influencing the fate of trace elements (arsenic, chromium, and zinc) in a small eutrophic lake with a seasonally anoxic hypolimnion (Lake Greifen). Arsenic and chromium are redox-sensitive trace elements that may be directly involved in redox cycles, whereas zinc is indirectly influenced by the redox conditions. We will illustrate how the seasonal cycles and the variations between oxic and anoxic conditions affect the concentrations and speciation of iron, manganese, arsenic, chromium, and zinc in the water column. The redox processes occurring in the anoxic hypolimnion are discussed in detail. Interactions between major redox species and trace elements are demonstrated. 

Following consumption of dissolved O2, the thermodynamically favored electron acceptor is nitrate (N03-). Nitrate reduction can be coupled to anaerobic oxidation of metal sulfides (Appelo and Postma, 1999), which may include arsenic-rich phases. The release of sorbed arsenic may also be coupled to the reduction of Mn(IV) (oxy)(hydr)oxides, such as birnessite CS-MnCb) (Scott and Morgan, 1995). The electrostatic bond between the sorbed arsenic and the host mineral is dramatically weakened by an overall decrease of net positive charge so that surface-complexed arsenic could dissolve. However, arsenic liberated by these redox reactions may reprecipitate as a mixed As(III)-Mn(II) solid phase (Toumassat et al., 2002) or resorb as surface complexes by iron (oxy)(hydr)oxides (McArthur et al., 2004). The most widespread arsenic occurrence in natural waters probably results from reduction of iron (oxy)(hydr)oxides under anoxic conditions, which are commonly associated with rapid sediment accumulation and burial (Smedley and Kinniburgh, 2002). In anoxic alluvial aquifers, iron is commonly the dominant redox-sensitive solute with concentrations as high as 30 mg L-1 (Smedley and Kinniburgh, 2002). However, the reduction of As(V) to As(III) may lag behind Fe(III) reduction (Islam et al., 2004). 

McArthur, J.M., Banerjee, D.M., Hudson-Edwards, K.A. et al. (2004) Natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of West Bengal and its worldwide implications. Applied Geochemistry, 19(8), 1255-93. 

Inorganic arsenic species, As111 and Asv, in natural water and anoxic seawater samples were not stable (Cutter et al., 1991). Rapid freezing and storage at —4°C was recommended as a means of preservation. Particulate samples were collected in acid-cleaned plastic bags, and then frozen. 

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. 

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