Arsenic release

Arsenic concentrations vary from below detection to above 500 parts per billion (ppb) (Fig. 1). The highest dissolved arsenic concentrations in the aquifer occur below the in-filled abandoned channel. Groundwater flow data provides strong evidence for near surface arsenic release. 

Nickson, R.T., McArthur, J.M., Ravenscroft, P., Burgess, W.G., Ahmed, K.M. 2000. Mechanism of arsenic release to groundwater, Bangladesh and West Bengal. Applied Geochemistry, 15, 403-413. 

Prediction of arsenic releases from the wastes and their bioavailability and toxicity assessments require solubility and... 

Site has information on arsenic release in the United States. 

These oxyhydroxide compounds coprecipitate-adsorb metals and arsenic released from the sulfide and organic reactions, fixing some metals in the oxidized zone (10, 23). These reactions can be seen in changes in iron... 

Harvey, M.C., Schreiber, M.E., Rimstidt, J.D. and Griffith, M.M. (2006) Scorodite dissolution kinetics implications for arsenic release. Environmental Science and Technology, 40(21), 6709-14. 

Helsen, L., Van den Bulck, E., Van Bael, M.K. and Mullens, J. (2003) Arsenic release during pyrolysis of CCA treated wood waste current state of knowledge. Journal of Analytical and Applied Pyrolysis, 68-69, 613-33. 

Schreiber, M.E., Gotkowitz, M.B., Simo, J.A. and Freiberg, P.G. (2003) Mechanisms of arsenic release to water from naturally occurring sources, eastern Wisconsin, in Arsenic in Ground Water (eds A.H., Welch and K.G. Stollenwerk), Kluwer Academic Publishers, Boston, MA, pp. 259-80. 

Over time, two-line ferrihydrite normally transforms into goethite or hematite in laboratory or natural environments (Rancourt et al., 2001, 839). However, extensive sorption of As(V) could delay the transformation (Ford, 2002). The crystallization of arsenic-bearing amorphous iron compounds often releases arsenic from the compounds (Welch et al., 2000, 599). In particular, while aging in seawater from Ambitle Island near Papua New Guinea, two-line ferrihydrites transformed into less arsenic-rich six-fine varieties. The arsenic released by the transformation of the ferrihydrites produced distinct crystals of claudetite (As203) (Rancourt et al., 2001, 838-839). 

DeLemos, J.L., Bostick, B.C., Renshaw, C.E. et al. (2006) Landfill-stimulated iron reduction and arsenic release at the Coakley Superfund Site (NH). Environmental Science and Technology, 40(1), 67-73. 

Gault, A.G., Islam, F.S., Polya, D.A. et al. (2005) Microcosm depth profiles of arsenic release in a shallow aquifer, West Bengal. Mineralogical Magazine, 69(5), 855-63. 

Islam, F.S., Gault, A.G., Boothman, C. et al. (2004) Role of metal-reducing bacteria in arsenic release from Bengal Delta sediments. Nature, 430(6995), 68-71. 

Price, R.E. and Pichler, T. (2006) Abundance and mineralogical association of arsenic in the Suwannee Limestone (Florida) implications for arsenic release during water-rock interaction. Chemical Geology, 228(1-3 Special Issue), 44-56. 

Wang, S. and Mulligan, C.N. (2006) Effect of natural organic matter on arsenic release from soils and sediments into groundwater. Environmental Geochemistry and Health, 28(3), 197-214. 

Dowling, C.B., Poreda, R.J., Basu, A.R. et al. (2002) Geochemical study of arsenic release mechanisms in the Bengal Basin groundwater. Water Resources Research, 38(9), 12.1-12.18. 

Yamazaki, C., Ishiga, H., Dozen, K. et al. (2000) Geochemical compositions of sediments of Ganges delta of Bangladesh - arsenic release from peat Earth Science, 54, 81-93. 

Langmuir, D., Mahoney, J. and Rowson, J.W. (2002) Arsenic releases from buried uranium mill tailings at McClean Lake application of geochemical concepts and license approved by the Canadian government. Abstracts with... 

Foley and Ayuso (2008) suggest that typical processes that could explain the release of arsenic from minerals in bedrock include oxidation of arsenian pyrite or arsenopyrite, or carbonation of As-sulfides, and these in general rely on discrete minerals or on a fairly limited series of minerals. In contrast, in the Penobscot Formation and other metasedimentary rocks of coastal Maine, oxidation of arsenic-bearing iron—cobalt— nickel-sulfide minerals, dissolution (by reduction) of arsenic-bearing secondary arsenic and iron hydroxide and sulfate minerals, carbonation and/or oxidation of As-sulfide minerals, and desorption of arsenic from Fe-hydroxide mineral surfaces are all thought to be implicated. All of these processes contribute to the occurrence of arsenic in groundwaters in coastal Maine, as a result of the variability in composition and overlap in stability of the arsenic source minerals. Also, Lipfert et al. (2007) concluded that as sea level rose, environmental conditions favored reduction of bedrock minerals, and that under the current anaerobic conditions in the bedrock, bacteria reduction of the Fe-and Mn-oxyhydroxides are implicated with arsenic releases. 

Erel, Y., Veron, A., and Halicz, L. (1997). Tracing the transport of anthropogenic lead in the atmosphere and in near-surface tills using isotopic ratios. Geochim. Cosmochim. Acta 61, 4495—4505. Foley, N. K., and Ayuso, R. A. (2008). Mineral sources and pathways of arsenic release in a contaminated coastal watershed. Geochem. Explor. Environ. Anal. 8, 59—75. 

Data from Bencko et al. (1977) indicate that arsenic released from coal-burning power plants in Czechoslovakia may have affected the hearing of children in the nearby communities. The coal cleaning and effluent treatment practices in the US and in most developed countries greatly reduce the level of toxic emissions from coal-burning power plants. 

There is much evidence for arsenic release into shallow sediment pore waters and overlying surface waters in response to temporal variations in redox conditions. Sullivan and Aller (1996) investigated arsenic cycling in shallow sediments from an unpolluted area of the Amazonian offshore shelf. They found pore-water arsenic concentrations up to 300 p.g in anaerobic sediments with nearly coincident peaks of dissolved arsenic and iron. The peaks for iron concentration were often slightly above those of arsenic (Figure 1). The magnitude of the peaks and their depths varied from place to place and possibly seasonally but were typically between 50 cm and 150 cm beneath the sediment-water interface (Sullivan and Aller, 1996). There was no correlation between pore-water arsenic concentrations and sediment arsenic concentrations (Figure 1). 

Experience with bioleaching of arsenic-rich gold ores has shown that the ratio of pyrite to FeAsS is an important factor controlling the speciation of the arsenic released (Nyashanu et al., 1999). In the absence of pyrite, —72% of the arsenic released was As(III), whereas in the presence of pyrite and Fe(III), 99% of the arsenic was As(V). It appears that pyrite catalyzed the oxidation of As(III) by Fe(III), since Fe(III) alone did not oxidize the arsenic (Nyashanu et al., 1999). 

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