Arsenic chemistry in soils

The pedosphere contains around 0.6-1.7 x 109 t of arsenic. The residence time of arsenic in soils in climates with moderate temperatures and precipitation is about 1000-3000 years (Matschullat, 2000), 303. Uncontaminated soils derived from the in situ weathering of bedrock usually inherent arsenic from 

Approximately 44 000 t of arsenic are annually removed from soils (Matschullat, 2000), 303. Major processes that eliminate arsenic from soils include microbial volatilization (up to 26,200 tyear-1 (Matschullat, 2000), 300-301), plant uptake, wind and water erosion, and leaching into precipitation, irrigation water, and groundwater (Matschullat, 2000 Bar-Yosef, Chang and Page, 2005). 

Although iron, manganese, magnesium, calcium, and aluminum arsenates are usually too water soluble to control arsenic mobility in soils (Inskeep, McDermott and Fendorf, 2002), 187, iron, aluminum, or manganese arsenates occur in some acidic soils. In particular, scorodite may form from the partial weathering of arsenian pyrite or arsenopyrite (Inskeep, McDermott and Fendorf, 2002), 187. Calcium arsenates may be present in alkaline calcium-rich soils (Matschullat, 2000), 303 (Mandal and Suzuki, 2002), 204. 

Like sediments, colloids are often important in sorbing and transporting arsenic in soils (Sadiq, 1997 Waychunas, Kim and Banheld, 2005). Colloids may consist of clay minerals, organic matter, calcium carbonate, and various aluminum, manganese, and iron (oxy)(hydr)oxides (Sadiq, 1997). Important iron (oxy)(hydr)oxides include goethite, akaganeite (/J-FeO(OH)), hematite, ferrihydrites, and schwertman- 

Australia Port Kembla, New South Wales 0.91 -19 (0-5 cm depth, Martley, Culson and Pfeifer 

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Sadiq, M. (1997) Arsenic chemistry in soils an overview of thermodynamic predictions and field observations. Water Air and Soil Pollution, 93(1-4), 117-36. 

The more troublesome problem is the biotransformation of arsenic into arsine gas. Four common soil fungi, two anaerobic bacteria and algae in surface water can generate a methylated version of arsine. Generally, see Arsenic Speciation in the Enviromnent by W. R. Cullen and K. J. Reimer, Chemistry Review (1989) Arsenic in the Soil Environment by E. Smith, R. Naidu, and A. M. Alston, Advances in Agronomy (1998) and Arsenic Chemistry in Soils An Overview of Thermodynamic Predictions and Field Observations by Muhammed Sadiq, Water Air and Soil Pollution (1997). 

Ruiz-Chancho, M.J., Lopez-Sanchez, J.F. and Rubio, R. (2007) Analytical speciation as a tool to assess arsenic behaviour in soils polluted by mining. Analytical and Bioanalytical Chemistry, 387(2), 627-35. 

II. CHEMISTRY OF INORGANIC ARSENIC (III) AND ARSENIC (V) IN SOILS AND NATURAL WATERS... 

Hsu PH (1989) Aluminum hydroxides and oxyhydroxides. In Dixon JB, Weed SB (ed) Minerals in soil environments, 2nd edn, pp 331-378 Inskeep WP, McDermott TR, Fendorf S (2002) Arsenic (V)/(III) cycling in soils and natural waters chemical and microbiological processes. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, New York, pp 183-215... 

Smith E, Naidu R, Alston AM (2002) Chemistry of inorganic arsenic in soils II Effect of phosphorus, sodium, and calcium on arsenic sorption. J Environ Qual 31 557-563... 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat (Woolson 1975). Arsenic phytotoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates (NRCC 1978). In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported (Woolson 1975). Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

Phosphorus is one of the most important elements in soil chemistry because it is involved in numerous reactions with many different components. In addition to the species described earlier, phosphate will also form species with uranium, arsenic, and zinc. It also reacts with organic matter and with humic and fulvic acids to form environmentally important species [33-37],... 

Arsenic in precipitation from unpolluted ocean air averages about 0.019 pg L 1 (Hering and Kneebone, 2002), 157 and terrestrial rainwater concentrations (at least over the USA) also have similar averages of around 0.013-0.032 pgL-1 ((Smedley and Kinniburgh, 2002), 522 Table 3.17). As the precipitation infiltrates into the subsurface, its chemistry changes as it reacts with sediments, soils, and rocks. Therefore, the arsenic chemistry of the groundwater of an area may be very different than its precipitation chemistry. 

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). 

The chemistry of arsenic in soil and aquatic ecosystems can bast be described as a complex array of homogeneous and hetergeneous chemical, biochemical, and geochemical reactions that together control the dissolved concentrations of arsenic in these systems. Although many of these reactions have been studied independently, the total description of the combined major reaction mechanisms that control the cyclic behavior of arsenic in environmental systems has largely been undeveloped. In the paper presented here, results obtained in laboratory and field studies are used to describe some of the major control mechanisms that affect the distribution as well as transformations of arsenic in an aquatic environment. 

Sadiq, M., and Lindsay, W. L., 1981, Selection of standard free energies of formation for use in soil chemistry, Colorado State University Experiment Station Techical Bulletin 134, Arsenic Supplement, 39 p. 

Massehelyn, P. H., and Patrick, W. H., Jr. (1994). Selenium, arsenic, and clu omium redox chemistry in wetland soils and sediments. In Biogeochemistry of Trace Elements, ed. Adriano, D. C., Science and Technology Letters, Northwood, Middlesex, England, 615-625. 

He has contributed to research on the interface between soil chemistry and mineralogy and soil biology. His special areas of research include the formation mechanisms of aluminum hydroxides and oxyhydroxides, the surface chemistry and reactivities of short-range-ordered precipitation products of Al and Fe, the influence of biomolecules on the sorption and desorption of nutrients and xenobiotics on and from variable charge minerals and soils, the factors that influence the sorption and residual activity of enzymes on phyllosilicates, variable charge minerals, organomineral complexes, and soils and the chemistry of arsenic in soil environments. 

Felbeck, G.T., Jr. 1965. Structural chemistry of soil humic substances. Adv. Agron. 17 327-368. Ferguson, J.F., and J. Gavis. 1972. A review of the arsenic cycle in natural waters. Water Res. 

In many previous chapters, the discussion of questions regarding various environmental aspects of environmental chemistry in air, water, and soil compartments touched upon the problems of heavy metals. However, we should pay more attention to these pollutants, which are of crucial environmental concern in the Asian region. In this chapter, the emphasis will be given to heavy metal emissions from coal (including lignite) burning power plants, and to the specific aspects of environmental behavior of the most dangerous contaminants, like arsenic, mercury and lead. The problems of heavy metal site remediation will be considered in Chapter 16. 

In natural waters, soils, and sediments, the As species of interest are the arsenate oxyanions, As(V) the arsenite oxyanions, As(III) monomethylarsonic acid, As(III) and dimethylarsinic acid, As(I). Arsenic chemistry is governed by many factors. The solubility of their salts, the complexing ability of solid and soluble ligands, the biological reactions, the pH and redox potential, and the presence of other ions are all reported to control As concentration and speciation. 

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