The trivalent mono-methylated (MMA III) and dimethylated (DMA III) arsenic species have been detected in lake water ( Hasegawa et al., 1994, 1999). Inorganic As III and As V are the major arsenic species in natural water, whereas minor amounts of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) can also be present. Under reducing conditions, the +3 valency state as arsenite (As III) is the dominant form the +5 valency state as arsenate (As V) is generally the more stable form in oxygenized environments ( Boyle & Jonasson, 1973 National Research Council, 1999 O'Neil, 2001 WHO, 2001).Īrsenic species identified in water are listed in Table 1. Arsenic can exist in four valency states: −3, 0, +3 and +5. Although elemental arsenic is not soluble in water, arsenic salts exhibit a wide range of solubilities depending on pH and the ionic environment. Arsenic compounds are found in rock, soil, water and air as well as in plant and animal tissues. Arsenic is the 20th most common element in the earth's crust, and is associated with igneous and sedimentary rocks, particularly sulfidic ores.
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