Arsenic [As, 33]

Arsenic is a metalloid of the group 5 in the periodic table of elements and occurs in the Earth’s crust at levels between 0.5 and 2.5 mg/kg. It is likely to concentrate in argillaceous sediment, up to about 15 mg/kg. About 80% of produced Arsenic has been used for pesticides. Due to its toxicity, the amount of Arsenic in pesticide has been reduced, but it is still a dominating element in pesticides. Due to the release of Arsenic from various industrial sources, especially from coal burning, its content in many soils is increased, sometimes even up to 20,000 mg/kg. Other sources of Arsenic are (1) landfills and other disposals, especially sludges; (2) chemical and allied products; and (3) lumber and various wood products. Arsenic readily changes valence state and reacts with soils to form species with varying mobility. In some Asian countries, excessive arsenic concentration in groundwater is a crucial problem associated with the cultivation of plants, especially rice.