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Arsenic [As, 33]

3.1 INTRODUCTION
Arsenic (As) 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. In igneous rocks, As concentrations range from 1.5 to 3.0 mg/kg, and in sedimentary rocks, it ranges from
1.7 to 400 mg/kg (average is about 3 mg/kg). It is likely to concentrate in coal, up to
82 mg/kg. In some brown coal, As content reached 1500 mg/kg (Smith et al. 1998).
It may be also accumulated in fly ash—up to 60 mg/kg. Arsenic is likely to be concentrated in shales and peats.
Global As production (without the United States) (arsenic trioxide, As 2 O 3 )
in 2010 was 54,500 t, with China and Chile producing 25,000 t and 11,500 t,
respectively (USGS 2011). Arsenic may be obtained from copper, gold, and lead
smelter dust as well as from roasting arsenopyrite, the most abundant ore mineral
of arsenic.
Arsenic occurs at various oxidation stages: –2, –3, +3, and +5. About 200 minerals of As are known. It easily forms complex anions (AsO
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) and is easily combined
with some metals (e.g., lellingit, FeAs 2 ; doineykite, Cu 3 As; nikieline, NiAs; and
sperrylite, PtAs 2 ). Its common minerals are arsenopyrite, FeAsS; orpiment, As 2 S 3 ,
reagal AsS; and arenolite, As 2 O 3 . Also, organic compounds of As occur in nature,
such as dimethylarsenic, trimethylarsenic, and arsenobetaine (AB).
About 80% of produced As has been used for pesticides. Due to its toxicity, the
amount of As in pesticide has been reduced, but it is still a dominating element in
pesticides (Deschamps and Matschullat 2011). Arsenic also has varied applications
such as wood preservation (e.g., chromate copper arsenate, a wood preservative,
stopped in recent years, is still used to preserve wood for nonresidential applications,
and the resulting As leaching from treated timber can increase the As content in the
soil nearby); production of photoelectric devices, Pb-acid batteries, and glassware;
and are used in Cu alloys to improve corrosion resistance. Arsenic was also used in
medicine until 1950 (Matschullat 2000).
3.2 SOILS
Arsenic contents in soils vary from <0.1 to 67 mg/kg, with the lowest in light sandy
soils and the highest in heavy loamy soils and organic soils (Table 3.1). Mean content
calculated for top soils in the United States is 7.2 mg/kg (Burt et al. 2003), whereas
this value for European soils is estimated at 11.6 mg/kg (FOREGS 2005). Average
background As concentration does not exceed 15 mg/kg. However, it may considerably vary, depending on the geology of the parent materials, which are the main
source of As in uncontaminated soils.
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