Arsenic

Definition

Arsenic, element 33, is a metalloid in row VB of the periodic table. The main oxidation states are arsine (−3) elemental As(0), arsenite (+3), and arsenate (+5). Arsenate, As(V), and arsenite, As(III), are most common, with HAsO₄ ²⁻ and H₂AsO₄ ¹⁻ predominating under oxic conditions and H₃AsO⁰ and H₂AsO₃ ²⁻prevalent in anoxic environments. Arsenic is found in minerals such as arsenosulfides (e.g., arsenopyrite, realgar), iron hydroxides and aluminosilicates (e.g., clays), fossil fuels, geothermal sources, and weathered volcanic and evaporitic deposits. Anthropogenic inputs may also be considerable as organoarsenicals such as roxarsone (3-nitro-4-hydroxy benzene arsonic acid) and monosodium and disodium methyl arsonate continue to see wide spread use. The toxicology of arsenic is well known; As(V) is an analog of phosphate and can disrupt oxidative phosphorylation, while As(III) binds to sulfhydryl groups and can inhibit respiratory enzymes. Nevertheless, arsenic is readily...