Chemical forms of As (i.e., fractionation of As) in soils were assessed using the sequential extraction procedure of Wenzel et al. (2001), which divides As in soils into five fractions, with a slight modification – (1) ammonium sulfate ((NH4)2SO4;0.05 M)-extractable As (i.e., non-specifically sorbed As); (2)NH4H2PO4 (0.05 M)-extractable As (i.e., specifically sorbed As);
(3) ammonium oxalate ((NH4)2C2O4; 0.2 M)-extractable As (i.e.,As associated with amorphous hydrous oxides of Fe and Al); (4)(NH4)2C2O4 (0.2 M)/ascorbic acid (0.1 M)-extractable As (i.e., As associated with crystalline hydrous oxides of Fe and Al); and (5)residual As fraction extracted with the USEPA method 3052, which digest siliceous and organically based matrices such as soils and sediments in a mixture of nitric acid, hydrofluoric acid, HCl, and hydrogen peroxide using microwave heating (US Environmental Protection Agency, 1996).