Arsenic in soils is largely associated with amorphous and crystalline hydrous oxides of Fe and Al
and the dominant chemical forms of As in the original soil sample (i.e., unwashed soil) was As associated with
amorphous hydrous oxides of Fe and Al. This implies that the success of soil washing is highly dependent on removal of
(NH4)2C2O4-extractable As according to the Wenzel’s sequential extraction procedure