The As extraction efficiency was the greatest when
H3PO4 (0.5 M) was used as a washing solution, and this was followed
by 2% Na dithionite in HCl (0.01 M) and HCl (1 M). The
acid-based washing solutions extracted more As than the neutral
phosphate solution, which removed approximately 32% of As in
soils (Fig. 1(a))