The soil washing condition and procedure using a neutral phosphate solution were developed in our previous study (Im et al.,2014). Briefly, 24 h soaking of As-contaminated soils in a 0.5 M
phosphate solution (pH 6.0), prepared from ammonium dihydrogen phosphate (NH4H2PO4) and diammonium hydrogen phosphate((NH4)2HPO4), at soil-to-solution (S/L) ratio of 1:5 was followed by 1 h washing at 200 rpm.