Stepwise sequential extraction of As-, Cu-, and Pb-contaminated paddy soil

In this study, we carried out sequential soil washing to investigate removal and fractionation change of arsenic (As), copper (Cu), and lead (Pb) contaminated soil. Stepwise extraction enhanced the extractability of metals compared to a single extraction. EDTA and basic conditions increased the extraction of As, while Cu and Pb were extracted more by acidic condition and EDTA. Alternate application of EDTA and NaOH was most effective and extracted 76% of As, 73% of Cu, and 83% of Pb. Fractionation analysis shows that the iron/manganese (Fe/Mn) oxyhydroxide fraction decreased in all metals. Especially, EDTA significantly decreased the fractionation of metals bound to Fe/Mn oxyhydroxide because of strong complexation of Fe-EDTA. Stepwise application of EDTA and NaOH can be used to simultaneously and significantly extract As, Cu, and Pb. Alternate application of EDTA and NaOH or strong acid and NaOH was more effective to extract As, Cu, and Pb simultaneously compared to sequential extraction by using a single agent. The fraction bound to Fe/Mn oxyhydroxide decreased significantly by chemical extraction using EDTA which has a markedly greater affinity with Fe than those with Cu and Pb.