The selected washing solutions are 1 M HCl (Choi et al., 2007), 0.5 M H3PO4 (Cheong and Kang,
2012), and 2% Na dithionite in 0.01 M HCl (Kim et al., 2012). All the washing experiments were carried out in triplicate using 1 L jars with 120 g soils and 600 mL washing solutions.