The soil (a) pH, (b) Eh, the concentrations of (c) dissolved organic carbon (DOC) and (d) Fe in pore water of the three levels of As contaminated soils of Guandu Plain during the growth period. Data means ± standard deviation. (As-L:16.3 mg As kg−1, As-M: 343.3 mg As kg−1, As-H: 512.3 mg As kg−1).