Association between ferrous iron accumulation and pentachlorophenol degradation at the paddy soil–water interface in the presence of exogenous low-molecular-weight dissolved organic carbon

Fourteen low-molecular-weight organic acids (organic acids) and eight neutral monosaccharides (monosaccharides) were used to investigate the intrinsic link between ferrous iron [Fe(II)] accumulation and pentachlorophenol (PCP) degradation at the paddy soil–floodwater interface. Using logistic curve fitting, significant differences were observed between Fe(II) accumulation with organic acids and monosaccharides. These differences were attributed to large variations in the dissociation constants and the number of carbon atoms per molecule. A significant relationship was observed between the maximum capacity of Fe(II) accumulation and PCP degradation. Correlations were established between environmental variables including PCP, NaOAc-/HCl-extractable Fe(II), water soluble organic carbon (WSOC), anodic peak oxidation potential (Ep) of Fe(II) species, oxidation–reduction potential (ORP), and pH. The increase in pH combined with WSOC consumption caused a decrease in Ep, which greatly enhanced the HCl-extractable Fe(II) accumulation and subsequently contributed to PCP degradation.

► We conducted kinetic experiments in a flooded paddy soil amended with organic sources.
► The model parameters of Fe(II) accumulation were related to PCP degradation.
► The anodic peak oxidation potential decreased with pH increase and/or WSOC consumption.
► The decrease in anodic peak oxidation potential enhanced Fe(III) reduction.
► The accumulation of HCl-extractable Fe(II) contributed to PCP degradation.