Effects of Low-Molecular-Weight Organic Acids on Sorption–Desorption of Phenanthrene in Soils

The impact of low-molecular-weight organic acids (LMWOAs) on the sorption–desorption of phenanthrene, used as a representative of polycyclic aromatic hydrocarbons, was investigated with a laboratory batch technique. Experiments were conducted with three types of soil samples containing various organic components: citric, oxalic, and malic acids. The sorption of phenanthrene by soils could be well described by a linear-type model irrespective of the addition of LMWOAs. The simulated distribution constant (Kd) and C-normalized distribution constant (Koc) for phenanthrene sorption decreased significantly with the addition of LMWOAs to the soils (P < 0.05). In contrast, the desorption amounts of phenanthrene were clearly enhanced by the addition of LMWOAs, and the impact of citric acid on the sorption–desorption of phenanthrene was generally more significant than those of oxalic or malic acids, probably due to their chemical structures and properties. Compared with the baseline soil samples, the desorption amounts of phenanthrene in the presence of LMWOAs were significantly decreased in soils after 60 d of cultivation (P < 0.05), whereby the level of the fractional soil organic C content (foc, %) increased proportionally with the inhibition strength of phenanthrene desorption in the presence of LMWOAs. Based on these observations, we suggest that the availability of polycyclic aromatic hydrocarbons can be enhanced with suitable types and concentrations of LMWOAs.