Desorption of phenanthrene and pyrene in soils by root exudates.

A batch experiment was conducted to evaluate the impact of root exudates on the desorption of phenanthrene and pyrene in soils. Rhizosphere model systems where soils are given artificial root exudates (AREs) have been utilized. ARE addition markedly influenced the desorption of phenanthrene and pyrene in soils, and the effects depended on ARE concentration, aging time, and soil properties. The desorption of phenanthrene and pyrene increased with ARE concentration of 0-1000 mmol/L. Soils with higher soil organic matter content (f(oc)) had lower desorption than soils with lower f(oc) values, at the same ARE concentration. The aging of phenanthrene and pyrene in soils markedly reduced the desorption of both compounds. The increment of phenanthrene and pyrene desorption was always higher with the addition of citric and oxalic acid than with the same concentration of AREs, indicating that the effects of AREs on desorption may be dominantly due to the organic acids.