The study of PAHs sorption and bioavailability to different crop roots could help to reveal the environmental behavior of PAHs in the ecosystem and evaluate the ecological risk of PAHs. However, there is little information about the differences in PAHs sorption to different roots and the bioavailability of the sorbed PAHs. In this paper, the experiments were conducted on the sorption/desorption of phenanthrene to soybean and wheat roots under different sorption times and different phenanthrene concentrations. The results showed that the trend of phenanthrene sorption in vivo was first increased and then decreased and finally reached a balance, which was related to the transport delay in vivo; the trend in dead and dried roots was first increased and then reached a balance. The greater specific surface area and the higher fat content, the faster the balance was. Freundlich isotherm was fitted better than Henry isotherm for dead and dried roots, Langmuir isotherm was best fitted in wheat roots. All of the fitted isotherms indicated that the distribution and the surface adsorption could control the phenanthrene sorption. Because of the special binding between living roots and phenanthrene, the fit effect was poor. The phenanthrene sorption capacity of soybean roots was higher than that of wheat, which was related to the high water content, fat content and membrane permeability. The phenanthrene sorbed on the roots was hard to desorb, and the desorption trends were wheat roots> soybean roots; living roots> dried roots> dead roots. The bioavailability of root-sorbed phenanthrene was consistent with the desorption results. Our results could provide data for the assessment of environmental risks of PAHs sorbed onto crop roots.
Keywords: adsorption/desorption; bioavailability; polycyclic aromatic hydrocarbons; roots; soybean; wheat.