Influences of Hydrosoluble and Lipophilic Rhizodeposits on Pyrene Sorption in Soil

Plants change the behavior of pollutants in soil by rhizodeposition in the process of physiochemistry. The effects of hydrosoluble and lipophilic extracts from celery rhizodeposits on pyrene sorption were investigated. The Freundlich sorption coefficient of pyrene decreased from 1143mgkg^-1 in the bulk treatment to 670, 795, and 1030mgkg^-1 in treatments with lipophilic+hydrosoluble, hydrosoluble, and lipophilic extracts, respectively. Although both hydrosoluble and lipophilic extracts inhibited pyrene sorption, they acted at different processes on soil organic matters (SOMs) and dissolved organic matters (DOMs). The analysis of three-dimensional fluorescence excitation-emission matrix spectroscopy revealed that the intensity of soluble humic-like substances increased from 5.73 in the bulk treatment to 7.74, 6.36, and 8.67 in treatments with hydrosoluble, lipophilic and hydrosoluble+lipophilic components, respectively. Images of DOMs by atomic force microscopy illustrated that the hydrosoluble extract greatly expanded the DOMs particles, while the lipophilic slightly shrank them. Moreover, the lipophilic extract dramatically softened SOMs with the glassy transition temperature declining from 50.6±0.5 to 29.7±2.0°C. These results not only provide insights into the mechanisms involved in pyrene sorption but also help us understand how rhizodeposition affects the pyrene bioaccessibility to some extent.