Partitioning of polycyclic aromatic hydrocarbons between plant roots and water

Partition of phenanthrene between water and roots was determined for 13 plant species using a batch equilibration technique. Partition coefficients (K _rt) from 734 to 2,564 L/kg were measured. A simple model to estimate the partition of organic contaminants between roots and water was developed based on the composition of plant roots and the 1-octanol/water partitioning coefficient. The estimates were close to the observed results, with differences of < 14%. The partition coefficients of phenanthrene by root cell walls were 13–84% greater than sorption by the corresponding roots. The cell wall fraction—the dominant fraction of root organic components—was identified as the primary domain for partition of phenanthrene. The measured hydroponic uptake of phenanthrene into roots was always less than phenanthrene partition by plant roots. A modified sorption model containing a quasi-equilibrium factor (α_pt) could reasonably predict hydroponic uptake by plant roots. The results obtained from this study provide insights into partition of highly lipophilic organic chemicals in roots, and provide convenient methods to estimate this partition as well as uptake of such chemicals in root–water systems.