Adsorption of naphthalene onto plant roots

Higher plants are being used to enhance the remediation of sods contaminated with recalcitrant organic compounds, but the mechanisms of dissipation have not been established. One possible step in the phytoremediation process is adsorption of the organic contaminant onto the surface of the roots and subsequent uptake and/or degradation. To determine the affinity of plant roots for naphthalene, a polycyclic aromatic hydrocarbon, adsorption was quantified for tall rescue (Festuca arundinacea Schreber) and alfalfa (Medicago sativa L.). Equilibrium adsorption for naphthalene was determined for fresh roots of each species at three growth stages. For both fescue and alfalfa, adsorption was described by the Freundlich isotherm. Adsorption increased by as much as a factor of four with later growth stage of the plants. Alfalfa roots had approximately twice the affinity for naphthalene than rescue roots, despite a greater surface urea per unit mass of root for fescue. Alfalfa also had a greater lipid content than fescue (10 g lipid/kg dry root vs. 4.5 g/kg), indicating that lipid content is a controlling factor in adsorption of naphthalene onto plant roots.