Transport via xylem of trichloroethylene in wheat, corn, and tomato seedlings

Transport via xylem of trichloroethylene (TCE) from roots to shoots in seedlings of wheat, corn, and tomato was measured following a 24-h exposure of plant roots to hydroponic solutions containing TCE. Dewdrops on plant leaves were also collected to test the foliar uptake by plants and the volatilization of TCE from shoot to air. Results indicated that the TCE concentration in xylem sap of wheat and corn decreased significantly with increasing TCE concentration in external solutions, where the initial concentration was set at 10-30 mg l(-1). The translocation stream concentration factor (TSCF) with the three plant species, defined as the ratio of the contaminant concentration in plant xylem sap to that in external solution, decreased sharply with increasing external TCE concentration or with increasing exposure time. Among the three plant species tested, the efficiency of TCE transport from roots to shoots followed the order of corn>wheat>tomato, based on the TCE concentration in xylem sap and the TSCF value. However, the TCE removal efficiency from external solution by three plant species followed the order of wheat>corn>tomato, because of the strong exchange of TCE between corn leaves and air and the rapid movement downward via phloem inside the plant. TCE concentrations in dewdrops collected from wheat and corn were far higher than in the xylem sap, especially with the corn.