Uptake and transformation of trichloroethylene by edible garden plants

Edible garden plants (carrots, spinach, and tomatoes) were grown to maturity inside continuous air-flow bioreactors, and were regularly irrigated with synthetic groundwater containing a mixture of 14C-labeled and unlabeled TCE. Two dose levels were tested (about 560 μg/L and 140 μg/L). Following TCE exposure for 31 to 106 days, different plant tissues and bioreactor compartments were analyzed for the 14C label. Radiolabel recoveries ranged from about 50% for low-dose reactors to about 70% for high-dose reactors. Most of the recovered 14C label volatilized (74–95%) and was trapped in the OrboR tubes that filtered the air exiting the reactors. A portion of the recovered label (5–25%) was sorbed to the soil. Although the percentage of the recovered 14C label found in plant material was relatively small (1–2%), the concentration of 14C label in edible plant tissue was higher than in the surrounding soil. On a harvest weight basis, accumulation factors ranged from 2.6 in high-dose tomato reactors to 32 in low-dose spinach reactors. If the radiolabel found by combustion of plants was TCE, the concentrations in edible tissue would range from 152 ppb for high-dosed tomatoes to 580 ppb for high-dosed spinach. However, neither TCE nor its commonly reported transformation products were detected by Purge & Trap GC-MS. Furthermore, the 14C label found in plant tissue could not be extracted into the organic solvent CS2 or into the inorganic solvent 10 N H2SO4. This suggests that TCE was taken up, transformed, and bound to plant tissue. Bound residues are generally believed to have lower toxicological effects than the parent compound.