Pii: S0043-1354(96)00303-x

-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 '4C-labeled and unlabeled TCE. Two dose levels were tested (about 560 Fg/L and 140 Fg/L). Following TCE exposure for 31 to 106 days, different plant tissues and bioreactor compartments were analyzed for the ~4C label. Radiolabel recoveries ranged from about 50% for low-dose reactors to about 70% for high-dose reactors. Most of the recovered ~4C label volatilized (74-95%) and was trapped in the Orbo ~ 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 ~4C label found in plant material was relatively small (1-2%), the concentration of ~4C 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 ~4C 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. © 1997 Elsevier Science Ltd. All rights reserved Key words--trichloroethylene, phytoremediation, vegetative uptake, bound residue INTRODUCTION carcinogen (Creech and Johnson, 1974). Consequently, regulatory agencies have set stringent Trichloroethylene (TCE) is one of the most prevalent standards or guidelines for TCE in drinking groundwater contaminants in the United States water, such as 5ppb by USEPA, 30ppb by (Westrick et al., 1984). TCE and other chlorinated WHO, and 50 ppb by Environment Canada. While aliphatics fall into a class of chemically stable TCE ingestion through drinking water is a common compounds commonly known as "safety solvents". route of exposure to humans, there are other Because they are resistant to combustion and exposure pathways that deserve consideration. One explosion, TCE and similar compounds were widely exposure pathway that has received limited scientific used as industrial solvents and degreasers for most of attention is the human ingestion of TCE contamithe twentieth century. The combination of extensive nated plants. This pathway may be important when use and chemical stability has led to widespread TCE plumes move off-property and individuals use contamination of groundwater and soil by this the contaminated groundwater to irrigate their ubiquitous and recalcitrant pollutant, gardens. TCE is cytotoxic to the human liver; necrosis and The uptake, transformation, and fate of TCE in fatty liver are primary signs of chronic TCE exposure vegetation are only partially understood, which (Piaa, 1986). Although other chronic effects are not precludes a comprehensive health risk assessment of well understood, the National Cancer Center has contaminated sites. A recent study by Anderson found that TCE induces hepatocellular carcinomas in and Walton (1995) indicated that 21% of the t~C mice (Williams and Weisburg, 1986). In addition, activity added as TCE to an enclosed bioreactor vinyl chloride, an intermediate product in the was assimilated by the soybean species Glycine reductive dechlorination of TCE, is a proven human max. The uptake of ~C was closely related to the amount of water taken up by Glycine max and by *Author to whom all correspondence should be addressed other plant species tested. Potential transformation of [Tel.: (319) 335-5065; Fax: (319) 335-5660; email: the TCE within the plants, however, was not pedro-alvarez@ uiowa.edu], investigated.