BIODEGRADATION OF TRICHLOROETHYLENE AND TOLUENE BY INDIGENOUS MICROBIAL-POPULATIONS IN SOIL

The biodegradation of trichloroethylene (TCE) and toluene, incubated s eparately and in combination, by indigenous microbial populations was measured in three unsaturated soils incubated under aerobic conditions . Sorption and desorption of TCE (0.1 to 10 mug ml-1) and toluene (1.0 to 20 mug ml-1) were measured in two soils and followed a reversible linear isotherm. At a concentration of 1 mug ml-1, TCE was not degrade d in the absence of toluene in any of the soils. In combination, both 1 mug of TCE ml-1 and 20 mug of toluene ml-1 were degraded simultaneou sly after a lag period of approximately 60 to 80 h, and the period of degradation lasted from 70 to 90 h. Usually 60 to 75% of the initial 1 mug of TCE ml-1 was degraded, whereas 100% of the toluene disappeared . A second addition of 20 mug of toluene ml-1 to a flask with residual TCE resulted in another 10 to 20% removal of the chemical. Initial ra tes of degradation of toluene and TCE were similar at 32, 25, and 18-d egrees-C; however, the lag period increased with decreasing temperatur e. There was little difference in degradation of toluene and TCE at so il moisture contents of 16, 25, and 30%, whereas there was no detectab le degradation at 5 and 2.5% moisture. The addition of phenol, but not benzoate, stimulated the degradation of TCE in Rindge and Yolo silt l oam soils, methanol and ethylene slightly stimulated TCE degradation i n Rindge soil, glucose had no effect in either soil, and dissolved org anic carbon extracted from soil strongly sorbed TCE but did not affect its rate of biodegradation.