TRICHLOROETHYLENE (TCE) AND TOLUENE EFFECTS ON THE STRUCTURE AND FUNCTION OF THE SOIL COMMUNITY

The effects of trichloroethylene (TCE) and toluene on indigenous soil communities were examined in soil microcosms, with special emphasis on community structure and function. Soil communities were exposed to TC E (1, 30 and 60 mu g ml(-1)) plus toluene (20 mu g ml(-1)), TCE only ( 1, 30 and 60 mu g ml(-1)), and toluene only (20, 60, 100 and 200 mu g ml(-1)) (all concentrations given as mu g ml(-1) soil solution after t aking into account sorption and volatilization). Soil microbial popula tions exposed to 30 or 60 mu g TCE ml(-1) plus 20 mu toluene ml(-1) or to toluene concentrations greater than 60 mu g toluene ml(-1), exhibi ted different sole carbon source utilization patterns than control soi ls, as revealed by Biolog Gram negative (GN) plates. These differences remained even 30 days after all the TCE and toluene had been removed from the system. Exposure to TCE alone did not alter Biolog patterns t o the same degree as TCE combined with toluene. Thirty and 60 mu g TCE ml(-1) either in the presence or absence of 20 mu g toluene ml(-1) sl ightly reduced basal respiration after 28 days of incubation, whereas substrate induced respiration was not affected. Total culturable heter otrophs were not sensitive to TCE and toluene, and were only slightly reduced after exposure to 200 mu g ml(-1) toluene for 45 days. Most pr otozoa were insensitive to TCE and toluene, but TCE was toxic to flage llates. Significant decreases in numbers of nematode types occurred af ter exposure to 30 or 60 pg TCE ml(-1). The nematode maturity index (M I), an index of diversity based on trophic groupings, was not sensitiv e to TCE or to TCE combined with toluene in an agricultural soil, wher eas the MI in a riparian soil was reduced by concentrations of 30 mu g TCE ml(-1). These results indicate that TCE and toluene adversely aff ect the biota of the soil ecosystem, sometimes for prolonged periods. (C) 1997 Elsevier Science Ltd.