Effects of trichloroethylene, tetrachloroethylene and dichloromethane on soil biomass and microbial counts.

Trichloroethylene, tetrachloroethylene and dichloromethane in concentrations of 10, 100, and 1000 micrograms per 100 g brown soil (dry weight) had different effects on soil microorganisms. The ATP content of the soil biomass decreased significantly in the first and second week of incubation when 100 micrograms of trichloroethylene and tetrachloroethylene were added to the soil, and it was strongly reduced during the two months of the experiment duration when 1000 micrograms of the individual chlorinated solvents under test was added. Similar inhibitory effects could be observed with soil fungi. Tetrachloroethylene in a dose of 1000 micrograms, however, exerted mainly a stimulative influence as shown by the counts of oligotrophic and copiotrophic aerobic soil bacteria and also by the total counts of anaerobic microorganisms. The same concentrations of trichloroethylene and dichloromethane inhibited both groups of aerobic bacteria in the soil. Actinomycetes were mainly inhibited by addition of 1000 micrograms of the volatile chlorinated solvents but they were not affected by lower concentrations. No significant effects were observed in aerobic spore-forming bacteria, and only slight effects were found also in the spore-forming anaerobic microorganisms of Clostridium sp. In conclusion, with the concentrations of chlorinated solvents which were from 10(3) to 10(6) higher than the actual 'in situ' soil contamination, some negative effects on soil microorganisms could be observed. However, one or two month after the soil was contaminated, the microbial counts increased again.