Effects of Chlorinated Organic Solvents on Microorganisms and Enzyme Activity in Soil

Abstract

When introduced into soil, chlorinated organic solvents may affect the soil microflora which plays an important role in the biogeochemical nutrient cycle. In our investigations, concentrations of 10, 100, and 1000μg per 100g soil (dry weight) affected variously the soil microorganisms. The results were as follows: 1) The ATP content of the soil biomass decreased significantly in the first and second week of incubation when 100μg of trichloroethylene and tetrachloroethylene were added to the soil, and the content was markedly reduced during the two month period of the experiment when 1000μg of the individual chlorinated organic solvents under test were added. 2) Tetrachloroethylene at the dose of 1000μg, however, exerted prevalently a stimulatory effect on the number of aerobic soil bacteria and also on the total number of anaerobic bacteria. The same concentrations of trichloroethylene and dichloromethane inhibited both groups of aerobic bacteria in the soil. No significant effects were observed with aerobic spore-forming bacteria. Fungi were the most sensitive group and their number was remarkably reduced by each concentration of the solvents used in the experiments. Similar inhibitory effects could be observed with soil biomass. 3) When 100μg chlorinated organic solvents were added, the activity of β-glucosidase, β-acetylglucosaminidase and partially also that of proteinase were decreased up to 28 days of incubation but the activity returned to the same or slightly higher level as in the control soil after two months of incubation. Trichloroethylene, tetrachloroethylene, and dichloromethane at the concentration of 1000μg per 100g soil primarily inhibited the activity of all the enzymes tested. However, after two months of incubation the enzyme activity especially that in the soil samples contaminated with tetrachloroethylene and dichloromethane was found to be the same as or higher than that in the control soil.