Influence of three organic solvents on soil microbial activity

Abstract

In recent years there has been much concern over the migration of organic pollutants to groundwater. Many organic solvents undergo biodegradation in the soil, but little information is available on the amount of protection soil can provide to groundwater. In this study, the growth response of soil microorganisms was measured when exposed to various concentrations of methyl isobutyl ketone (MIBK), tetrahydrofuran (THF), and xylene. Three Arizona soils were used in the experiment: Canelo loam, Mohave sandy loam, and river sand. Microbial activity was measured using two methods, carbon dioxide evolution and dilution plate counts. The plate count method was found to have a high degree of experimental error. Because of this error, definite statements could not be made about the influence of the test solvents on microbial numbers using this technique. The CO₂ evolution experiments indicated that xylene and THF at concentrations of 0.1 and 0.5% were more readily biodegraded than MIBK at similar concentrations. At 1.0%, all three solvents were generally toxic. Overall, the organisms in the Mohave sandy loam were shown to best deal with the solvents followed by Canelo loam and then river sand. Higher soil surface area appeared to enhance the ability of the soil to biodegrade solvents.