An in Situ Respirometric Technique to Measure Pollution-Induced Microbial Community Tolerance in Soils Contaminated with 2,4,6-Trinitrotoluene

Long-term exposure to 2,4,6-trinitrotoluene (TNT) can induce changes in the structure and activities of soil microbial communities. Such changes may be associated with an elevated microbial tolerance. An in situ respirometry technique based on the analysis of the substrate-induced respiration response to freshly added TNT was used to examine soil microbial tolerance to TNT at the community level. The specific growth rate derived by fitting an exponential equation to respiration data was taken as the measurement endpoint. Microbial tolerance was evaluated using a tolerance index defined as the ratio of the specific growth rate at a spiking dose of 2000 μg TNT/g soil to that of the control with no spiked TNT. Three soils with long-term exposure histories (TNT level in soil: 1.5, 32, and 620 μg TNT/g, respectively) exhibited significantly higher microbial community tolerance to TNT than two uncontaminated control soils. A soil containing 29,000 μg TNT/g exhibited the highest tolerance. Findings from this study support the hypothesis that pollution-induced community tolerance can be used as a means of identifying those compounds that have exerted selective pressure on the community.