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

doi:10.1006/eesa.2000.1934

Ecotoxicology and Environmental Safety

Volume 47, Issue 1, September 2000, Pages 96-103

https://doi.org/10.1006/eesa.2000.1934 Get rights and content

Abstract

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.

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2,4-DNT and its amino derivatives frequently co-occur with the relatively stable transformation products of the reductive (bio)transformation pathway of TNT, such as 2-amino-4,6-dinitrotoluene (2-ADNT), and 4-amino-2,6-dinitrotoluene (4-ADNT) in soil contaminated with nitroaromatic EMs (Jenkins, 2004; Monteil-Rivera et al., 2009; Travis et al., 2008). This has precluded investigators from partitioning the effects of the parent materials and their transformation products on the soil microbial community and biologically-mediated endpoints, such as organic carbon mineralization (Fuller and Manning, 1998; Gong et al., 2000; Kuperman et al., 2017) and necessitated the present investigation of the ecotoxicological effects of selected individual EMs on biologically-mediated organic matter decomposition using environmentally realistic exposure levels. Concentrations of 117, 19, and 20 mg/kg were reported for 2,4-DNT, 2-ADNT, and 4-ADNT, respectively, in soil at Joliet Army Ammunition Plant (Wilmington, IL) by Simini et al. (1995).
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Pollution induced community tolerance (PICT) to Cu²⁺, and co-tolerance to nanoparticulate Cu, ionic silver (Ag⁺), and vancomycin were measured in field soils treated with Cu²⁺ 15 years previously. EC₅₀ values were determined using substrate induced respiration and correlations made against soil physicochemical properties, microbial community structure, physiological status (qCO₂; metabolic quotient), and abundances of genes associated with metal and antibiotic resistance. Previous level of exposure to copper was directly (P < 0.05) associated with tolerance to addition of new Cu²⁺, and also of nanoparticle Cu. However, Cu-exposed communities had no co-tolerance to Ag⁺ and had increased susceptibly to vancomycin. Increased tolerance to both Cu correlated (P < 0.05) with increased metabolic quotient, potentially indicating that the community directed more energy towards cellular maintenance rather than biomass production. Neither bacterial or fungal community composition nor changes in the abundance of genes involved with metal resistance were related to PICT or co-tolerance mechanisms.
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The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) may influence soil microbial communities by altering the balance between resident populations. Our objective was to assess the effect of environmentally relevant levels (ERLs) of 2,4-D on microbial community function and on the population dynamics of 2,4-D degrading bacteria using a microcosm approach. The most probable number approach was used to enumerate 2,4-D-degrading soil bacteria. Carbon substrates utilization was tested with a microtiter-based oxygen sensor system to evaluate short-term functional shifts caused by herbicide treatment. Shifts in the community in response to potential toxicity of 2,4-D were assessed in the agricultural soil and a reference forest soil using the pollution-induced community-tolerance (PICT) approach. Results indicated that the agricultural soil had a stable 2,4-D degrading population able to use the herbicide as C and energy source, which increases immediately after an ERL dose of 2,4-D and remains high for about 1 month after exposure has ceased. An enhanced, dose-dependent response to 2,4-D as substrate was observed in the microtiter assay, while heterotrophic bacterial activity appeared mostly unchanged. The PICT assay showed higher tolerance to 2,4-D in the agricultural soil than in the unexposed forest soil. Our results suggest that agricultural use of 2,4-D at recommended level leads to selection for (1) a copiotrophic degrader population and (2) a persistently herbicide-tolerant, but functionally similar, microbial community.
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Regular ArticleAn in Situ Respirometric Technique to Measure Pollution-Induced Microbial Community Tolerance in Soils Contaminated with 2,4,6-Trinitrotoluene☆

Abstract

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