Assessment of 2,4,6‐trinitrotoluene toxicity in field soils by pollution‐induced community tolerance, denaturing gradient gel electrophoresis, and seed germination assay

Abstract

AbstractDetermining the toxicity of contaminants to soil organisms under field conditions is hampered by site‐specific and temporal factors that modulate contaminant availability. Assessing the pollution‐induced community tolerance (PICT) of indigenous microbial communities integrates these complex environmental factors. The purpose of this study was to determine if the PICT response was proportional to 2,4,6‐trinitrotoluene (TNT) concentrations in soil, if changes detected by PICT were also evident in soil microbial community composition, and if the PICT response correlated with phytotoxicity assays. Microorganisms extracted from TNT‐contaminated field soils were mixed with a solution containing six different concentrations of TNT and inoculated into Biolog ECO plates. The utilization rate of substrates was determined over a 7‐d period. Denaturing gradient gel electrophoretic analysis of a portion of the gene encoding 16S rDNA described the structure of the soil microbial community. Phytoindicators (Poa compressa and P. palustris L.) of TNT pollution were identified and used to assess TNT phytotoxicity in soil samples. The TNT (in Biolog wells) greatly inhibited microbial communities from locations with low in situ TNT exposure. The inhibition of microbial use of L‐asparagine, L‐phenylalanine, and D‐glucosaminic acid by TNT (in Biolog wells) increased as TNT concentration in soil decreased. Locations differing in ECO‐PICT response also differed in their microbial community composition and TNT phytotoxicity. Decreased phytotoxicity of field soils corresponded to decreases in PICT. The results from this study indicated that ECO‐PICT is an effective assay to rapidly detect TNT exposure and toxicity in soil microbial communities.