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

Determining the toxicity of contaminants to soil organisms under field cond itions is hampered by site-specific and temporal factors that modulate cont aminant availability. Assessing the pollution-induced community tolerance ( PICT) of indigenous microbial communities integrates these complex environm ental factors. The purpose of this study was to determine if the PICT respo nse was proportional to 2,3,6-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 i nto Biolog ECO plates. The utilization rate of substrates was determined ov er a 7-d period. Denaturing gradient gel electrophoretic analysis of a port ion of the gene encoding 16S rDNA described the structure of the soil micro bial community. Phytoindicators (Poa compressa and P. palustris L.) of TNT pollution were identified and used to assess TNT phytotoxicity in soil samp les. The TNT (in Biolog wells) greatly inhibited microbial communities from locations with low in situ TNT exposure. The inhibition of microbial use o f L-asparagine, L-phenylalanine. and D-glucosaminic acid by TNT (in Biolog wells) increased as TNT concentration in soil decreased. Locations differin g in ECO-PICT response also differed in their microbial community compositi on and TNT phytotoxicity. Decreased phytotoxicity of field soils correspond ed to decreases in PICT. The results from this study indicated that ECO-PIC T is an effective assay to rapidly detect TNT exposure and toxicity in soil microbial communities.