Reduction in denitrification activity in field soils exposed to long term contamination by 2,4,6-trinitrotoluene (TNT)

Terrestrial sites contaminated with 2,4,6-trinitrotoluene (TNT) are a wides pread and persistent problem and often contain non-vegetated areas with TNT concentrations well in excess of 1000 mg kg(-1). In this study, we examine d the effect of TNT on denitrification activity in field soils, and compare d the sensitivity of denitrifying: enzymes to TNT. DNA probes assessed the prevalence of nirS, nirK and nosZ (encoding cd(1) or copper nitrite reducta se and nitrous oxide reductase, respectively), denitrifying genotypes in th e culturable and total microbial community. The nitrate (NaR), nitrite (NiR ) and nitrous oxide (N2OR) reductase activities in field soil and in isolat es were assessed by gas chromatography. The relative occurrence of the nirK , nirS or nosZ genotypes increased in the cultured community and in total u ncultured community DNA as nitroaromatic concentrations increased. However, denitrifying activity decreased in response to increasing TNT concentratio ns! with an IC50 for NaR+NiR+nitric oxide reductase (NOR) of 400 mg TNT kg( -1) soil and for N2OR of 26 mg TNT kg(-1) soil. The denitrifying activity o f four soil isolates also decreased in response to TNT, with N2OR activity being three times more sensitive to TNT than NaR+NiR+NOR activity. Interest ingly, there were 118 times more nirK isolates than nirS isolates in uncont aminated soil but only 1.5 times more in soil containing 17400 mg kg(-1) TN T. The results from this study indicated that TNT reduced denitrification a ctivity in field soils, and N2OR was much more sensitive to TNT than NaR+Ni R+hTOR. Crown copyright (C) 2000 Published by Elsevier Science B.V. All rig hts reserved.