Effects and bioavailability of 2,4,6-trinitrotoluene in spiked and field-contaminated soils to indigenous microorganisms

The response of potential nitrification activity (PNA), nitrogen-fixation a ctivity (NFA), and dehydrogenase activity (DHA) in soil to 2,4,6-trinitroto luene (TNT) was assessed. Two garden soils of contrasting texture (sandy lo am vs clay loam) were spiked with TNT (25-1,000 mg TNT/kg). Soil microbial activities and TNT residues were analyzed 1 week later. The estimated IC50 (concentration causing 50% inhibition) ranged from 39 to 533 mg/kg of the a cetonitrile-extractable (AE) TNT (1 week after spiking), depending on indic ators and soils. The lowest LOEC (lowest-observed-effect concentration) was 1 mg AE TNT/kg. Field soil (0-15 cm) was collected from three known contam inated sites in an abandoned TNT manufacturing facility. Microbial toxicity significantly correlated to TNT levels in these soils. The LOEC and NOEC ( no-observed-effect concentration) values were sire and indicator specific, with the lowest LOEC bring 1 mg AE TNT/kg and the lowest NOEC being 0.4 mg AE TNT/kg. The IC50 of the pooled held samples was 51 mg AE TNT/kg for PNA or 157 mg AE TNT/kg for DHA. These results indicate that microbial response s were consistent and comparable between the laboratory and the field and t hat TNT could significantly inhibit soil microbial activities at very low l evels. Both AE TNT and deionized water-extractable (DW) TNT concentrations correlated well with microbial toxicity, but AE TNT provided a better evalu ation of TNT bioavailability than did DW TNT.