Anaerobic incorporation of the radiolabeled explosive TNT and metabolites into the organic soil matrix of contaminated soil after different treatmentprocedures

Four bioreactor designs were performed to evaluate the level of incorporati on of C-14-labeled 2,4,6-trinitrotoluene (TNT) and metabolites into the org anic soil matrix of different anaerobically treated contaminated soils. The contaminated soils were amended with molasses slivers (80:20 % per weight) as auxiliary substrate to enhance microbial activity. After 5 weeks (biore actors 1 and 2), 8 weeks (bioreactor 3) and 12 weeks (bioreactor 4) of anae robic incubation, we determined 41%, 58%, 72%, and 54%, respectively, of th e initially applied radioactivity immobilized in various soil fractions. Af ter alkaline hydrolyses of the solvent-extracted soils, low quantities of r adiolabel were found in the humic and fulvic acid fractions, whereas the bu lk of C-14 activity was found to be strongly bound to the humin fraction (s olid soil residues). The amounts of solvent extractable radioactivity were 53%, 40%, 16%, and 29% for bioreactors 1, 2, 3, and 4, respectively. The le vel of TNT transformation at the end of the experiments was within 90-94%. Regarding the results presented in this study, we can assume that there is the possibility of high incorporation levels of TNT metabolites into the so il organic matrix mediated by microbial cometabolism under strictly anoxic conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.