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Enzymatic Transformation and Binding of Labeled 2,4,6-Trinitrotoluene to Humic Substances during an Anaerobic/Aerobic Incubation

^a Institut für Bodenkunde, Universität Rostock, Justus-von-Liebig-Weg 6, D-18051 Rostock, Germany
^b LabAlliance, 349 N. Science Park Rd, State College, PA 16803
^c Lab. of Soil Biochemistry, The Pennsylvania State Univ., 129 Land and Water, University Park, PA 16802

* Corresponding author (jmbollag{at}psu.edu)

Received for publication June 2, 2000. Organic pollutants are degraded in soil and simultaneously non-extractable residues are formed. However, proof is lacking that this fixation has a detoxifying effect. We investigated the transformation and binding of 2,4,6-trinitrotoluene (TNT) with catechol or soil humic acid as cosubstrates. Carbon-14-labeled TNT and its reaction products were quantified by radiocounting; extractable compounds were identified by high performance liquid chromatography (HPLC). Bound and extractable residues of ¹⁵N-labeled TNT and metabolites were studied by ¹⁵N nuclear magnetic resonance spectroscopy (¹⁵N NMR). Since TNT is not easily transformed under oxidizing conditions an anaerobic/aerobic treatment was used. Anaerobic microorganisms from cow manure were used to reduce TNT during the anaerobic phase and subsequently, a laccase from Trametes villosa was used in the aerobic phase to oxidatively couple the metabolites to humic matter. Seventy-four percent of TNT was immobilized with catechol as cosubstrate, but only 25% with humic acid. With catechol the main extractable component was TNT, while with humic acid it was mostly the metabolite 4-aminodinitrotoluene. For both co-substrates, the spectra of immobilized metabolites obtained by solid-state ¹⁵N-cross polarization magic angle spinning (CPMAS) NMR spectroscopy showed signals in the chemical shift region for protonated aromatic amino compounds. However, in the presence of catechol, an additional signal from non-extractable nitro groups was found, which could represent sequestered TNT. The partially reduced metabolites of TNT that formed non-extractable residues in humic acid are not likely to be remobilized easily and are thus regarded as detoxified.

Abbreviations: 4ADNT, 4-amino-dinitrotoluene • CPMAS, cross polarization magic angle spinning • DMP, 2,6-dimethoxyphenol • HPLC, high performance liquid chromatography • NMR, nuclear magnetic resonance • TNT, 2,4,6-trinitrotoluene

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