Mineralization of RDX by the white rot fungus Phanerochaete chrysosporium to carbon dioxide and nitrous oxide

Biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in liquid cultures (initially at 62 mg/L) was studied using the white rot fungus Phanerochaete chrysosporium. With RDX as the main source of nitrogen, complete disappearance occurred after 60 d. The major products of RDX transformation were CO2 and N2O, and both gases appeared after a 2-d lag period. Following 60 d, an average of 52.9% [UL-C-14]-RDX was mineralized to CO2, 10.7% was taken up as biomass by the fungi, and 28.3% remained in the aqueous phase as unidentified metabolites. Of the nitrogen in RDX, 62.0% was transformed to N2O. Transformation of ring-labeled [N-15]-RDX, with subsequent analysis by GC-MS, indicated that the N2O was composed of one nitrogen atom from the RDX ring and the other nitrogen from one of the nitro group substituents. Oxidation of RDX was correlated with manganese peroxidase (MnP) enzyme activity (lignin peroxidase (LIP) activity was absent). Traces of 1-mononitroso-3,5-dinitro-1,3,5-triazine were evident throughout the course of the experiment. Results of this study provide new information regarding N2O as a major product of RDX mineralization. Quantification of N2O at sites contaminated with RDX may be an important parameter for monitored natural attenuation.