Metabolism of the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a contaminated vadose zone

• Published in: Chemosphere (Oxford) 2008-11, Vol.73 (9), p.1492-1498
• Main Authors: Ronen, Zeev, Yanovich, Yuval, Goldin, Regina, Adar, Eilon
• Format: Article
• Language: English
• Subjects: 4-Nitro-2,4-diazabutanal; Aeration Zone; aerobic conditions; anaerobic conditions; Applied sciences; aquifers; Bacteria - classification; Bacteria - genetics; Bacteria - metabolism; Base Sequence; biodegradation; Biodegradation, Environmental; Biological and physicochemical properties of pollutants. Interaction in the soil; Cytochrome P450; Denitration; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Explosive Agents - analysis; Explosive Agents - metabolism; explosives; Gordonia; Gordonia sp; groundwater; groundwater contamination; hexahydro-1,3,5-trinitro-1,3,5-triazine; Mineralization; Molecular Sequence Data; Nitrates - metabolism; Nitroso-RDX; nucleotide sequences; pollutants; Pollution; Pollution, environment geology; ribosomal RNA; Soil - chemistry; Soil and sediments pollution; soil bacteria; soil depth; Soil Microbiology; Soil Pollutants - analysis; Soil Pollutants - metabolism; Spingomonas; Triazines - analysis; Triazines - metabolism; vadose zone; water pollution; water table
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2008.07.041

The aim of this study was to explore biodegradation potential of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a deep contaminated unsaturated zone over Israel’s coastal aquifer. While anaerobic biodegradation potential was observed throughout the profile down to the water table at a depth of 45 m, aerobic biodegradation was limited to the surface of the unsaturated zone. Traces of nitroso-RDX intermediates were detected in the soil samples, indicating possible in situ activity. Polymerase chain reaction and denaturing gradient gel electrophoresis analysis revealed that the microbial population in the soil consisted of protobacteria, but no known RDX degraders were detected. However, a 16S rRNA gene sequence most similar to Sphingomonas sp. was detected at all depths. Biodegradation rates were faster in the surface (0 and 1 m) versus deeper soil samples (22 and 45 m) and were not affected under anaerobic conditions by the presence of nitrate, indicating a concurrent reduction of both compounds. RDX half-life in the surface soil was mostly dependent on carbon content and to lesser extent on soil moisture. Biomineralization of RDX to CO 2 was confirmed by incubating surface soil with 14C-labeled RDX. An aerobic RDX-degrading bacterium, identified as Gordonia sp., was isolated from the soil: it degraded RDX aerobically and produced 4-nitro-2,4-diazabutanal. This study, the first to explore RDX biodegradation in the deep vadoze zone, indicates biodegradation potential throughout the profile, which is likely to support natural attenuation.