BIODEGRADATION AND MINERALIZATION OF ISOTOPICALLY LABELED TNT AND RDX IN ANAEROBIC MARINE SEDIMENTS

摘要

The lack of knowledge on the fate of explosive compounds 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5triazine (RDX), particularly in marine ecosystems, constrains the application of bioremediation techniques in explosive-contaminated coastal sites. The authors present a comparative study on anaerobic biodegradation and mineralization of N-15-nitro group isotopically labeled TNT and RDX in organic carbon-rich, fine-grained marine sediment with native microbial assemblages. Separate sediment slurry experiments were carried out for TNT and RDX at 23 degrees C for 16 d. Dissolved and sediment-sorbed fractions of parent and transformation products, isotopic compositions of sediment, and mineralization products of the dissolved inorganic N pool ((NH4+)-N-15, (NO3-)-N-15, (NO2-)-N-15, and N-15(2)) were measured. The rate of TNT removal from the aqueous phase was faster (0.75 h(-1)) than that of RDX (0.37 h(-1)), and N-15 accumulation in sediment was higher in the TNT (13%) than the RDX (2%) microcosms. Mono-aminodinitrotoluenes were identified as intermediate biodegradation products of TNT. Two percent of the total spiked TNT-N is mineralized to dissolved inorganic N through 2 different pathways: denitration as well as deamination and formation of NH4+, facilitated by iron and sulfate reducing bacteria in the sediments. The majority of the spiked TNT-N (85%) is in unidentified pools by day 16. Hexahydro-1,3,5trinitro- 1,3,5-triazine (10%) biodegrades to nitroso derivatives, whereas 13% of RDX-N in nitro groups is mineralized to dissolved inorganic N anaerobically by the end of the experiment. The primary identified mineralization end product of RDX (40%) is NH4+, generated through either deamination or mono-denitration, followed by ring breakdown. A reasonable production of N-2 gas (13%) was seen in the RDX system but not in the TNT system. Sixty-eight percent of the total spiked RDX-N is in an unidentified pool by day 16 and may include unquantified mineralization products dissolved in water. (C) 2016 SETAC