Biodegradation and mineralization of isotopically labeled TNT and RDX in anaerobic marine sediments

Thivanka Ariyarathna, Penny Vlahos, Richard W. Smith, Stephen Fallis, Thomas Groshens, Craig Tobias

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

The lack of knowledge on the fate of explosive compounds 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (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 15N-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°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 (15NH4 +,15NO3 ,15NO2 , and 15N2) 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 15N accumulation in sediment was higher in the TNT (13%) than the RDX (2%) microcosms. Mono-amino-dinitrotoluenes 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-1,3,5-trinitro-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 N2 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. Environ Toxicol Chem 2017;36:1170–1180.

Original languageEnglish (US)
Pages (from-to)1170-1180
Number of pages11
JournalEnvironmental Toxicology and Chemistry
Volume36
Issue number5
DOIs
StatePublished - May 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Health, Toxicology and Mutagenesis

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