title: Using compound-specific isotope analysis to assess biodegradation of nitroaromatic explosives in the subsurface.
abstract: Assessing the fate of nitroaromatic explosives in the subsurface is challenging because contaminants are present in different phases (e.g., bound to soil or sediment matrix or as solid-phase residues) and transformation takes place via several potentially competing pathways over time-scales of decades. We developed a procedure for compound-specific analysis of stable C, N, and H isotopes in nitroaromatic compounds (NACs) and characterized biodegradation of 2,4,6-trinitrotoluene (TNT) and two dinitrotoluene isomers (2,4-DNT and 2,6-DNT) in subsurface material of a contaminated site. The type and relative contribution of reductive and oxidative pathways to the degradation of the three contaminants was inferred from the combined evaluation of C, N, and H isotope fractionation. Indicative trends of Δδ(15)N vs Δδ(13)C and Δδ(2)H vs Δδ(13)C were obtained from laboratory model systems for biodegradation pathways initiated via (i) dioxygenation, (ii) reduction, and (iii) CH3-group oxidation. The combined evaluation of NAC isotope fractionation in subsurface materials and in laboratory experiments suggests that in the field, 86-89% of 2,4-DNT transformation was due to dioxygenation while TNT was mostly reduced and 2,6-DNT reacted via a combination of reduction and CH3-group oxidation. Based on historic information on site operation, our data imply biodegradation of 2,4-DNT with half-lives of up to 9-17 years compared to 18-34 years for cometabolic transformation of TNT and 2,6-DNT.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Reto S
authors.initials: RS
authors.lastname: Wijker
authors.forename: Jakov
authors.initials: J
authors.lastname: Bolotin
authors.forename: Shirley F
authors.initials: SF
authors.lastname: Nishino
authors.forename: Jim C
authors.initials: JC
authors.lastname: Spain
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry* / Q000378:metabolism*; D001673:Biodegradation, Environmental; D016956:Burkholderia cepacia / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D003903:Deuterium / Q000032:analysis; D053834:Explosive Agents / Q000737:chemistry* / Q000378:metabolism*; D009161:Mycobacterium / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000032:analysis; D011549:Pseudomonas / Q000378:metabolism; D012989:Soil Pollutants / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001555:Benzene Derivatives; D002247:Carbon Isotopes; D053834:Explosive Agents; D009587:Nitrogen Isotopes; D012989:Soil Pollutants; D003903:Deuterium