S27: Fate of the Insensitive Explosive 3-Nitro-1,2,4-Triazole-5-One (NTO) in Soil

Ammunition stability is a major concern to the safety of the warfighter and equipment. Current munitions are highly susceptible to explosion from fires, bullets, and high velocity fragments. Several new explosive formulations containing 2,4-dinitroanisole and/or 3-nitro-1,2,4-triazole-5-one (NTO) have met safety and performance criteria as insensitive munitions for the replacement of formulations containing 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3-5-trinitro-1,3,5-triazine (RDX). However, very little is known about the toxicity, mobility, or recalcitrance of these new insensitive explosives. We hypothesized that similar microbial mechanisms for nitroreduction and denitration of TNT and RDX would occur for NTO. To determine whether bacteria could transform NTO, a variety of bacterial species were cultured in rich and nitrogen-limited media with NTO. Also, soil microcosms amended with NTO were incubated with or without added carbon or nitrogen sources to determine the potential for NTO to be utilized as a growth or co-metabolic substrate by mixed microbial populations. Concentrations of NTO in soil and bacterial growth media were monitored by HPLC. NTO was co-metabolized by six bacterial species in a rich medium and by four species in a mineral salts medium. Both Gram positive and Gram negative bacterial species were represented and degraded approximately 30 to 90% of the NTO in 48 h. A potential metabolite peak was observed by HPLC/MS with a molecular mass of 101. This mass is consistent with the molecular structures of 3-amino-1,2,4-triazole-5-one or urazole. Thus, the co-metabolic transformation of NTO is hypothesized to occur by microbial nitroreductases.