Nitroaromatic explosives have contaminated millions of acres of soil and water across the globe since World War II with known mutagenic, carcinogenic, and ecotoxicological effects. Recently, the U.S. Army initiated a shift away from traditional explosive compounds, such as trinitrotoluene (TNT) and hexahydrotrinitrotriazine (RDX), towards new, insensitive high explosive formulations. The new formulations approved for use include “IMX-101” and “IMX-104,” which contain 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). These mixtures are less prone to accidental detonation making storage, transport, and implementation of these formulations safer for soldiers. Furthermore, initial research indicates that these compounds are less toxic than the older analogues. Despite the apparent benefits, the new explosives have higher solubility (approximately 3-300 times) than the compounds they are replacing, and NTO and NQ are fairly recalcitrant to aerobic biodegradation. The refractory nature and high solubility of the compounds raises concerns about leaching and water contamination considering the previous scale of environmental contamination from production and use of legacy explosives, while feasible strategies for cleaning up the new chemicals from soil and water have not been developed. Therefore, there is a critical need for understanding of the mechanisms of biodegradation these compounds will undergo in the environment and in engineered systems. In addition, a number of questions remain about the photochemistry of the compounds and how they may transform in sunlit surface water. Accordingly, this thesis examines biological transformations of DNAN and NTO in vegetative, fungal, and bacterial organisms, as well as photolysis of NTO and NQ in aqueous solution and DNAN in plant leaves. I identified 34 novel biotransformation products of DNAN using stable-isotope labeled DNAN and high resolution mass spectrometry. Most identified biotransformation products were the result of a nitro-group reduction as the first metabolic step. Arabidopsis plants, a Rhizobium bacterium, and a Penicillium fungus all further metabolized DNAN to produce large, conjugated compounds, and no mineralization was observed in the systems studied. All three organisms reduced both para- and ortho-nitro groups of DNAN, with a dramatic preference for ortho reduction. I found that photodegradation of DNAN and its plant metabolites within Arabidopsis leaves could impact the phytoremediation of DNAN and other contaminants. Soil slurries acclimated to nitroaromatic wastewater degraded DNAN with and without carbon and nitrogen amendments and NTO with added carbon. Organisms capable of degrading DNAN and NTO were isolated, and NTO was transformed to urea, amino-triazolone, and hydroxyl-triazolone. Photolysis of NTO sensitized singlet oxygen formation and yielded hydroxyl-triazolone, nitrite, nitrate, and ammonium. The rate of photolysis of NTO increased over the neutral pH range, and natural organic matter quenched the photolysis of NTO. An unknown volatile product accumulated in the headspace of sealed reactors after NTO photolysis. Singlet oxygen degraded NTO and formed nitrite in stoichiometric yield. Photolysis of NQ produced nitrite and nitrate, but at high pH, the reaction occurred much faster than at neutral pH, and the mass balance of inorganic nitrogen was much lower. Further work should be done to investigate the mechanisms of and products from NTO and NQ photolysis.

NTO (3-nitro-1,2,4-triazol-5-one) is one of the new explosive compounds used in insensitive munitions (IM) and developed to replace traditional explosives, TNT and RDX. Data on NTO fate and transport is needed to determine its environmental behavior and potential for groundwater contamination. In this study, we measured how NTO in solution interacts with different types of soils and related soil properties to transport and fate behavior. We conducted a series of kinetic and equilibrium batch soil sorption experiments and saturated column transport studies under steady-state and transient conditions. NTO adsorbed very weakly to the studied soils. Adsorption coefficients (Kds) measured for NTO in a range of soils in batch experiments were less than 1 cm³ g⁻¹. There was a highly significant negative relationship between measured NTO adsorption coefficients and soil pH (P = 0.00011). In kinetic experiments, first order transformation rate estimates ranged between 0.0004 h⁻¹ and 0.0221 h⁻¹. There was a general agreement between batch and column-determined fate and transport parameters. However, transport studies showed an increase in the NTO transformation rate as a function of time, possibly indicating microbial growth.

New explosive compounds that are less sensitive to shock and high temperatures are being tested on military ranges as replacements for 2, 4, 6-trinitrotoluene (TNT) and hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX). One of the two compounds being tested is 2, 4-dinitroanisole (DNAN), which has good detonation characteristics and is one of the main ingredients in a suite of explosive formulations being tested. Data on the fate and transport of DNAN is needed to determine its potential to reach groundwater and be transported off base, a result which could create future contamination problems on military training ranges and trigger regulatory action. In this study, I measured how DNAN in solution interacts with different types of soils from across the United States. I conducted kinetic and equilibrium batch soil adsorption experiments, saturated column experiments with DNAN and dissolution and transport studies of insensitive munitions (IMX-101, IMX -104), which include DNAN, 3-nitro-1,2,4-triazol-5-one (NTO), nitroguanidine (NQ) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), under steady state and transient conditions. In the rate studies, change in DNAN concentration with time was evaluated using the first order kinetic equation. Solution mass-loss rate coefficients ranged between 0.0002 h-1 and 0.0068 h-1. DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3 L kg-1, and Freundlich coefficients between 1.3 and 34 mg1-n Ln kg-1. Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil. In saturated miscible-displacement experiments, it was shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-amino-4-nitroanisole (2-ANAN) and 4-amino-2-nitroanisole (4-ANAN). Dissolution miscible-displacement experiments demonstrated that insensitive munition compounds dissolved in order of aqueous solubility as indicated by earlier lab and outdoor dissolution studies. The sorption of NTO and NQ was low, while RDX, HMX, and DNAN all adsorbed to the soils. DNAN transformed in soils with formation of amino-reduction products, 2- ANAN and 4-ANAN. Adsorption parameters determined by HYDRUS-1D generally agreed with batch and column study adsorption coefficients for pure NTO and DNAN. The magnitudes of retardation and transformation observed in these studies result in significant attenuation potential for DNAN in soils, which would reduce risk of groundwater contamination.

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Abiotic transformation of compounds in the natural environment by metal oxides plays a significant a role in contaminant fate and behavior in soil. The ability of birnessite, ferrihydrite and green rust to abiotically transform insensitive munitions compounds (IMCs) parent (2,4 dinitroanisole [DNAN] and 3-nitro-1,2,4-triazol-5-one [NTO]), and daughter products (2-methoxy-5-nitro aniline [MENA], 2,4-diaminoanisole [DAAN]of DNAN; and 5-amino-1, 2, 4-triazol-3-one [ATO] of NTO) was studied in batch reactors under strictly controlled pH and ionic strength. The objectives of the study were to (i) assess the abiotic transformation potential of soluble DNAN, MENA, DAAN, NTO and ATO by birnessite, ferrihydrite and green rust, and (ii) identify inorganic reaction products. The study was carried out at metal oxide solid to IMC solution ratios (SSR) of 0.15, 1.5 and 15 g kg⁻¹ for birnessite and ferrihydrite and 10 g kg⁻¹ for green rust. Aqueous samples were collected at time intervals between 0 to 3 days after the reaction initiation and analyzed using HPLC with UV detection. Results indicated that DNAN was resistant to oxidation by birnessite and ferrihydrite at given solid to solution ratios. MENA was susceptible to rapid oxidation by birnessite (first order rate constant, 𝑘=1.36 h⁻¹ at 15 g kg⁻¹ SSR). The nitro groups from MENA largely mineralized to nitrite (NO₂⁻). In contrast, ferrihydrite did not oxidize MENA. DAAN was susceptible to oxidation by both birnessite and ferrihydrite, but about a six times higher oxidation rate was observed with birnessite (𝑘=1.18 h⁻¹) as compared to ferrihydrite (𝑘=0.22 h⁻¹) at an SSR of 1.5 g kg⁻¹. There was a complete loss of DAAN from solution after 5 min with birnessite at an SSR 15 g kg⁻¹ (𝑘≥90.5 h⁻¹). CO₂ evolution experiments indicate mineralization of 15 and 12 % of carbon associated with MENA and DAAN, respectively; under aerobic conditions with birnessite at an SSR of 15 g kg⁻¹. NTO was resistant to oxidation by birnessite and ferrihydrite at any SSR; however, there was slight initial loss from solution upon reaction with ferrihydrite at 0.15 and 1.5 g kg⁻¹ SSR and complete loss at 15 g kg⁻¹ SSR due to adsorption. ATO was susceptible to oxidation by birnessite and sorption by ferrihydrite. The first order rate constants (𝑘) for ATO with birnessite at 0.15 and 1.5 g kg⁻¹ SSR are 0.04 and 3.03 h⁻¹ respectively. There was complete loss of ATO from solution with birnessite at 15 g kg⁻¹ SSR (𝑘 ≥ 90.2 h⁻¹) within 5 min of reaction. Transformation products analysis revealed urea, CO₂ and N₂ as major reaction products with 44 % urea recovery and recovery of 51.5 % of ATO carbon as CO₂ and 47.8 % of ATO nitrogen as N₂ at 15 g kg⁻¹ SSR. The oxidation of ATO in the presence of birnessite was found to be independent of dissolved O₂. The results indicate that ATO, the major reductive (bio)transformation product of NTO, is readily oxidized by birnessite in soil. NTO was found strongly sorbed to ferrihydrite as compared to that of ATO. The results of the green rust experiment indicate rapid abiotic reduction of parent compounds NTO and DNAN to their reduced aminated daughter products. NTO was generally reductively transformed to 5-amino-1, 2, 4-triazol-3-one (ATO) within 10 min and completely reacted in 20 min. DNAN was rapidly transformed to its reduced daughter products MENA and 4-methoxy-5-nitroaniline (iMENA). The reduction occurred with a distinctive, staggered regioselectivity. Over the first 10 min, the para-nitro group of DNAN was selectively reduced, generating iMENA. Thereafter the ortho-nitro group was preferentially reduced, generating MENA. Both iMENA and MENA were subsequently transformed to the final reduction product DAAN within 1 day. X-ray absorption near edge spectroscopy data suggested oxidative transformation of green rust to lepidocrocite-like mineral forms, accounting for 94 % of the mineral products in the case of NTO reaction as compared to 62 % in the case of DNAN. The results taken as whole suggest that complete abiotic transformation of IMCs could be achieved by coupled stepwise green rust and birnessite treatments.