This research project will quantify the magnitude of 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) loss, retention, and mineralization under conditions representing a wide range of surface water environments encountered in situ. It will provide kinetic parameters suitable for direct incorporation into fate and transport models for these insensitive high explosives (IHE). The objectives are organized around the following questions: 1) At what rate is the surface water IHE load attenuated during transport? 2) What fraction of the IHE loss from surface water is attributable to complete mineralization to inert inorganic constituents? 3) What fraction of the IHE loss from surface water is attributable to retention in the sediment as parent compound and/or organic derivatives? 4) How does sediment mineral type and natural organic matter content influence the fate of IHE? 5) Do the kinetics associated with these processes fundamentally change as a function of different IHE loads? 

This project will use stable isotope labeled DNAN and NTO to quantify the rates of parent compound loss from the overlying water, mineralization to inert inorganic constituents, and retention of IHE+ organic derivatives in sediments. The work will be conducted in a series of controlled sediment-water core microcosm experiments that encompass the range of surface water environments likely to be encountered across temperate and subtropical landscapes. Isotopelabeled IHE can be supplied at variable concentrations as a single pulse or as a steady state supply as dictated by sediment conditions and/or reaction rates. DNAN will be labeled with ¹³C and NTO with ¹⁵N. This differential labeling scheme permits the most abundant element in each compound to be labeled thereby maximizing the strength of the label and resultant sensitivity of the tracer technique. Experiments will be performed with both DNAN and NTO coincidentally since different isotope labels are imparted to each compound. With this labeling scheme ¹³C-DIC will be the mineralization product for DNAN, and ¹⁵N–DIN (NO_2,3^- , NH₄⁺, N₂O, and N₂) will be the mineralization products for NTO. Isotope tracer modeling will be used to derive the kinetics and rates of the various IHE loss/transformation pathways.

The Department of Defense (DoD) will derive multiple benefits from the results of the project. Aqueous IHE loss and mineralization rates will provide benchmark natural attenuation values for DNAN and NTO, under varied organic matter and sediment scenarios. Such information serves as a point of reference for natural attenuation at a given site. More specifically, the sediment retention and mineralization rates/kinetics for IHE provide useful for tools for building and parameterizing IHE fate and transport models in surface water environments. The work addresses the following challenges with parameterizing loss terms: 1) using the appropriate kinetics governing loss from overlying water, retention of parent/derivative compounds in sediments, and mineralization; 2) identifying what system characteristics (e.g. sediment type, organic matter [OM]) could be used as proxies for functionalizing processes in model-space; and 3) establishing uncertainties in rates/constants. A succinct summary of this information will be compiled for a webinar and a standalone project publication. Lastly, results from this work can serve as a template for quantifying transformations of other contaminants in other environments using a similar isotope tracer approach. (Anticipated Project Completion - 2023)

Ariyarathna, T., S. Twarz, and C. Tobias. 2023. Adsorption and Removal Kinetics of 2,4-Dinitroanisole and Nitrotriazolone in Contrasting Freshwater Sediments: Batch Study. Journal of Environmental Toxicology & Chemistry. 42:46-59. doi.org/10.1002/etc.5509.

Ariyarathna, T., S. Fallis, S. Twarz, and C. Tobias. 2023. Adsorption and Removal Kinetics of 2,4-Dinitroanisole (DNAN) and Nitrotriazolone (NTO) in Contrasting Fresh-Water Sediments: Batch Study. Journal of Environmental Toxicology and Chemistry, 42(1):46-59. doi.org/10.1002/etc.5509.

Davis, M., S. Fallis, and C.R. Tobias. 2021. Synthesis of [¹³C](C1–C6),[¹⁵N](N1,N2)-labeled 2,4-dinitroanisole (DNAN) and [¹³C](C3,C5),[¹⁵N](N6)-labeled 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO). Journal of Energetic Materials, 41(2):129-143. doi.org/10.1080/07370652.2021.1929573.