To provide a complete assessment of the potential environmental effects of insensitive munitions constituents (IMCs), it is necessary to consider the transformation products and their fate and effects. The transformation of the highest priority IMCs—2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-trizole-5-one (NTO)—has only recently been subjected to detailed investigation, so little is known about their transformation products, and even less is known about the fate and effects of these products. The currently available data on the environmental fate determining properties of IMC degradation products are limited, and rely heavily on estimation methods, most of which have not been validated for compounds of this type.

The overall goal of this project is to lay the foundation for comprehensive assessment of the fate and effects of IMC degradation products on training ranges and other DoD sites. The scope includes three major research objectives: (i) determination of IMC transformation pathways and products, (ii) determination of the fate determining properties of IMC transformation products, and (iii) development of models that describe the fate and transport of IMC transformation products. By integrating these three objectives into one concerted and coordinated multi-investigator effort, it is expected that an assessment of the consistency and accuracy of the information on all aspects of this problem will be provided, thereby increasing confidence in the reliability of the modeling results.

This study will focus on the transformation of two major IMCs (DNAN and NTO), but the models will be designed to accommodate a range of IMC parent compounds and daughter projects. The models will include all of the fate-determining processes (volatilization, sorption, etc.), but with emphasis on transformation, the relative rates of competing transformation pathways, and the resulting variation in intermediate/products concentrations as a function of space and time.

The approach juxtaposes experimental and modeling tasks within each objective, so that each can benefit from the results of the other, resulting in the highest confidence in the overall outcome. Objective 1 (Product/Pathway Identification) will adapt and use state-of-the-art algorithms for predicting contaminant transformation, with calibration and validation with experimental data obtained with bench-scale microcosm experiments. Objective 2 will adapt and use the most promising algorithms for prediction of contaminant fate determining properties, with calibration and validation against new and previously measured property data. Objective 3 will develop and test a numerical (kinetic) model for IMC transformation and link this kinetic/reaction model to the leading reactive-transport model for characterizing DoD training sites with respect to IMC fate and effects.

The benefits of this project will span both specific and general applications. The specific application will be to enable DoD training site managers to include consideration of IMC transformation and products into the modeling done for evaluation of exposure assessment scenarios, risk, remediation, etc. For this type of application, technology transfer will occur through integration directly into the Training Range Environmental Evaluation and Characterization System (TREECS). General applications of the results from this project will be through advancement of methods for prediction of transformation pathways, chemical properties, and reactive-transport models that could be adapted for assessing the environmental fate of other classes of contaminants. The application of methods developed in this project certainly could be applied to other MCs, but might also be extended to chlorinated solvents, or even emerging contaminant classes such as per- and polyfluorinated alkyl substances (PFASs). (Anticipated Project Completion - 03/2020)

Torralba-Sanchez, T.L., E.J. Bylaska, A.J. Salter-Blanc, D.E. Meisenheimer, M.A. Lyon, and P.G. Tratnyek. 2020. Reduction of 1,2,3-Trichloropropane (TCP): Pathways and Mechanisms from Computational Chemistry Calculations. Environmental Science: Processes & Impacts, 22(3), 606-616. doi.org/10.1039/c9em00557a.

Torralba-Sanchez, T.L. and P.G. Tratnyek. 2020. R Script for the Automated Generation of Reaction Coordinate Diagrams (RCDs) of Chemical Reaction Energies and Transformation Networks (1.0). Zenodo. doi.org/10.5281/zenodo.3611472.

Bylaska, E.J., D. Song, E.S. Ilton, S. O’Leary, T.L. Torralba-Sánchez, and P.G. Tratnyek. 2021. Chapter Five - Building Toward the Future in Chemical and Materials Simulation with Accessible and Intelligently Designed Web Applications. Annual Reports in Computational Chemistry, Elsevier, 17:163-208. doi.org/10.1016/bs.arcc.2021.09.003.