DoD is responsible for assessing the environmental exposure resulting from the testing and training activities associated with military munitions. Of greatest concern is the potential of off-site exposure to these materials and their degradation products primarily as a result of movement through surface waters and underlying aquifers. Modeling systems and databases currently exist where the user is responsible for defining the individual chemicals and their properties necessary to conduct chemical exposure and risk assessments. These data are required input into the U.S. Army Groundwater Modeling System (GMS), the Adaptive Risk Assessment Modeling System (ARAMS), and the Training Range Environmental Evaluation and Characterization System (TREECS).
The objective of this effort was to develop an Environmental Fate Simulator (EFS) that provides managers of military training and testing ranges estimates of the vulnerability of these aquifers and surface waters to new and proposed energetic materials and their potential transformation products. During the evolution of this project, the name of the EFS was changed to the Chemical Transformation Simulator (CTS) to better convey the primary function of the simulator. Our working hypothesis was that there is a substantial amount of process science published in the peer-reviewed literature concerning the transport and transformation of existing N-based munitions (e.g., TNT, 2,4-DNT and RDX) and related N-based chemicals (i.e., nitro aromatics, aromatic amines and substituted azobenzenes) that can be encoded through the use of cheminformatics applications. Consequently, this process science could then be applied to predicting the transport and transformation for the emerging N-based munitions for which little fate data exists
The primary focus of this project was development of two major components of the CTS: the Physicochemical Properties Calculator (PPC) and the Reaction Pathway Simulator (RPS). The selection of calculators supporting the PPC was based on their accessibility and their ability to ensure complete coverage of the molecular descriptors required for fate modeling. Development of the RPS allowed for the encoding of the process science underlying the environmental fate of existing munitions. This process began with a thorough review of the literature concerning the transformation pathways of the chemicals of interest, including existing N-based munitions and related N-based chemicals. The process science was then encoded with Chemical Terms Language and Smart Reaction Smile Strings, which then provides the dominant transformation products as a function of environmental conditions based on chemical structure analysis.
The result of this work is the development of the Chemical Transformation Simulator: A Cheminformatics-based Tool for Predicting Transformation Pathways and Physicochemical Properties. This is a web-based tool that is running on EPA’s CGI cloud servers and is fully accessible to DoD personnel. In addition to the PPC and the RPS, a chemical editor was incorporated that allows the user to enter the chemical(s) of interest by providing a chemical structure, SMILES string, CAS# or common name.
The output of the RPS is based on the selection and execution of reaction libraries that represent one-step reactions for transformation of reactive functional groups (e.g., reduction and hydrolysis). These one-step reactions represent viable transformation pathways based on the identification and subsequent transformation of reactive functional groups. The functional group transformations list extend beyond those typically found in the N-based munitions. The expanded reaction libraries address other classes of chemicals (e.g., halogenated solvents) that are of interest to both DoD and EPA. A reaction library for human metabolism for phase 1 biotransformations developed by ChemAxon also is available through the CTS. The PCP provides a consensus approach that allows the user to compare output generated by a number of calculators that take different approaches to calculating specific physicochemical properties. The calculators include (1) SPARC (SPARC Performs Automated Reasoning in Chemistry), which uses a mechanistic-based approach, (2) EPI Suite, which uses a fragment-based approach, (3) TEST (Toxicity Estimation Software Tool), which uses QSAR-based approaches, and (4) ChemAxon plug-in calculators, which use an atom-based fragment approach. The output derived from these calculators enables the user to compare the calculated data with measured data in readily accessible web-based databases.
Through the integration of the cheminformatics applications with software technologies, the CTS will be able to provide for the eventual seamless consumption by modeling toolsets for assessing environmental exposure and subsequent human/ecological receptor health risks associated with loading and fate/transport of residual energetic materials (and their degradation products).