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Prediction of Hydrolysis Products of Organic Chemicals under Environmental pH Conditions
Stevens, C., J. Patel, Jack Jones, AND E. Weber. Prediction of Hydrolysis Products of Organic Chemicals under Environmental pH Conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 51(9):5008–5016, (2017). https://doi.org/10.1021/acs.est.6b05412
This paper presents the development of an abiotic hydrolysis reaction library to predict the molecular structure of hydrolysis transformation products of organic chemicals under environmentally relevant conditions. The paper describes the approach used to develop the reaction schemes within the library and the methods used to rank the schemes, enabling qualitative prediction of the most likely route of transformation when more than one structural fragment susceptible to hydrolysis is present in a molecule of interest. The library will be implemented in the Chemical Transformation Simulator (CTS), a web- based software tool under development in ORD/NERL. The predictions from CTS will support the application of environmental fate and transport models to assess the potential environmental exposure of vulnerable organisms to toxic organic chemicals dissolved in groundwater, surface water, and runoff.
Cheminformatics-based software tools can predict the molecular structure of transformation products using a library of transformation reaction schemes. This paper presents the development of such a library for abiotic hydrolysis of organic chemicals under environmentally relevant conditions. The hydrolysis reaction schemes in the library encode the process science gathered from peer-reviewed literature and regulatory reports. Each scheme has been ranked on a scale of one to six based on the median half-life in a data set compiled from literature-reported hydrolysis rates. These ranks are used to predict the most likely transformation route when more than one structural fragment susceptible to hydrolysis is present in a molecule of interest. Separate rank assignments are established for pH 5, 7, and 9 to represent standard conditions in hydrolysis studies required for registration of pesticides in Organisation for Economic Co-operation and Development (OECD) member countries. The library is applied to predict the likely hydrolytic transformation products for two lists of chemicals, one representative of chemicals used in commerce and the other specific to pesticides, to evaluate which hydrolysis reaction pathways are most likely to be relevant for organic chemicals found in the natural environment.