Reaction Library to Predict Direct Photochemical Transformation Products of Environmental Organic Contaminants in Sunlit Aquatic Systems

Abstract

Cheminformatics-based applications to predict transformation pathways of environmental contaminants are useful to quickly prioritize contaminants with potentially toxic/persistent products. Direct photolysis can be an important degradation pathway for sunlight-absorbing compounds in aquatic systems. In this study, we developed the first freely available direct phototransformation pathway predictive tool, which uses a rule-based reaction library. Journal publications studying diverse contaminants (such as pesticides, pharmaceuticals, and energetic compounds) were systematically compiled to encode 155 reaction schemes into the reaction library. The execution result of this predictive tool was internally evaluated against 390 compounds from the compiled journal publications and externally evaluated against 138 compounds from the regulatory reports. The recall (sensitivity) and precision (selectivity) were 0.62 and 0.35, respectively, for internal evaluation, and 0.56 and 0.20, respectively, for external evaluation, when only the products formed from the first reaction step were counted. This predictive tool could help to narrow the data gaps in chemical registration/evaluation and inform future experimental studies.

Prioritizing Direct Photolysis Products Predicted by the Chemical Transformation Simulator: Relative Reasoning and Absolute Ranking

“…The collection of two different databases is detailed by Yuan et al (2020). 4 Briefly, DB-J-ENV represents a data compilation based on peerreviewed journal publications and includes 390 parent contaminants (pharmaceuticals, pesticides, and so forth) and their direct photolysis products under environmentally relevant conditions; DB-EFSA-ENV represents a data compilation based on the European Food Safety Authority (EFSA) reports 12 and includes 138 parent contaminants (pesticides) and their direct photolysis products under environmentally relevant conditions. DB-J-ENV served as the training set for library improvement and was used for internal evaluation, and DB-EFSA-ENV was used for external evaluation.…”

“…Each modification of the direct photolysis reaction library was used to predict photoproducts and was evaluated against our internal evaluation set DB-J-ENV and external evaluation set DB-EFSA-ENV, as previously described. 4 Briefly, we counted the number of experimentally observed products (N O ), the number of experimentally observed products that are correctly predicted (N OP ), and the number of predicted products (N P ) up to each desired reaction generation. Recall values (N OP,i /N O_all ) were calculated as the fraction of correctly predicted products up to a certain generation i (N OP,i ) among all experimentally observed products of all generations (N O_all ), and precision values (N OP,i /N P,i ) were calculated as the fraction of correctly predicted products up to a certain generation i (N OP,i ) among all predicted products up to generation i (N P,i ).…”

“…To narrow this knowledge gap, we developed the first freely available reaction library to predict direct photolysis products in silico. 4 This cheminformatic tool is currently hosted on the platform of the Chemical Transformation Simulator (CTS) developed by the United States Environmental Protection Agency (U.S. EPA): https://qed.epa.gov/cts/. 5 The photolysis reaction library covers 155 reaction schemes, which were collected from environmentally relevant literature from the 1960s onward.…”

UV/Vis+ photochemistry database: Structure, content and applications

“…Under the influence of natural sunlight, some of these SOCs are likely to transform through photolysis to more toxic products or to be photo-persistent. To meet the large data demand for risk assessment of SOCs, a cheminformatics-based direct photolysis reaction library is being developed as part of the United States Environmental Protection Agency’s Chemical Transformation Simulator (CTS) project to predict the direct photolytic transformation products formed from organic contaminants in waters [ 48 ]. Both the literature and data service of UV/vis + Photochemistry Database are useful in developing and applying such a predictive tool.…”

Computational Approaches for the Prediction of Environmental Transformation Products: Chlorination of Steroidal Enones

“…6 Yuan et al also recently extended the capability of CTS by demonstrating that its cheminformatics approach can also predict transformation products (with 40% accuracy) of direct photolysis based on reported reaction pathways. 7 A similar approach was developed by Wackett et al 8−15 for biotransformation pathways. The Biocatalysis/Biodegradation Database, now maintained by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG), offers a rules-based pathway prediction system for microbial degradation of chemical compounds.…”