Profiling chemicals based on chronic toxicity results from the U.S. EPA ToxRef database

Abstract

Background: Thirty years of pesticide registration toxicity data have been historically stored as hardcopy and scanned documents by the U.S. Environmental Protection Agency (EPA). A significant portion of these data have now been processed into standardized and structured toxicity data within the EPA's Toxicity Reference Database (ToxRefDB), including chronic, cancer, developmental, and reproductive studies from laboratory animals. These data are now accessible and mineable, within ToxRefDB and are serving as a primary source of validation for U.S. EPA's ToxCast research program in predictive toxicology. Objectives: We profiled in vivo toxicities across 310 chemicals as a model application of ToxRefDB, meeting the need for detailed anchoring end points for development of ToxCast predictive signatures. Methods: Using query and structured data-mining approaches, we generated toxicity profiles from ToxRefDB based on long-term rodent bioassays. These chronic/cancer data were analyzed for suitability as anchoring end points based on incidence, target organ, severity, potency, and significance. Results: Under conditions of the bioassays, we observed pathologies for 273 of 310 chemicals, with greater preponderance, (> 90%) occurring in the liver, kidney, thyroid, lung; testis, and spleen. We observed proliferative lesions for 225 chemicals, and, 167 chemicals caused progression to cancer-related pathologies. Conclusions: Based on incidence, severity, and potency, we selected 26 primarily tissue-specific pathology end points to uniformly classify the 310 chemicals. The resulting toxicity profile classifications demonstrate the utility of structuring legacy toxicity information and facilitating the computation of these data within ToxRefDB for ToxCast and other applications.