Evaluation of CATMoS models for estimating pesticide ecotoxicity
EPA uses the in vivo acute rat oral LD50 to assign hazard classifications for acute oral toxicity for pesticides before they are approved for marketing. These classifications determine the precautionary statements placed on the pesticide label for acute human exposure. The in vivo acute rat oral LD50 is also used by EPA as a surrogate for acute oral toxicity to all mammalian wildlife. The rat LD50 is predicted by the Collaborative Acute Toxicity Modeling Suite (CATMoS), an in silico predictive tool for estimating acute oral toxicity based on molecular structure. EPA and NICEATM scientists and collaborators evaluated how well CATMoS predicted acute oral toxicity LD50 values of pesticides with available in vivo acute rat oral LD50 data (Bishop et al. 2024). The evaluation included 177 pesticides registered for use in the United States, mostly fungicides, herbicides, and insecticides. Most of the evaluated pesticides fell into the lower-toxicity Categories III and IV, and for these CATMoS predictions were found to correlate well with in vivo data, although it was felt that in some cases CATMoS estimates for toxicity might result in a more stringent label warning than animal tests would require. There were too few chemicals evaluated from the higher-toxicity Categories I and II to support a conclusion about CATMoS performance for more toxic substances. This analysis will help inform whether CATMoS can be used to estimate acute oral toxicity from pesticides to identify toxicity categories and assess risk to wildlife.