EPA Publishes Default Values Used In New Chemical Risk Assessments Under TSCA

On November 24, 2025, the U.S. Environmental Protection Agency (EPA) released the key default values that it uses in its risk assessments of new chemicals under the Toxic Substances Control Act (TSCA). EPA is making the assumptions available on its website in the New Chemicals Division Reference Library. EPA states that it expects the publication of the default values "to improve efficiency, reducing the likelihood that submissions need to be reworked or resubmitted."

According to EPA, providing these established numeric assumptions will help new chemical submitters better understand EPA's chemical assessment process and develop higher-quality submissions. This is the latest in a series of steps that EPA has taken to improve efficiency, worker protections, and transparency in new chemical reviews. In June 2024, Michal Ilana Freedhoff, Ph.D., then Assistant Administrator of EPA's Office of Chemical Safety and Pollution Prevention, announced four new initiatives in