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 EPA's review of new chemicals under TSCA: engineering checklist; worker protections; updated statistics for new chemical review timelines; and the New Chemicals Division Reference Library. More recently, in April 2025, EPA announced the availability of new resources intended to help companies with the requirements in EPA's December 2024 final rule governing the review of new chemicals. According to EPA, the new materials "provide companies with clear instructions on how to include required data elements in the current system used for new chemical submissions while the agency works to update that system."

EPA notes that under TSCA Section 5, it is required to review new chemicals before they may be manufactured, processed, or used, to determine whether they present an unreasonable risk of injury to human health or the environment. The reviews include an assessment of how much of the chemical may be released into the environment and the potential exposure levels in the workplace. EPA states that "[w]hen chemical-specific information is not available or substantiated — such as the type of containers used to transport the chemical or the quantity of residue that remain in process equipment before they are cleaned out — EPA uses assumptions to assess levels of environmental release and worker exposure during the lifecycle of a new chemical."

EPA used three primary sources to create this assumption guide:

• EPA models hosted in the Chemical Screening Tool for Exposures and Environmental Releases (ChemSTEER);

• EPA's Generic Scenarios Documents; and

• The Organisation for Economic Co-operation and Development's (OECD) Emission Scenario Documents (ESD).

EPA considers the guide "an evolving document" that may be updated in the future. EPA states that it "welcomes the submission of representative data to NewChemicalDefaults@epa.gov from industrial sectors to ensure that the inputs and assumptions used in new chemical reviews are grounded in gold standard science, fit for purpose and appropriate for use."

Commentary

Bergeson & Campbell, P.C. (B&C^®) welcomes increased transparency on new chemical review. While this announcement is an important step, more improvement is needed. For example, ChemSTEER (last updated in 2015), EPA's Generic Scenarios, and the OECD ESDs are not new; all have been available for years, if not decades. It is, nevertheless, useful for newer submitters to understand and have access to these key resources. The more significant issue is under what circumstances EPA will deviate from the baseline assumptions described in these documents. Although EPA suggests that chemical-specific information could move the needle, EPA does not describe in this guidance, for example, what it deems to be "substantiated adequately" or "relevant documentation." We have experienced instances in which a submitter has provided data to refine EPA's release and exposure scenarios, only to have EPA rely on the generic scenarios in preference to the submitted data. We also have experienced instances in which EPA deviates from these scenarios for more conservative assumptions. These examples are not uncommon. It is as important that EPA ensure that its assessments consistently follow its own guidance as it is for submitters to understand what that guidance is.