EPA Increases Transparency and Efficiency of Chemical Program by Releasing Common Assumptions Used in Assessing New Chemicals
Released Nov. 24, 2025
Today, U.S. Environmental Protection Agency (EPA) is publishing the key “default values” used in its risk assessments of new chemicals under the Toxic Substances Control Act (TSCA). Default values are assumptions used by EPA in environmental release and occupational exposure assessments. The agency is making these assumptions available on its website in the New Chemicals Division Reference Library. This initiative marks another step forward in the agency's ongoing commitment to transparency by providing valuable information to stakeholders involved in the review of new chemicals. The publication of the default values is also expected to improve efficiency, reducing the likelihood that submissions need to be reworked or resubmitted.
Providing these established numeric assumptions in an easy-to-read summary will help new chemical submitters better understand EPA’s chemical assessment process and develop higher-quality submissions. This is the latest of many steps the agency is taking to improve the chemical risk assessment and risk management processes in support of Pillar 3 of Administrator Zeldin’s Powering the Great American Comeback initiative: Permitting Reform, Cooperative Federalism, and Cross-Agency Partnerships
Under TSCA section 5, EPA 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. In these reviews, EPA must assess how much of the chemical may be released into the environment and the potential exposure levels in the workplace. When 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 Emission Scenario Documents.
The guide is considered an evolving document and may be updated in the future. EPA welcomes the submission of representative data to NewChemicalDefaults@epa.govfrom 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.
Learn more about default values used in EPA’s new chemicals risk assessments.