EPA Releases Default Values Guide for TSCA New Chemical Risk Assessments

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On November 24, 2025, EPA released a guide listing common “default values” for environmental releases and worker exposures used by the agency in risk assessments of new chemical substances under the Toxic Substances Control Act (TSCA).

What Are Default Values?

Default values are assumed engineering values used by EPA when chemical-specific information is unavailable.  For example, the guide shows that EPA assumes that 3% of a new chemical substance remains in a 55-gallon drum as residue if the drum is emptied by pumping, while 0.6% remains if it is emptied by pouring.

“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,” an EPA press release states.  “The publication of the default values is also expected to improve efficiency, reducing the likelihood that submissions need to be reworked or resubmitted.”

What’s Included

The guide includes default values used to model environmental releases the following situations:

  • Transferring liquid material to/from transport containers
  • Transferring solid material to/from transport containers
  • General industrial/commercial processes
  • Transferring solid materials (e.g., transferring/unloading/loading of solid powders)
  • Industrial/commercial use of coatings

The guide also includes default values used to model inhalation or dermal worker exposures from situations involving handling solids (e.g., raw materials or formulated products) or liquids containing the new chemical substance.

EPA provides two example situations demonstrating how the default values are applied to real-world scenarios, including how the assumptions change if submitters provide additional information.

In the press release, EPA said that it considers the guide to be an evolving document that may be updated in the future.  The guide, and other guidance for new chemical submissions, can be found at EPA’s New Chemicals Division Reference Library.