Technical Guidance Summarizes Default Values in EPA Risk Assessments

The “default values” EPA uses in its risk assessments of new chemicals have been made available online in the agency’s New Chemicals Division Reference Library, EPA announced on Nov. 24. According to the agency, these values are the “assumptions used by EPA in environmental release and occupational exposure assessments” during reviews in which “chemical-specific information is not available or substantiated” with relevant documentation. For example, the agency may use default values when it does not know the type of containers that are used to transport a chemical or how much chemical residue might remain in process equipment before cleaning.

The new document, Common Engineering Defaults Used in EPA’s New Chemical Assessments (PDF), includes two tables: one focused on common models used by the agency to estimate environmental releases and one that covers common models and default values EPA uses to estimate dermal and inhalation exposures to workers. According to the agency, these values come from its Chemical Screening Tool for Exposures and Environmental Releases, its “Generic Scenarios” documents for occupational exposure and release assessment, and Emission Scenario Documents published by OECD, the Organization for Economic Cooperation and Development, an international organization focused on finding solutions to social, economic, and environmental challenges.

Section 5 of the Toxic Substances Control Act requires EPA to assess potential levels of environmental release and worker exposure during the lifecycle of new chemicals. The agency believes that the publication of these default values will “help new chemical submitters better understand EPA’s chemical assessment process and develop higher-quality submissions,” an agency news release explains.

The new technical guidance is available as a PDF from the EPA website.