Reference Exposure Levels (RELs) for 1,4-Dichlorobenzene

The Office of Environmental Health Hazard Assessment (OEHHA) has adopted new Reference Exposure Levels (RELs) for 1,4-Dichlorobenzene for use in the Air Toxics Hot Spots Program. RELs are airborne concentrations of a chemical that are not anticipated to result in adverse noncancer health effects for specified exposure durations in the general population, including sensitive subpopulations. The adopted RELs cover different types of exposure to 1,4-Dichlorobenzene in air: infrequent 1-hour exposures, repeated 8-hour exposures, and continuous long-term exposure.

A draft document for the 1,4-Dichlorobenzene RELs was released on November 29, 2024 to solicit public comment and was discussed at two public workshops (December 16, 2024 and January 7, 2025) during the subsequent 45-day public review period. No public comments were received. The document was peer reviewed by the State’s Scientific Review Panel (SRP) on Toxic Air Contaminants in February 2025 before being finalized.

The 1,4-Dichlorobenzene REL values are as follows:

Acute REL (for infrequent 1–hour exposures): 8,700 micrograms per cubic meter (μg/m3) (1,500 parts per billion (ppb))
Chronic REL (for long–term exposures): 5 µg/m3 (0.8 ppb)
8–Hour REL (for repeated 8–hour exposures): 10 µg/m3 (1.7 ppb)

Adoption Memo

• 1,4-Dichlorobenzene Reference Exposure Levels Technical Support Document (July 18, 2025)

SRP Draft (January 14, 2025)

• Notice of Public Meeting
  • SRP Slides
  • Meeting Transcript

First Draft (November 29, 2024)

• Notice of Public Comment Period
• Amendment to Notice of Public Comment Period
• Public Comments – none received
• Public Workshop Presentation

Please direct any inquiries concerning technical matters or document availability to:

Rima Woods, Ph.D., Chief
Air Toxicology and Risk Assessment Section
Office of Environmental Health Hazard Assessment

Rima.Woods@oehha.ca.gov