Notice of Adoption of Reference Exposure Levels for Carbonyl Sulfide

The Office of Environmental Health Hazard Assessment (OEHHA) is adopting new Reference Exposure Levels (RELs) for carbonyl sulfide (COS) 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 COS in air: infrequent 1-hour exposures, repeated 8-hour exposures, and continuous long-term exposure.

OEHHA is required to develop guidelines for conducting health risk assessments under the Air Toxics Hot Spots Program (Health and Safety Code Section 44360(b)(2)). In response to this statutory requirement, OEHHA develops RELs for many air pollutants, including COS. The COS RELs were developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for the Derivation of Noncancer Reference Exposure Levels” (OEHHA, 2008). These chemicals will also be added to the list of Toxic Air Contaminants that may disproportionately impact children, pursuant to Health and Safety Code Section 39669.5(b)(1). 

A draft document for the COS RELs was released on October 17, 2014, to solicit public comment and were discussed at public workshops in Sacramento and Diamond Bar, CA during the subsequent 60-day public review period. The documents were revised to reflect public comments, and peer-reviewed by the State’s Scientific Review Panel on Toxic Air Contaminants (SRP) in June 2015 before being finalized.

The REL values are as follows:

Carbonyl Sulfide:

  • Acute REL (for a 1-hour exposure): 660 µg/m3 (270 ppb)
  • 8-Hour REL (for repeated 8-hour exposure): 10 µg/m3 (4 ppb)
  • Chronic REL (for long-term exposure): 10 µg/m3 (4 ppb)

Please direct any inquiries concerning technical matters or availability of the documents to:

Dr. John Budroe, Chief
Air Toxicology and Risk Assessment Section
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA 94612