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Cobalt and Cobalt Compounds Cancer Inhalation Unit Risk Factor (IUR) Document - Scientific Review Panel on Toxic Air Contaminants (SRP) Review Draft

The Office of Environmental Health Hazard Assessment (OEHHA) is releasing a draft document summarizing the carcinogenicity and derivation of cancer inhalation unit risk factors (IURs) for cobalt and cobalt compounds.  IURs are used to estimate lifetime cancer risks associated with inhalation exposure to a carcinogen. This document will be reviewed and discussed by the Scientific Review Panel on Toxic Air Contaminants (SRP) at its meeting on October 4, 2019 in Sacramento, CA. 

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 IURs for many air pollutants. The IURs were developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for Cancer Potency Factors,” finalized by OEHHA in 2009.

A draft of the cobalt and cobalt compounds IUR document was released for a 60-day public review and comment period on March 8, 2019.  Three sets of comments were received.  Those comments and OEHHA’s responses to those comments are also available at this time.  The cobalt and cobalt compounds IUR document was revised in response to those comments. The values proposed are as follows:

Cobalt metal and water-insoluble cobalt compounds
Inhalation Unit Risk Factor                        8.0 × 10-3 (µg/m3)-1
Water-soluble cobalt compounds (normalized to cobalt content)
Inhalation Unit Risk Factor                         8.6 × 10-4 (µg/m3)-1

We are not seeking further comments from the public on the draft document.

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

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

E–mail: John.Budroe@oehha.ca.gov
Telephone: (510) 622-3145

Information about dates and agenda for meetings of the Scientific Review Panel can be obtained from the California Air Resources Board web page.

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