Office of Environmental Health Hazard Assessment

Air Toxicology and Epidemiology

Revised Proposed Reference Exposure Levels for 1,3-butadiene

The Office of Environmental Health Hazard Assessment (OEHHA) is adopting an acute and an 8-hour Reference Exposure Level (RELs) and a revised chronic REL for 1,3-butadiene.  The values of the RELs are listed in the table below.  These values and the supporting document are now added to the appendices of the Technical Support Document for the Derivation of Noncancer Reference Exposure Levels.  Further, OEHHA, following the analysis presented in the document, hereby adds  1,3-butadiene to the list of Toxic Air Contaminants that may cause infants and children to be especially susceptible to illness, pursuant to Health and Safety Code Section 39669.5(b)(2).

Download the document 1,3-BUTADIENE REFERENCE EXPOSURE LEVELS (RELs) as a pdf file here

Acute, 8-hour, and Chronic Reference Exposure Levels for 1,3-Butadiene

Acute Toxicity (for a 1-hour exposure)
Inhalation reference exposure level

660 µg/m3

8-Hour REL (for repeated 8-hour exposures)
Inhalation reference exposure level

9 µg/m3

Chronic REL (for continuous 24-hours per day exposure)
Inhalation reference exposure level

2 µg/m3

The Office of Environmental Health Hazard Assessment (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 has developed revised RELs for 1,3-butadiene.  (A REL is an airborne level of a chemical at or below which non-cancer health effects are not anticipated for specified exposure durations.)  These were developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for the Derivation of Noncancer Reference Exposure Levels” (OEHHA, 2008), and replace existing values which were developed using previous guidance.  This method allows for the estimation of acute, 8-hour and chronic RELs for use in Air Toxics Hot Spots program risk assessments.  The new guidance reflects current scientific knowledge and techniques, and in particular explicitly includes consideration of possible differential effects on the health of infants and children, in accordance with the mandate of the Children’s Environmental Health Protection Act (Health and Safety Code sections 39669.5 et seq.). 

A draft of the 1,3-butadiene RELs was released on May 18, 2012 to solicit public comment, and was discussed at public workshops in Oakland and Diamond Bar, CA in July 2012. The document was then revised to reflect public comments, and peer reviewed by the State’s Scientific Review Panel on Toxic Air Contaminants (SRP).  It was initially presented to the SRP on October 16, 2012.  A revised version of the document reflecting comments of the SRP was discussed at a second meeting held on April 2, 2013.  At the latter meeting, the SRP approved the document describing the RELs and their derivation, subject to one specific change (and some editorial adjustments).  Following a discussion of the 8-hour and chronic RELs which was reported on pages 54 – 79 of the transcript of the April 2 SRP meeting (, OEHHA agreed that it was appropriate to increase the value of the toxicodynamic component of the interspecies uncertainty factor from √10 to 10.  This has the effect of lowering the 8-hour and chronic RELs by a factor of approximately three.  This change was incorporated into the final version with explanatory text, which was approved by the SRP. 

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