Reconsideration of Listing of Methyl-n-butyl Ketone and Consideration of Listing of 2,5-Hexanedione

Methyl-n-butyl ketone was originally added to the Proposition 65 list in 2009 on the basis of reproductive toxicity via the Labor Code mechanism2. In 2014, OEHHA initiated reconsideration by the DARTIC of several chemicals, including methyl‑n‑butyl ketone, based on changes to the federal regulations that affected the basis for the original listing via the Labor Code mechanism. Specifically, in March 2012, the federal Occupational Safety and Health Administration (OSHA) amended the regulations contained in the Code of Federal Regulations, Title 29, section 1910.1200. These changes affected the use of this section as a definitive source for identifying chemicals as known to cause reproductive toxicity by the Labor Code mechanism. During its reconsideration of methyl-n-butyl ketone on March 19, 2014, the Committee deferred making a decision and requested additional information both on this chemical and its active metabolite, 2,5-hexanedione. In response to that request, OEHHA has revised the hazard identification document for methyl-n-butyl ketone and added information on the reproductive toxicity of 2,5-hexanedione.


This notice marks the beginning of a 45-day public comment period on this document. The public comment period will close on Monday, October 12, 2015. Copies of the document are available from OEHHA’s web site. The document may also be requested from OEHHA’s Proposition 65 Implementation Office by calling (916) 445-6900.

OEHHA must receive comments and any supporting documentation on the hazard identification document by 5:00 p.m. on Monday, October 12, 2015.

We encourage you to submit comments in electronic form, rather than in paper form. Comments transmitted by e-mail should be addressed to Please include “Methyl n-Butyl Ketone and 2,5‑Hexanedione” in the subject line. Comments submitted in paper form may be mailed, faxed, or delivered in person to the addresses below:

Mailing Address: Michelle Robinson
Office of Environmental Health Hazard Assessment
P.O. Box 4010, MS-12B
Sacramento, California 95812-4010
Fax: (916) 323-2265
Street Address: 1001 I Street
Sacramento, California 95814

Related Content