California’s Office of Environmental Health Hazard Assessment has published Hazard Identification Documents to assist the state’s Developmental and Reproductive Toxicant Identification Committee (DART-IC) when it reconsiders the scientific evidence to determine if Methyl-n-Butyl Ketone should remain on the Proposition 65 list of developmental and reproductive toxicants.
Methyl-n-butyl ketone was originally added to the Proposition 65 list in 2009 as a reproductive toxicant via the Labor Code mechanism as a result of its inclusion in the American Congress of Government Industrial Hygienists Threshold Level Values.
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.
In 2014, OEHHA initiated reconsideration by the DARTIC of several chemicals, including methyl-n-butyll ketone, based on changes to the federal regulations that were affected by changes to federal OSHA regulations.
During its reconsideration of methyl-n-butyl ketone on March 19, 2014, the DART-IC 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.
Methyl butyl-n-ketone, MBK, also known as 2-Hexanone is a ketone used as a general solvent and in paints. It dissolves cellulose nitrate, vinyl polymers and copolymers, and natural and synthetic resins. It has a very low MAK value and is recommended as a solvent because it is photochemically inactive.
2-Hexanone is absorbed through the lungs, orally and dermally. Its metabolite 2,5-Hexanedione is neurotoxic. Animal tests have shown that the neurotoxic effect of 2-hexanone may be potentiated by simultaneous administration of 2-butanone (methyl ethyl ketone, MEK).
The DART-IC will consider whether to maintain the listing of methyl-n-butyl ketone or remove it from the Proposition 65 list at the committee’s next meeting on November 9, 2015.
OEHHA is encouraging public comments on the reconsideration of methyl-n-butyl ketone. Interested parties can submit comments to:
Michelle RobinsonOffice of Environmental Health Hazard AssessmentP.O. Box 4010, MS-12BSacramento, California 95812-4010Fax: (916) 323-2265Street Address: 1001 I StreetSacramento, California 95814
The deadline for interested parties to submit public comments is October 12, 2015.