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California adds methyl isobutyl ketone, a widely used solvent, to the Prop. 65 list of chemicals

Methyl isobutyl ketone (CAS No. 108-10-1) is a very widely used solvent.  The Office of Health Hazard Assessment (known affectionately as OEHHA [o-we-hah]) published a notice Sept. 16, 2011, that it intended to list MIK pursuant to the "labor code mechanism" (see for an overview of Prop. 65 and an explanation of the labor code mechanism).  The publication initiated a 30-day comment period that closed Oct. 17, 2011.  OEHHA has now added MIK to the Prop. 65 list of chemicals as a carcinogen.

An overview of various human toxicity assessments of MIK can be found at  An overview of various animal studies can be found at  Animal studies indicate that MIK is a carcinogen.  See

Litigation involving a listed chemical under Prop. 65 cannot be brought during the initial year following the listing.  Thus, on or after Nov. 4, 2012, it would seem very likely that numerous Prop. 65 cases will be filed given the widespread use of MIK.  See and  In the U.S. between 100 million and 500 million pounds of MIK are produced.  See  Additionally, several tens of millions of pounds are imported.  See

Prop. 65 litigation has been dominated for many years by cases filed based on lead exposure.  Recently, the phthalate DEHP [sic] has become popular, often combined with allegations related to lead.  It is reasonable to anticipate that there will be a "feeding frenzy" in late 2012 as plaintiffs file MIK cases.

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