Methyl Isobutyl Ketone (MIBK)
MIBK is used as a chemical intermediate, a solvent for manufacturing paints, rubbers, pharmaceuticals, other chemicals, and industrial cleaners. It is used in the semiconductor industry. MIBK is very efficient at dissolving resins used in paints, inks, lacquers, and other
types of surface coatings. Synonyms for MIBK are hexone, isobutyl methyl ketone, and isohexanone. MIBK is a Food and Drug Administration (FDA)-approved indirect food additive for adhesives, paper and paperboard, and polymers.
The panel, under an EPA enforceable consent agreement, sponsored and published the results of a 2-generation reproductive effects study on MIBK. The panel also prepared the technical support documents for MIBK under ICCA’s HPV chemical review program.
NTP Studies of MIBK
In February 2007, the National Toxicology Program (NTP) issued its final technical report (TR-538) on toxicology and carcinogenesis studies on the inhalation of MIBK in rats and mice. Under the conditions of these 2-year studies, NTP researchers determined that there was some evidence of carcinogenic activity of MIBK in male F344/N rats. They also determined that there was equivocal evidence of carcinogenic activity of MIBK in female F344/N rats, and that there was some evidence of carcinogenic activity of MIBK in male and female B6C3F1 mice.
The panel is presently reviewing the NTP study findings and conducting additional research on male rats to compare data with the NTP study conclusions. An analysis of the findings and data for mice is also underway by panel toxicologists.
MIBK Hazardous Air Pollutant Delisting
The panel supports the delisting of MIBK as a HAP. The panel’s delisting petition presented extensive information on MIBK's potential health and environmental effects, environmental releases, and resulting ambient air concentrations. Hazard information included in the petition illustrates MIBK’s low acute and chronic toxicity and low environmental toxicity. Air dispersion modeling results showed that ambient concentrations of MIBK, even at the highest fenceline levels at the largest industrial emitters, are below levels of concern. Accordingly, the panel continues to support MIBK’s removal from the CAA HAPs list.
On July 19, 2004, EPA published a notice of completeness on the MIBK delisting petition. The petition is currently on hold pending the completion of the panel’s research and analysis of the NTP study findings.