Notes:
1. No PEL or IDLH has been established. One of four rats died after a 6-hour exposure to vapors from heated (55°C) artificial butter flavoring containing 285 ppm diacetyl (~64% of total VOCs), but no deaths occurred among groups of six rats exposed to 203 ppm diacetyl (~68% of total VOCs) or 352 ppm diacetyl (~61% of total VOCs) (Hubbs et al., 2002).
2. A cause-effect relationship between diacetyl and bronchiolitis obliterans is difficult to assess because of mean diacetyl exposure levels ranging over four orders of magnitude for workplaces with affected individuals. In addition, food-processing and flavor-manufacturing employees with this lung disease were exposed to other volatile agents (CDC, 2007; Kanwal et al., 2006; Kreiss et al., 2002; Kullman et al., 2005; Lockey et al., 2002; NIOSH 2004, 2006).
3. Diacetyl is known to react with the amino acid arginine in proteins (Riordan, 1979) and inhibits enzymes that are important for protecting cells from oxidative damage, such as superoxide dismutase (Borders et al., 1985) and glutathione reductase (Boggaram and Mannervik, 1982) and glyoxalase I (Lupidi et al., 2001).
4.Diacetyl is metabolized to acetoin by diacetyl reductase, an ubiquitous enzyme that is uncompetitively inhibited by butyric acid (Nakagawa et al., 2002). Butyric acid is found along with diacetyl in some butter flavoring mixtures (Hubbs et al., 2002).
