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A 14-week vapor inhalation toxicity study of methyl isobutyl ketone
R D Phillips1, E J Moran, D E Dodd
1Exxon Biomedical Sciences, Inc., East Millstone, New Jersey 08873.
Abstract:
In a 2-week probe study male and female Fischer-344 rats and B6C3F1 mice were exposed 6 hr/day to 2000, 500, 100, or 0 ppm methyl isobutyl ketone (MIBK). At 2000 ppm there was a slight increase in male rat liver weight (absolute and relative). The only changes observed histologically were increases in regenerative tubular epithelia and hyalin droplets in kidneys of male rats exposed to 2000 or 500 ppm. Exposure levels for a subchronic study were 0, 50, 250, or 1000 ppm methyl isobutyl ketone vapors 6 hr/day, 5 days per week, for 14 weeks. The 14 weeks of exposure had no adverse effect on the clinical health or growth of rats or mice. Male rats and male mice exposed to 1000 ppm MIBK had a slight but statistically significant increase in liver weight and the liver weight/body weight ratio. Liver weight was also increased slightly in male mice exposed to 250 ppm. No gross or microscopic hepatic lesions related to MIBK exposure were observed. Furthermore, the only microscopic change observed was an increase in the incidence and extent of hyalin droplets within proximal tubular cells of the kidneys of male rats exposed to 250 and 1000 ppm of MIBK. The relevance of the male rat kidney tubular effect to humans is not known. In conclusion, other than the male rat kidney effect, exposure of male and female rats and mice to MIBK at levels up to 1000 ppm for 14 weeks was without significant toxicological effect.
Insights
Methyl isobutyl ketone (MIBK) exposure showed minimal toxicity in rats and mice. The primary effect was kidney tubule changes in male rats, with unknown relevance to human health.
Area of Science:
- Toxicology
- Occupational Health
- Chemical Safety
Background:
- Methyl isobutyl ketone (MIBK) is an industrial solvent.
- Understanding MIBK toxicity is crucial for workplace safety assessments.
Purpose of the Study:
- To evaluate the toxicological effects of MIBK exposure in rodents.
- To determine safe exposure levels for MIBK in animal models.
Main Methods:
- Rodents (Fischer-344 rats and B6C3F1 mice) were exposed to MIBK via inhalation in probe and subchronic studies.
- Exposure durations were 2 weeks (probe) and 14 weeks (subchronic), with varying concentrations.
- Clinical health, growth, organ weights, and histopathology were assessed.
Main Results:
- A probe study at 2000 ppm MIBK showed slight male rat liver weight increase and kidney tubule changes.
- Subchronic exposure (14 weeks) up to 1000 ppm MIBK did not affect overall health or growth.
- Male rats and mice showed slight liver weight increases at higher MIBK concentrations.
- Kidney tubule effects (hyalin droplets) were observed in male rats at 250 and 1000 ppm.
Conclusions:
- MIBK exposure up to 1000 ppm for 14 weeks had minimal toxicological effects in rats and mice.
- The observed kidney tubule changes in male rats require further investigation for human relevance.
- MIBK appears to have a low toxicity profile, with specific target organ effects noted in male rats.