[Federal Register Volume 61, Number 242 (Monday, December 16, 1996)]
[Notices]
[Page 66055]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-31776]


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DEPARTMENT OF HEALTH AND HUMAN SERVICES

National Toxicology Program; Availability of Technical Report on 
Toxicology and Carcinogenesis Studies of Isobutyl Nitrite

    The HHS' National Toxicology Program announces the availability of 
the NTP Technical Report on the toxicology and carcinogenesis studies 
of isobutyle nitrite which is used as an intermediate in the syntheses 
of aliphatic nitrites. It is also an ingredient of various incenses or 
room odorizers and is used as a euphoric. The chemical has also been 
used as a jet propellant and in the preparation of fuels.
    Toxicology and carcinogenicity studies were conducted by inhalation 
administration of isobutyl nitrite to groups of 56 F344/N rats and 60 
B6C3F1 mice of each sex at exposures of 0, 37.5, 75, or 150 ppm 
(equivalent to 0, 158, 315, or 630 mg/m3) for 6 hours per day, 5 
days per week, for 103 weeks.
    Under the conditions of these 2-year studies, there was clear 
evidence of carcinogenic activity\1\ of isobutyl nitrite in male and 
female F344/N rats based on the increased incidences of alveolar/
bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma 
(combined). There was some evidence of carcinogenic activity of 
isobutyl nitrite in male and female B6C3F1 mice based on the 
increased incidences of alveolar/bronchiolar adenoma and alveolar/
bronchiolar adenoma or carcinoma (combined) in males and females. The 
increased incidence of thyroid gland follicular cell adenoma in male 
mice may have been related to isobutyl nitrite exposure.
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    \1\ The NTP uses five categories of evidence of carcinogenic 
activity observed in each animal study: two categories for positive 
results (``clear evidence'' and ``some evidence''), one category for 
uncertain findings (``equivocal evidence''), one category for 
studies that cannot be evaluated because of major flaws 
(``inadequate study'').
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    Exposure of rats and mice to isobutyl nitrite by inhalation for 2 
years resulted in increased incidences of alveolar epithelial 
hyperplasia (male and female rate and mice), thyroid gland follicular 
cell hyperplasia and splenic hemosiderin pigmentation (male mice), and 
serous exudate and atrophy of the olfactory epithelium of the nose 
(female mice).
    Exposure of rats to isobutyl nitrite by inhalation for 2 years 
resulted in decreased incidences of mononuclear cell leukemia in males 
and females.
    Questions or comments about the Technical Report should be directed 
to Central Data Management at P.O. Box 12233, Research Triangle Park, 
NC 27709 or telephone (919) 541-3419.
    Copies of Toxicology and Carcinogenesis Studies of Isobutyl Nitrite 
(CAS No. 542-56-3) (TR-448) are available without charge from Central 
Data Management, NIEHS, MD E1-02, P.O. Box 12233, Research Triangle 
Park, NC 27709; telephone (919) 541-3419.

    Dated: November 13, 1996.
Samuel H. Wilson,
Deputy Director, NIEHS
[FR Doc. 96-31776 Filed 12-13-96; 8:45 am]
BILLING CODE 4140-01-M