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Hamsters
Feron et al. (1982) exposed groups of male and female Syrian golden hamsters to room air (0 ppm) or
to decreasing concentrations of acetaldehyde. The initial concentration was 2500 ppm (4500 mg/m 3 ),
which was gradually decreased (between weeks 9 and 44) to 1650 ppm (2970 mg/m 3 ) 6 hours/day, 5
days/week for 52 weeks. Acetaldehyde-induced nonneoplastic lesions were seen in the nose, larynx,
and trachea. Tumors were seen in both the nose (adenoma, adenocarcinoma, and anaplastic
carcinoma) and the larynx (carcinoma in situ, squamous cell carcinoma, and adenosquamous
carcinoma). The tumor incidences were 2/27 (7%) and 6/23 (26%) in males and 1/26 (4%) and 4/26
(20%) in females for the nose and larynx, respectively; no nasal or laryngeal tumors were observed in
the controls. Only the increases in laryngeal tumors were statistically significant (p < 0.05) compared to
controls. Under the conditions of this study, acetaldehyde was considered to be carcinogenic in male
and female hamsters.
In a second part of the above study (Feron, 1979), groups of male Syrian golden hamsters were
exposed by inhalation to 0 or 1500 ppm (2700 mg/m 3 ) acetaldehyde vapor 7 hours/day, 5 days/week
for 52 weeks. The animals also received a concurrent, weekly intratracheal instillation of 0, 0.625,
0.125, 0.225, 0.5, or 1 mg benzo[a]pyrene (BaP) in saline for the same duration. Simultaneous
exposure to acetaldehyde and BaP induced marked nonneoplastic lesions in the nasal cavity and trachea
which disappeared after the 26-week recovery period. No respiratory tract tumors were seen in
hamsters exposed to acetaldehyde alone. Various types of benign and malignant respiratory tract
tumors were found in male hamsters treated with BaP or BaP plus acetaldehyde. The results of this
study indicated no evidence for carcinogenicity of acetaldehyde and limited evidence of cocarcinogenicity.
This study had a number of methodological limitations such as the exposure level
exceeding the maximum tolerated dose (MTD).
Feron et al. (1982) repeated the above study using male and female Syrian golden hamsters. Some of
the animals were also treated with subcutaneous injections of 0.0625% diethylnitrosamine (DENA)
once every 3 weeks. The enhancing effect of BaP-initiated respiratory tract tumor formation observed
in this study was similar to that observed in the previous study (Feron, 1979). There was no evidence
that acetaldehyde exposure increased the incidence or affected the type of DENA-induced tumors in
any part of the respiratory tract. Based upon these findings, the authors concluded: “acetaldehyde is an
irritant as well as a carcinogen to the nose and larynx with a weak initiating and a strong ‘promoting’
(co-carcinogenic) activity.”
IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
The IARC concluded that there is inadequate evidence in humans and sufficient evidence in
experimental animals for the carcinogenicity of acetaldehyde (IARC, 1985). Therefore IARC classified
acetaldehyde as class 2B, a possible human carcinogen. The U.S. EPA, using the guidelines for
Carcinogen Risk Assessment, has classified acetaldehyde as a Group B2 probable human carcinogen,
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