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N-nitrosomorpholine, for life (Haas et al., 1973). Males received 24.6, 49.2 or 98.4 mg/kg body
weight; females recieved 28.1, 56.2 or 112.4 mg/kg body weight. Treatment-related increases in the
incidence of respiratory tract tumors (primarily in the nasal cavity and trachea) were observed.
Lijinsky et al. (1976) exposed male Sprague-Dawley rats (30/exposure group) to N-nitrosomorpholine
in drinking water (8 or 40 mg/l, 5 days/week; total dose 0.21 and 1.05 mM, respectively) for 30
weeks. The animals were then observed for the remainder of their lifetime. Hepatocellular (benign or
malignant) tumors were reported in 11/30 and 16/30 low- and high-dose animals, respectively.
Hemangioendothelial tumors were reported in 1/30 and 2/30 low- and high-dose animals, respectively.
The authors did not report the inclusion of a control group in this study.
Ketkar et al. (1983) exposed male and female Syrian golden hamsters (30/sex/group) to 0.001, 0.005
or 0.01% N-nitrosomorpholine in the drinking water for life; untreated control groups (50 animals/sex)
were also included. Increased incidences of benign and malignant tumors of the respiratory tract
(primarily papillary polyps, papillomas and epidermoid carcinomas of the larynx and trachea) and the
gastrointestinal tract (primarily liver tumors, including hepatocellular adenomas and carcinomas) were
observed in both males and females. No corresponding tumors were observed in the control groups.
Tumor incidence data is listed in Table 1.
Table 1.
N-nitrosomorpholine-induced tumor incidence in male and female Syrian golden
hamsters (Ketkar et al., 1983)
Dose group Average dose 1
(mg/kg-day)
Tumor type Tumor incidence 2
male controls 0 respiratory tract 0/50
male low dose 1.2 8/29
male mid dose 6 13/29
male high dose 12 21/30
male controls 0 liver tumors 0/50
male low dose 1.2 4/29
male mid dose 6 9/29
male high dose 12 18/30
female controls 0 respiratory tract 0/50
female low dose 1.36 14/28
female mid dose 6.82 16/30
female high dose 13.6 22/30
female controls 0 liver tumors 0/50
female low dose 1.36 0/28
female mid dose 6.82 2/30
female high dose 13.6 6/30
1. Doses as reported by Gold et al. (1987).
2. Tumor incidences as reported by Gold et al. (1987).
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