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incidence of mammary tumors. Control groups included a negative control (sesame oil only) and a
positive control (7,12-dimethylbenz[a]anthracene). No tumors were observed in treated animals, but a
3% incidence was observed in the negative controls and 100% incidence in positive control animals.
Osanai et al. (1976) treated 26 male ICR/JCL mice (plus 39 untreated control mice) with feed
containing 0.1% 3,3’-dichlorobenzidine for 12 months with an interim sacrifice group at 6 months.
Hepatomas were observed in all treated animals at 6 and 12 months (p < 0.01) and among control
animals at an incidence of 0%, 9.5% (2/21) and 38.55% (5/13) at 6,12, and 18 months, respectively.
Tatematse et al. (1977) fed 22 male Wistar rats a diet containing 0.3% 3,3’-dichlorobenzidine alone or
in sequence with o-N-butyl-N-(4-hydroxybutyl)nitrosamine (0.1% in drinking water), N-[4-(5-nitro-2-
furyl)-2-thiazolyl]formamide (0.15% in the diet) and N-fluorenylacetamide (0.025% in the drinking
water) over a four week period. Twelve untreated animals served as controls. Animals were observed
for a 40 week period. Only animals receiving combined exposures showed effects which included
some bladder tumors and histological changes of the liver.
Saffiotti et al. (1967) and Sellakumar et al. (1969) report on a feeding study in which Syrian golden
hamsters (30/sex/group) were exposed to 0.1% or 0.3% 3,3’-dichlorobenzidine in feed; an untreated
control group (30/sex) was included. No significant carcinogenic effects were observed in the 0.1%
3,3’-dichlorobenzidine group. The 0.3% 3,3’-dichlorobenzidine group, however, showed increased
incidence of transitional cell carcinomas of the bladder (4/30 treated, 0/30 control; p = 0.056 by
Fisher’s exact test). Other observations included some liver-cell and cholangiomatous tumors.
A single study suggests that 3,3’-dichlorobenzidine may act as a transplacental carcinogen (Golub et al.,
1974). Pregnant female BALB/c mice given 2 mg 3,3’-dichlorobenzidine (in 0.1 ml sesame oil) five
times during the last week of pregnancy, showed increased incidence of lymphoid leukemia among the
offspring of exposed animals (7/24 treated, 0/30 control; p < 0.01). This effect, however, could also
have occurred by exposure via lactation.
IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
An IARC (1982) review of the human epidemiological studies deemed them inadequate for evaluating
carcinogenicity due to the relatively small size of the cohorts, inadequate time since first exposure,
and/or incomplete follow-up of exposed workers.
The only carcinogenesis studies amenable to the development of cancer potency values are those
conducted by Stula et al. (1975, 1978) showing the induction of granulocytic leukemia, mammary
adenocarcinoma, and Zymbal gland carcinoma in rats and papillary transitional cell carcinomas of the
bladder and hepatocellular carcinomas in beagle dogs exposed to 3,3’-dichlorobenzidine. Limitations
of the other available studies including poor study design, inadequate scope of endpoints, and unclear
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