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exposed to arsenicals for 20 months and to EDB for 111 months. Had these been included in either the
analysis of those exposed for more than six years to EDB or the analysis of the Michigan facility
mortalities, the results would have been found to be statistically significant (p < 0.05).
Animal Studies
The carcinogenic activity of EDB has been demonstrated in a number of studies using mice and rats by
dermal, oral, inhalation and intraperitoneal routes of administration. Tumors occurred in both test
species at sites local to, and distant from, the site of first chemical contact.
The National Toxicology Program (NTP) conducted an inhalation carcinogenesis bioassay for EDB in
male and female Fischer 344 rats and B6C3F 1 mice (50 animals/sex/group) (NTP, 1982). The
durations of exposure were 90 weeks at 40 ppm, 103 weeks at 10 ppm and 104 weeks for controls.
NTP concluded that EDB was carcinogenic to rats, causing increased incidences of carcinomas,
adenocarcinomas, and adenomas of the nasal cavity, hemangiosarcomas of the circulatory system
(spleen), mesotheliomas of the tunica vaginalis (males only), adenomatous polyps of the nasal cavity
(males only), fibroadenomas of the mammary gland (females only) and alveolar/bronchiolar adenomas
and carcinomas (females only). EDB was also carcinogenic for mice, causing increased incidences of
alveolar/bronchiolar adenomas and carcinomas, hemangiosarcomas of the circulatory system (females
only), fibrosarcomas in the subcutaneous tissue (females only), carcinomas of the nasal cavity (females
only), and adenocarcinomas of the mammary gland (females only). The tumor incidence by site for rats
and mice are shown in Tables 1 and 2, respectively.
Table 1:
Results of the NTP (1982) inhalation bioassay of EDB in Fischer-344 rats.
Tumor Sex Control 10 ppm 40 ppm
Nasal cavity: Adenocarcinoma M 0/50 20/50 a 28/50 a
F 0/50 20/50 a 29/50 a
Carcinoma M 0/50 0/50 21/50 a
F 0/50 0/50 25/50 a
Adenomatous polyps M 0/50 18/50 a 5/50 e
F 0/50 5/50 e 5/50 e
Adenomas M 0/50 11/50 a 0/50
F 0/50 11/50 a 3/50
Squamous cell carcinoma M 0/50 3/50 3/50
F 1/50 10/50 5/50
Lung alveolar/bronchiolar carcinomas or adenomas F 0/50 0/48 5/47
Tunica vaginalis mesotheliomas M 1/50 8/50 c 25/50 a
Mammary fibroadenomas F 4/50 29/50 a 24/50 a
Circulatory system hemangiosarcomas M 0/50 1/50 15/50 a
F 0/50 0/50 5/50 e
Pituitary adenomas M 0/45 7/48 b 2/47
F 1/50 18/49 a 4/45
a p = 0.001; b p = 0.008; c p = 0.015; e p = 0.028
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