Ten out of 12 South African baboons (Papio ursinus) survived exposure to
amosite asbestos dust for periods ranging from 242 days to 898 days at an
aerosol level ranging between 1,100 and 1,200 fibers per milliliter. After exposure, they were kept under observation until they died; the total residence time of
amosite varied from 1.2-10.2 years. All underwent detailed postmortem necropsy examinations. All baboons had
asbestosis. Five of the baboons developed malignant diffuse
mesothelioma; three peritoneal, and two pleural with peritoneal invasion. These results indicate that
amosite is highly carcinogenic. Since it is difficult to accomplish follow-up of persons exposed to
amosite asbestos because of the geographic location of the
amosite mines and mills in South Africa (a majority of the workers being migrant laborers from countries bordering on the Transvaal), it is therefore probable that cases of peritoneal
mesothelioma have been missed. If human beings are likely to react to
amosite as do baboons, epidemiological follow-up should include identification of abdominal as well as
thoracic neoplasms.