Document kD2pkQ9JZJQp9Mdx74am76byJ

f i i i bres - es* ungs by cili*. rr orn:nlly . Prom rn Jjpyjcd si9- r a::*I length *"r arc the hv rertolintar .iK- fibres. ' C'r.reii- ; in still ` Dclirm jur-.-- Of y ex- he) it*: if':, to 1 in a].' in but r.r.t * r<. iv.J.l'.y. . cy.'yUi.oiC iore use - e? - In the USA fcntcrline et el (1973) studied the mortality experience in re tirees from the asbestos industry. After adjustment for cumulative dost expo sure* men exposed only to chrysotilc revealed a respiratory cancer mortality (not distinguished between bronchial carcinoma and mesothelioma) 2.4 times the expected} exposure to a combination of chrysotilc and crocidolite increased the ratio to 5.3. Asbestos cement industry workers only expose) to chrysotile showed a respiratory cancer mortality ratio of 1.4; those exposed to mixed chrysotilc and crocidolite had a rstio of 6.1. These data lead to the conclusion that in relation to mesolhul i cr..a crocidolite is more carcinogenic than chrysotilc or. amosite. This is in agreement with the Report of the Advisory Committee on Asbestos Cancers (1ARC 1973). i In rat experiments (Wagner ct al 1973) mesotheliomas were observed after intrapleural inoculation with all types of asbestos and other non-asbestos fibrous materials . In asbestos a considerable proportion of animals developed mesothelioma - this happened in lesser proportions with the other materials as aluminium silicate* glass fibres, etc. The risk of developing pleural mesothe lioma after injection was proportional to the dose. The chemical properties of the fibres proved to haw a minor influence in developing the tuniorj their physical properties appear to be responsible for carcinogenesis. Pott ct al (1972a, b) car.u.- to the sarv conclusion after intraperi lonccil injection of fibrous materials in rat* end the following develop*.*of tumors. In these ani mal experiments fibies reach the pleural end peritoneal cavity in a distinctly unnatural way* in asbestos exposed human beings one has.clearly to realize the role of these physical properties in relation to the possibility of the various types of fibres reaching the target orgtns in sufficient quantities. Stanton (1973) reported th* results of experiments in ^ats^iK^applying various types of asbestos, fibrou? glass and fibrous alumi ni umoxi to the pleural cavity by open thoracotomy. The incidence of pleural mesothelioma showed that the carcinogenity seems to be related to fibre-sizes <2.5u in dia meter and )0-)8p in length. Present evidence (not yet published) suggests that fibres about 0.75p and 1.5p in diameter e;id between 10 and 60p length, may be especially important. No tumours developed if crocidolite or chrysotilc were pulverized to a non-fibrous form. So the structural properties determine to a great extent whether inhaled asbestos is deposited in the lung, and whether Bool 0760 PRODUCED BY FORD