Document 3NN7LL3LOkZqGN3b8VpdXEe7D

/ Si.itmin VII. amp Nmmawm Kxrr.mm:ntal .of as- i hnf. Jn 't>(a h.M '.causing -sure to STUDIES OF CARClNOOKNKSlfi OF ASBESTOS FIBERS AND THEIR NATURAL OILS* J. S. Hsringlun und t`.j. C. Roc Chute* Realty Rearareh Iralilulr, Inetitute uf Cancer Research Royal Cancer Hvxpilal, i.vndon, Enyloml ':* .plexed. Tbf &todr of action of asbestos in producing asbeslosis and neoplasia > fcondi- Is at present little understood. Pulmonary fibrosis, the main feature of 'logical inhesloni*. has been ascribed to mechanical or chemical factors, or to a !r. cases '/nod in. combination of both; the mechanism of carcinogenic action is almost com pletely unknown. '.tor re- Two forms of neoplasia in man ere associated with exposure to asbestos: \ve an- bronchogenic carcinoma' and diffuse pleural mesothelioma.' 'tween mem- rtsbeft* . ild be *v ob- ild be . flbro- }iries. . y`iturbi Tbt }t in Tat Tver* or AssistOS Invoivld in Malignancy in Man "Asbestos" is the generic name given to a class of fibrous mineral silicates which may vary considerably in physical and chemical composition. In vj nomr studies in the past the term asbestos has been used without proper definition and the type of material used remains unidentified. .. A priori, the demonstration of differences in the carcinogenic activity between different types of asbestos, either in epidemiological or experimen tal studies, would open the way to a critical inveatigation of asbestos circinogenesis.* Studies of mortality by district of residence' have suggested that expos ure to crocidolite asbestos in the North-Western Cape carries with it rn*y. ml distinct risk of developing malignant disease.' In the ease of the crocidolite ' KIM* ln'^li*'"North-'Wtatern Cape, asbestos mining districts showed s . three-fold excess of deaths from lung cancer as compared with adjoining i- districts,nd as compared with control districts of similar populationand- . -<*d '..'j : ierree of ufbahixation.yTbls.)^teromparun'ii^mpbi^nt's!ncetnc'fiwra7 >c3; Africa, as Wsewhere, lung cancer mortality is much tower In rural than in* "* Urban districts. The excess was seen in both males and females. Similar figures for cancer mortality in the eastern and north-eastern ires*, where chrysotile and amosite asbestos are mined and milled revealed so excess mortality from any form of cancer. In these regions, however,"; the relative proportion of the population exposed to the asbestos Is eon-' tldorsbly reduced by comparison with that in the North-Western Cape. Although Ute standardised mortality ratio* might suggest that exposure toj This investigation has been supported by grants to the Chester Beatty Be- eaerth Institute (Institute of Cancer Research, Royal Cancer Hospital) front., Ilse Msdieal Research Council and tbs Britlth^BmpIrs-f"--' - .. .-&*&*&**&& MW: SCF-FA-0031 PRODUCED BY FORD