Document 3JRrpv6Lw2NKY53D3mnwo55vy

llnriiigtiiu & |caM-: AkIii'xIum mui Thfii4 Oiln Ml Iniaiii'p In MIMmlll* i tobacco smoking . J^Ukeft Into ' /cancer incidence i Comparison the.. *I*|'IiIi'mI anil I>VIiiiIiiik>iiU| *uiiwUrell*'ii ivlilrh |iply ! Ills ej.|nniil iIKTciviicv In L'ervlruipenk-li v in man of lhcnc I wo tyiies of closely-related, amjihlbole asbento*. He has reported that nunc of the factor* examined.'' explain* satisfactorily the absence of pleural mesothelioma in the Trana ml. Trbl we^nelude minerajogical differences between the two areas..in-^-i .i'altjr!:'^ftproductfon and the exlent1 of environmental pollution and sxbcstosls.' Recently, in North America, primary peritoneal tumor* have been found in workers exposed to chryaotile.*-" Previous Exmsimental Stumu ivolved no matchthe. othar ^ ;.-. arcomata have been produced in rats after the subcuUneous and intrant t^toneal lnioetFon of asbeetoiof'an"undIecio^ type2"i':The fibers'Srere^ S?The ngursi .nit they indicate longer (0.6 to 1.0 cm.) than those used in other studies. Two other sili- C|tes,>ugiteapdlrempiit^ialkdtJ>roduc<J.utnora,underTth^.sam*i-=-- ,..Jfr3e<. ... 52floni^olHfe>e^j^T^^^pyl^entjfr^^M'mfr^ai?,thcmwTm potman group of rock-forming ferromagneslan silicates,1' and has the formula iCa. Mg. Ke1*, Al> (Si. Alls O*. Tremoiite is an amphibole mineral, NOSTH-WksTIXK commonly of fibrous nature and with the formula Car Mg& [Sii. 0] (OH.D.. '. Wagner, in 1962," induced pleural mesotheliomata by inoculating various rth-Welters Cape dusts directly into the pleural cavity of rata. Pleural, tumors were found 31 49 65 /- G2= sen mined on a excessive lung Jollte) mining t969 (TABLE 1) 1 of amoslte in Western Cape. cmu, observed . either occupaaehestoa mines 1. On the other ied to amoaite me of the geo- ans wltitl finely-divided aHic/$owSef'(99.9 per'cent'Slthyr A rat exposed lo 1 chrysotile dust cloud also developed a pleural mesothelioma. No tumors developed in rata which had received carbon black. Experiments at present In progress and reported by Skidmore and Wagner elsewhere in this mono graph," show that crocidolite, chrysotile, silica powder and to a lesser extent, amoslte, all induce pleural mesotheliomata in guinea pigs after intrapleural injection. Malignant tumors have been produced in fowls by crocidolite and amoslte." though It la too early to determine their relative carcinogenicity in this species. Possible Moots or Action or Asbestos as a Cabcinocln At present the following possible mechanisms of carcinogenesis are und*r consideration: (1) That carcinogenesis is due entirely, or in part, to organic materials associated with the fiber, either naturally or as a .result of contamina tion or treatment of the asbestos during processing; (2) that It is due to the presence of certain carcinogenic metals or metalcomplexes In asbestos; 13; that It Is an "Oppenheimer Effect," that.is to say, that it is induced by the prolonged residence in the tissues of chemlcally-inert material Incapable of being rapidly removed by phagocytosis. 1 W. ^ S. PRODUCED BY FORD