Fibre typeandconcentration inthelungs ofworkers inan asbestos cementfactory

ABSTRACrThepredominant asbestos fibre typeusedintheproduction ofasbestos cement is chrysotile. Theuse ofasbestos inrelation tofibre typeina Norwegianasbestos cement plant during 1942-80 was 91-7%chrysotile, 3-1%amosite, 4-1%crocidolite, and1 1% anthophyllite respectively. Electron microscopy andx ray microanalysis oflungtissue samplesofasbestos cementworkers whohaddiedofmalignant pleural mesothelioma or bronchogenic carcinoma showed acompletely inverse ratio withregard tofibre type.Thepercentageofchrysotile asbestos inlungtissue varied between 0% and9% whereas thecorresponding numbersfortheamphiboles were 76%and99%.Thesedifferences are discussed withrespecttothebehaviour ofdifferent fibre typesinthehumanbodyandtotheoccurrence ofmalignant mesothelioma inthisasbestos cementfactory. Analysis offibres inhumanlungtissue maybeused fortheverification ofprevious exposure toasbestos. Theamountoffibres deposited inthelungs mayalso reflect thetotal dose(concentration x yearsof exposure) towhich anindividual hasbeenexposed. Nevertheless, variations indeposition, clearance rate, anddurability ofdifferent typesoffibres should beborneinmindwhensuchdataarecompared. Thefactthatchrysotile iscleared more efficiently orevendissolved inlungtissue often results inarelatively larger percentage ofamphibole fibres inthelungprovided that amixedtypeasbestosexposure hasoccurred. Thisdifference isespecially important incases ofmesothelioma asithas beenarguedthatcrocidolite hasthehighest mesothelioma producing potential followed byamosite andchrysotile,' anassumption supported bythe studies ofDementetalandWeiss whoreported no mesotheliomas intwoplants whereonlychrysotile hadbeenused.23 Contrary tothese reports, Newhouseetalfound10mesotheliomas ina cohort apparently exposed onlytochrysotile.4 Theassociation between fibre typeanddisease hasbeenfurther clarified byMcDonald etalwhoshowedthat cases of mesothelioma andreferents weresimilar with respect tochrysotile content inthelungs, whereas therewas a substantial excessofamosite and crocidolite in thecasescomparedwiththe