Comparison oftheresults ofasbestos fibre dustcounts inlungtissue obtained byanalytical electron microscopy andlight microscopy

SUMMARYTheefficiency ofthelight microscope withthat oftheelectron microscope indetecting asbestos fibres inhumanlungtissue wascomputed. Necropsy material from55patients whohad died fromasbestos related diseases wasanalysed independently byphase contrast microscopy and electron microscopy. Asexpected thenumberoffibres identified using electron microscopy was higher thanthat identified bylight microscopy. Byadjusting theelectron microscope fibre counts to allow forthelimited resolving powerofthelight microscope, however, asignificant correlation of thenumber offibres identified using thetwomethods wasobtained. Thebest correlation wasfound withspecimens containing crocidolite (correlation coefficient 0-79) andamosite (correlation coefficient 074), while chrysotile gaveamuchlower correlation (correlation coefficient 015). The cumulated fibre diameter distribution obtained using theelectron microscope suggests that thelight microscope isabletovisualise only5%ofcrocidolite, 26-5%ofamosite, and0-14%ofchrysotile present inlungtissue. Therefore, although itispossible, using theelectron microscope, topredict theasbestos fibre count that wouldbeobtained bylight microscopy, thereverse prediction cannot bemade: itisimpossible todetermine theproportion ofthevarious asbestos mineral types using the light microscope. Inrecent years animportant aspect inthestudy of diseases induced byasbestos hasbeenthetype offibre andtheamountofexposure that mayresult inpathological changes.1 Considerable progress hasbeen madeinthis field since thedevelopment oftechniques that enable single asbestos fibres inhumantissues to beidentified using electron microscopy andelectron microprobe analysis.` Light microscope studies havebeenmadeonlung tissue toassess secular trends inferruginous body concentrations overaperiod oftimewiththeaimof establishing theproportion ofpeople indifferent cities andtownsinwhomferruginous bodies canbe found.6 Other studies havebeenperformed todeterminewhether there isarelation between theconcentrations offibrous particles andferruginous bodies detected inthelungs anddifferent diseases.7- 9These studies, using thelight microscope, wereallperformedassuming thattheferruginous bodies observed wereallformed onasbestos mineral fibres andthat theuncoated fibres observed werealso asbestos, although itiswellknownthatthey cannotbe identified using anoptical microscope.