Document 3JeV0q9Y26D5w9LZ2rdp7y593

- 71 - dolitc) was present and in 41 eases chrysotilo. It is not known however to what extent this control group might he considered representfitive for the whole population. Gross et al (197.iL), using lightritrorcopy and electronmicroscopy, found asbestos fibres in lung*-. of people prcsur.aMy not occupationally exposed to asbestos. In addition to identifiable chrysotjle fibres they found much lar ger numbers of minora) fibres of unknown compos!tion? fibres from glass or rockwool and ceramic aluminium silicate were identified; in addition fibres from the skeleton of plants and diatom fragments were found. The authors measured the fibre content of nc*n-occupationol)y asbestos exposed subjects (more females than males) from Pittsburgh (high industrial cmoV.e emission) and Charleston (relatively clrar seaco.a*-t cor.rjr.ity) . The average concentra tion in the Pittsburgh group was more than three times that in the Charleston group; the average concentration of mineral fibres war. sever, times as high. Nevertheless, the range of concontrati otis as found was of an entirely dif ferent magnitude than in asbestotic lungs: the percentage of mineral fibres identified as chrysotilo asbestos was ?i; this is estimated to be over 9S>% in asbestotic: lungs. The discussion nj. to which sire of fibre should be looked for has not been settled. As hoc (1974) mentioned in hir. commentary on a conference on the biological Fffv*i*. c.f ingested Asbestos: "Some stand by the doctrine enunciated several years ago that only fibres whose length lies between f. and ?Syn. are signi f i cant ** and #>:ary however ere firmly convinced that it is the submicroscopic particle that can penetrate cells and cause damage although they may be fairly rapidly degraded, and that thene arc- the ones that should be measured. Since one large fibre can break up into a multi hour of small fibres, a resolution of this disagreement is urgently necessary" (se. chapter VJ ) . The existence of this disagreement means that the use of both the lighUnicroscope and clectronmicroscope is neecssory; this implies that the investigations can only be done on a small scale making it impossible to screen larger groups from the population at the moment: electronmicrorcopic investignt ions can be done in only a limited number of institutes and cost much time and money. The screening of larger groups of the population 8001 0764 PRODUCED BY FORD