Document MJENzjBBXE1q168X5npmGYNwx

OCT 1 1 2005 15:41 FR C1STI ICIST 613 952 9303 TO 12145201181 I 350 CHRYSOTILE ASBESTOS--LARGER ET AL P. 05/16 pled with relatively short-term biological res been made with amphibole asbestos types, idence, insured recovery of characteristic eg, amosite.10 fibers. This chemical and physical instability cf In contrast to experimental animal chrysotile has made the quantitative extrac studies, the amount of asbestos recovered tion of asbestos fibers from the lungs from lungs of persons occupationally ex of exposed individuals a problem that posed to the fiber has ranged from reported has not yet been completely solved. (See values of 0.6% to 0.001% of lung weight18-19 Nagelschmidt20 for discussion.) As an alter Nagelschmidt noted20 that the recovery of native, it has been considered useful to at chrysotile asbestos from lung tissue is always least obtain those fibers which had become low and recovery of amphibole asbestos gen coated (the "asbestos bodies"). While there erally high for human cases. are no data to quantitatively relate the pres The second reason for the difficulty in ence of such asbestos bodies to the remain extracting unaltered chrysotile fibers from der of the asbestos present, it has been human lungs lies in the fact that the nature thought that it may at least reflect, to an of chrysotile asbestos is such that it tends to undetermined degree, the presence of asbes break down chemically and physically after tos in general. Moreover, individual asbestos prolonged biological residence. This is espe bodies can be removed for analysis of their cially true of chrysotile fibers that have sepa coating and, more germane to the current rated into their fine unit fibrils. problems, of their central, fibrous cores. Chrysotile asbestos is chemically unstable A useful method to obtain individual as- even in distilled water.21-22 An aqueous solu bestos bodies for study is to isolate them by tion with a pH below 10.8 will cause the micromanipulation.6 It should be noted, fiber to be leached of some of its magnesium. however, that micromanipulation must be Chemical instability in a biological environ done under the optical microscope, generally ment has been demonstrated several times. using low magnification. This inevitably pro Morgan and Holmes,38 following the duces a biased selection of large asbestos "daughter" decay products of radioactive bodies from lung tissue,1018-28 since by de chrysotile asbestos, showed that magnesium finition the only bodies that can be manipu was rapidly leached from the chrysotile lated are those that can be seen at such low fibers while in biological residence. This was magnifications! Micromanipulation of as- also indicated by the work of Langer et al.10 bestos bodies precludes small asbestos bodies Electron microprobe studies of chrysotile as from analysis. Micromanipulation of asbes- bestos fibers removed from the lungs of ham tos bodies from human lung tissue, therefore, sters indicated a wide range of magnesium leads to particle selection. On the basis of values in contrast to the narrow range in the the physical and chemical differences ob fibers before injection. Similar results have served experimentally and determined theo- been obtained in analyses of fibers and retically for chrysotile and amphibole types, bodies removed from lung tissue of a Cana it may be concluded that the large recover dian chrysotile miner. able fibers and bodies, selected by using the These findings are consistent with optical optical microscope, are more likely to be studies previously reported,20-2* in which amphibole asbestos than unaltered chryso chrysotile asbestos removed from the lungs tile. of workmen exposed to this fiber was found Timbrell et al27 observed that what is seen not to possess the same optical characteris by light microscopic methods often differs tics as did the materials to. which they were from what may be observed by electron mi- exposed. Rather, the findings reflected chem croscope methods and that respirable-size ically degraded fibers. fractions need not have the same size distri Marked physical changes in chrysotile bution or properties as those observed in the may also take place in vivo. The chrysotile gross overall sample. Similarly, Lynch and fiber composed of bundles of fibrils--breaks Ayer28 in describing the inadequacies of the open, and the individual unit fibrils are sepa imjpinger method of particle counting, con rated. This has been demonstrated by Suzu cluded that only about one in 100 fibers ki and Churg.25 No such observations have present in the air could be seen by light ( | ' > j j I ! 1 ; : i j ! I RECEIVED time OCT. Arch Environ Health--Vol 22, March 1971 2:43PM