Document MJdK7m981ER8nvmRqp9jKzL8j

step profile; pcuclty of *P* and i nonttaestot fiber (x 20,000). ly 1970 ! offerruginous bodies faolntrvTfrom lungs of I urban dwellers In sufficient numbers to yield statistically significant doto. [ Although identification of the central fiber of ferruginous bodies and of naked fibers has been accomplished by [ electron dif fraction'0 and electron rnicroprobe analy st* these techniques are laborious and time consuming. Furthermore, for the large- icale investigation necessary rto obtain sta tistically reliable data, extensive use of the above techniques could prove enormously expensive, since it would tendto monopolize the costly equipment involved and the time of trained technicians. j Also, the need exists for a method which would facilitate acquisition of necessary data rapidly and economically. This commu nication suggests a means to satisfy these needs. A procedure, essentially a screening method, is described for classifying naked fibers and the central filaments of ferrugi nous bodies into asbestos or nonasbestos fibers. The cores of ferruginous bodies are made accessible for such classification by freeing them from the encrusting ferrugi nous shell by chemical or physical means, ic, either with oxalic acid or ultrasonic vibra tions. i based on the multi-unit composition of asbestos fiber* and tho unitary structure of nonnsbesto* fibers. A surface viow (scanning electron microcofio) of tho former nt a magnification of approximately 20.000X shows longitudinal, par allel delineation of individual fibrils (Fig 3). The surface view of a nonasbestos fiber is devoid of such longitudinal line* (Fig 4). To test the validity of these concepts, elec tron photomicrographs were made of the ends of several chryaotile, amosite, and croddolite fiber*, as well as the end* of a similar number of glass, ceramic aluminum silicate, and silicon carbide fiber*, all of which had diameter* with in a range of 0.1a to 2.0a. Without the observ er's knowing the identity of the fiber* on the photographs, the Utter could be sorted easOy, quickly, and correctly into asbestos and nonas bestos categories based on the above concepts. A magnification of 20,000 or 25,000X appeared optimal for this purpose. However, the method is not free of possible error. According to the findings of J. P. Leineweber, PhD, (written communication, Octo ber 1969), the end* of occasional asbestos fibers, particularly those substantially thinner than la, may cause them to be categorized wrongly. For such fibers, higher magnifications and use of the scanning microsoo|>c is advised. Comment Materials and Method The classification of inhaled, fibers isolated (mm lungs'* ia based on the fait that asbestos Ebert are composed of compactly apposed finer fibrils, whereas nonasbestos fibers ars homoge neous units. Becaute of this difference in ttrucj lure, the fractured ends of these two types of fibers differ in a very important way. The end of an asbestos fiber ia irregular and resembles that of a bundle of fragile sticks which hat been broken transversely. As might be expected, dif ferent fibers of the bundle break at somewhat different points. At an appropriate magni fication, therefore, (as described below, using electron microscopy) the fractured end pre sents an irregular profile with multiple steplike projections and depressions, some of the steps being shallow and others deep (Pig I). In contrast, inhaled transparent fiber* other than asbestos but of similar diameter are likely to be homogenous in character, and, because of this, to fracture so as to present uninterrupted lin ear profile* at the fractured ends' (Pig 2). Another important difference between inbaled asbestos and nonasbestos fibers is also A basic criterion of asbestos fiber identi fication is its tendency toward longitudinal splitting. Initially, there was uncertainty in some photographs in which several fibers known to be glass (one thick and one or two much thinner) were found parallel and in close apposition, giving the appearance of possible longitudinal splitting (Fig 5). The profiles of the fractured ends were interrupt ed also. However, the interruption consisted of only one or two steps; and there was sufficient width of uninterrupted linear profile to allow differentiation from asbes tos. As the diameter of the fiber in question decreases, the component subunits also be come smaller so that the magnification must be increased to visualize them. The chance for error appears to increase with substan tial decreases in diameter below 0.1p. How ever, inasmuch as the average diameter of naked fibers isolated from lungs of city dwellers in our experience is about 2/x (un published data), we believe the chance of error will be small. Arch^Enoiron Health--Vol 20, May 1970 a 000 PRODUCED BY FORn