Document aodnvpBreq3BJnr7yYmBrG5M

FILE NAME: Hercules Chemical (HERC) DATE: 1948 DOC#: HERC011 DOCUMENT DESCRIPTION: Book Excerpt from Occupational Medicine and Industrial Hygiene - Asbestosis OCCUPATIONAL MEDICINE AND INDUSTRIAL HYGIENE By KUTHEHFORD T. JOHNSTONE, A.B., M.D. Consultant in Industrial Health; Lecturer at the University of California, Los Angeles Formerly Assistant Professor of Medicine, University of Pittsburgh School of Medicine; Formerly Director of Department of Occupational Diseases, Golden State Hospital With One Hundred Seventeen Illustrations Seven in Color St. Louis THE C. V. MOSBY COMPANY 1948 334 OCCUPATIONAL MUDICINL AND INDUSTRIAL IIYUILNL a binder is extensively used as a refractory for furnace lin in g , at tenu peratnres at which ordinary brick would sol ten or me . . >ma " " ' has the advantage of a lower coefficient of expansion than ordinal v buck, tu t expands less when heated to high temperatures. Sihca Tt higii temperatures must be protected from the act,on o. metallic oxides and "basic" slags (those rich in metallic oxides) since these ma M * n - l will, aiica lo form fusible iHca.es. But s.hcu h n ck res highly sit,cions slogs and .nolle.. glass, hence may be os. .1 lo. Imi k furnaces for manufacture of glass, glazes, and enamels. Finely divided silica slowly reuetawilh alkaline luUon. even m room tcmpcriilurc, iorming soluble silicates, or le ( / nljx. nviv become coated with a gelatinous hydrous silicate, so tl <l - "me presently "els lo a hard mass. When finely divided s.l.ca mured with lime (OaO) and exposed lo slcam, Hie mixlure sets to a hard mass, r itlr a le d calcium silicate. This reaction Is the basis ot an rn.port.nl industry--the production ot sand-lime brick. K c . r ^ l " " ' ^ . silica, bleb * - " X S the air, the produce is quite transparent. ^ Asbestos and Talc.-Asbcstos is any one of * ^ 1 B bronstfknte minerals The Iwo most im portant varieties are hydiated magnesiun ilieates ' One of these is short fihered hut very intusiblc and acid res stant t Is accor lin g l, used for packing steampipes and furnaces and is I ,e,l in I h i X n t o i industries for filtering acids. The longer-fihered l.l,, hcat-rcsisiant varicly. coming principally from eastern O m a d a , . woven into (ireproof fabrics. The librous structure d * l l g ; I- , linlfine of the silicate tetrahedra to lorin long chains. A bundle oftlicse chains, with cations intervening between them, constitutes an ashesos fiber. Closelv related (o asbestos is laic, also a hydrated magnesium siliealc T liisis a while mineral will, a flaky texture. It is soft enough to he scratched with the fingernail, and so smooth as to he almost greasy the touch It is used in cosmetics, for filling writing paper, for Ihnshi h eothe and for polishing glass and metals. Soapstone s e t in c. ect, cal switchboards and for sinks and table tops, is a relative of talc. I he United States produces over 100,000 tons of the two minerals eacli yea.. CHAPTER XXX ASBESTOSIS Asbestosis is a comparatively new disease. The first comprehensive reports regarding asbestosis came from the English writers in the years between 1920 and 1925. In America in the early thirties studies were made hv Lanza, Sayers, Bloomfield, and others. Asbestos is a hydrated magnesium silicate. Occupational exposure occurs in those trades where it is used for packing, insulating, or fire proofing, or where it is combined with cotton or other material in textile processes. . Signs and Symptoms.--As in silicosis,1 the first sign is dyspnea, the cough is usually dry, and auscultation reveals few, if any, physical signs. Loss of weight is usually noticeable, the color is pale, and cyanosis is a fairly early sign. After some time, tine, crackling rales may be heard, and the chest appears emaciated and lacks the robust character noticed in silicosis. Early asbestosis must be differentiated from acute emphy sema. If tuberculosis is present, the symptoms may take on the character of this disease, but this complication is far less frequent than in silicosis. Pathology.-- P ulmonary C hanoks.-- The pulmonary fibrosis of asbestosis is diffuse in character, peribronchial, and basal in location in contrast to sili cosis in which the fibrosis is nodular in character and present in the upper part of the lungs. As the process continues, the fibrosis extends into almost all portions of the lung tissue. Bronchiolcctasis and bron chiectasis arc present within the substance of the fibroid areas, and bronchopneumonia and acute tracheobronchitis often cause the death of these patients. The pleurae, especially in the basal regions, are thickened and adherent. In some cases the pleural sac is completely obliterated; in others a fibrous or serous exudate may be present within it. Action of Asbestos and Silica.--1 he difference between chrysotile asbestos and quartz silica in their mode of action has caused considerable speculation as well as experimentation. Gardner2 particularly, at the Saianac Laboratory, carried on intensive study of these two materials. He felt that while the action of free silica is chemical in nature, the action of asbestos is mechanical. He stated: "We have come to the conclusion that inhaled asbestos fibres are irritating not because they are silicates but because they are slitr fibres which mechanically irritate the lungs. Unlike the free silicas, these minerals will not stimulate fibroblasts in any part of the body; onlv those in the lungs are affected. It was inferred that these organs were 368 ASISI2ST0SIS 369 aflected because the movements ol respiration are so much more rapid and continuous than those ot other viscera. Then it was discovered that it asbestos was ground very finely so that few of the fibres were longer that 2 microns in length the irritating property of the asbestos was prac tically destroyed. Inhalation experiments with such fine chrysotile asbes tos were carried out over a period of several years. No fibrosis has developed in spite ot the tact that an average atmospheric concentration ol 125 million particles per cubic feet of air has been maintained. In contrast in a previously reported experiment one-third this concentration of long fibre asbestos dust produced well marked fibrosis after about two years." If the effect of asbestos were chemical, one would expect that a decrease in size would accelerate tissue response. With free silica large particles have little effect, but as their size decreases cellular reaction becomes more vigorous and even constitutional symptoms may ensue. With fibrous asbestos the reverse is true. The histology of early asbestosis does not suggest a chemical injury. Even under the most extreme conditions that can be created by artificial injection there is no preliminary phase of tissue necrosis with infiltration ot leucocytes as occurs with high concentrations of very fine quartz. The connective tissue cells merely multiply very slowly in areas where the asbestos fibres are caught in the bronchioles. As collagen forms and contracts, the air spaces are obliterated by scar tissue. In experimental animals, at least, this change is not a progressive one after cessation of exposure to the dust as is the case in the response to quartz. Perhaps the reason is the deposition of the peculiar iron-containing coating on the surface of the inhaled fibres giving rise to the characteristic "asbestosis bodies" (Figs. 50 and 51). Finally, it is most suggestive that among dozens of different silicate minerals only the five known as asbestos, which are unique because they are fibrous iu structure, should be commonly recognized as pul monary irritants. The variation in chemical composition within this group is greater than that between them and many other silicates. In tact, clnysotile asbestos has the same chemical formula as a nonfibrous silicate, serpentine, which is physiologically inert. Obviously irritation would seem to be associated with the physical rather than the chemical composition of these minerals. One point of practical significance may be indicated by these obser vations: namely, that very finely ground asbestos is not dangerous. This conclusion has support in clinical observation, for it has long been known that at the Thetford Mills there was no clinical asbestosis even though in former years the atmosphere was very dusty and tile dust was extremely tine. The tact that fabrication of fibres of the same mineral in American plants could produce disease was one of the puzzling fea- OCCUPATIONAL MEDICINE AND INDUSTRIAL IYOIENE 372 OCCUPATIONAL MUOICINK ANI) INDUSTIUAT- HYOIKNli tures of this disease. But these experiments offer a plausible explanation. The fine (lust in the mills is composed of serpentine and extremely short chrysotile fibres; that in the spinning and weaving mills contains many more long fibres. Microscopic Appearance....In the early phases of the disease there is a thickening of the alveolar septa as a result of fibroblastic prolifera tion. The alveolar spaces contain numerous alveolar phagocytes. With progression of the disease, fibrosis becomes more marked and the alve olar structure gradually disappears, and in its place there is now dense fibrous tissue. The few remaining alveoli which lie in the area of fibrous tissue arc lined by a low cuboidal epithelium and have a glandular appearance (Fig. 52). Scattered throughout the lung in both the diseased and healthy parts are spindle-shaped structures (first described by McDonald') known as asbestosis bodies. These bodies arc slender in their center and bulbous at each extremity. Many are arranged like strings of graduated heads with the largest at the end of the chain. X-Ray Findings.--Certain peculiarities exist here as contrasted to silicosis. In asbestosis, the lesions may be bilateral or largely unilateral. According to the experience of Pendergrass,3 the roentgenologic findings in asbestosis are largely limited to the lower half or two-thirds of the lung fields, while in silicosis the upper portions of the lungs are also involved. In moderately advanced asbestosis, x-rays will reveal lessened ventilation of the lung fields, the parietal pleura is thickened, and there is a "ground-glass" appearance to the picture. The vascular shadows lose their identity. Modulation is absent. Pendergrass3 feels that a roentgenologic diagnosis of early asbestosis is unreliable and that the condition must be moderately or markedly advanced to make a differ ential diagnosis from the roentgenograms (Fig. 53). Medicolegal Aspects.--It is felt that the time necessary to develop asbestosis is, on the average, from seven to nine years in a fairly high concentration; with a less severe concentration, from fifteen to twenty years. The allowable concentration is 10,000,000 particles per cubic fool of air, of a size between 0.5 and 5. Once established, the disease is progressive, even after the cessation of exposure. The basis for diagnosis is similar to that given under Silicosis. References 1. Lanza, A. J.: Asbestosis, J.A.M.A. 106: 368 (Feb.)', 1936. 2. Gardner, L. U.: Recent Developments in Relation to Silicosis, Indlist. Med. 9: 45 (Feb.), 1940. 3. Pendergrass, F. P.: Silicosis and Asbestosis, New York, 1938, Oxford Univer sity Press. M cD o n a ld , S.: H is to lo g y o f P u l m o n a r y A s b e s to s i s , B r i t . M . J., 2 : 1ft2f, 1927. (cry disa bon ally dogi of hi As A gat ii rem he ; Irei) min dosi Vali note stili ers 3 film mor ohsc dysp The nulli culai prrs invo area pria lumi prcs and be p (beri DilVi