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FILE NAME: Hercules Chemical (HERC) DATE: 1948 DOC#: HERC006 DOCUMENT DESCRIPTION: Book Excerpt from Industrial Hygiene and Toxicology - Asbestosis INDUSTRIAL HYGIENE IMI TOXICOLOGY FRANK A. PATTY, Editor Contributors : J. BROZEK L. F. CURTISS E. E. DART W. B. DEICHMANN F. F. HEYROTU F. R. HOLDEN G. W. JONES R. A. KEHOE D. O. HAMBLIN J. B. LITTLEFIELD I. HARTMANN C. P. MC CORD F. A. PATTY L. SCHWARTZ II. SPECHT J. H. STERNER J. F. TREON W. N. WITHERIDGE VOLUME I 19 4 8 INTERSCIENCE PU B LI S HE RS , INC., NEW YORK IN T E R SC IE N C E P U B L ISH E R S L T D ., LONDON DUST IN THE CAUSATION OF OCCUPATIONAL DISEASE 511 of aluminum by physicians for therapeutic or prophylactic purposes, makes only metallic aluminum available. Some investigators, notably Hannon,73have reported marked success in the treatment of patients with severe disability. However, when purely objective criteria have been used to measure disability the results have been somewhat less striking. Gardner, Dworski, and Delahant74 have suggested that variations in response to aluminum therapy may be due in part to the nature of the dust that has caused the silicosis. They suggest that dust which is primarily free silica may react with aluminum more readily than dust which contains high per centages of iron. The use of aluminum generally in industry for the therapy or prophylaxis of silicosis should be contemplated only with the utmost caution. I. ASBESTOSIS Asbestos is a hydrated magnesium silicate. More than 90 per cent of the raw mineral used in this country and Great Britian is produced in the Canadian chrysotile mines. Asbestos is used in two general types of manufacturing processes. It may be used either by itself or mixed with other insulating materials such as diatomaceous earth for fireproofing, packing, or insulating; or it may be combined with cotton and woven as a textile for fireproof and heat-resistant clothing and other substances. Lanza76estimates that there are about 10,000 persons exposed to asbes tos in the United States. Most observers feel that the incidence of asbestosis in American asbestos workers is quite low. Asbestosis has, however, been reported more frequently in England and Canada. Lanza, McConnell, and Fehnel76concluded from their study of asbestosis that: Prolonged exposure to asbestos dust causes pulmonary fibrosis different from that produced in silicosis and demonstrable by roentgenogram. Clinically it appears to be milder than silicosis. Definite cardiac enlargement frequently was found to be associated with asbestosis. A predisposition to tuberculosis, due to asbestos dust, was not indicated al though it was not known to what extent asbestosis may add to the mortality from pneumonia and acute nontuberculous pulmonary infections. Symptoms. The onset of asbestosis, as of silicosis, is slow although symptoms are apt to be somewhat more marked than in silicosis. In silicosis there may be marked x-ray findings with little complaint of symptoms, whereas the opposite is likely to be the case in asbestosis. As in silicosis, dyspnea is the cardinal symptom. Anorexia occurs frequently in advanced stages, and cyanosis and clubbing of the fingers are apt to appear with greater constancy in asbestosis. Pathology. The fibrosis in asbestosis is diffuse and tends to predominate in the basal portions of the lungs in contrast to the generalized nodular fibrosis of silicosis MJ. W. G. Hannon, Trans. Can. Inst. Mining Met., 48, 180 (1944). " L . U. Gardner, M. Dworski, and A. B. Delahant, J. Ind. Hyg. Toxicol., 26, 211 (1944). " A. J. Lanza, J. Am. Med. Assoc., 106, 368 (1936). " A . J. Lanza, W. J. McConnell, and J. W. Fehnel, U S. Pub. Health RepU., SO, 1 (1935) 512 EDWARD E. DART with a predominance in the upper portions of the lung. Bronchiectasis and bronchiolectasis are frequent, especially in the more fibrous portions. Whereas the prolifera tion of fibrous tissue is caused by chemical action in silica exposure, it is induced by mechanical action in asbestos exposures. Gardner77found that the fibrosis-producing character of asbestos could be almost eliminated by grinding the fibers so that no particles more than 2 p. in length were present. As previously mentioned, asbestos is classified among the inert dusts. Microscopic Anatomy. Johnstone78 described the microscopic appearance; of the lungs somewhat as follows: in the early phases of the disease there is thickening of the alveolar septa which results from fibroblastic proliferation. The alveolar spaces contain numerous phagocytes. With progression of the disease fibrosis be comes more marked; the alveolar structure gradually disappears, and in its place there is now dense fibrous tissue. The few alveoli that remain in the area of fibrosis are lined with low cuboidal epithelium giving them an almost glandular appearance. Scattered throughout the lung in both the diseased and healthy parts are spindle-shaped structures described first by McDonald.79 These bodies are 20 to 100 n in length and are bulbous on one or both ends so that they appear club- or dumbbell-shaped. They are brownish in color, do not stain, and give a Prussian-blue reaction for iron. Simson80has produced these bodies in guinea pigs by experimental exposure to atmosphere containing asbestos. Lynch81concludes that these "curious bodies" signify exposure to asbestos dust but do not necessarily indicate asbestosis. X-Ray Examination. For an excellent review of roentgenographic findings in both silicosis and asbestosis the reader might well refer to Pendergrass.82Character istic differences in the roentgenographic findings in silicosis and asbestosis are tabulated below: Asbestos! Silicosis Fibrosis diffuse (film may have ground glass appearance from pleural involve ment). Findings may be either bilateral or uni lateral. Lesions largely in the lower one half or two thirds of the lung fields. Emphysema in upper portion of lung fields. Fibrosis nodular. Findings characteristically bilateral. Lesions predominately in the upper twothirds of the lung fields. Emphysema in lower portion of lung fields. Control. Prevention of asbestosis depends entirely upon preventing exposure to concentrations of dust sufficiently high to produce the characteristic reaction. " L. U. Gardner, Ind. Med., 9, 45 (1940). TMR. T. Johnstone, Occupational Diseases. Saunders, Philadelphia, 1942. TMS. McDonald, Brit. M e d . ./., 2, 1025 (1927). 80F. W. Simson, Brit. Med. J., 1, 885 (1928). 81K . M. Lynch, J. Am. Med. Assoc., 109,1947 (1936). 82E. P. Pendergrass, "Roentgen-Ray Diagnosis in Silicosis and Asbestosis," in A. J. Lanza, Silicosis and. Asbestosis. Oxford Univ. Press, New \o r k , 1938. DUST IN THE CAUSATION OF OCCUPATIONAL DISEASE 513 Dreessen, DallaValle, Edwards, Miller, and Sayers83 have found evidence to indicate that 5,000,000 particles per cubic foot of air is a satisfactory figure for the maximum permissible atmospheric concentration of asbestos to which workers may be exposed. Definite permissible standards, however, have not been established. VI. Dust Causing Minimal Fibrosis or No Fibrosis Gardner77has pointed out that any known inorganic dust other than free silica and the asbestos silicates may produce nonspecific dust reactions, as described on page 486. X-ray markings may be found in other conditions such as chronic infection and heart disease. No interference with pulmonary function or disability is produced by dust of this type and there is no influence on susceptibility to tuberculosis. A. SILICATES McCord,81from a number of sources, has compiled a list of the commonly used silicates, which is presented here: Olivine--a magnesium silicate widely present in all basic rocks. Many varieties of this stone are known. Calcium silicate--nonexistent in nature, but a common product of industry; may be found at blast furnaces and in production of cement and hydrated limes. Other silicates of calcium are known. Willemite--a zinc silicate (rare). Sodium silicate ( m e l a ) - the well-known water-soluble silicate, commonly called water glass. This is widely used in industry, notably as a filler in soaps. This is the only crystalline silicate of sodium, the others being amorphous glass. Tremolite--a magnesium-calcium silicate. Asbestos--tremolite, actinolite, clirysotile, or amianthus, all of which are essentially mag nesium silicates. Jade--another form of magnesium-calcium silicate. Crocidolite-- "blue asbestos." It is a sodium iron silicate. Talc--a hydrated magnesium silicate with extensive industrial application. Soapstone--a form of talc. Agalite--a variety of talc resembling asbestos. It is used in the coating of paper, and as a paper filler. Meerschaum--also called sepiolite. It is closely akin to talc. Serpentine--hydrated silicate of magnesium. It is a common building stone. S illim a n ite-aluminum-containing silicate. The source of many stone tools of the stone age Topaz--a. semiprecious stone of silicate origin. Chemically it is an aluminum fluosilicate. Fuller's earth--a hydrated silica-aluminum compound, associated with ferric oxide. Kaolin (kaolinite)--many related silicates of mixed constituency. Clays--hydrated aluminum silicates containing iron. Titanium, quartz and mica, are likely to be present in clays. " W. C. Dreessen, J. M . DallaValle, T. I. Edwards, J. W. Miller, and It. R. Sayers. U.S. Pub. Health Bull. No. 241 (1938). MC. P. McCord, Ind. Med., 2, 4 (1933). 2^0 MANUAL OF INDUSTRIAL HYGIENE AND MEDICAL SERVICE IN WAR INDUSTRIES Issued under the Auspices of the Committee on Industrial Aledicine of the D ivision of M ed ical Sciences of the N a tio n a l Research Council PREPARED BY THE DIVISION OF INDUSTRIAL HYGIENE, NATIONAL INSTITUTE OF HEALTH, UNITED STATES PUBLIC HEALTH SERVICE WILLIAM M. GAFAFER, D.Sc. Editor W. B. SAUNDERS COMPANY PHILADELPHIA AND LONDON 1943 THE PROBLEM OF OCCUPATIONAL DISEASE 151 expansion, lessened capacity for work, absence of fever, increased susceptibility to tuberculosis (some or all of which symptoms may be present), and by characteristic X-ray findings." Classification.-- On the basis of the structural changes induced in the lung and the type of dust, the pneumoconioses or pul- monaiy fibroses may be classified as follows (compare refer ence 43) : 1. Simple benign pneumoconiosis, which is virtually a deposi tion of dust in the pulmonary tissues usually accom panied by pigmentation, and includes, for example, anthracosis induced by coal dust and siderosis induced by iron. It does not incapacitate and roentgenologically shows as a maximum change only an exaggeration of linear pulmonic m arkings and is of clinical interest only by way of differential diagnosis. Such cases should never be diagnosed as silicosis. 2. Silicosis, which is a pathologic pulmonary reaction due to free silica; for example, sandblasters' silicosis. This type of pneumoconiosis results in a classical nodular fibrosis of both lungs, demonstrable both in the X-ray and at post mortem. Massive fibrosis, varying degrees of pig mentation, atelectasis, emphysema, fibrous pleurisy, bronchitis, cavitation, and pneumothorax are among the concomitant pathologic changes.4-1 3. Mixed, form s, th a t is, silicosis resulting from the inhala tion of mixtures of varying amounts of free silica and more inert pneumoconiogenic dust constituents, for ex ample, anthracosilicosis and siderosilicosis. Most cases of silicosis undoubtedly come under this classification. 4. Asbestosis, a characteristic diffuse, interstitial fibrosis of the lungs induced by fibrous minerals which, according to animal experimentation, is due to the mechanical ac tion of the asbestos, producing a ground-glass appear ance on the X-ray. It may cause disability and a few fatal cases have been recorded. Etiology. Silicosis is incurable and large numbers of work men are potentially exposed to conditions favoring the develop ment of the disease. The m ajority of cases of this chronic pulmonary disease occur among workers engaged in mining,45 quarrying, ceramics industry, tunnel construction, sandblasting and foundry work. Inhalation of siliceous dust almost invariably results in sili- THE PROBLEM OF OCCUPATIONAL DISEASE 153 Symptoms and signs do, however, assist in the determ ination of disability. Among the symptoms and signs of importance are shortness of breath, particularly upon exercise; cough, usually dry ; chest pain, varying from a feeling of tightness in the chest to the sharp, excruciating pain typical of pleurisy ; hemoptysis ; general complaints such as digestive disturbances, insomnia, and dizziness ; decrease in chest expansion ; prolonged expiration, especially in association with emphysema ; altered breath sounds ; rales ; and the presence of areas of increased density in the lungs. Infection may complicate the picture at any time and is usually manifested by pleural pain, fever, night sweats, weight loss, aggravation of dyspnea, anorexia, weakness, and a cough produc ing large amounts of blood-tinged sputum. Diagnosis.-- In establishing a diagnosis of one of the pneumo conioses, all of the following three factors should be considered.* 1. An occupational history which reveals definite prolonged exposure to siliceous dust or asbestos dust. 2. Symptoms and physical signs which furnish valuable in formation in (a) gauging the extent to which pneumo coniosis has progressed, (b) showing the degree of dis ability, and (c) excluding other diseases. 3. X-ray findings, which, if classified on the basis of the systern recommended by the U. S. Public Health Service, show bilateral ground-glass, nodular, or a more ad vanced type of lung-field marking. So long as the chest roentgenograms show predominantly linear pulmonic m arkings, silicosis or modified silicosis need not be given serious consideration. It is when the shadows in the lung field assume a ground-glass, granular or nodular appearance th a t they become specific and assume more diagnostic charac teristics. Using Irvine and S teuart's analogy,48 the usual linear pulmonic markings are likened to the branches of a tree and the granular, stippled, or nodular lung-field m arkings simulate the leaves. Complete foliation then means silicosis. Viewed stereo scopically, the films a t this stage will show fine nodulation. Some w riters describe a related change in the lung-field appearance as reticulation.49 Although not definitely determined, this type of lung-field m arking may result from the inhalation of mixed dusts. L ater stages will show massive areas of fibrosis, and if infection is present the X-ray shadows tend to be asymmetrical. Asbestosis is exceptional from the standpoint that the pul * In the field of forensic medicine it has been frequently demonstrated that autopsy studies will yield essential information. 154 PREVENTION AND CONTROL OF DISEASE IN INDUSTRY monary fibrosis is caused by dust containing little if any free silica. The asbestotic patient will usually show clinical symptoms and signs which are out of proportion to the apparently small amount of pulmonary involvement shown by the chest roent genogram. Large massive shadows are very rarely seen in the chest roentgenogram except in the presence of a complicating infection. On the contrary, the diffuse interstitial fibrosis is manifested by a ground-glass appearance, frequently with fine pinpoint stippling of the middle and lower lung fields. It pro gresses to term inal diffuse fibrosis usually without nodular pre dominance in about twenty years.50 A shaggy appearing cardiac silhouette due to involvement of superimposed lung structures and pleuropericarditis is not infrequent. Asbestosis bodies may be demonstrated in the sputum or the lung tissue. Medical Control Measures.--All applicants for employment in dusty trades should be examined by X-ray. Periodic medical ex aminations at intervals of one year to possibly three years, in cluding X-ray study of the chest, should be made of all workers in dusty trades in order to detect evidence of active pulmonary tuberculosis and early silicotic changes. The length of the inter val between examinations depends mainly on the degree of haz ard and the prevalence of endemic tuberculosis. Clinical study of patients suspected of having pulmonary tuberculosis should be made to determine the dynamic status of such complication. No worker should be rejected on preemploy ment examination or removed from work, which he is accus tomed to perform, merely because of a diagnosis of simple silicosis, but rath er the atmospheric dust in which he works should be brought within safe limits. The worker whose first roentgeno gram shows healed prim ary tuberculosis should not be denied employment in a dusty trade on this account alone. If the worker has minimal, arrested, or healed reinfection tuberculosis, he should be allowed to continue his work but should be observed with the same precautions as a man with simple silicosis. Close medical supervision is recommended for all silicotic workers in order to control or prevent serious complications of the common respiratory infections. Benzene (Benzol) Poisoning Benzene (benzol) is an excellent solvent for gums, resins, fats, and oils, and as such has found many industrial .applica tions. It is used in the m anufacture of rubber, rubber goods,