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Monday, 28 February 2011 23:47

Respiratory System: The Variety of Pneumoconioses

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This article is devoted to a discussion of pneumoconioses related to a variety of specific non-fibrous substances; exposures to these dusts are not covered elsewhere in this volume. For each material capable of engendering a pneumoconiosis upon exposure, a brief discussion of the mineralogy and commercial importance is followed by information related to the lung health of exposed workers.

Aluminium

Aluminium is a light metal with many commercial uses in both its metallic and combined states. (Abramson et al. 1989; Kilburn and Warshaw 1992; Kongerud et al. 1994.) Aluminium-containing ores, primarily bauxite and cryolite, consist of combinations of the metal with oxygen, fluorine and iron. Silica contamination of the ores is common. Alumina (Al2O3) is extracted from bauxite, and may be processed for use as an abrasive or as a catalyst. Metallic aluminium is obtained from alumina by electrolytic reduction in the presence of fluoride. Electrolysis of the mixture is carried out by using carbon electrodes at a temperature of about 1,000°C in cells known as pots. The metallic aluminium is then drawn off for casting. Dust, fume and gas exposures in pot rooms, including carbon, alumina, fluorides, sulphur dioxide, carbon monoxide and aromatic hydrocarbons, are accentuated during crust breaking and other maintenance operations. Numerous products are manufactured from aluminium plate, flake, granules and castings—resulting in extensive potential for occupational exposures. Metallic aluminium and its alloys find use in the aircraft, boat and automobile industries, in the manufacture of containers and of electrical and mechanical devices, as well as in a variety of construction and structural applications. Small aluminium particles are used in paints, explosives and incendiary devices. To maintain particle separation, mineral oils or stearin are added; increased lung toxicity of aluminium flakes has been associated with the use of mineral oil.

Lung health

Inhalation of aluminium-containing dusts and fumes may occur in workers involved in the mining, extraction, processing, fabrication and end-use of aluminium-containing materials. Pulmonary fibrosis, resulting in symptoms and radiographic findings, has been described in workers with several differing exposures to aluminium-containing substances. Shaver’s disease is a severe pneumoconiosis described among workers involved in the manufacture of alumina abrasives. A number of deaths from the condition have been reported. The upper lobes of the lung are most often affected and the occurrence of pneumothorax is a frequent complication. High levels of silicon dioxide have been found in the pot room environment as well as in workers’ lungs at autopsy, suggesting silica as a potential contributor to the clinical picture in Shaver’s disease. High concentrations of aluminium oxide particulate have also been observed. Lung pathology may show blebs and bullae, and pleural thickening is seen occasionally. The fibrosis is diffuse, with areas of inflammation in the lungs and associated lymph nodes.

Aluminium powders are used in making explosives, and there have been a number of reports of a severe and progressive fibrosis in workers involved in this process. Lung involvement has also occasionally been described in workers employed in the welding or polishing of aluminium, and in bagging cat litter containing aluminium silicate (alunite). However, there has been considerable variation in the reporting of lung diseases in relation to exposures to aluminium. Epidemiological studies of workers exposed to aluminium reduction have generally shown low prevalence of pneumoconiotic changes and slight mean reductions in ventilatory lung function. In various work environments, alumina compounds can occur in several forms, and in animal studies these forms appear to have differing lung toxicities. Silica and other mixed dusts may also contribute to this varying toxicity, as may the materials used to coat the aluminium particles. One worker, who developed a granulomatous lung disease after exposure to oxides and metallic aluminium, showed transformation of his blood lymphocytes upon exposure to aluminium salts, suggesting that immunologic factors might play a role.

An asthmatic syndrome has frequently been noted among workers exposed to fumes in aluminium reduction pot rooms. Fluorides found in the pot room environment have been implicated, although the specific agent or agents associated with the asthmatic syndrome has not been determined. As with other occupational asthmas, symptoms are often delayed 4 to 12 hours after exposure, and include cough, dyspnoea, chest tightness and wheeze. An immediate reaction may also be noted. Atopy and a family history of asthma do not appear to be risk factors for development of pot room asthma. After cessation of exposure, symptoms may be expected to disappear in most cases, although two-thirds of the affected workers show persistent non-specific bronchial responsiveness and, in some workers, symptoms and airway hyperresponsiveness continue for years even after exposure is terminated. The prognosis for pot room asthma appears to be best in those who are immediately removed from exposure when the asthmatic symptoms become manifest. Fixed airflow obstruction has also been associated with pot room work.

Carbon electrodes are used in the aluminium reduction process, and known human carcinogens have been identified in the pot room environment. Several mortality studies have revealed lung cancer excesses among exposed workers in this industry.

Diatomaceous Earth

Deposits of diatomaceous earth result from the accretion of skeletons of microscopic organisms. (Cooper and Jacobson 1977; Checkoway et al. 1993.) Diatomaceous earth may be utilized in foundries and in the maintenance of filters, abrasives, lubricants and explosives. Certain deposits comprise up to 90% free silica. Exposed workers may develop lung changes involving simple or complicated pneumoconiosis. The risk of death from both nonmalignant respiratory diseases and lung cancer has been related to the workers’ tenure in dusty work as well as to cumulative crystalline silica exposures during the mining and processing of diatomaceous earth.

Elemental Carbon

Aside from coal, the two common forms of elemental carbon are graphite (crystalline carbon) and carbon black. (Hanoa 1983; Petsonk et al. 1988.) Graphite is used in the manufacture of lead pencils, foundry linings, paints, electrodes, dry batteries and crucibles for metallurgical purposes. Finely ground graphite has lubricant properties. Carbon black is a partially decomposed form used in automotive tires, pigments, plastics, inks and other products. Carbon black is manufactured from fossil fuels through a variety of processes involving partial combustion and thermal decomposition.

Inhalation of carbon, as well as associated dusts, may occur during the mining and milling of natural graphite, and during the manufacture of artificial graphite. Artificial graphite is produced by the heating of coal or petroleum coke, and generally contains no free silica.

Lung health

Pneumoconiosis results from worker exposure to both natural and artificial graphite. Clinically, workers with carbon or graphite pneumoconiosis show radiographic findings similar to those for coal workers. Severe symptomatic cases with massive pulmonary fibrosis were reported in the past, particularly related to the manufacture of carbon electrodes for metallurgy, although recent reports emphasize that the materials implicated in exposures leading to this sort of condition are likely to be mixed dusts.

Gilsonite

Gilsonite, also known as uintaite, is a solidified hydrocarbon. (Keimig et al. 1987.) It occurs in veins in the western United States. Current uses include the manufacture of automotive body seam sealers, inks, paints and enamels. It is an ingredient of oil-well drilling fluids and cements; it is an additive in sand moulds in the foundry industry; it is to be found as a component of asphalt, building boards and explosives; and it is employed in the production of nuclear grade graphite. Workers exposed to gilsonite dust have reported symptoms of cough and phlegm production. Five of ninety-nine workers surveyed showed radiographic evidence of pneumoconiosis. No abnormalities in pulmonary function have been defined in relation to gilsonite dust exposures.

Gypsum

Gypsum is hydrated calcium sulphate (CaSO4·2H2O) (Oakes et al. 1982). It is used as a component of plasterboard, plaster of Paris and Portland cement. Deposits are found in several forms and are often associated with other minerals such as quartz. Pneumoconiosis has been observed in gypsum miners, and has been attributed to silica contamination. Ventilatory abnormalities have not been associated with gypsum dust exposures.

Oils and Lubricants

Liquids containing hydrocarbon oils are used as coolants, cutting oils and lubricants (Cullen et al. 1981). Vegetable oils are found in some commercial products and in a variety of foodstuffs. These oils may be aerosolized and inhaled when metals that are coated with oils are milled or machined, or if oil-containing sprays are used for purposes of cleaning or lubrication. Environmental measurements in machine shops and mills have documented airborne oil levels up to 9 mg/m3. One report implicated airborne oil exposure from the burning of animal and vegetable fats in an enclosed building.

Lung health

Workers exposed to these aerosols have occasionally been reported to develop evidence of a lipoid pneumonia, similar to that noted in patients who have aspirated mineral oil nose drops or other oily materials. The condition is associated with symptoms of cough and dyspnoea, inspiratory lung crackles, and impairments in lung function, generally mild in severity. A few cases have been reported with more extensive radiographic changes and severe lung impairments. Exposure to mineral oils has also been associated in several studies with an increased risk of respiratory tract cancers.

Portland Cement

Portland cement is made from hydrated calcium silicates, aluminium oxide, magnesium oxide, iron oxide, calcium sulphate, clay, shale and sand (Abrons et al. 1988; Yan et al. 1993). The mixture is crushed and calcined at high temperatures with the addition of gypsum. Cement finds numerous uses in road and building construction.

Lung health

Silicosis appears to be the greatest risk in cement workers, followed by a mixed dust pneumoconiosis. (In the past, asbestos was added to cement to improve its characteristics.) Abnormal chest radiographic findings, including small rounded and irregular opacities and pleural changes, have been noted. Workers have occasionally been reported to have developed pulmonary alveolar proteinosis after the inhalation of cement dust. Airflow obstructive changes have been noted in some, but not all, surveys of cement workers.

Rare Earth Metals

Rare earth metals or “lanthanides” have atomic numbers between 57 and 71. Lanthanum (atomic number 57), cerium (58), and neodymium (60) are the commonest of the group. The other elements in this group include praseodymium (59), promethium (61), samarium (62), europium (63), gadolinium (64), terbium (65), dysprosium (66), holmium (67), erbium (68), thulium (69), ytterbium (70) and lutetium (71). (Hussain, Dick and Kaplan 1980; Sabbioni, Pietra and Gaglione 1982; Vocaturo, Colombo and Zanoni 1983; Sulotto, Romano and Berra 1986; Waring and Watling 1990; Deng et al. 1991.) The rare earth elements are found naturally in monazite sand, from which they are extracted. They are used in a variety of alloy metals, as abrasives for polishing mirrors and lenses, for high-temperature ceramics, in fireworks and in cigarette lighter flints. In the electronics industry they are used in electrowelding and are to be found in various electronic components, including television phosphors, radiographic screens, lasers, microwave devices, insulators, capacitors and semiconductors.

Carbon arc lamps are used widely in the printing, photoengraving and lithography industries and were used for floodlighting, spotlighting and movie projection before the wide-scale adoption of argon and xenon lamps. The rare earth metal oxides were incorporated into the central core of carbon arc rods, where they stabilize the arc stream. Fumes which are emitted from the lamps are a mixture of gaseous and particulate material composed of approximately 65% rare earth oxides, 10% fluorides and unburnt carbon and impurities.

Lung health

Pneumoconiosis in workers exposed to rare earths has been exhibited primarily as bilateral nodular chest radiographic infiltrates. Lung pathology in cases of rare earth pneumoconiosis has been described as an interstitial fibrosis accompanied by an accumulation of fine granular dust particles, or granulomatous changes.

Variable pulmonary function impairments have been described, from restrictive to mixed restrictive-obstructive. However, the spectrum of pulmonary disease related to inhalation of rare earth elements is still to be defined, and data regarding the pattern and progression of disease and histological changes is available primarily only from a few case reports.

A neoplastic potential of the rare earth isotopes has been suggested by a case report of lung cancer, possibly related to ionizing radiation from the naturally occurring rare earth radioisotopes.

Sedimentary Compounds

Sedimentary rock deposits form through the processes of physical and chemical weathering, erosion, transport, deposition and diagenesis. These may be characterized into two broad classes: Clastics, which include mechanically deposited erosion debris, and chemical precipitates, which include carbonates, shells of organic skeletons and saline deposits. Sedimentary carbonates, sulphates and halides provide relatively pure minerals that have crystallized from concentrated solutions. Due to the high solubility of many of the sedimentary compounds, they are rapidly cleared from the lungs and are generally associated with little pulmonary pathology. In contrast, workers exposed to certain sedimentary compounds, primarily clastics, have shown pneumoconiotic changes.

Phosphates

Phosphate ore, Ca5(F,Cl)(PO4)3, is used in the production of fertilizers, dietary supplements, toothpaste, preservatives, detergents, pesticides, rodent poisons and ammunitions (Dutton et al. 1993). Extraction and processing of the ore may result in a variety of irritant exposures. Surveys of workers in phosphate mining and extraction have documented increased symptoms of cough and phlegm production, as well as radiographic evidence of pneumoconiosis, but little evidence of abnormal lung function.

Shale

Shale is a mixture of organic material composed mainly of carbon, hydrogen, oxygen, sulphur and nitrogen (Rom, Lee and Craft 1981; Seaton et al. 1981). The mineral component (kerogen) is found in the sedimentary rock called marlstone, which is of a grey-brown colour and a layered consistency. Oil shale has been used as an energy source since the 1850s in Scotland. Major deposits exist in the United States, Scotland and Estonia. Dust in the atmosphere of underground oil shale mines is of relatively fine dispersion, with up to 80% of the dust particles under 2 mm in size.

Lung health

Pneumoconiosis related to the deposition of shale dust in the lung is termed shalosis. The dust creates a granulomatous and fibrotic reaction in the lungs. This pneumoconiosis is similar clinically to coal workers’ pneumoconiosis and silicosis, and may progress to massive fibrosis even after the worker has left the industry.

Pathologic changes identified in lungs with shalosis are characterized by vascular and bronchial deformation, with irregular thickening of interalveolar and interlobular septa. In addition to interstitial fibrosis, lung specimens with shale pneumoconiosis have shown enlarged hilar shadows, related to the transport of shale dust and subsequent development of well-defined sclerotic changes in the hilar lymph nodes.

Shale workers have been found to have a prevalence of chronic bronchitis two and one-half times that of age-matched controls. The effect of shale dust exposures on lung function has not been studied systematically.

Slate

Slate is a metamorphic rock, made up of various minerals, clays and carbonaceous matter (McDermott et al. 1978). The major constituents of slate include muscovite, chlorite, calcite and quartz, along with graphite, magnetite and rutile. These have undergone metamorphosis to form a dense crystalline rock that possesses strength but is easily cleaved, characteristics which account for its economic importance. Slate is used in roofing, dimension stone, floor tile, flagging, structural shapes such as panels and window sills, blackboards, pencils, billiard tables and laboratory bench tops. Crushed slate is used in highway construction, tennis court surfaces and lightweight roofing granules.

Lung health

Pneumoconiosis has been found in a third of workers studied in the slate industry in North Wales, and in 54% of slate pencil makers in India. Various lung radiographic changes have been identified in slateworkers. Because of the high quartz content of some slates and the adjacent rock strata, slateworkers’ pneumoconiosis may have features of silicosis. The prevalence of respiratory symptoms in slateworkers is high, and the proportion of workers with symptoms increases with pneumoconiosis category, irrespective of smoking status. Diminished values of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are associated with increasing pneumoconiosis category.

The lungs of miners exposed to slate dust reveal localized areas of perivascular and peribronchial fibrosis, extending to macule formation and extensive interstitial fibrosis. Typical lesions are fibrotic macules of variable configuration intimately associated with small pulmonary blood vessels.

Talc

Talc is composed of magnesium silicates, and is found in a variety of forms. (Vallyathan and Craighead 1981; Wegman et al. 1982; Stille and Tabershaw 1982; Wergeland, Andersen and Baerheim 1990; Gibbs, Pooley and Griffith 1992.)

Deposits of talc are frequently contaminated with other minerals, including both fibrous and non-fibrous tremolite and quartz. Lung health effects of talc-exposed workers may be related to both the talc itself as well as the other associated minerals.

Talc production occurs primarily in Australia, Austria, China, France and the United States. Talc is used as a component in hundreds of products, and is used in the manufacture of paint, pharmaceuticals, cosmetics, ceramics, automobile tires and paper.

Lung health

Diffuse rounded and irregular parenchymal lung opacities and pleural abnormalities are seen on the chest radiographs of talc workers in association with the talc exposure. Depending on the specific exposures experienced, the radiographic shadows may be ascribed to talc itself or to contaminants in the talc. Talc exposure has been associated with symptoms of cough, dyspnoea and phlegm production, and with evidence of airflow obstruction in pulmonary function studies. Lung pathology has revealed various forms of pulmonary fibrosis: granulomatous changes and ferruginous bodies have been reported, and dust-laden macrophages collected around the respiratory bronchioles intermingled with bundles of collagen. Mineralogical examination of lung tissue from talc workers is also variable and may show silica, mica or mixed silicates.

Since talc deposits may be associated with asbestos and other fibres, it is not surprising that an increased risk of bronchogenic carcinoma has been reported in talc miners and millers. Recent investigations of workers exposed to talc without associated asbestos fibres revealed trends for higher mortality from non-malignant respiratory disease (silicosis, silico-tuberculosis, emphysema and pneumonia), but the risk for bronchogenic cancer was not found to be elevated.

Hairspray

Exposure to hairsprays occurs in the home environment as well as in commercial hairdressing establishments (Rom 1992b). Environmental measurements in beauty salons have indicated the potential for respirable aerosol exposures. Several case reports have implicated hairspray exposure in the occurrence of a pneumonitis, thesaurosis, in heavily exposed individuals. Clinical symptoms in the cases were generally mild, and resolved with termination of exposure. Histology usually showed a granulomatous process in the lung and enlarged hilar lymph nodes, with thickening of alveolar walls and numerous granular macrophages in the airspaces. Macromolecules in hairsprays, including shellacs and polyvinylpyrrolidone, have been suggested as potential agents. In contrast to the clinical case reports, increased lung parenchymal radiographic shadows observed in radiological surveys of commercial hairdressers have not been conclusively related to hairspray exposure. Although the results of these studies do not allow definitive conclusions to be drawn, clinically important lung disease from typical hairspray exposures does appear to be an unusual occurrence.

 

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