Asbestiform Fibers Nonoccupational Health Risks (1984) / Chapter Skim
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5 Effects of Asbestiform Fibers on Human Health
5 Effects of Asbestiform Fibers on Human Health
Pages 97-164
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From page 97... ...
A discussion of health consequences that have been associated with nonoccupational exposure of humane to asbestos and other asbestiform fibers is followed by a description of occupational epidemiological studies. NATURE OF EVIDENCE Three lines of evidence -- clinical, epidemiological, and laboratory- are considered when determining whether a particular environmental agent may cause adverse effects on human health.
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From page 98... ...
there is a failure to adequately take into account the presence of other factors that may be involved in addition to, or instead of, the major factor being examined. In laboratory experiments in animals, the investigator has the great advantage of being able to exercise control over the conditions of observation, rather than having to rely on observations of natural phenomena as in most nonintervention clinical and epidemiological studies.
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From page 99... ...
have updated Koch's postulates and applied them to environmental toxicology. ID evaluating relationships between exposure to hazardous environmental agents and adverse health effects, it is useful to proceed beyond identifying and confirming the hazard to quantifying the risks under various conditions.
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From page 100... ...
Asbestos exposure among insulation workers who do not smoke cigarettes increases the risk for lung cancer up to about 5 times (Harmond et al., 1979~. Together, the cigarette smoking and asbestos exposure appear to produce a multiplicative effect, i.e., the lung cancer rate is inc reased up to 50-fold above background .
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Epiglottis Ail Visceral _ Pleura Parietal _ Pleura Alveol i ~ Figure 5 101 ~ Esophagus Trachea- /~\\ \ Peritoneal Cavity ~ Diaphragm I Cavity Pharynx Main Bronchus See Figure 5-1B Pleural Cavity (the pleura consists of the membrane enveloping the lungs and lining e chest cavity)
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From page 102... ...
Interaction of asbestos with fibroblasts within the interstitial space can result in fibrosis, whereas interaction of asbestos with alveolar epithelial cells can give rise to lung cancer. (Drawing from Guyton, 1971.)
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Fiber Deposition Various factors influence the deposition of inhaled particles in the respiratory tract. When nonfibrous compact dust particles are inhaled, the ones greater than about 5 Am in diameter are generally trapped in the nasal passages before reaching the respiratory system (Walton, 1982~.
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From page 105... ...
Early researchers discovered the presence of asbestos bodies as well as asbestos fibers in pulmonary tissues of exposed workers, especially in those with asbestosis ~ Cooke, 1927, 1929; Cooke and Hill, 1930; Gloyne, 1929; Sebastien et al., 1979~. Asbestos bodies are asbestos fibers coated with an iron-protein material that is readily visible with a light microscope.
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Churg (1983b) examined mineral fibers2 in the pulmonary tissues of 20 patients with no known occupational exposure to asbestos.
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Some other cancers may also be related to asbestos exposure (Selikoff et al..
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In addition, mesothelioma is rare, and most cases investigated seem to have been associated with asbestos exposure. The diagnostic process often begins with observations of respiratory symptoms that establish functional impairment.
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Lung function tests are often useful in diagnosing diseases that might be related to asbestos, although pulmonary tests alone do not lead to a definitive diagnosis. There are two basic groups of lung function tests: Spirometric tests.
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and not clinically relevant. At present there is no practical way to identify individuals immunologically or genetically susceptible to disease from asbestos exposure.
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Physical examination and pulmonary function tents often yie id findings consistent with chronic bronchitis, especially in smokers, perhaps with a localized wheeze , but as tumor invasion continuer, the symptoms and signs of localized airway obstruction or metastases appear. Later symptoms can include loss of appetite, weight loss, pain, general malaise, and weakness.
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It is more difficult to diagnose peritoneal mesothelioma than pleural mesothelioma. The diagnosis is confirmed only by microscopic examination, and even this may be difficult Or impossible if the tumor is sufficiently undifferentiated.
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From page 113... ...
Classically, asbeseosis has been regarded as a restrictive lung disease, but clinically one often finds evidence of obstructive lung disease, especially among smokers, or a mixed obstructive and restrictive physiological abnormality (Becklake, 1976~. Results of well-designed epitemiological studies of the relative effects of smoking and asbestos exposure on small airways obstruction are not available.
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From page 114... ...
Diffuse pleural thickening, plaques, calcification, and effusion are nonmalignant changes in the pleura that have been associated with asbestos exposure (Albelda et al., 1982; Epler et al., 1982; Weiss et al., 1981~. mese changes, usually detected by .
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From page 115... ...
Because of the difficulties in diagnosing mesothelioma and determining exposure to asbestiform fibers, the background rate of mesothelioma is not knows. In one study of 4,539 canes from 22 countries between 1959 and 1976, there was no definite or probable history of exposure for 38: of the subjects (McDonald and McDonald, 1977~.
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From page 116... ...
However, since the levels of general ambient exposures to asbestos were not known, the possibility that the residual cases might also be attributable to asbestos exposures cannot be discounted. Epidemiological data have led to questions about the characteristics of fibers that are associated with mesothelioma.
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From page 117... ...
No estimates of neighborhood levels of asbestos fibers or other carcinogens were available for either area of study. Natural Sources of Asbestiform Plbers Asbestos-related diseases have been associated with exposure to naturally occurring mineral fibers in Turkey, Finland, and Bulgaria (Bards et al., 1981; K1viluoto, 1960; Zolov et al., 1967~.
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A review of 275 chest radiographs in one hospital near such an area in Nevada showed background levels of pleural plaques (2X) and pleural thickening (62)
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It seems likely that these mesotheliomas arise from respiratory exposure to asbestiform fibers. EPIDEMIOLOGICAL STUDIES OF EFFECTS RESULTING FROM THE INGESTION OF ASBESTOS IN DRINKING WATIER ~ Epidemiologica' studies of the effects of asbestos in drinking water in six geographical areas of the United States and Canada have been extensively reviewed and critiqued (Marsh, 1983; Workshop on Ingested Asbestos, 1983~.
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Given the difficulty of determining individual exposure, results of these epidemiological studies cannot be taken as strong evidence about the extent to which lageation of drinking water containing asbestiform fibers might increase the risk of GI cancer. The NRC Safe Drinking Water
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cancers that might be expected from ingestion of asbestos-containing drilling water and concluded that their risk estimates are consistent with the results of the epidemiological drinking water studies conaldered. OCCUPATIONAL EPIDEMIOLOGICAL STUDIES -- METHODOLOGICAL CONSIDERATIONS Evaluation of potential health effects from nonoccupational exposure to asbestiform fibers depends primarily on results of epidemiological studies of occupational groups.
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(See Consumer Product Safety Commission, 1983, for a detailed assessment of exposure estimates among the various asbestos studies.) There may also be variability in reporting causes of death, ascertainment of deaths, and diagnostic accuracy of the reported cause of death.
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These studies indicate the variety of occupations and industries where asbestos exposure has occurred and the types of asbestos commerc ial ly used. The epidemiological study by Doll ( 1955)
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and fro. Consueer Product Safety Co~i~sion (1983, p.
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. [Study of cancer incidence (Cle~esen and H]
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Manufactur~ng Chrysotile. Most asbestos exposures associated with manufacturing processes involve mixed fiber types, but Dement et al.
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In a case-control study that corrected for total asbestos exposure, 5 of 6 cases had definitely worked with crocidolite, whereas 2 of 10 controls had. A cohort of 1,34S retired asbestos products workers employed from 1941 to 1967 had increased risks for lung cancer (SMR = 2.7, 63 observed/23.3 expected)
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studied cancer incidence among 6,372 Danish males who worked in asbestos-cement factories between 1944 and 1976. There were 55 cases of respiratory cancer compared to 33 expected, based on Danish Cancer Registry incidence rates.
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A five-fold increase in lung cancer risk was associated with asbestos exposure in both smokers and nonsmokers (Hammond et al., 1979~. Elmes and Simpson (1977)
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(1983b) reported that only one of 308 deaths in a chrysotile asbestos textile plant was attributable to mesothelioma.
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These investigators also reported that mesothelioma risk does not appear to be affected by cigarette smoking. Among male asbestos workers who never smoked cigarettes regularly, eight mesotheliom~ deaths were observed, the same number as expected based on the age-specific death rates for all asbestos workers.
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Measurements of exposure intensity are lacking in most studies. Where such measurements have been attempted, it is still difficult to estimate earlier asbestos exposures when only dust measurements were obtained.
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Mortality studies of asbestos textile workers exposed to a variety of fiber types have had mixed results. Mancuso and Coulter ( 1963)
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From page 136... ...
(1979) , who Studier workers in a plant that uset 99% chrysotile and 1: crocitolite ant amosite, reported 76 teethe from noninfectious, nonmalignant respiratory diseases among males, whereas 16.4 had been expec ted .
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More recent studies have confirmed the general observations of these early investigators, although disease prevalence has varied from industry to industry. Selikoff and his colleagues studied insulation workers exposed to chrysotile and amosite.
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Baselga-Monte and Segarra (1978) studied 1,262 Barcelona factory workers exposed to mixed-fiber asbestos and established a relationship between individual risk and cumulative dose (fibers/cm3)
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The relationship between lung function and radiographic findings associated with asbestos exposure was further studied by Lumley (1977) , who reported highly significant decreases in lung function with pulmonary fibrosis and diffuse pleural chickening, somewhat less of a decrease when there were only plaques, and no difference if only pleural calcification was pre sent .
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From page 140... ...
Summary Morbidity studies of occupationally exposed asbestos workers have documented that asbestosis, diffuse pleural thickening, pleural plaques, dyspnea, and altered pulmonary function are associated with all types of exposure to asbestos. Generally, prevalence of these indices is lower among those who mine ant mill asbestos-bearing ore than among those who subsequently produce or use asbestos products.
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From page 141... ...
It concluded, "There is no evidence to indicate that inhaling fiberglass is associated with either permanent respiratory impairment or carcinogenesis; however, the final verdict as far as the latter is concerned must await the findings of long-term mortality studies." In a review article on the health effects of man-made mineral fibers, Gross (1982) concluded that "exposure has not caused an increased risk of developing lung cancer or non-malignant respiratory disease." In Table 5-5, 10 cross~ectional studies of pulmonary function and disease among workers exposed to fibrous glass or rock wool are summarized.
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From page 142... ...
Fibrous glass 340 production workers of Prevalcacc of aaa11 opacities Hill et al., 1982 whoa 81S had worked greater in hen who had worked more then 10 years. wore than 15 years in coeperi son to those who had worked leas (39S vet 9S)
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In general, no large excesses of respiratory cancer or nonmalignant respiratory disease were observed in the entire study group. However, some excesses were found upon examination of subgroups within each cohort.
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- D 14/19. were employed at some time between 1968 and 1977 Fibrous glass 2, 576 Canadian men who act rock wool worked at fess t 90 days in f ibrous glass produc tion between 1955 and 1977 woo 1 Fibrous glass, 16, 730 U S men who rock wool, worked at least 1 year and a lag in insulation produc t ion be tween 1945 and 1963.
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There in some evidence that a small excess of respiratory cancer has occurred among persons who produce MMMF-~either fibrous glass or mineral wool.
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From page 146... ...
The evidence that MMMF causes nonmalignant respiratory disease is equivocal. Although some studies have reported an excess of nonmalignant respiratory disease among fibrous glass production workers, the excess was small and was found only in a subset of the nonmalignant respiratory diseases.
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From page 147... ...
There was no significant difference in lung function, respiratory symptoms, or pneumoconiosis between workers and controls, although there was a significant increase in bilateral pleural thickening among the workers. Results of pulmonary pathology studies have also provided evidence of fibrosis in workers exposed to talc that does not contain fibers (Vallyathan et al., 1981~.
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From page 148... ...
Clinical and epidemiological data indicate that a reduction in cigarette smoking should be encouraged, especially in view of its multiplicative effect in causing lung cancer in conjunction with asbestos exposure. Those in the medical profession and the general public should be informed about the possible exposures to asbestiform fibers and the health effects resulting therefrom.
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From page 149... ...
1976. Mortality patterns among fibrous glass production workers.
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1982. Interstitial accumulation of inhaled chrysotile asbestos fibers and consequent formation of microcalcifications.
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1983. Influence of mineral fibers from noncommercial asbestos sources on the induction of neoplasia.
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1982 . Estimates of dose-response for respiratory cancer among chrysotile asbestos textile workers.
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1979. Asbestos exposure : Factors associated with excess cancer and respiratory disease mortality.
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Presented at the Biological Effects of Man-Made Mineral Fibers, Occupational Health Conference, WHO~E] JRO, Copenhagen, April 20, 1982 .
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1972b. Chemical characterization of uncoated asbestos fibers from the lungs - of asbestos workers by electron microprobe analysis.
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Presented at the Biological Effects of Man-Made Mineral Fibers, Occupational Health Conference, WHO-EURO, Copenhagen, April 20, 1982. World Health Organlsation.
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1979. Combined effects of asbestos exposure and tobacco smoking on Finnish anthophyllite miners and millers.
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Presented at the Biological Effects of Man-Made Mineral Fibers, Occupational Health Conference, WHO~EVRO Copenhagen, April 20, 1982. World Health Organization.
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1980a. The incidence of pleural mesothelioma in chrysotile asbestos textile workers.
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Presented at the Biological Effects of Manmade Mineral Fibers, Occupational Health Conference, WHO-EURO, Copenhagen, April 20, 1982. World Health Organization.
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Presented at the Biological Effects of Man-Made Mineral Fibers, Occupational Health Conference, WHO-EURO, Copenhagen, April 20, 1982. She ttigara, P
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Presented at the Biological Effects of Man-Ha de Mineral Fibers, Occupation-l Health Conference, WHO-EURO, Copenhagen, April 20, 1982. World Health Organization.
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1960. Diffuse pleural mesothelioma and asbestos exposure in the North Western Cape Province.
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1981. Pleural plaques and cigarette smoking in asbestos workers.
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