Mortality of white South African gold miners.

OBJECTIVES: This two part study aimed to determine whether there was an excess mortality generally or for some diseases among middle aged white South African gold miners on the Witwatersrand and whether the underground dust exposure of these miners contributed to the development of lung cancer, chronic obstructive pulmonary disease (COPD), or ischaemic heart disease (IHD). METHODS: A cohort of 4925 white miners in South Africa, born between 1 January 1916 and 31 December 1930 who were alive and working in the vicinity of Johannesburg on 1 January 1970, then aged between 39 and 54, was followed up for 20 years by which time 2032 had died. Most were gold miners (about 87% had worked 85% or more of their shifts in gold mines). Standardised mortality ratios (SMRs) were calculated as percentages of the number of deaths observed in the cohort for a condition as stated on the death certificate divided by the number expected on the basis of concurrent mortality in the reference population (the total age specific white male population of South Africa). A case-control analysis was performed for three diseases (lung cancer, COPD, and IHD), the results of which are presented for those miners in the cohort who had spent at least 85% of their service on gold mines and had worked at least 15% of their shifts underground. RESULTS: The SMR for all causes of death was 129.6%, raised because of excess mortality due to the following causes: lung cancer (SMR = 139.8%), IHD (124.1%), COPD (189%) and cirrhosis of the liver (155.3%). Smoking was confirmed to be the main risk factor for lung cancer and COPD although cumulative dust exposure was found to increase the risk of COPD in conjunction with smoking. No significant risk of lung cancer resulted from exposure to dust. High blood pressure and smoking were found to increase the risk of IHD, but no association between IHD and the quetelet index (weight/height2) was found. CONCLUSIONS: The most significant and unexpected finding was the 30% increase in the SMR for all causes. Very little of this increase could be attributed to mining and the main factor for this was probably the adoption of an unhealthy lifestyle by these men (compared with other South African white men) particularly smoking (86% were smokers) and alcohol consumption.

Investigation of the relative contributions of cigarette smoking and mineral dust exposure to activation of circulating phagocytes, alterations in plasma concentrations of vitamin C, vitamin E, and beta carotene, and pulmonary dysfunction in South African gold miners.

OBJECTIVES: To determine the relative effects of cigarette smoking and mineral dust exposure on numbers and activity of circulating phagocytes, plasma nutritional antioxidant state, and pulmonary function in South African gold miners. METHODS: Pulmonary function was assessed spirometrically, whereas reactive oxidant generation by circulating phagocytes, and plasma concentrations of the nutritional antioxidative nutrients vitamin C and vitamin E and beta carotene were measured with chemiluminescence, spectrophotometry, or high performance liquid chromatography respectively. RESULTS: Cigarette smoking, but not mineral dust exposure, was associated with increased numbers and pro-oxidative activity of circulating neutrophils and monocytes, decreased plasma concentrations of vitamin C, and pulmonary dysfunction. DISCUSSION: In this study group occupational exposure to mineral dust has not been found to promote increases in the numbers or reactivity of circulating phagocytes or to be a significant cause of pulmonary dysfunction, the changes found being due primarily to cigarette smoking.

Emphysema and airway obstruction in non-smoking South African gold miners with long exposure to silica dust.

OBJECTIVE: Occupational exposure to silica dust is associated with significant impairment of lung function. The present study investigates which pathological changes in the lung are associated with impairment of lung function in silica dust exposed workers who were life-long non-smokers. METHODS: 242 South African white gold miners who were lifelong non-smokers and who had a necropsy at death were studied. The pathological features identified at necropsy were the degree and type of emphysema, the presence of airway disease, and the degree of silicosis in the lung parenchyma and pleura. These features were related to lung function tests done a few years before death, to type of impairment (obstructive or restrictive), and to cumulative silica dust exposure. RESULTS: The degree of emphysema found at necropsy was not associated with a statistically significant impairment of lung function or with dust exposure. The degree of silicosis in the lung parenchyma and the large airways disease (based on mucus gland hyperplasia) were associated with a statistically significant impairment of lung function. The large airway disease was, however, not positively associated with dust exposure or silicosis. In miners with a moderate or a higher degree of limitation of airflow the main findings were silicosis, heart disease, and obesity. The presence of small airways disease could not be established from the necropsy material. CONCLUSION: The results indicate that the level of exposure to silica dust to which these miners were exposed, without a confounding effect of tobacco smoking, is not associated with a degree of emphysema that would cause a statistically significant impairment of lung function. Silicosis of the lung parenchyma was associated with loss of lung function. Other factors that may play a part in impairment of lung function in these miners are obesity and heart disease.

Occupational noise exposure and blood pressure: longitudinal and cross-sectional observations in a group of underground miners.

The question of an association between occupational noise exposure and blood pressure has important public health implications. The harmful effects of hypertension are well known, and noise is considered the most pervasive of all occupational exposures. Most previous studies have looked cross-sectionally at blood pressure and noise exposures in workers. The present study examined historic medical and personnel records of 2,197 white male South African miners. At approximately 3-y intervals, the job title, diastolic and systolic blood pressures, height, weight, and use of medication for hypertension were recorded. Noise levels were estimated, based on noise measurements of individual jobs and work areas. In the cross-sectional analyses, multiple linear regression was used with blood pressure as the dependent variable; age, body mass index (BMI), and noise exposure were the independent variables. Longitudinal analyses were performed for those miners who had observations at four or more time periods, by calculating regression coefficients for individuals for blood pressure and noise, controlling for age and BMI. Additional longitudinal analyses compared blood pressure changes between two points in time for individual miners with changes in noise exposure, controlling for changes in age and BMI. The results of the cross-sectional and longitudinal analyses indicated no association between blood pressure and noise exposure. On the basis of these results, it does not appear that occupational noise exposure has an effect on blood pressure. Inconsistencies in the literature and shortcomings in the present study indicate that additional study is needed.

Correlation between radiological and pathological diagnosis of silicosis: an autopsy population based study.

The radiological findings for the profusion of rounded opacities were compared to pathological findings for parenchymal silicosis in 557 gold miners who had, on average, 2.7 years between the radiological and pathological examination. Three readers read the radiographs, and ILO category 1/1 or more was defined as a positive diagnosis of silicosis. The sensitivity values were 0.393, 0.371, and 0.236, and the specificity values were 0.987, 0.965, and 0.978, for the three readers, respectively. The sensitivity of the readers improved with increasing degree of autopsy silicosis, but a large proportion of those with a moderate and marked degree of silicosis were not diagnosed radiologically. The diagnostic sensitivity of the radiological test could be improved by using category 0/1 as a cutoff point for workers exposed to a high average concentration of respirable silica dust. The diagnostic specificity of radiology could be improved by using category 1/0 or 1/1 as a cutoff point for a positive diagnosis for workers exposed to a low average concentration of respirable silica dust.

Risk of silicosis in a cohort of white South African gold miners.

The risk of silicosis was investigated in a cohort of 2,235 white South African gold miners who had, on average, 24 years of net service from 1940 to the early 1970s and who were followed up to 1991 for radiological signs of onset of silicosis (ILO category 1/1 or more). There were 313 (14%) miners who developed signs of silicosis at an average age of 55.9 years. The latency period was largely independent of the cumulative dust exposure. In 57% of the silicosis, the radiological signs developed, on average, 7.4 years after mining exposure ceased. The risk of silicosis increased exponentially with the cumulative dust dose, the accelerated increase being after 7 mg/m3-years. At the highest exposure level of 15 mg/m3-years, which represents approximately 37 years of gold mining at an average respirable dust concentration of 0.4 mg/m3, the cumulative risk for silicosis reached 77%. In conclusion, the risk of silicosis was strongly dose dependent; however, the latency period was largely independent of the dose.

The mortality of amphibole miners in South Africa, 1946-80.

A cohort was established in 1981 of all 7317 white male employees in the amosite and crocidolite mines in South Africa whose names had appeared in the personnel records (initiated between 1945 and 1955) of the major companies. Some of the men had been employed as early as 1925, but only 8% had had more than 10 years of service. Three subcohorts were defined: 3212 men whose only exposure to asbestos was to amosite; 3430 exposed to crocidolite; and 675 to both amphiboles. No deaths or losses to view occurred before 1946, and 5925 men (81%) were known to be alive at the end of 1980. Losses to view numbered 167 (2%), and there had been 1225 deaths (17%), an excess of 331 over the number of deaths expected on the basis of the mortality of all white South African males. The fibre related excesses were of mesothelioma, lung cancer, and other respiratory diseases, but there were other excesses perhaps mainly related to socioeconomic factors including lifestyle. When cause of death was determined according to "best evidence" (after study of clinical, radiological, biopsy, and necropsy reports in conjunction with the death certificate), there were 30 deaths due to mesothelioma (22 pleural, six peritoneal, two other) and 65 due to cancer of trachea, bronchus, and lung. Various analyses of these deaths showed that crocidolite had higher toxicity than amosite for lung cancer and this was most pronounced for mesothelioma; there can now be no question that crocidolite is far more dangerous than amosite at least in so far as mesothelioma is concerned. Nevertheless, crocidolite induced mesothelioma appeared only in men who had been exposed for long periods, at least 12 months, but on average about 15 years.

Distribution of silicotic collagenization in relation to smoking habits.

Controversy regarding the association between silicosis and lung cancer has been clouded by the fact that studies examining this association generally do not include information on smoking. A causal association between smoking and silicosis would seriously confound the association between silicosis and lung cancer. The current analysis assessed the association between silicosis and smoking using data on deceased white gold miners who underwent postmortem examination between 1976 and 1981. Smoking histories and exposure information were available. A subset analysis in a group of deceased miners for whom more detailed smoking and exposure information was available confirmed the findings of the larger analysis. Both analyses showed a slight inverse relationship between smoking and silicotic collagenization of the parenchyma and a stronger negative relationship between smoking and silicotic collagenization of the pleura, controlling for age and cumulative exposure to silica dust. No association between silicotic collagenization of the hilar glands and smoking was detected. The data should not be construed as advocating that workers exposed to silica dust should smoke. The hazards of cigarette smoking are likely to far outweigh the hazards of silicosis. The data suggest that the lack of smoking histories in studies of the association between silicosis and lung cancer probably does not seriously confound risk estimates. The distribution of silicotic collagenization in the lungs of smokers and nonsmokers is consistent with enhanced mucus interception, more central deposition in the lungs, and proportionally more lymphatic clearance to the hilum (as opposed to the pleura) of silica particles in smokers compared to nonsmokers.

Emphysema type in relation to silica dust exposure in South African gold miners.

The relationship between silica dust exposure in gold mines and the type of emphysema was studied in a group of 1,553 white gold miners who had undergone autopsy examination between 1974 and 1987. Of particular interest was the contrast between centriacinar and panacinar emphysema as they relate to silica exposure and the presence of silicosis. Subjects with significant emphysema, that is, with an emphysema score of 30% or more, were classified as having predominantly panacinar or predominantly centriacinar emphysema, and compared to those without emphysema (emphysema score less than or equal to 10%). Of those who had significant emphysema (greater than or equal to 30%), 24% had predominantly panacinar, 43% predominantly centriacinar, and 33% were classified as mixed. The odds ratios (OR) for the association between each emphysema type and dust exposure (one unit of the cumulative dust index) were found to be statistically significant and of equal magnitude [1.019, with a 95% confidence interval (CI) of 1.005 to 1.033 for panacinar and 1.019 with a 95% CI of 1.007 to 1.031 for centriacinar emphysema]. In 163 nonsmokers insignificant panacinar emphysema was more common than centriacinar emphysema. The results indicate that a miner with 20 yr in high-dust occupations has a 3.5 (1.7;6.6) times higher odds of having a significant degree of emphysema at autopsy than a miner not in a dusty occupation. This is likely to be true of smoking miners only because there were only four nonsmokers with an emphysema score between 30 and 40%.(ABSTRACT TRUNCATED AT 250 WORDS)

Asbestos disease at low exposure after long residence time in amphibole miners.

Short reports of several studies carried out in South Africa which have a bearing on the health effects of low exposures to asbestos are presented. It is stressed that the findings refer solely to amphibole asbestos. Average fiber exposure of 1 or less or a cumulative exposure of less than 2-5 fibers/ml years is associated with the development of asbestosis increasing in frequency with residence time.

Silica exposure, silicosis, and lung cancer: a mortality study of South African gold miners.

The effects of exposure to gold mining dust with a high concentration of free silica and tobacco smoking on mortality from lung cancer was assessed in a sample of 2209 white South African gold miners who started mining exposure during 1936-43, and were selected for a study of respiratory disorders in 1968-71 when they were aged 45-54. The mortality follow up was from 1968-71 to 30 December 1986. The relative risk for the effect of dust cumulated to the start of the follow up period was estimated as 1.023 (95% confidence interval (CI) 1.005-1.042) for a unit of 1000 particle-years. The combined effect of dust and tobacco smoking was better fitted by the multiplicative model than the additive model, suggesting that the two exposures act synergistically. No association between lung cancer and silicosis of the parenchyma or pleura was found, but a positive association existed between silicosis of the hilar glands and lung cancer.

Combined effect of silica dust exposure and tobacco smoking on the prevalence of respiratory impairments among gold miners.

The combined effect of underground gold mining dust with a high content of free silica and tobacco smoking on the prevalence of respiratory impairment was examined among 2209 South African gold miners and 483 nonminers. The subjects were grouped as having normal function; minimal, moderate or marked obstruction; marked obstruction with restriction; or pure restriction on the basis of their lung function profiles. Each profile group was compared with the normal group for exposure prevalences, and additive and multiplicative relative risk models were applied to test for departure from the additivity of individual effects. Departure from additivity was found to increase progressively with the severity of obstructive impairment. The results indicated that approximately 94% of the cases with the most severe respiratory impairment (N = 191) could have been prevented through the elimination of tobacco smoking. In conclusion, tobacco smoking was found to potentiate the effect of dust on respiratory impairments.

Evidence for an amphibole asbestos threshold exposure for asbestosis assessed by autopsy in South African asbestos miners.

In an attempt to determine whether there exists a threshold asbestos dose below which asbestosis does not occur, data on 807 men who had worked on amphibole asbestos mines and undergone autopsy were analysed. When exposure was expressed as fibre-years no asbestosis was found at autopsy when exposure was up to 2 fibre-years, even after 31-45 years of residence time. In the group exposed to greater than 2-5 fibre-years asbestosis was found. When exposure was expressed as average fibre concentration asbestosis occurred below 2 fibres per ml (f ml-1) and the prevalence increased with residence time. In conclusion, if a threshold dose for asbestosis does exist it is at approximately 2 fibre-years if off-shift exposure is ignored.

Silica exposure, silicosis, and lung cancer: a necropsy study.

Recent studies of the association between lung cancer and silicosis and silica dust have been inconclusive; some showing positive association and some showing none. The present study matched 231 cases of lung cancer with 318 controls by year of birth. Subjects were selected from the necropsy records of the National Centre for Occupational Health. Data on intensity and duration of exposure to silica dust were obtained from personnel records. Presence or absence of lung cancer and the presence and severity of silicosis of the parenchyma, pleura, and hilar glands were documented from necropsy reports. Smoking data were abstracted from records of routine examinations. No case-control differences were noted for any of the exposure indicators including cumulative dust exposure, total dusty shifts, weighted average intensity of exposure, total underground shifts, and shifts in high dust. Similarly, no association was found between lung cancer and the presence or severity of silicosis and any site. Stratified analyses showed neither significant nor suggestive trends when case-control comparisons for silicosis were examined by level of dust exposure or smoking. Reasons for disparity between these results and those of some other studies may include concomitant exposures to radon daughters, asbestos, diesel emissions, and cigarette smoking; idiosyncracies of the compensation process; and the possibility of a threshold in the relation(s).

Progression of irregular opacities in asbestos miners.

All white and mixed race men who were employed in South African asbestos mines and mills between 30 November 1970 and 30 November 1975 were studied. The men who had two radiographs available, the first taken some time between the above two dates and the latest available radiograph which had to be at least two years after the first one numbered 1454: 793 continued exposure after the first radiograph and 661 did not. The films were read by a panel of three readers. Data available included age, years of exposure to asbestos and other mining, intensity of exposure to asbestos and other dust, and smoking habit. Progression was expressed as the difference between the average readings of radiograph 2--radiograph 1 in minor categories per year of irregular opacities. Changes in pleural abnormality were also measured. No differences of progression in the profusion or change in size of the irregular opacities were found between the two groups or in the number of zones affected. "New attacks" appeared equally frequently between the two groups. No difference in the change in extent of any type of pleural change was seen. It appears that once a dose of asbestos sufficient to initiate the disease has been retained it is inexorably progressive.