Risk of asbestosis in crocidolite and amosite mines in South Africa.

X-rays of all while and mixed-race men employed in crocidolite and amosite mines and mills were read independently by three experienced readers according to the ILO U/C classification. Abnormality was regarded as present if reported by two or more readers. Parenchymal abnormality, defined as the presence of small irregular opacities of profusion 1/0 or greater, was found in 7.3% of the workers. Pleural thickening was found in 4.5% of the workers, costophrenic angle obliteration in 3.2%, and pleural calcification in 1.7%. The prevalences of both pleural and parenchymal abnormality were strongly related to the duration of exposure to asbestos at work. The overall prevalence of abnormality increase from 4.0% in men with exposure for 1 year or less to 47.9% in men with more than 15 years of exposure. After taking into account the effects of age and duration of asbestos exposure, the prevalence of pleural abnormality was not predicted by fiber concentration. However, white men working with amosite tended to develop a higher prevalence of pleural abnormality than did those working with crocidolite. Compared to whites, men of mixed race, who only work with crocidolite, had a high prevalence of pleural abnormality in each exposure duration category. In contrast to pleural abnormality, the prevalence of parenchymal abnormality, after taking into account the effects of age and duration of exposure, was significantly predicted by fiber concentration but not by race or asbestos type. Our results suggest that parenchymal abnormality in workers in South African asbestos mines could be largely prevented by reducing exposure to fibers visible under the light microscope. However, this may not be the case for pleural abnormality.

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.

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.

Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa.

A cross-sectional radiological survey of 2,245 men who were employed in South African asbestos mines was conducted in 1976. Since 1976, the lungs of 172 of these men who died have been examined to establish the presence of asbestosis or other pneumoconiosis. The x-ray readings (ILO/UC 1971) were compared with the pathological findings. A high prevalence of false positive readings, particularly for two of the three readers, was found. False negative readings were also very prevalent. Detailed information about asbestos and other mining exposure, smoking habit, age, height, and weight were examined to determine what influence they may have had in inducing false positive findings. Other dust exposure and smoking appeared to be possible factors, whereas age and obesity were probably not. It is suggested that the term "small irregular opacities" requires more precise definition.

Active pulmonary tuberculosis discovered at post-mortem examination of the lungs of black miners.

The prevalence of active pulmonary tuberculosis and pneumoconiosis in black mine workers who died while working on mines and came to autopsy is reported. All black mine workers are regularly examined radiologically during life and those with pulmonary tuberculosis or pneumoconiosis are compensated and sent home (after treatment in the case of tuberculosis) and would not enter this autopsy series. Details are given of the prevalence of tuberculosis separately for gold, coal and asbestos miners. Tuberculosis was age-related in all three cases. In black gold miners the presence of a slight degree of silicosis not detected radiologically in life was associated with a significantly increased prevalence of pulmonary tuberculosis compared to gold miners without silicosis. This was not found to be the case in those in whom asbestosis or coal workers' pneumoconiosis was found at autopsy.

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.

Change in the prevalence of active pulmonary tuberculosis discovered at autopsy in black miners.

The prevalence of active pulmonary tuberculosis at autopsy in two groups of Black miners who had died while working on the mines during the periods 1961-1963 and 1974-1978 was investigated. Radiographs had been taken regularly in both groups while they were alive to detect early tuberculous lesions. If any such lesions were found, the worker was excluded from the populations which were being studied. A highly significant secular decrease in the prevalence of active pulmonary tuberculosis was found. Possible explanations for this finding are discussed and it is concluded that there may be a decline in the incidence of tuberculosis in Blacks.

Forced expiratory volume and expiratory flow rate in Black miners and in a control group.

The peak expiratory flow rate and the forced expiratory volume and 1 second were measured in 772 Black miners who did not have pneumoconiosis, tuberculosis or chronic bronchitis. The same tests were done in 164 non-mining workers. It was found that exposure to dust associated with the miners' work had no effect on the results of these tests.

Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers.

A statistically significant association between cigarette smoking and radiologic readings of irregular opacities was observed in a case-control study of 430 South African asbestos miners (OR = 3.03; 95% confidence interval, 1.50; 6.11). In another case-control study of 487 dead South African asbestos miners, no positive association between smoking and autopsy findings for asbestosis was observed (OR = 0.50; 95% confidence interval, 0.20; 1.29). The association between greater than slight asbestosis (moderate and marked) and smoking (yes/no) was not significant (Fisher's exact test, p = 0.44), and the adjusted odds ratio was 1.25 with 95% confidence interval (0.20; 7.78). In addition, the certification in life for asbestosis, based on chest roentgenogram readings for irregular opacities, was also found to have a tendency to be related to smoking. Thus, the findings of these studies do not support the hypothesis that smoking is associated with the presence of asbestosis at autopsy or that smoking and asbestos dust act synergistically in producing asbestosis at autopsy. But the findings of this and other studies suggest that smoking does produce some change in the lung structure that can be visible on the roentgenogram and can be wrongly interpreted as irregular opacities caused by asbestosis.

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.

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.

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 posterior pleural junction line in pneumoconiosis. A report of 3 cases with thickening.

Disease may change the position or cause thickening or distortion of the posterior pleural junction line. Pleural changes associated with silica or asbestos exposure may also result in radiologically recognisable thickening of the line. Three examples are presented.

Hearing loss in white South African goldminers.

Hearing thresholds of 2,667 white South African goldminers were determined in a cross-sectional survey. Median hearing thresholds at 1,000 Hz were comparable to those expected for men living in a developed society. For the frequencies 3,000-6,000 Hz, which are most affected by industrial noise, hearing thresholds were greater than expected and worsened with age relative to expected losses. The percentage of social impairment of hearing ranged from 0% in the youngest age group to 21.6% among those 58 years of age and over. Data from two surveys on the use of hearing protection indicate that it increased from 13.2% in 1979 to 17.2% in 1982. This level is probably still too low given the pervasiveness of noise in the goldmining industry. Some of the difficulties associated with a hearing conservation programme in the industry are discussed.

Prediction equations for lung function in black industrial workers at Palabora Mining Company.

In the course of a study on the health effects of vermiculite, 653 black rural industrial workers had their lung function measured. Since the study revealed no health effects of their industrial environment, the group was used to determine prediction equations for black men. Vital capacity, forced vital capacity, forced expiratory volume in 1 second, and peak flow were appreciably higher than the predicted values for blacks in the USA. The predicted values were, however, lower than those reported for white non-smokers but significantly higher than those reported for a non-smoking group of black miners in South West Africa/Namibia.