A cross-sectional epidemiological study of the respiratory health and exposure to airborne dust and quartz of current workers in opencast coalmines

1.Little is known of the influence of surface mining on the health of its workforce or on nearby communities. One recent study of US opencast coalminers showed that exposures of workers to mixed dust were on average low but sometimes rose to high levels. In the US study a few cases of pneumoconiosis were found in men who had worked only above ground. In some men this was thought to be silicosis pneumoconiosis caused by airborne quartz, judged radiologically and from past occupational histories.There is to our knowledge no published information available on the dust concentrations experienced by workers in British opencast coalmines, nor on the frequency of pneumoconiosis among them. In the absence of such information, it is difficult to say what dust or health surveillance procedures would be desirable for the industry. Under the current COSHH regulations, the industry needs to determine these procedures.Furthermore the control limit for personal exposure to airborne quartz has recently been revised, and information on dust and quartz exposures and health of opencast coalminers would inform decisions on the interpretation of the new regulations.In order to examine exposures to dust and quartz, and respiratory health, in British opencast coalminers, British Coal Opencast commissioned the Institute of Occupational Medicine to carry out an independent study of opencast coalminers in Britain.2. The aims of the study were to determine (i) the respiratory health status of workers currently employed in opencast mining in Britain; (ii) the health and dust surveillance measures which should be adopted by the industry in the future; and (iii) whether there is evidence that the dust generated by opencast mining operations affects the respiratory health of those working there.3. Nine opencast sites were selected from England, Scotland and Wales. They consisted of medium and large sites, in which conditions were thought to be representative of the majority of the industry. Preference was given to the longest operating sites, where health effects, if present, might be expected to be most easily detected. Three smaller sites were also visited to ascertain that the procedures and processes undertaken were similar to those on the larger sites. All persons listed as being employed at the nine sites were invited to attend a medical survey in mobile caravans situated near to the site offices. Chest radiographs, respiratory symptoms, smoking and occupational history questionnaires and breathing tests were employed to characterise the respiratory health status of the workforce.4. Additionally comprehensive surveys were performed of the usual exposures to airborne dust and quartz experienced by employees in each kind of job. During a two day survey at each site about sixty men on average, selected by job, wore standard modern fine respirable dust samplers on the lapel, with belt-mounted pumps, to measure their personal dust exposures, averaged over a full shift. Two similar additional one-day surveys took place at four of the sites at intervals of several weeks or months to provide information on possible seasonal or other variations in dust conditions. These measurements and inspection of the work processes were used to classify the workforce into 29 distinct occupational groups, within which exposures to dust and quartz were expected to be similar. All dust samples were weighed and analysed for quartz content.5. Airborne dust concentrations were in most cases low. Respirable airborne mixed dust concentrations, based on 626 valid samples, ranged from zero to 20mg m-3, the majority of measurements (over 98%) being below 4mg m-3. The highest dust levels were found among drillers, stemmers, shotfirers, dozer drivers and some disposal point workers. Quartz concentrations were mostly (86%) below O.lmg m-3 (the UK occupational exposure standard before 1992) and in 183 samples (29%) no quartz was detected. Exposure to quartz concentrations greater than O.lmg m-3 were found amongst the drilling/shotfiring workers and dozer drivers but not among disposal point workers. There were also 9 samples (1.4% of the total) greater than 0.4mg m-3, the new maximum exposure limit. Exposures to dust and quartz were calculated for each worker as years worked in five broad combined occupational groups representing different production stages of the mining process which were associated with dust conditions ranging from generally dust free jobs, such as office work, to dusty jobs, such as drilling.6. One thousand two hundred and forty nine employees participated in the medical surveys,including 25 women employed in non-process work. This represents 88% of the 1414 employees identified by the employers (BCC and contractors) as working on the sites at the time of the surveys. The chest radiographs were interpreted, according to the standard international method (International Labour Office, 1980), by three doctors experienced in the interpretation of radiographs of dust-exposed workers.This method requires an assessment by each reader of the profusion of small spots (opacities) on the chest radiographs, according to a twelve point scale of severity. Categories O/- and 0/0, the first and second points on the scale,would be considered normal. Category 0/1 (the third point) is on the borderline between normality and abnormality, and category 1/0, the fourth point, represents definite but slight abnormality. These assessments merely represent descriptions of the appearances (spots) on the radiograph, and do not constitute a diagnosis. Thus not all men with small opacities have pneumoconiosis, since aging, smoking and other disease can also contribute to these appearances. Some men with small opacities are likely to be found in any industrial population. For example, in a recent study of a non dust-exposed population (post office and telecommunications workers), the frequency of category 1/0 or more was 2.7%. The focus of this study has therefore been not on the frequency of pneumoconiosis but on whether radiographic small opacities are unduly frequent in this population, and to what extent they can be shown to be associated with dust exposure as well as aging and smoking. The shape of these opacities is also described by the readers according to whether they have a rounded or irregular appearance, because different relationships may be observed between the different shapes of opacities and dust exposure, age and smoking.7. In general the film readers found few radiographic abnormalities.The frequency of small opacities category 1/0 or greater was 4.4%. Years worked in the dustiest opencast jobs was significantly related to the probability of having category 0/1 profusion or greater, irrespective of the shape of the small opacities,, allowance having been made for the effects of age and smoking. The relative risk of attaining category 0/1 doubled for every ten years worked in these obs compared to an employee of the same age not exposed to dusty work. For example, the absolute risk of 2.2% of attaining category 0/1 for a non-dust exposed, non-smoker aged 40 would rise to 4.5% if the same man had worked for 10 years in the dustiest opencast jobs. For a current smoker the equivalent risks are 5.8% for non-dust exposed and 26.0% for dust exposed employees, indicating the combined effect of smoking and period of dust exposure. A significant effect was also observed for category 1/0 or greater. These relationships were also apparent when the 198 men who had previously worked as underground miners were excluded. Five men had category 2 pneumoconiosis. One of these and another man with category 1 also had progressive massive fibrosis. These men worked at four different sites, including the three sites having the highest frequency of men with category 1/0+: none of them had worked at any time as an underground coalminer.8. Chronic bronchitis persistent cough and phlegm) was reported by 13% and symptoms of asthma by 5% of the workforce at these sites. Estimates of the frequency of chronic bronchitis in other occupational populations vary according to smoking habit and occupational exposures. For example in our study of telecommunication workers it was 6% and in wool textile workers 9%. From our recent studies the frequency of asthma in the general adult population is estimated to be about 5% – 8%. The presence of these respiratory conditions was unrelated to any index of exposure to dusty opencast jobs but chronic bronchitis was associated with smoking and with years spent in dusty trades outside the opencast mining industry, such as underground coalmining, quarrying and brickmaking. 9. Lung function was measured by a simple breathing test, the results of which were not influenced by work in opencast mining. Lung function was adversely affected by smoking but was not related to dusty work within the industry. There was a suggestion that one type of breathing abnormality was associated with the length of time that men had worked in non surface mining dusty jobs, indicating the possibility of airflow obstruction (bronchial narrowing)related to previous employment outside opencast mining.10. We conclude that a small group of men working close to operations generating high airborne quartz levels have a small risk of developing pneumoconiosis.This probably, in some cases, represents silicosis (a pneumoconiosis related to quartz exposure) associated with activities involving removal of the stone overburden from the underlying coal seams. There was no evidence that opencast mining was associated with chronic bronchitis or asthma. 11. We would recommend increased measures to control dust and quartz levels in the dustier jobs followed by an annual programme of monitoring of airborne dust and quartz in the high risk occupations. All process workers should receive chest radiographs at least every three years. Follow up studies of the longer running sites would be advisable to study the influence of dust control measures on personal exposures and consequent effects on the health of the workers. Additionally a prospective study to quantify the relative risks of different exposures to quartz would provide invaluable information on the relative safety of exposure to various levels of quartz and mixed dust in the opencast mining industry, which would inform decisions on the interpretation of the new control limits. “”