Epidemiological studies of respiratory health and dust exposure in hard rock quarry workers and ex-workers

This work forms part of a joint study between the Institute of Occupational Medicine and the Health and Safety Executive’s Epidemiology and Medical Statistics Unit (EMSU) designed to answer the following research questions: what are (1) the relationships between indices of exposure to respirable dust, including silica, and radiographic abnormalities in quarry and ex-quarry workers and (2) the relationships in quarry and ex-quarry workers between exposure to respirable dust including silica, and mortality from all causes, and from pneumoconiosis, lung cancer and chronic obstructive pulmonary disease. This report addresses the first objective only; the mortality study has principally been conducted and will be reported by EMSU.Under the ‘Owners’ control scheme for respirable dust’, owners of all 100 hard rock quarries in Scotland agreed to participate in a study of dust conditions at these quarries and chest radiographic abnormalities in current workers. Data gathered during a series of compliance monitoring dust surveys, repeated approximately every six months, have been obtained as part of this scheme since 1984 by either the IOM or the quarry owners. The majority of dust samples, (all personal samples), were analysed by the IOM and a smaller number were analysed by two other laboratories. At least one survey was carried out at 85 and at least five surveys for 28 quarries included in the research. No quarry was surveyed more than six times.These dust data were supplemented by three one-week dust sampling exercisescarried out at four of the quarries to investigate variations due to weather, season,workplace conditions, occupation, rock type, etc. Some duplicate samples werealso obtained. All dust samples were analysed either by infraredspectrophotometry, or, in some IOM analyses, by X-ray diffraction. The IOM collated and stored the results of as many of the routine surveys as were made available.Seventy quarries participated in a medical survey of their current employees. Full size chest radiographs were taken and questionnaires on smoking and occupational histories were administered to all available employees.The quarry owners were also asked to co-operate in the tracing of ex-workers and, on the basis of a range of different rock types and good personnel records, 26 quarries were selected and agreed to take part in an additional medical survey of men who had previously worked at these quarries. Men traced through quarry and other records were invited to participate. Where possible these surveys were carried out in the lOM’s mobile X-ray unit sited at a participating quarry or at a location near to one or more quarries (61% of surveys of current workers). British Coal’s Radiological Service carried out a smaller proportion of X-ray surveys of current workers (33%) and local-hospital radiography departments took chest radiographs of men who did not live close to a conveniently located site or if numbers in a particular area were small. Such men were interviewed by trained IOM personnel.Eighty per cent of the identified quarries participated in the dust surveys and 70% took part in medical surveys: the remainder having closed or refused or being ineligible for inclusion in the “”Owners’ scheme””. Eighty seven per cent of 1322 current employees attended the medical survey and 34% of 1244 identified leavers agreed to participate in a medical survey. However, only 64% of these men actually attended.Chest radiographs of current workers were read for clinical purposes and, on the basis of pneumoconiosis observed at three of the quarries, two additional quarries were included in the leavers’ study (the third had already been selected on theprevious criteria) but were excluded from the estimation of prevalence of pneumoconiosis among leavers owing to their non-random selection. The appearances on radiographs were interpreted by a panel of three physicians experienced in the assessment of pneumoconiosis according to standard criteria (ILO 1980) for profusion and shape of small opacities, both individual and median readings being used in the subsequent analyses. A group of 300 radiographs of non-dust exposed employees and ex-employees from another industry were also included in these readings for comparison purposes.Results of compliance monitoring dust surveys indicated a wide range of respirable dust and quartz concentrations, which in many cases exceeded the concurrent occupational exposure limits for quartz (O.lmgm-3, now changed to a maximum exposure limit of 0.4mgm-3). Crusher and screens operators had on average the highest concentrations; quartz concentrations, which were dependent on rock type, were mostly greater than O.lmgm-3 in a few occupations at certain quarries extracting rock with a high quartz content.The detailed research environmental surveys confirmed the differences in dust concentrations between occupations (workers at crushers and screens being highest) and also demonstrated clear seasonal effects: in winter dust concentrations wereabout half those in the summer. Some of these reductions in concentrations were related to improved equipment at the quarries. Dust concentrations measured during compliance surveys were higher than during research surveys at three out ofthe four quarries: the measurements at the fourth were similar. Quartz concentrations at all surveys showed a similar pattern to the dust concentrations except for one quarry where the differences in concentration were no longer apparent.Overall dust and quartz concentrations were of the same order of magnitude during compliance and research surveys: where the compliance values were higher this could be attributed to seasonal factors, replacement of equipment between surveys and to a lesser extent exclusion of less dusty jobs during compliance monitoring.During a survey at one of the four special quarries fibres of amphibole asbestos were found in airborne dust near to the crushers, probably as a result of metamorphic changes in the parent rock. Concentrations as high as 0.57 fibres ml-1 were observed at a tertiary crusher.Lifetime dust and quartz exposures were estimated from the 70 quarries for which medical data were also available. A total of 1505 samples was available for examination of the: effects ; ofpotential-explanatory factors, such as year and seasonof sample, rock. type and occupation. Lifetime cumulative dust and quartz exposures were estimated from these data and occupational histories.One thousand one hundred and forty nine current workers attended the medical surveys (including 32 women, none of whom had any significant radiographic abnormalities). Overall 8.2% of 1117 male workers had a median profusion of small opacities of category 0/1 or greater and 4.7% had category 1/0 or greater. The highest profusion observed was category 3/3 and all three readers observed large opacities on only two radiographs. Two hundred and eight radiographs of the 241 leavers examined were available for derivation of prevalence of radiological abnormalities. Median profusions of 11.7% and 6.8% were observed for category 0/1+ and 1/0+ respectively. The highest median profusion obtained was 2/2 and only two radiographs were classified as having any large opacities by two out of three readers. The same readers’ classification of the radiographs of employees from the non-dustry industry gave 3.7% (2.8% among currently employed workers) with a median profusion of category 1/0 or more. Amongst both current and ex-workers frequency of radiographic abnormality increased with age and smoking habit. Only one man with category 2/1 or more had spent more than three years in dusty occupations other than quarrying.After allowing for age and smoking habits the profusion of small opacities was greater in current quarry workers with higher cumulative dust, but not quartz, exposures: a cumulative dust exposure of 40ghm-3 (approximately equivalent to 13 years exposure as a crusher or screens operator) increased the risk of developing median profusion of category 0/1+ or 1/0+ by a factor of 1.4 (95% confidence limits: 0.97, 2.2). However, analysis of the results for the median reading at the 28 quarries at which leavers were also examined did suggest an increased prevalence of small opacities (1/0+) among current men with increasing cumulative quartz exposure (significant at the 5% level), but this effect was significantly less for leavers. Conversely, results from one reader suggested that there was no effect of quartz exposure among current men but a significant additional effect of quartz in leavers.We conclude that with appropriate precautions there are sufficient similarities in the methods of dust sampling during routine compliance monitoring and special research surveys to justify the use of compliance monitoring data for epidemiological research purposes, although there are practical difficulties in using routine rather than specially collected data. The prevalence of radiological abnormality among Scottish current and ex-quarry workers is slightly greater than that observed among a group of non-dust exposed workers. However, we have demonstrated a clear association between cumulative exposure to respirable quarry dust and increased risk of developing profusion of small opacities, an effect which is more marked for ex-quarry workers. A relationship among current workers between cumulative quartz exposure and radiological abnormality suggests that some of this abnormality may represent silicosis. The quarry industry should take suitable measures to reduce the dust levels in the dustiest occupations in the industry.There is a relative risk of 17.4 that a quarry worker would attain category 1/0 or more if he had worked for 30 years in a respirable dust concentration of 5mgm-3, compared to a non-dust exposed worker of similar age and smoking habit. This increased risk was statistically significant for the readings of one film reader. Such risks cannot be stated with any degree of reliability in relation to quartz exposure.Additional studies are therefore, recommended to improve exposure and risk estimates by interviews ;of quarry -staff at all participating quarries to obtain detailed quarry histories and working practices. Estimates of past concentrations could then be revised in the light of these histories, allowance being made for seasonal effects and different lengths of the working week. Additional refinements might be needed to address the problems associated with quartz exposure. “”