Risks of respiratory disease in the heavy clay industry

Objectives-Little information is available on the quantitative risks of res piratory disease from quartz in airborne dust in the heavy clay industry. A vailable evidence suggested that these risks might be low, possibly because of the presence in the dust of other minerals, such as illite and kaolinit e, which may reduce the harmful effects of quartz. The aims of the present cross sectional study were to determine among workers in the industry (a) t heir current and cumulative exposures to respirable mixed dust and quartz; (b) the frequencies of chest radiographic abnormalities and respiratory sym ptoms; (c) the relations between cumulative exposure to respirable dust and quartz, and risks of radiographic abnormality and respiratory symptoms. Methods-Factories were chosen where the type of process had changed as litt le as possible during recent decades. 18 were selected in England and Scotl and, ranging in size from 35 to 582 employees, representing all the main ty pes of raw material, end product, kilns, and processes in the manufacture o f bricks, pipes, and tiles but excluding refractory products. Weights of re spirable dust and quartz in more than 1400 personal dust samples, and site histories, were used to derive occupational groups characterised by their l evels of exposure to dust and quartz. Full size chest radiographs, respirat ory symptoms, smoking, and occupational history questionnaires were adminis tered to current workers at each factory. Exposure-response relations were examined for radiographic abnormalities (dust and quartz) and respiratory s ymptoms (dust only). Results-Respirable dust and quartz concentrations ranged from means of 0.4 and 0.03 mg.m(-3) for non-process workers to 10.0 and 0.62 mg.m(-3) for kil n demolition workers respectively. Although 97% of all quartz concentration s were below the maximum exposure limit of 0.4 mg.m(-3), 10% were greater t han this among the groups of workers exposed to most dust. Cumulative expos ure calculations for dust and quartz took account of changes of occupationa l group, factory, and kiln type at study and non-study sites. Because of th e importance of changes of kiln type additional weighting factors were appl ied to concentrations of dust and quartz during previous employment at fact ories that used certain types of kiln. 85% (1934 employees) of the identifi ed workforce attended the medical surveys. The frequency of small opacities in the chest radiograph, category greater than or equal to 1/0, was 1.4% ( median reading) and seven of these 25 men had category greater than or equa l to 2/1. Chronic bronchitis was reported by 14.2% of the workforce and bre athlessness, when walking with someone of their own age, by 4.4%. Risks of having category greater than or equal to 0/1 small opacities differed by si te and were also influenced by age, smoking, and lifetime cumulative exposu re to respirable dust and quartz. Although exposures to dust and to quartz were highly correlated, the evidence suggested that radiological abnormalit y was associated with quartz rather than dust. A doubling of cumulative qua rtz exposure increased the risk of having category greater than or equal to 0/1 by a factor of 1.33. Both chronic bronchitis and breathlessness were s ignificantly related to dust exposure. Conclusions-Although most quartz concentrations at the time of this study w ere currently below regulatory limits in the heavy clay industry, high expo sures regularly occurred in specific processes and occasionally among most occupational groups. However, there are small risks of pneumoconiosis and r espiratory symptoms in the industry, although frequency of pneumoconiosis i s low in comparison to other quartz exposed workers.