Risks of respiratory disease in the heavy clay industry.

OBJECTIVES: Little information is available on the quantitative risks of respiratory disease from quartz in airborne dust in the heavy clay industry. Available evidence suggested that these risks might be low, possibly because of the presence in the dust of other minerals, such as illite and kaolinite, 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) their current and cumulative exposures to respirable mixed dust and quartz; (b) the frequencies of chest radiographic abnormalities and respiratory symptoms; (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 little as possible during recent decades. 18 were selected in England and Scotland, ranging in size from 35 to 582 employees, representing all the main types of raw material, end product, kilns, and processes in the manufacture of bricks, pipes, and tiles but excluding refractory products. Weights of respirable dust and quartz in more than 1400 personal dust samples, and site histories, were used to derive occupational groups characterised by their levels of exposure to dust and quartz. Full size chest radiographs, respiratory symptoms, smoking, and occupational history questionnaires were administered to current workers at each factory. Exposure-response relations were examined for radiographic abnormalities (dust and quartz) and respiratory symptoms (dust only). RESULTS: Respirable dust and quartz concentrations ranged from means of 0.4 and 0.04 mg.m-3 for non-process workers to 10.0 and 0.62 mg.m-3 for kiln demolition workers respectively. Although 97% of all quartz concentrations were below the maximum exposure limit of 0.4 mg.m-3, 10% were greater than this among the groups of workers exposed to most dust. Cumulative exposure calculations for dust and quartz took account of changes of occupational group, factory, and kiln type at study and non-study sites. Because of the importance of changes of kiln type additional weighting factors were applied to concentrations of dust and quartz during previous employment at factories that used certain types of kiln. 85% (1934 employees) of the identified workforce attended the medical surveys. The frequency of small opacities in the chest radiograph, category > or = 1/0, was 1.4% (median reading) and seven of these 25 men had category > or = 2/1. Chronic bronchitis was reported by 14.2% of the workforce and breathlessness, when walking with someone of their own age, by 4.4%. Risks of having category > or = 0/1 small opacities differed by site and were also influenced by age, smoking, and lifetime cumulative exposure to respirable dust and quartz. Although exposures to dust and to quartz were highly correlated, the evidence suggested that radiological abnormality was associated with quartz rather than dust. A doubling of cumulative quartz exposure increased the risk of having category > or = 0/1 by a factor of 1.33. Both chronic bronchitis and breathlessness were significantly related to dust exposure. CONCLUSIONS: Although most quartz concentrations at the time of this study were currently below regulatory limits in the heavy clay industry, high exposures regularly occurred in specific processes and occasionally among most occupational groups. However, there are small risks of pneumoconiosis and respiratory symptoms in the industry, although frequency of pneumoconiosis is low in comparison to other quartz exposed workers.

LFA-1 and ICAM-1 in homotypic aggregation of rat alveolar macrophages: organic dust-mediated aggregation by a non-protein kinase C-dependent pathway.

We have examined the role of cell adhesion molecules in the homotypic aggregation of rat alveolar macrophages after exposure to wool and grain dusts. Molecules such as bacterial lipopolysaccharide (LPS) and phorbol myristate acetate (PMA) can upregulate adhesion molecules, resulting in aggregation of lymphocytes. In rats treated intratracheally with an inspirable sample of wool dust collected from the air of British wool textile mills, and sieved grain dust, aggregates of macrophages were present in the bronchoalveolar lavage (BAL). Our hypothesis was that substances present on the dust surface could activate and upregulate adhesion molecules of the CD11/CD18 complex on the BAL cells and account for the aggregates. Macrophages from untreated rats form aggregates in vitro, which averaged 19 cells/aggregate; when treated with both wool and grain dusts, this rose to 25 and 24 cells/aggregate, respectively. LPS, PMA, and the proinflammatory cytokine tumor necrosis factor (TNF) also caused increases in aggregate size. Staurosporine, an inhibitor of protein kinase C (PKC), reduced the number of cells per aggregate from 35 cells/aggregate in LPS- and PMA-treated macrophages to 18 cells/aggregate, the same as untreated. In contrast, staurosporine had no effect in reducing the size of aggregates produced by the organic dusts. Removal of divalent cations, which are essential for maintaining integrin stability and PKC activity, resulted in complete abolition of aggregate formation. Treatment with monoclonal antibodies to lymphocyte function-associated antigen-1 (LFA-1) alpha and beta and intercellular adhesion molecule-1 (ICAM-1) resulted in the inhibition of aggregate formation in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)