Summary.-Five groups of rats were treated by inhalation for 12 months with the U.I.C.C. preparations of the 3 main commercially used asbestos types, chrysotile, crocidolite and amosite. The experiment was designed so that the effects of both fibre mass and fibre number could be examined. The results indicated that chrysotile dust caused far more lung fibrosis than either amphibole type even when the fibre numbers in the dust clouds were similar. All malignant pulmonary neoplasms found during this study occurred in animals treated with chrysotile. The fibre-number calculations used for the generation of dust clouds were evaluated using the parameters recommended by the Health and Safety Executive in 1976, by which all fibres over 5 ,um long are counted using a phase-contrast light microscope. When fibrelength distributions were calculated using a scanning electron microscope, however, it was found that the chrysotile clouds used in this study contained many more fibres over 20 ,um long than either of the amphibole clouds. The results, therefore, support previous suggestions that long asbestos fibres are more dangerous than short. They also indicate that neither a single mass standard, nor the present fibre-number standards are satisfactory.

The pathology and dust content of lungs from 261 coalminers in relation to the appearances of their chest radiographs taken within four years of death were examined. Radiological opacities of coalworkers' pneumoconiosis were more profuse the more dust was retained in lungs. Among the men who had mined low rank coal-that is, with a relatively high proportion of ash-the increase in profusion was most closely related to the ash component of the dust, whereas in men who had mined high rank coal both coal and ash increased in the lungs in relation to radiological profusion. The fine p type of opacity was found to be associated with more dust and a higher proportion of coal and less ash than the nodular r opacity, and was also more likely to be associated with emphysema. The pathological basis of the different types of opacity found on the radiographs of coalminers related to the number, size, and nodularity of the dust lesions. Larger fibrotic lesions were likely to appear as r opacities, whereas fine reticular dust deposition was most likely to present as p opacities, q opacities showing a mixture of appearances. The study has shown that the composition of dust retained in the lung, as well as its amount, makes an important contribution to the radiographic appearances of pneumoconiosis. In particular, the r type of lesion on the radiograph of a low rank coalminer indicates the possibility of a silicotic like lesion.The relation between exposure to coalmine dust and the radiographic profusion of small opacities in simple pneumoconiosis has been well documented. '-3 The primary relation appears to be with exposure to mixed respirable dust, and no generally applicable additional effect of the ash component of the dust has been shown.3 Consequently it seems logical to suppose that radiographic opacities are due largely to an accumulation of dust and, indeed, such an association between retained dust and profusion of opacities has been clearly shownm.45Most workers, however, describe groups in which the radiological changes appear disproportionate for the amount of dust in the lungs and recognise that factors other than the mass of retained dust contribute to the radiographic picture. It has been noted, for example, that the higher the proportion of coal in the retained dust, the more dust is required to produce a given radiological category,6 and Caplan found that the radiological category was more closely associated with the profusion of fibrotic nodules in the lung than with the profusion of dust foci of all types.7The principal aim of the present study was to examine further the factors that affect the relation between the profusion of small opacities and the mass of retained lung dust. Additional aims were to determine the pathological basis for the three types of small rounded opacity and to verify the reported association of both the p type of small rounded opacity8 and irregular opacities9 with the presence of emphysema. Methods SOURCE AND CLASSIFICATION OF RADIOGRAPHSThe study was based on 261 men drawn from a...

Two studies of coke workers in Britain, comprising 6,767 men, gave similar results. The proportion of lung cancer deaths was about 20% higher than in manual workers generally. The excess occurred primarily among younger men. The ratio of lung cancers to all other cancers was also higher than expected, with limited data showing no evidence of excessive tobacco consumption. Death rates from other causes were generally favorable. Overall the lung cancer death rates in oven workers were similar to those in non-oven men, but in both studies some indications of a job-specific excess were noted. These findings are compared with results from earlier studies in the United States and Canada where a much higher excess lung cancer mortality was found in oven men, particularly those with longer exposure times. We discuss possible reasons for the differences, and conclude that the results reported now contribute further evidence that exposure to coal carbonization fumes can cause lung cancer.

The lungs of 490 British coal miners were examined for comparisons of the lesions of coal workers' pneumoconiosis with lung dust content and dust exposure. Variations were found in histological appearances that formed a range, the extremes of which indicated two separate patterns of disease. In men from high rank collieries, whose lung dust had a high carbon content and little ash, most of the nodules of simple pneumoconiosis were evenly pigmented with dust, and where progressive massive fibrosis (lesions greater than 1 cm in diameter) had developed, this appeared to be by the enlargement of a single lesion. In men from low rank collieries where the ash content of lung dust was high, the centers of the nodules were often free of dust particles and in extreme cases these lesions were very similar to silicotic nodules. If PMF developed in these cases, it often appeared to be by the fusion of closely spaced groups of smaller nodules. While there appeared to be little difference between the lung dust composition of men from high rank collieries and the dust to which they had been exposed, in men from low rank collieries the proportion of the noncoal minerals in the lungs was usually higher than it had been in the mine dust. This indicated some form of differential retention of these components, which was progressively more marked in men with the more serious grades of pneumoconiosis.

Nitrogen dioxide and nitric oxide are toxic gases which may be met in a variety of industries. Exposure of workers to high levels of nitrogen dioxide in particular may result in acute pulmonary oedema and bronchiolitis obliterans.' 2 Exposure of animals to levels around twice the threshold limit value for prolonged periods has caused pulmonary overinflation associated with obstructive lesions in proximal bronchioles, an appearance resembling, though not identical with, emphysema.34 Coalminers may be exposed to both nitrogen dioxide and nitric oxide either after shotfiring or from diesel engines. In the past such exposures have occasionally been high,56 resulting in acute pulmonary toxicity,7 and it has been suggested that such exposures have led to chronic lung damage characterised also by overinflation.7 Furthermore, it has been suggested that chronic exposure to low levels of oxides of nitrogen, as in houses using gas cookers and central heating, may lead to respiratory impairment, especially in children.89 Evidence, however, on the possible effects of relatively low level exposure in industry has hitherto been lacking.Received 3 February 1983 Accepted 18 April 1983 We have taken the opportunity of investigating the levels of oxides of nitrogen occurring in British coalmines and of categorising exposures of working miners to these gases between 1972 and 1979 to determine whether effects on the respiratory system can be detected. MethodsInvestigations were carried out in the remaining nine collieries from the National Coal Board's Pneumoconiosis Field Research (PFR). These collieries represent a wide range of mining conditions.'0 All working miners from these pits were considered in the study but only the respiratory health records of those miners exposed to relatively high or low levels of oxides of nitrogen were used. In each colliery over a 20 year period detailed records had been kept of the time spent by each miner in different occupational groups, these groups having previously been defined on the basis of exposures to dust for the purposes of the PFR.'0 A minimum of five shift average measurements of nitrogen dioxide and nitric oxide concentrations was made for each occupational group at each colliery, the samples being taken by randomly selected members of the group. 214 on 11 May 2018 by guest. Protected by copyright.