A study of the importance of dust composition in relation to pneumoconiosis in coalminers. Final report on CEC Contract 6253-32/8/018

During the first ten years of the Pneumoconiosis Field Research, dust samples were taken with the standard thermal precipitator (STP). The quantity of dust collected in this way was too small for compositional analysis using the infra-red methods adopted for the analysis of respirable dusts taken with MRE gravimetric samplers during the later period of the research. For this reason studies of the importance of quartz and other minerals in coal workers’ pneumoconiosis made use of interference microscope determinations of the mineralogical composition of the STP samples.Subsequent development of a micro infra-red (IR) method for quartz analysis provided the possibility of obtaining more reliable data for the STP samples. This report describes the application of the micro infrared technique to the analysis of the old STP samples and examines the new data in relation to the previous compositional and pneumoconiosis progression data.The micro analysis technique has now been developed to recover and bulk thermal precipitator dust deposits for weighing and the determination of the ash, quartz, kaolin and mica contents. The technique was initially used to analyse STP dust samples retained from previous comparative field trials of the standard thermal precipitator and the MRE gravimetric sampler. The compositions of these STP samples were compared with the data previously obtained for the simultaneously sampled MRE respirable dusts using ashing and infra-red techniques. The analytical results for other bulked STP dusts could then be adjusted for instrumental bias to give values comparable with the compositions of respirable dusts. A representative selection of the STP samples taken during the first ten years of the Pneumoconiosis Field Research were analysed by the new technique. These samples were equivalent to those evaluated by interference microscopy for the previous study of the effect of dust composition in coalworkers’ pneumoconiosis. After adjustment of the STP results for instrumental bias, it was found that the new micro IR data from the STP samples were in agreement with the IR compositions of respirable dust sampled in the second ten-year period of the Pneumoconiosis Field Research. However, the estimates of quartz, kaolin and mica in the STP samples were generally higher by the micro IR technique than by interference microscopy. he differences observed between the two analytical techniques showed considerable variation both within and between collieries.In the previous study, the attack rate of pneumoconiosis among a group of 3154 faceworkers was examined as a function of the individual exposures to respirable dust and its various mineral constituents, derived from the interference microscope measurements of composition. Corresponding exposures have not.yet been calculated directly from the micro IR analysis data, but the previously calculated exposures have been adjusted on a colliery basis to take account of the differences between the two sets of compositional data. Use of the adjusted exposure values in place of the original values resulted in only small changes in the dust-disease correlations. The estimates of pneumoconiosis progression at individual collieries from the regression equations, differed little from those based directly on the interference microscope data. Thus, the data from the re-analysis of STP samples from the first ten years of the Pneumoconiosis Field Research have not, as yet, explained the substantial variations between the observed and expected values of progression at individual collieries. In addition, the revised correlations between dust exposure and disease have not indicated any notable effects of dust composition on the progression of coalworkers’ pneumoconiosis. It is concluded that the mass concentration of respirable dust, unadjusted for composition, remains the most suitable index of the dust hazard in British coalmines. A further opportunity to study the effects of composition in pneumoconiosis will be possible when the individual exposures for the second ten years of the research are computed for X-ray/dust exposure correlations. It will also be possible at this stage to derive individual exposures directly from the micro-analysis data for the first ten-year period.