Case 3: An Epidemic of Accelerated Silicosis in Oilfield Sandblasters
Background
Silicosis (the pneumoconiosis caused by inhalation of free crystalline silica dust) is perhaps the oldest recognized occupational lung disease. Epidemics of silicosis have occured repeatedly in the US since the 1890's. Sand-blasting with crystalline silica is one of the potentially most hazardous occupations for silicosis risk. In the early 1980's rising oil prices led to a production boom in the Permian Basin, and West Texas sandblasters were employed to capacity preparing pipes tanks and manifolds. Working conditions were extremely dusty (breathing zone air samples recorded respirable free silica between 400-700 µg/m3), little or no respiratory protection was used, and sand was continually recirculated until it was too fine to be no longer useful. Although abrasive blasting with crystalline silica has been banned in most industrialized nations for several decades, its use is still permitted in the US and Canada. As a result, numerous unfortunate heavily exposed workers have developed accelerated silicosis (an uncommon type of silicosis developing after very heavy exposure). The prognosis for accelerated silicosis is often of progressive disease, even after exposure ceases. A few have died, and several of them have had lung biopsies, which have been the subject of our study.
Aims of the Study
The pathology and lung particulate burden has not been well studied in accelerated silicosis. We have used our in situ quantitative methodology to determine the lung burden of inorganic particulates in several cases from this epidemic. The results in a single case and some summary data are used to illustrate applications of this analytical approach. In addition to qualitative results, the quantitative results allow examination of dose-response relationships and multivariate analyses of complex data.
Materials
Lung tissue from biopsy or autopsy was processed in the standard manner in pathology laboratories, with fixation in formalin, embedding in paraffin, preparation of 5µm sections for light microscopy, and mounting of 5µm sections on carbon discs, followed by deparaffination for SEM/EDX analysis. For qualitative analysis a region of interest, such as a silicotic nodule, was located, the inorganic particulates located using backscattered electon imaging, and individual particles analyzed by EDX. Distribution maps were also recorded. For quantitative analysis our morphometric technique developed in 1983 was used. Briefly, this consists of searching random fields at a standard magnification, counting, measuring and analyzing all particles identified in the BEI. The results provide concentrations by particle type in particles per volume of lung tissue. Results of over 800 such analyses are stored in our database and comparisons of any one or a group with other cases can be made. Statistical analyses are used to examine the relationship of lung particulate burden of one type of particle vs another with pathologic response (e.g. fibrosis) or clinical (e.g., chest x-ray, pulmonary function tests) or demographic (e.g., exposure history) information.
Discussion
As expected, some of the highest concentrations of silica in our database experience are found in this group of sandblasters. The histogram shows how the silica concentrations in this group compare to the overall database observations. The database is comprised primarily of analyses of occupationally exposed individuals, with the 'normals' or 'controls' having lung dust burdens usually <107 particles/cm3 lung. In addition to silica, aluminum silicates and metals, especially Cr and Ti (likely reflecting the paints and coatings used) were commonly found in the sandblasters' lungs. An important observation is that only the silica particle concentration (and not that of any other particle type s) correlated with the severity of lung fibrosis, chest x-ray and pulmonary function impairment. Concentrations of the different particle types observed allowed discrimination of patients by employers, likely reflecting different work materials and practices.
Conclusion
This case and epidemic brief description illustrates how analysis of lung tissue particulate burden may be useful in investigation of a single case or series of cases.
