Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust m onitoring data, are being conducted by the National Institute for Occupatio nal Safety and Health (NIOSH) and Tongji Medical University in China. The g oal of these projects is to establish exposure-response relationships for t he development of diseases such as silicosis or lung cancer in cohorts of p ottery and mine workers. It is necessary to convert Chinese dust measuremen ts to respirable silica measurements in order to make results from the Chin ese data comparable to other results in the literature. This article descri bes the development of conversion factors and estimates of historical respi rable crystalline silica exposure for Chinese workers. Ambient total dust c oncentrations (n > 17 000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988-1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional C hinese samplers in 20 metal mines and nine pottery factories in China. Thes e data were used to establish conversion factors between respirable crystal line silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988-1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/cop per, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tun gsten mines. Conversion factors for individual facilities within each indus try were also calculated. Analysis of variance revealed that mean conversio n factors are significantly different among facilities within the iron/copp er industry and within the pottery industry. The relative merits of using f acility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the hist orical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations. Published by Elsevier Science Ltd on behalf of Briti sh Occupational Hygiene Society.