An analysis of historical total and respirable silica (14808607) dust exposures in the Chinese mining and pottery industries was performed. Current data on total and respirable silica dust exposures collected in iron and copper mines were combined with a retrospective job exposure matrix that used exposure information where available on the free silica content of dusts to estimate total and respirable silica dust exposures in 20 mines (ten tungsten, six iron and copper, and four tin mines) and nine pottery factories for the period 1950 to 1987. Altogether, 6,805 historical estimates based on 2.1 million industrial hygiene monitoring data points were obtained information were constructed. Across all facilities combined, the mean total dust exposures during the periods 1950 to 1959, 1960 to 1968, 1969 to 1980, and 1981 to 1987 were 17.6, 6.26, 4.91, and 3.85mg/m3, respectively. The corresponding mean respirable silica dust exposures were 3.89, 0.90, 0.56, and 0.43mg/m3. By specific industry and across the 1950 to 1987 period, total dust exposures decreased from 11.82 to 10.44mg/m3 in the pottery industry, from 18.09 to 1.65mg/m3 in the tungsten mines, from 13.61 to 3.11mg/m3 in the iron and copper mines, and from 21.19 to 2.63mg/m3 in the tin mines. The respirable silica exposures in these industries averaged across the 1950 to 1987 period were 0.71mg/m3 in the pottery factories, 1.75mg/m3 in the tungsten mines, 0.32mg/m3 in the iron and copper mines, and 1.31mg/m3 in the tin mines. The mean respirable silica exposures averaged across the entire 38 year period rations were: underground mining 1.43mg/m3, surface mining 0.67mg/m3, and ore dressing 1.27mg/m3. Within the pottery industry, mud preparation workers employed as ore mixers had the highest respirable silica exposures.
Dr Mustafa Dosemeci, Occupational Studies Section, National Cancer Institute, Building EPN, Room 418 Rockville, MD 20892, USA.