[Evaluation of historical exposure to silica dust for the workers employed in geologic exploration industry]

To evaluate their level of exposure to silica dust in the workers employed in geologic exploration industry using a quantitative method.

Monitoring data of exposure to silica dust since 1950s were collected for the workers in various jobs from the factories and mines of the bureaux of geological exploration in the nine provinces, with 30,000 pieces of figures in total. Job title and history of employment were determined for 1,627 employees. Levels of exposure to silica dust in various factories and mines were estimated based on the data mentioned-above, including amount of respirable dust, total dust in the lungs, and proportion of free silica dust to the total silica dust.

Concentration of total silica dust was 14 mg/m3 in average in the factories and mines, with a range of 29 mg/m3 during the earlier years to 3 mg/m3 in recent years, and that of respirable silica dust was 3 mg/m3, in average, with (28.0 +/- 8.2)% of free silica dust. Different indices of exposure to silica dust were calculated for individuals, based on their history of employment and level of exposure.

Assessment of exposure to silica dust during the past years, based on the monitoring data, could provide basis for evaluation of dose-response relationship.