Estimating the quartz exposure of South African gold miners.

The possibility that dust and silica exposure estimates in epidemiological studies of South African gold miners have been underestimated has been postulated for some years. These exposure estimates were obtained by converting particle number concentrations measured with konimeters and thermal precipitators to respirable mass concentrations, primarily on theoretical considerations. A detailed review of the methodology has revealed that the theoretically based dust and silica estimates were probably underestimated. In the absence of systematic side-by-side thermal precipitator and modern respirable mass measurements in the South African gold mines, the true relationship between the respirable mass concentrations and the theoretically derived concentrations cannot be known. However, with many uncertainties, we estimate that the quartz exposures of South African miners derived from past theoretically based conversions from particle number to respirable mass underestimate the actual quartz exposures by a factor of about 2.