Determination and Prediction of Respirable Dust and Crystalline-Free Silica in the Taiwanese Foundry Industry

Background: Respirable crystalline silica (RCS) has been recognized as a human carcinogen; however, the measurement and analysis of RCS in small-scale foundries is rare and difficult. This study aimed to measure respirable dust and RCS levels among 236 foundry workers in Taiwan and used these data to establish predictive models for personal exposure. Methods: Personal sampling of various production processes were measured gravimetrically and analyzed using the X-ray diffraction method. Multiple linear regression was used to establish predictive models. Results: Foundry workers were exposed to geometric means and geometric standard deviations of 0.52 ± 4.0 mg/m³ and 0.027 ± 15 mg/m³ for respirable dust and RCS, respectively. The highest exposure levels were observed among workers in the sand blasting process, with geometric means of 1.6 mg/m³ and 0.099 mg/m³ for respirable dust and RCS, respectively. The predictive exposure model for respirable dust fitted the data well (R² = 0.75; adjusted R² = 0.64), and the predictive capacity for RCS was higher (R² = 0.89; adjusted R² = 0.84). Conclusions: Foundry workers in the sand blasting process may be exposed to the highest levels of respirable dust and RCS. The developed models can be applied to predict respirable dust and RCS levels adequately in small-scale foundry workers for epidemiological studies.