Respiratory exposure to crystalline silica among ceramic industry workers in Iran: Exposure levels, deterministic risk assessment, Monte Carlo simulation, and spirometric indices

Background The ceramic industry is an important component of Iran’s manufacturing sector; however, its complex production processes can generate respirable crystalline silica (RCS), a well-established occupational hazard associated with adverse respiratory outcomes. Objectives This study aimed to characterize RCS exposure levels, assess associated occupational health risks, and evaluate pulmonary function among ceramic workers in Iran. Methods A cross-sectional study was conducted among ceramic workers using a Similar Exposure Group (SEG) approach. A total of 79 personal respirable dust samples were collected across seven production tasks. RCS concentrations were determined according to NIOSH Method 7601 using a JENWAY 6105 UV/Visible spectrophotometer. Deterministic health risk assessment and Monte Carlo simulation (1,000 iterations) were performed based on the U.S. EPA methodology. Pulmonary function was assessed using spirometry, including forced expiratory volume in one second (FEV 1 ), forced vital capacity (FVC), and the FEV 1 /FVC ratio. Associations between RCS exposure and pulmonary function parameters were evaluated statistically. Results Mean RCS concentrations varied substantially across production tasks, ranging from 0.02 mg/m 3 in glazing operations to 0.50 mg/m 3 in crushing operations. Exposure levels among crusher workers and ball-mill spray operators significantly exceeded the occupational exposure limit of 0.025 mg/m 3 (p < 0.05). Deterministic risk assessment yielded hazard quotient (HQ) values below 1; however, Monte Carlo simulation showed that the 95th percentile HQ slightly exceeded 1, indicating an increased non-carcinogenic risk under high-exposure scenarios. Spirometric results were predominantly within normal ranges, although borderline obstructive and restrictive patterns were observed among packing and furnace workers. Significant negative correlations were observed between RCS concentration and FEV 1 (r s = −0.77, p = 0.04) and the FEV 1 /FVC ratio (r s = −0.78, p = 0.03). Conclusions Ceramic workers, particularly those involved in crushing and ball-mill operations, may experience substantial RCS exposure and increased respiratory health risks. The observed associations between RCS exposure and reduced pulmonary function highlight the need for effective engineering controls, respiratory protection programs, routine exposure monitoring, and periodic medical surveillance to reduce occupational health risks in the ceramic industry.