Determination of respirable crystalline silica (RCS) characteristics and factors related to respiratory symptoms among RCS exposed workers in sandstone and stone mortar processing in two provinces of Thailand

Sandstone processing and stone mortar workers were at high risk of exposure to silica dust, which was generated while working and resulting in respiratory symptoms and diseases. This analytic cross-sectional study aims to determine crystalline silica concentrations in two different sizes of dust, namely respirable dust (RD) and particulate matter less than 2.5 (PM2.5), and their characteristics, and to assess respiratory symptoms as well as associated factors. The data were collected between September and November 2023 among RCS-exposed workers in two provinces of Thailand. The personal air samplings were collected throughout the full shift according to NIOSH 7602, and EPA- IP-10. The morphology and Silica elements were examined using SEM-EDX. The interview questionnaire was used to assess respiratory symptoms. Mean, standard deviation, frequency, and percentage, were used to describe demographic data, RCS concentration RD and PM2.5 characteristics, and respiratory symptoms. Chi-square was used to test for bivariate associations, and logistic regression was used for analysis of the association between respiratory symptoms and associated factors. Statistical significance was defined as the p-value less than 0.05.The total 212 participants were 140 sandstone workers and 72 stone mortar workers. Most of them 67% were male. The average work experience was 13.51 ± 10.06 years. Only 47% were currently smoking and 42.9% worn masks during work. The mean concentrations of RCS were 0.83 ± 0.68 mg/m3 and 0.61 ± 0.83 mg/m3 for RD and PM2.5, respectively. The highest concentration was found in stone mortar polishing. The SEM images of RD and PM2.5 exhibited an irregular shape with a range of sizes less than 1-5 microns. The highest respiratory symptoms were phlegm (61.8%) while wheezing was the lowest symptoms. Education levels, work experience, type of task, wearing masks, and types of masks were factors significantly associated with respiratory symptoms (p-value 0.003, 0.003, <0.001, 0.001, and 0.018). The uneducated workers, polishing workers, 10 years of work experience workers, and those who did not wear masks were a group of workers who had a chance of developing respiratory symptoms. In conclusion, the RCS concentration in sandstone and stone mortar processing exceeded the OSHA standard (0.05 mg/m3) and Thailand regulation (0.025 mg/m3). The provision of personal protective equipment and the improvement of working environments are crucial in reducing respiratory symptoms among these household workers. Eventually, the early detection of respiratory symptoms can prevent more severe diseases.