Effects of high silica exposure on respiratory disorders among stone-mortar workers in Northern Thailand

Abstract

© 2019, SEAMEO TROPMED Network. All rights reserved. Particulate matter less than ten micrometers in diameter (PM10 ) containing crystalline silica if inhaled can cause respiratory symptoms. We aimed to determine exposure levels of Thai stone-mortar workers to PM10 containing crystalline silica and its potential link to respiratory disorders. This cross-sectional study was conducted among all available workers who had worked at stone-mortar factories for at least one year in the study area. Subjects were divided into two groups: stone cutters (n=29) and stone grinders (n=28). We had a control group which consisted of 20 age and sex matched agricultural workers. All subjects were aged ≥18 years. We measured the exposure levels to PM10 containing crystalline silica using a filter-based gravimetric method. We obtained a history of respiratory symptoms from each subject using the American Thoracic Society Division of Lung Disease questionnaire (ATS-DLD-78A). We checked the respiratory effect of exposure using a lung function test and by performing chest radiographs. We used the chi-square, Fisher’s exact and Kruskal-Wallis tests and multiple linear regression analysis to examine associations between selected variables and respiratory disorders. The mean crystalline silica levels found among stone cutter subjects (mean±SD, 0.096±0.094 mg/m3) and stone grinder subjects (mean±SD, 0.130±0.106 mg/m3) were significantly greater (p<0.001) than those found in controls (mean±SD, 0.004±0.005 mg/m3). The numbers of subjects with abnormal chest radiographs and abnormal FEV1 /FVC ratios in the exposed groups were significantly higher than the abnormal numbers found in controls. Three cases of silicosis were diagnosis among stone cutters and grinders but none among controls. The crystalline silica levels found in the studied stone cutters and grinders were negatively associated with the percent predicted levels for FEV1 (p=0.002), FVC (p=0.011), and FEV1 /FVC (p=0.002). Our findings show PM10 containing crystalline silica exposure is associated with respiratory disorders and lung function impairment among studied stone-mortar workers. Stone cutters and grinders in the study area should be monitored for the presence of silica exposure and silicosis. Personal protective equipment should be available and mandatory for these high risk groups in the study area.