Relationship between occupational hazards exposure and respiratory health among sewage workers in the peninsular Malaysia

Occupational lung diseases among sewage workers remain a major health issue given their significant association with exposure to hydrogen sulphide (H2S) and Particulate Matter 2.5 (PM 2.5) that exist in Sewage Treatment Plants (STPs). Nevertheless, studies that explore the relationship between the exposure duration and the hazard concentration, as well as its effect on respiratory health, are limited. Therefore, this study was performed to investigate the association between occupational hazards exposure and respiratory health among Indah Water Konsortium (IWK) sewage workers. The cross-sectional study was carried out at 11 STPs located in the Peninsular Malaysia involving 191 sewage workers. The participants were assessed via the British Medical Research Council (BMRC) questionnaire and the spirometry test. Moreover, the area air sampling was collected at three different working sites in each STP to evaluate the physical air quality and concentration of PM 2.5 and H2S. The determinants for the prevalence of work-related respiratory symptoms were identified using the Logistic Regression (LR), while the linear regression analysis was employed to determine the predictors for the deterioration of lung function. The correlation analysis was conducted between the individual cumulative PM 2.5 and H2S exposures and their effects on the lung function of sewage workers. Based on the results, chronic cough (34.0%) was the most frequent symptom among the sewage workers, followed by chronic phlegm (26.2%), shortness of breath (7.9%), and chest tightness (3.7%). Additionally, workers working at Sludge Treatment Facility (STF) and non-STF sites exhibited a higher H2S and PM 2.5 exposure compared to office workers. Five significant determinants of the prevalence of respiratory symptoms among sewage workers were identified comprising shift work (Adjusted Odds Ratio (AOR), 95% CI: 23.50, 1.90–616.52), working at an STF site (25.46, 2.06–314.29), a longer working duration (in years) (1.21, 1.01–1.44), and individual cumulative exposure to PM 2.5 (9.01, 1.98–83.33), and H2S (1.04, 1.01–1.07), respectively. Besides, four final predictors of the lung function deterioration were identified, namely individual cumulative H2S exposure, workplace safety compliance, history of cardiopulmonary diseases, and daily exposure duration to hazards. Ultimately, the cumulative H2S exposure recorded a significant negative exposure-response correlation with %FEV1 (p < 0.001), %FVC (p = 0.025), and FEV1/FVC ratio (p < 0.001). In conclusion, the exposure-response relationships were identified between the cumulative PM 2.5 and H2S exposure and the prevalence of respiratory symptoms and lung function parameters among the IWK sewage worker.