Background: Charcoal processing activities can increase the risk of adverse respiratory outcomes.
Objective: To determine dose-response relationships between occupational exposure to charcoal dust, respiratory symptoms and lung function among charcoal-processing workers in Namibia.
Methods: A cross-sectional study was conducted with 307 workers from charcoal factories in Namibia. All respondents completed interviewer-administered questionnaires. Spirometry was performed, ambient and respirable dust levels were assessed in different work sections. Multiple logistic regression analysis estimated the overall effect of charcoal dust exposure on respiratory outcomes, while linear regression estimated the exposure-related effect on lung function. Workers were stratified according to cumulative dust exposure category.
Results: Exposure to respirable charcoal dust levels was above occupational exposure limits in most sectors, with packing and weighing having the highest dust exposure levels (median 27.7 mg/m3, range: 0.2-33.0 for the 8-h time-weighted average). The high cumulative dust exposure category was significantly associated with usual cough (OR: 2.1; 95% CI: 1.1-4.0), usual phlegm (OR: 2.1; 95% CI: 1.1-4.1), episodes of phlegm and cough (OR: 2.8; 95% CI: 1.1-6.1), and shortness of breath. A non-statistically significant lower adjusted mean-predicted % FEV1 was observed (98.1% for male and 95.5% for female) among workers with greater exposure.
Conclusions: Charcoal dust levels exceeded the US OSHA recommended limit of 3.5 mg/m3 for carbon-black-containing material and study participants presented with exposure-related adverse respiratory outcomes in a dose-response manner. Our findings suggest that the Namibian Ministry of Labour introduce stronger enforcement strategies of existing national health and safety regulations within the industry.
Keywords: Exposure; Lung impairment and respiratory symptoms; Namibia; Respirable charcoal dust.