The activities associated with the open dumping of municipal solid waste emit air pollutants, including bioaerosols that contaminates the air around dumpsites, rendering it unsafe for dumpsite workers and residents living near dumpsites. Quantitative data on the exposure to bioaerosols from open dumpsites are scarce, thus impeding the development of effective interventions that would reduce the risk of respiratory diseases among dumpsite workers and residents living near dumpsites. The specific objectives for this study included (i) to identify the key working areas and activities of the workers at open dumpsites; (ii) to identify the most important groups of local residents that may be affected by contaminated air due to the waste management activities carried out at open dumpsites; (iii) to obtain background information regarding the respiratory health condition of the workers and the local residents in order to determine the extent to which they suffer respiratory diseases that may be related to exposure to the contaminated air from dumpsite; (iv) to measure the concentrations of bioaerosols at key locations on the open dumpsite to determine the impact of different waste management activities and seasonal variations on bioaerosol concentrations; (v) to analyse the bioaerosol data and to compare the ambient concentrations to concentrations at the controls; (vi) to quantify the potential health risk associated with exposure to pathogenic bioaerosols from the open dumpsites using the Quantitative Microbial Risk Assessment (QMRA) tool.
A cross sectional respiratory health survey was conducted in the study area between 12th -27th January 2017 with a total 414 respondents (workers = 149, resident = 145 and control = 120). A six-stage Anderson sampler and the SKC button sampler were used to measure ambient bioaerosol concentration and exposure concentration during key activities at the dumpsite respectively. The four bioaerosols indicator groups (total bacteria, gram-negative bacteria, Aspergillus fumigatus and total fungi) measured were expressed as cfu m-3. Using the Markov chain model, the deposition of inhaled bioaerosols in the workers lungs was computed. The infection risk estimates were computed using the beta-Poisson dose response model and the results reported within the QMRA framework.
The result of the cross-sectional survey shows that cough was the most reported by the respondents. In all, up to 27% of respondents reported one or more symptoms of cough and phlegm and up to 8.7% reported three or more symptoms (cough, phlegm, asthma etc.). On the dumpsite, while chronic cough particularly affected smokers, it had a prevalence of 38%. Chronic phlegm and asthma was prevalent at 31% and 2% respectively. Only chronic cough and chronic phlegm showed prevalence that were significantly higher that the controls (p < 0.001). Daily exposure duration was associated with chronic cough with odds ratio of 1.2 (95% CI 1–1.4, p < 0.05) but not with chronic phlegm and asthma. Years of work >5 years showed was not associated chronic cough, chronic phlegm asthma. Among residents, chronic cough particularly affected the non-smokers and had the prevalence of 31.7%. Chronic phlegm and asthma was prevalent at 28.9% and 8.2% respectively. Only chronic cough and chronic phlegm showed significantly higher prevalence compared to the control (p < 0.001). Daily exposure duration was also associated with chronic cough with odds ratio of 1.2 (95% CI 1.1–1.3, p < 0.001) but not with chronic phlegm and asthma. The frequent visit of a resident to the dumpsite had an associated odds ratio of 3.8 (95% CI 1.6–8.4, p < 0.001), 4 (95% CI 1.1-14.4, p < 0.05) and 6.8 (95% CI 1.3-33, p < 0.01) for chronic cough, chronic phlegm and asthma respectively, when compared to the controls. Only years of work <10 years showed associated with chronic cough with odds ratio 4.2 (95% CI 1.4–12.4, p < 0.01) when compared to the controls.
At the 95th percentile, the ambient concentration of total bacteria was 2189 cfu m-3, gram-negative bacteria 2352 cfu m-3, total fungi 824 cfu m-3 and Aspergillus fumigatus 300 cfu m-3, and were significantly higher in magnitude than the control by 2-3 log (p< 0.05). The concentration of bioaerosols at the active operational area was the highest in comparison to the other three sampling locations. However, there were no significant differences in concentration across the four sampling points for total bacteria, gram-negative bacteria and the total fungi. Aspergillus fumigatus, on the other hand, recorded a drastic decrease in concentrations up to 80-81% between the active operational area and the boundary. The particle size distribution shows that the workers were at risk of inhaling air contacting 41%, 46%, 63%, 76% of total bacteria, gram-negative bacteria, total fungi and Aspergillus fumigatus respectively, that were of sizes capable of penetrating deep into the tracheobronchial and the pulmonary region of the lungs, posing a greater human health risk.
This study has shown that exposure to bioaerosols were also associated with specific activities undertaken at the dumpsite. Workers were exposed to bioaerosol concentrations up to 106 cfu m-3 during scavenging, waste sorting and site monitoring. These concentrations were 3-log higher than the mean concentration measured in the ambient air. The result shows that on a daily basis, workers were likely inhaling bioaerosols at concentrations ranging from 8.9 × 105 -1.8 × 107 cfu m-3 of total bacteria, 4.0× 105-8.1× 106 cfu m-3 of gram-negative bacteria and 3.29× 105-1.5× 106 cfu m-3 of Aspergillus fumigatus that were of sizes capable of penetrating deep into the tracheobronchial and the pulmonary region of the lungs when undertaking scavenging, waste sorting and site monitoring. These concentrations were higher than expected limit by the UK Environment Agency.
The result of the QMRA showed that that the activities at the dumpsite may contribute more to the likelihood of workers developing either respiratory infection or GI infection than anything else. The infection risk from inhaling contaminated air containing spores of Aspergillus fumigatus were in the magnitude of (10-1) all locations and activity types on the dumpsite. However, the risk of infection from ingesting E.coli O157:H7 from ambient exposures across all locations on the dumpsite ranged from 10-3-10-2 for the conservative and 10-4-10-3 for the least conservative of pathogen-indicator ratio. While the risk of infection due to undertaking scavenging, waste sorting and dumpsite monitoring were in the magnitude of 10-1.
Overall, this study suggests that the high prevalence of respiratory disease among the workers and the residents are indications of exposure to contaminants in the air from the dumpsite, which includes bioaerosols, as the prevalence were similar among the workers and the residents. The risk estimates show that of infection from bioaerosols were high irrespective the activity the workers undertook at the dumpsite.
