Brick kiln pollution and its impact on health: A systematic review and meta-analysis

Background: Brick kiln emissions contribute to ambient air pollution and poor health in workers and individuals living near the brick kilns; however, data on the effects of brick kiln pollution on the environment and health are limited. Methods: We conducted a systematic review and meta-analysis to summarize existing evidence on the adverse effects of brick kiln emissions. Sources were extracted from electronic databases and manually through citation searching. We included studies if they contributed data on brick kiln pollutant concentrations, emission factors or source contributions to ambient air pollution, health outcomes among brick kiln workers (BKWs) or community members living near brick kilns, or a comparison between BKWs and unexposed participants. We estimated pooled, sample-size-weighted means and standard deviations for personal exposures by job type and computed mean emission factors and pollutant concentrations by brick kiln design. We calculated mean differences in lung function between BKWs and controls and risk differences of respiratory symptoms between BKWs and controls or for participants living near and far away from brick kilns using a fixed effects meta-analysis. Results: Our search yielded 1015 articles; 208 (20%) were assessed for eligibility and 101 (10%) were included in our review. We identified three studies through manual searching. Of 104 studies, 74 (71%) were conducted in South Asia. The most evaluated pollutants (whether kiln emissions, source contributions, or personal exposures) were particulate matter (PM; n=48), sulfur dioxide (SO2; n=24) and carbon monoxide (CO; n=22), and the most evaluated health outcomes were respiratory health (n=34) and musculoskeletal disorders (n=9). On average emissions of PM and CO were higher among traditional than improved brick kilns. Mean respirable silica exposures were only measured in 4 (4%) studies and were as high as 620 μg/m3, exceeding the NIOSH recommended exposure limit by a factor of over 12. BKWs had worse lung function, more respiratory symptoms, more musculoskeletal complaints, and more inflammation when compared to unexposed participants. Conclusion: On average, BKWs had worse health outcomes when compared to unexposed controls but study quality supporting the evidence was low. Few studies reported silica concentrations or personal exposures, but the few that did suggest that exposures are high. Further research is needed to better understand the relationship between brick kiln pollution and health among workers, and to evaluate exposure mitigation strategies.