Objective This study aimed to determine whether workers in fixed chimney Bull’s trench kilns (FCBTK) experience greater occupational exposure to air pollutants and more pronounced respiratory impairment than those in zigzag kilns, and to evaluate how seasonal production variations affect the relationship between exposure and respiratory outcomes. We hypothesized that FCBTK workers would demonstrate higher pollutant exposure and greater respiratory dysfunction, with seasonal peaks exacerbating these differences. Methods A cross-sectional comparative study was conducted in Jaranwala, district Faisalabad, between April to August (Low) and November to January (High) in 2022–2023, among 160 male workers from 20 kilns (10 FCBTK, 10 zigzag). Ambient PM2.5, PM10, CO, and SO2 were measured at kiln worksites using calibrated portable monitors. Spirometry was performed according to ATS/ERS guidelines and expressed as % predicted (GLI 2012). Seasonal pollutant levels were assessed where available. Associations between pollutants and lung function were evaluated using correlation and multivariable logistic regression models adjusted for age, smoking, BMI, and employment duration. Results Ambient CO, SO2, PM2.5, and PM10 levels were significantly higher at FCBTK sites than zigzag kilns (e.g., CO: 12.8 ± 2.9 vs. 8.4 ± 2.2 ppm; mean difference 4.4 ppm, 95% CI 3.6–5.2; p < 0.001). Seasonal data showed sharp increases in pollutant concentrations during peak kiln activity months, with FCBTK sites reaching mean PM2.5 levels of 168 µg/m3 vs. 94 µg/m3 in zigzag kilns, PM10 levels of 280 µg/m3 vs. 160 µg/m3, CO levels of 15.4 ppm vs. 9.6 ppm, and SO2 levels of 92 ppb vs. 58 ppb. These seasonal peaks were accompanied by more pronounced declines in lung function, with mean FEV1% predicted dropping by 9.4% and FVC by 7.8% among FCBTK workers compared to 4.1% and 3.5% declines, respectively, in zigzag kiln workers. Overall, FCBTK workers had lower mean FEV1% predicted (82.6 ± 9.4 vs. 88.7 ± 8.1; difference − 6.1, 95% CI − 8.8 to − 3.4; p < 0.001) and higher prevalence of abnormal spirometry (22.5% vs. 10.0%; difference 12.5%, 95% CI 2.1–22.9; p = 0.03). CO exposure independently increased the odds of abnormal spirometry by 42% per ppm (adjusted OR 1.42, 95% CI 1.16–1.74). Conclusion FCBTK workers face substantially higher pollutant exposure and more pronounced respiratory impairment than zigzag kiln workers, with seasonal peaks marked by extreme elevations in PM2.5, PM10, CO, and SO2, which further exacerbate the risk of lung function decline. Transition to cleaner kiln technologies, coupled with occupational health surveillance and targeted seasonal interventions, could markedly improve respiratory outcomes in this workforce. Graphical abstract

Occupational air pollutant exposure and seasonal variation in respiratory outcomes among brick kiln workers

期刊论文
发表日期：

2026年3月24日

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Sohaib Hasnain,
Nadia Akram,
Asim Mansha,
Toheed Asghar,
Khalid Mahmood Zia

摘要

Objective

This study aimed to determine whether workers in fixed chimney Bull’s trench kilns (FCBTK) experience greater occupational exposure to air pollutants and more pronounced respiratory impairment than those in zigzag kilns, and to evaluate how seasonal production variations affect the relationship between exposure and respiratory outcomes. We hypothesized that FCBTK workers would demonstrate higher pollutant exposure and greater respiratory dysfunction, with seasonal peaks exacerbating these differences.

Methods

A cross-sectional comparative study was conducted in Jaranwala, district Faisalabad, between April to August (Low) and November to January (High) in 2022–2023, among 160 male workers from 20 kilns (10 FCBTK, 10 zigzag). Ambient PM_2.5, PM₁₀, CO, and SO₂ were measured at kiln worksites using calibrated portable monitors. Spirometry was performed according to ATS/ERS guidelines and expressed as % predicted (GLI 2012). Seasonal pollutant levels were assessed where available. Associations between pollutants and lung function were evaluated using correlation and multivariable logistic regression models adjusted for age, smoking, BMI, and employment duration.

Results

Ambient CO, SO₂, PM_2.5, and PM₁₀ levels were significantly higher at FCBTK sites than zigzag kilns (e.g., CO: 12.8 ± 2.9 vs. 8.4 ± 2.2 ppm; mean difference 4.4 ppm, 95% CI 3.6–5.2; p < 0.001). Seasonal data showed sharp increases in pollutant concentrations during peak kiln activity months, with FCBTK sites reaching mean PM_2.5 levels of 168 µg/m³ vs. 94 µg/m³ in zigzag kilns, PM₁₀ levels of 280 µg/m³ vs. 160 µg/m³, CO levels of 15.4 ppm vs. 9.6 ppm, and SO₂ levels of 92 ppb vs. 58 ppb. These seasonal peaks were accompanied by more pronounced declines in lung function, with mean FEV₁% predicted dropping by 9.4% and FVC by 7.8% among FCBTK workers compared to 4.1% and 3.5% declines, respectively, in zigzag kiln workers. Overall, FCBTK workers had lower mean FEV₁% predicted (82.6 ± 9.4 vs. 88.7 ± 8.1; difference − 6.1, 95% CI − 8.8 to − 3.4; p < 0.001) and higher prevalence of abnormal spirometry (22.5% vs. 10.0%; difference 12.5%, 95% CI 2.1–22.9; p = 0.03). CO exposure independently increased the odds of abnormal spirometry by 42% per ppm (adjusted OR 1.42, 95% CI 1.16–1.74).

Conclusion

FCBTK workers face substantially higher pollutant exposure and more pronounced respiratory impairment than zigzag kiln workers, with seasonal peaks marked by extreme elevations in PM_2.5, PM₁₀, CO, and SO₂, which further exacerbate the risk of lung function decline. Transition to cleaner kiln technologies, coupled with occupational health surveillance and targeted seasonal interventions, could markedly improve respiratory outcomes in this workforce.

Graphical abstract