Lung function may recover after coal mine fire smoke exposure: a longitudinal cohort study

Background and objective The 2014 Hazelwood coalmine fire exposed residents in nearby Morwell to high concentrations of particulate matter <2·5 µm (PM 2·5 ) for approximately 6 weeks. This analysis aimed to evaluate the long-term impact on respiratory health. Methods Adults from Morwell and the unexposed town of Sale completed validated respiratory questionnaires and performed spirometry, gas transfer and oscillometry 3·5-4 years (Round 1) and 7·3-7·8 years (Round 2) after the fire. Individual PM 2·5 exposure levels were estimated using chemical transport models mapped onto participant-reported time-location data. Mixed-effects regression models were fitted to analyse associations between PM 2·5 exposure and outcomes, controlling for key confounders. Results From 519 (346 exposed) Round 1 participants, 329 (217 exposed) participated in Round 2. Spirometry and gas transfer in Round 2 were mostly lower compared with Round 1, excepting FVC (increased) and FEV 1 (minimal change). The effect of mine fire-related PM 2·5 exposure changed from a negative effect in Round 1 to no effect in Round 2 for both pre-(p=0·005) and post-bronchodilator FVC (p=0·032). PM 2·5 was not associated with gas transfer in either round. For post-bronchodilator reactance and area under the curve, a negative impact of PM 2·5 in Round 1 showed signs of recovery in Round 2 (both p<0·001). Conclusion In this novel study evaluating long-term respiratory outcomes after medium-duration high concentration PM 2·5 exposure, the attenuated associations between exposure and respiratory function may indicate some recovery in lung function. With increased frequency and severity of landscape fires observed globally, these results inform public health policies and planning. KEY MESSAGES Evidence is currently lacking on the long-term sequelae of high concentration PM 2·5 exposure, from extreme wildfire events lasting weeks to months, on lung physiology and function. We found that previously observed deficits in adult lung function, measured using spirometry, gas transfer and oscillometry 3.5 years after a prolonged coal mine fire, may recover in the longer-term. With increased frequency of prolonged landscape fires observed globally, these results inform public health policies and planning.