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

Abstract

Background and objective: The 2014 Hazelwood coal mine 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 forced vital capacity (FVC) (increased) and forced expiratory volume in 1 second (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-bronchodilator (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.

Keywords: COPD epidemiology; Occupational Lung Disease; Respiratory Function Test; Respiratory Measurement.

Figure 1. Models of spirometry as a function of mine fire-related PM_2.5. *p values for the interaction term between exposure and round. All models adjusted for education, employment, asthma and smoking status. Pre-BD outcomes also adjusted for whether inhaled medication was withheld. BD, bronchodilator; FEF, forced expiratory flow; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; PM_2.5, particulate matter <2.5 µg/m³; R1, round 1; R2, round 2.

Figure 2. Models of gas transfer as a function of mine fire-related PM_2.5. *p values for the interaction term between exposure and round. All models adjusted for education, employment, spirometric chronic obstructive pulmonary disease (COPD) and smoking status. Hb, haemoglobin; Kco, carbon monoxide transfer coefficient; PM_2.5, particulate matter <2.5 µg/m³; R1, round 1; R2, round 2; T_Lco, transfer/diffusion factor of the lung for carbon monoxide; VA, alveolar vol.

Figure 3. Models of oscillometry as a function of mine fire-related PM_2.5. *p values for the interaction term between exposure and round. All models adjusted for age, gender, height, weight, education, employment, asthma, spirometric chronic obstructive pulmonary disease (COPD) and smoking status. Pre-BD outcome also adjusted for whether inhaled medication was withheld prior to spirometry. Ax5, area under the reactance curve at 5 Hz; BD, bronchodilator; PM_2.5, particulate matter <2.5 µg/m³; R1, round 1; R2, round 2; R5, resistance at 5 Hz; R5−19, difference in resistance at 5 and 19 Hz; X5, reactance at 5 Hz.