Health effects of bushfire smoke exposure

2017-02-20T23:58:30Z (GMT) by Bhatnagar Haikerwal, Anjali
Bushfires (wildfires) are becoming more frequent and widespread due to the warming climate. The rate of prescribed (fuel reduction) burning has also increased to reduce the intensity of future bushfires. Smoke from bushfires can disperse widely and substantially diminish air quality and is therefore of public health concern. The most important risk related measure of smoke is fine particulate matter (PM2.5 aerodynamic diameter <2.5µm). These particulates are significantly elevated during bushfire smoke episodes and could affect large populations away from the fire source. While there has been substantial research into the impacts of ambient particulate pollution on health outcomes, there has been limited research into the impacts of bushfire smoke, despite the higher exposure levels involved. This thesis aimed to examine the health impacts of bushfire smoke exposure. In particular the thesis investigated the impact of bushfire fine particulate matter exposure (PM2.5) on cardiovascular and respiratory health effects during the Victorian 2006-2007 bushfires. Furthermore, the thesis explored the impact of smoke from prescribed burning on air quality and the potential effects on health. A systematic review was conducted to identify and evaluate studies examining the impact of bushfire particulate matter (PM) on cardiorespiratory morbidity and mortality. The review indicated consistent and positive associations of PM from bushfire smoke with respiratory morbidity and all-cause mortality, and inconsistent associations with cardiovascular morbidity and cause specific mortality. The coarser particulate matter (PM10 aerodynamic diameter <10µm) was most commonly measured, with few studies investigating the effects of bushfire PM2.5. Ground based air quality monitors were a common form of PM measurement in a majority of studies. However, monitored data only provides information from areas surrounding the monitors and therefore cannot adequately represent the bushfire smoke impacts in areas that lack monitoring facilities such as rural/regional areas. This lack of spatially resolved air quality data was a limitation in most studies and an important reason for uncertainties in the health outcomes during bushfire smoke episodes. In order to address the knowledge gaps highlighted in the systematic review, the thesis investigated the association between bushfire PM2.5 exposure and cardiovascular and respiratory health outcomes using modelled air quality data covering a large geographical area. A time stratified case cross-over study investigated associations between daily average PM2.5 concentrations and cardiovascular and respiratory health endpoints during the 2006-2007 Victorian bushfires. The study utilised fine spatially resolved modelled estimates of bushfire PM2.5 data from a blended model (CSIRO’s air pollution model coupled with a chemical transport model). The highly sophisticated modelling technique enabled projections of air quality data from wider geographical areas including areas heavily impacted by bushfire smoke (rural/regional areas). Health data were obtained from comprehensive health based administrative registries. The cardiovascular and respiratory health outcomes examined were out of hospital cardiac arrest, ischaemic heart disease (IHD), acute myocardial infarction, angina, asthma and chronic obstructive pulmonary disease. Conditional logistic regression analysis was conducted controlling for temperature and relative humidity A significant positive association was observed between bushfire PM2.5 exposure and cardiovascular and respiratory health endpoints. An increase in risk was observed for out of hospital cardiac arrests, IHD related hospital admissions and emergency department (ED) visits, and asthma related ED visits. In addition, older adults showed a strong association with cardiorespiratory health outcomes. Men showed a positive association for out of hospital cardiac arrests and women a positive association with hospitalisation for IHD and ED presentations for asthma during the bushfire period. The thesis also explored key issues relating to pollution events during prescribed burning and the potential impacts on human health. The findings from the studies that investigated the impact of smoke from prescribed burning on air quality showed increased PM2.5 concentrations during burning episodes. The annual occurrence of prescribed burning and poor air quality observed during these events need to be investigated in the context of growing evidence of adverse health effects due to bushfire PM exposure. The thesis contributes to this important area of debate. The knowledge and evidence from this thesis will inform policy and practice and help build capacity in the understanding and management of adverse health effects during bushfire smoke events.