Prolonged exposure to smoke from bushfire creates severe physical and mental consequences


The physical and mental burden of prolonged exposure to bushfire smoke is vastly underestimated by official statistics that are based upon admissions into the health system, finds a large survey of residents affected by the widespread bushfires close to Canberra, Australia’s capital city, in the summer of late 2019 and early 2020.

Improved knowledge in this area will improve initiatives that are aimed at building resilience among individuals and communities impacted by these catastrophic events.

Prolonged exposure to bushfire smoke creates a heavy mental and physical burden not portrayed by official statistics of admissions into the health system, finds a new study, published in Frontiers in Public Health.

It highlights the urgent need for improved knowledge in this area to support and build resilience among individuals and communities that are impacted by these catastrophic events.

“We found that almost every single respondent to our survey experienced at least one physical health symptom that they attributed to the smoke,” explains Professor Iain Walker, co-author of the study, and based at the Research School of Psychology, Australian National University, Australia.

“In addition, about one-half of our respondents reported symptoms of anxiety and depression, as well as sleep loss.”

“Just less than one-fifth of respondents sought help from a medical practitioner, despite the widespread reporting of negative health burdens in our survey,” he continues. “This shows that the rate of people presenting into the health system is much less than the number of people who experience health symptoms when exposed to bushfire smoke.”

Widespread devastation

Air pollution from bushfires is known to increase the likelihood of death in humans and it especially affects people with pre-existing respiratory and cardiovascular problems. Its impacts on mental health are not so well understood.

The Australian summer of late 2019 to early 2020 saw fires burn 10m hectares (nearly 25m acres), which spread blanketing, choking smoke over an even larger area. As soon as was possible after this event, the researchers of this study conducted a survey of residents in the area to get a more thorough assessment of the impact of bushfire smoke on the community.

“Our survey of residents living in and around Canberra, Australia’s capital city, asked a wide range of questions about the physical and mental health symptoms the participants had experienced, as well as how their behaviors changed during the bushfire period. For example, staying indoors to avoid the smoke, which in turn reduces physical activity,” explains Walker.

Over 2000 people responded to the survey, which was administered via post, door to door visits, social media, and telephone contact to maximize the number and range of individuals reached.

Widespread negative health burden

“The survey showed that physical health effects were more extensive than previously thought and that there were very high levels of anxiety and depression,” reports Walker.

“It is likely that official statistics greatly underestimate the prevalence of health problems because of the major hurdles in the way of anyone presenting into the system, and we think many residents were motivated to avoid overburdening the health system at a time when it was stretched.”

Walker explains that improving our understanding in this area is important to help design better public health communications and service delivery.

“There is a real need for improved knowledge on the long-term effects of exposure to bushfire smoke, and how these effects vary across different segments of the population. We are conducting further studies to understand how bushfires continue to affect the mental health of people impacted by these fires and the smoke, and how we can build resilience among individuals and communities.”

Wildfires are a global occurrence. Changes in temperature and precipitation patterns from climate change are increasing wildfire prevalence and severity (Westerling et al. 2006; Settele et al. 2014) resulting in longer fire seasons (Flannigan et al. 2013; Westerling et al. 2006) and larger geographic area burned (Gillett et al. 2004).

Wildfire smoke contains many air pollutants of concern for public health, such as carbon monoxide (CO), nitrogen dioxide, ozone, particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (Naeher et al. 2007). Current estimated annual global premature mortality attributed to wildfire smoke is 339,000 (interquartile range of sensitivity analyses: 260,000–600,000) (Johnston et al. 2012), but the overall impact on public health in terms of respiratory, cardiovascular, and other morbidity effects is unknown. A better synthesis of current knowledge on the health effects of wildfire smoke is needed to guide public health responses.

Wildfire smoke epidemiology is an active area of research (Henderson and Johnston 2012) with new methods uncovering associations that were previously undetectable. Studies of health outcomes associated with wildfire smoke exposure tend to be retrospective and researchers have to rely on administrative health outcome data such as mortality or hospitalization records.

Achieving adequate statistical power has been challenging because such severe outcomes are less common, fires tend to be episodic and short in duration, and exposed populations from individual events are often small. Many recent studies have increased statistical power by investigating very high exposure events that last for longer periods, large populations over many years in regions with frequent fires, more common health outcomes such as medication dispensations, or a combination of these methods.

Previous reviews of wildfire health impacts have either not included the full range of health end points associated with community exposure to wildfire smoke (Dennekamp and Abramson 2011; Henderson and Johnston 2012) or have summarized the literature without critical analysis of specific studies (Finlay et al. 2011; Liu et al. 2015; Youssouf et al. 2014). Our review follows a modified version of the systematic review methodology outlined in Woodruff and Sutton (2014) to analyze studies critically and to only evaluate the strongest evidence.


Our critical review demonstrated consistent evidence of associations between wildfire smoke exposure with general respiratory morbidity and with exacerbations of asthma and COPD (Table 1). Mounting epidemiological evidence and plausible toxicological mechanisms suggest an association between wildfire smoke exposure and respiratory infections, but inconsistencies remain. Increasing evidence suggests an association between wildfire smoke exposure and all-cause mortality, especially from more recent, higher-powered studies (e.g., Johnston et al. 2011; Morgan et al. 2010; Faustini et al. 2015).

The current evidence for cardiovascular morbidity from wildfire smoke exposure remains mixed; many studies are inconclusive or negative, but some have demonstrated significant increases for specific cardiovascular outcomes, such as cardiac arrests.

Toxicological findings are consistent with cardiac effects through evidence of systemic inflammation and increased coagulability. Most of the other end points of interest, including birth outcomes, mental health, and cancer have not been sufficiently studied.

Our review highlights the lack of information about which populations are most susceptible to wildfire smoke exposure. People already diagnosed with asthma or COPD are more susceptible. We found inconsistent evidence of differential effects by age or SES. Two studies have suggested differential effects by Australian indigenous status with no investigation of other ethnic groups.

Many gaps exist in understanding the public health implications of exposure to wildfire smoke. Larger studies with greater statistical power and more spatially refined exposure assessments are needed to better characterize impacts on mortality, cardiovascular disease, birth outcomes, and mental health effects.

Currently, evidence exists of exacerbation, but not incidence, of asthma and COPD from wildfire smoke exposure. In temperate parts of the world, where wildfire smoke exposure is episodic, it is unlikely that changes in asthma incidence would be observed. Studies have not been conducted in populations more chronically exposed to wildfire smoke.

Additionally, other health outcomes associated with wildfire smoke exposure have not yet been sufficiently studied, such as otitis media, which has been associated with exposure to secondhand tobacco smoke (Kong and Coates 2009), air pollution from woodsmoke (MacIntyre et al. 2011) and recently wildfire smoke (Yao et al. 2016).

Human experimental studies of exposures to wildfire smoke could help clarify biological mechanisms. Very little information exists on health effects associated with measures of pollutants in wildfire smoke other than PM, such as ozone or PAHs. Although this review combined results from studies of various types of fires, it is possible that smoke originating from peat fires, forest fires, grassland fires, and agricultural burning could lead to differential health effects due to different constituents in the smoke. T

o our knowledge, no studies have yet investigated chronic exposure to wildfire smoke, but many populations in Southeast Asia, Africa, and Latin America are exposed regularly for extended periods (Johnston et al. 2012).

Characterization of the exposure–response function is critical for setting smoke levels for public health warnings or interventions, and it is not yet known whether current levels based on undifferentiated PM sufficiently characterize the effects of wildfire smoke.

Four studies (Arbex et al. 2010; Chen et al. 2006; Johnston et al. 2002; Sastry 2002) have attempted to identify effects at different exposure levels, but these studies are hard to compare because of differences in exposure assessment methods, health outcomes, types of fires, and population susceptibilities.

reference link :

More information: Physical and Mental Health Effects of Bushfire and Smoke in the Australian Capital Territory 2019–20, Frontiers in Public Health (2021). … 89/fpubh.2021.682402


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