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White Coat Black Art
·
The Dose
How does wildfire smoke affect long-
term health? Researchers are trying to
find out
Evidence of harmful health effects is growing, but more work is needed, experts say
Isabelle Gallant
· CBC Radio · Posted: Jun 01, 2023 4:00 AM EDT | Last Updated: June
1
A gas station in Tantallon, N.S., just outside Halifax, on Tuesday. A wildfire in the community has been burning since Sunday and has now grown to 837 hectares. (Brett Ruskin/CBC)
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The Dose
24:44
How do atmospheric pollutants affect my health, especially around wildfire smoke?
It's been an early start to the wildfire season in Canada, with more than one million hectares burned in Alberta alone and thousands of people forced to evacuate their homes across Western Canada and in parts of the Maritimes.
Wildfire smoke has also been affecting air quality for millions of people in this country, causing short-term health effects such as burning eyes, sore throat, cough and headache.
If you have an underlying respiratory or cardiovascular health condition, you are more at risk.
"I always talk about people with chronic respiratory diseases like asthma and COPD as the canaries in the coal mine of wildfire smoke," Sarah Henderson, an epidemiologist who researches wildfire smoke, told Dr. Brian Goldman, host of CBC's
The Dose
.
Have you noticed the price of fire insurance going up? We want to hear from
you for an upcoming story. Send an email to ask@cbc.ca.
"They are very sensitive to it and more sensitive to wildfire smoke than to other kinds of air pollution," said Henderson, the scientific director of environmental health services at the B.C. Centre for Disease Control.
Smoky skies in Vancouver on May 18. Exposure to wildfire smoke has been shown to cause increased risk of cardiovascular conditions for those with underlying heart problems. (Ben Nelms/CBC)
As Canadians learn to deal with the immediate health effects of wildfire smoke — from running indoor air purifiers to adjusting outdoor plans — researchers are gradually learning more about the long-term impacts smoke exposure could have on the body.
It's an important area of research, they say, because more of us are going to be exposed to smoke in the coming years — and in increasing amounts — as
wildfires increase in intensity and size
.
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"What we're seeing is communities having really big exposures in one summer, or exposures that last for weeks or months, summer after summer," said Henderson.
"We just don't have a lot of evidence yet about what the health impacts of those longer-term patterns are going to be."
What makes wildfire smoke harmful?
The chemical makeup of wildfire smoke is complex, said Henderson.
"It depends on what's burning, it depends on how hot it's burning, and it depends on what the weather conditions are around the fire. So the mix of gasses and particles can be really different depending on those conditions," she said.
One of the known dangers of wildfire smoke is particulate matter, measured in micrometres, or microns. Any particles smaller than 2.5 microns — known as PM2.5
— can infiltrate the lungs and cross the blood-brain barrier.
Thick smoke from wildfires blanketed Calgary on May 16. Researchers say more evidence is needed on the mental health impacts of wildfires and wildfire smoke. (James Young/CBC)
But what exactly is in that PM2.5 depends on what materials are burning: vegetation or human-made structures and fuels.
Smoke from fires that burn human-made materials is going to be more complex, said Henderson.
"There's a lot of material when we're talking about communities or houses that are burning, and so it's a very thick type of smoke," she said.
Wildfire smoke in the short term
When PM2.5 gets into your lungs, your body's immune system kicks into gear, similar to the way it would treat a virus or bacteria, said Henderson.
But those tiny smoke particles can't be killed the way viruses or bacteria can be, so your immune system just keeps working.
That can bring on systemic inflammation in the body, which can lead over time to chronic diseases such as heart disease, said Dr. Courtney Howard, an ER physician in Yellowknife who researches wildfires and health.
Wildfires burned around Kelowna, B.C. in May, causing a decrease in air quality in the city. (Winston Szeto/CBC)
Studies have shown people with underlying heart problems have
an increased risk for heart attack
and other cardiovascular issues after being around wildfire smoke.
Along with people who have respiratory or cardiovascular conditions, young children and pregnant women are some of the most vulnerable to the effects of wildfire smoke, said Howard.
"Little ones breathe faster per unit of body weight than people who are bigger, and so they end up with a larger exposure to the air pollution than adults at a similar level of air pollution," Howard said.
Very young infants are of particular concern, said Henderson, because their lungs are extremely sensitive and still growing.
If that growth is disrupted by wildfire smoke, it could mean lung issues throughout their lives, she said.
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WATCH
/ Why Nova Scotia is having a tough start to wildfire season
What's behind Nova Scotia's wildfires? | About That
6 months ago
Duration9:15
Two wildfires covering more than 7,000 hectares of land have forced more than 15,000 people from their homes in Nova Scotia. Andrew Chang talks to Environment Canada's David Phillips about how the fires got out of control so quickly, and how this could be just the beginning of a challenging season.
Henderson also pointed to
studies that have been done
on
the effects of wildfire smoke
on developing fetuses.
"There's not really enough to feel super confident about the results, but what we see is that the infants are a slightly lower birth weight," she said.
There is also evidence around a higher risk of preterm birth for people with gestational diabetes exposed to wildfire smoke, and
some evidence around birth defects
, she added.
Smoke linked to increasing cancer rates
There are studies linking higher rates of cancer with exposure to wildfire smoke, including
a 2022 study in the Lancet
that looked at population data in Canada over 20 years.
It found that long-term exposure to wildfire smoke might increase the risk of lung cancer and brain tumours, but the study's authors said further work is needed.
Long-term trauma for natural disaster evacuees part of uncounted climate costs
CBC EXPLAINS
How wildfires are changing in Canada
Though it's not related to a wildfire, Henderson pointed to research from Australia around exposure to smoke from a coal mine fire in 2014 that affected a nearby community for weeks.
"What they do see is
some higher rates of cancer in that community
that they were able to detect within five years of that fire occurring," Henderson said.
More research needed on mental health impacts
Researchers say the mental health impacts need to be studied more.
"There's not a lot of literature yet on the mental health impacts of wildfires. What we have shows that it does have an adverse impact on our mental health," said Howard.
And PM2.5 could have direct impacts on the brain itself, said Henderson, who did
a recent study on cognition during smoky periods
using data from Lumosity, a brain-
training platform.
"What we saw is that when it was smoky, there were these small decrements to people's cognitive performance," said Henderson.
Study suggests link between smoke and flu season
A study in 2020 in Environment International
used hospital data to look at rates of influenza following the wildfire season in the state of Montana, which typically lasts from July to September.
The study found that after a bad wildfire season, rates of influenza in Montana were three to five times higher than normal, said lead author Erin Landguth, associate professor in the school of public and community health sciences at the University of Montana.
Halifax-area wildfire has left 'visible scars on the community,' official says
Wind, dry heat fuelling wildfires across B.C., with little sign of relief in forecast
Landguth said she was shocked by her findings about just how long after the fire season there were higher rates of flu, given that most previous air pollution research had focused on short-term health impacts in the days following wildfire smoke exposure.
She cautioned that her study results can't be extrapolated to other states or countries, and nor should they be used to draw conclusions about what is happening in the body due to wildfire smoke.
Landguth and her team are currently running models for all of the western U.S. for influenza correlated with wildfires, building on the Montana research.
"It's really important that we understand and we can extrapolate the results in a meaningful way," said Landguth.
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Media Report Source
CBC/Radio Canada. (2023, June 1). How does wildfire smoke affect long-term health? researchers are trying to find out | CBC radio
. CBCnews. https://www.cbc.ca/radio/whitecoat/the-dose-wildfire-smoke-1.6860689 Link to Journal Article
https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(22)00067-5/fulltext
Critical Appraisal
Step 1
The author’s central purpose is to investigate whether exposure to wildfires can lead to an increased risk of cancer.
A population-based observational cohort study was done in Canada on 1996. The study excluded individuals younger than 25 or older than 90 and those who lived in major cities. It focused on areas with exposures to wildfires within 20km-50km radius.
This study yielded both qualitative and quantitative results as the survey gave provided us with numerical data on how many people contracted cancer in this area and how long they have had the disease, but also the type of cancer they had.
The results from the study revealed that the wildlife exposure was associated with slightly increased incidence of lung cancer and brain tumours.
The interpretation of these findings were that long term exposure to wildfires might increase the risk of lung cancer and brain tumours, but further work is needed to develop long-term estimates.
The Canadian Census Health and Environment Cohort who held the study in 1996 then followed up with approximately 3-6 million individuals for mortality and cancer outcomes from 1996 to 2015.
In terms of statistics, multivariable Cox proportional hazards models were used to estimate any connections between the exposure to wildfires and the incidence of various forms of rather fatal cancer.
In the models, there were some differences in baseline covariates between those exposed to a wildfire and those who weren’t.
These results provided the conclusion that there is an indication that there can be an elevated risk in cancer for those near wildfires, but because of the complexity of the situation and the numerous variables, one cannot conclude there is a direct relationship.
This left the question rather unsolved, but provided additional information on the statistics of those who are exposed to wildfires and how many contract some form of cancer.
This study has provided a significant amount of factual information since it “is the first study in the world to examine associations between wildfires and the incidence of several cancer outcomes”.
Before this study, there was very little or no information on any epidemiological analyses that investigated this issue.
Step 2
The study was conceptualized by SW, but RTB and SW designed the study. JK prepared the data and verified it alongside LP and TC, and JK contributed to all the statistical analyses.
The research was conducted in the 1996 Canadian Census Health and Environment Cohort from 1996 to 2015.
The author conduced this research to gain more information on the connection between wildfires and a risk of cancer.
The research went much above the authors’ local area as it pertained to all cities of Canada excluding any major ones and those that do not have wildfires.
This study was unique as there weren’t any similar researchers or laboratories trying to investigate this connection.
The research was funded by the Canadian Institute for Health Research and Fonds de recherche du Quebec.
There was little known about the relationship between the exposure to wildfires and cancer risk, and with the recent ravaging wildfires, this piqued an interest to delve into this issue. But there wasn’t much information known at the time of this research.
As a result of there being little information on this issue and the uproar in wildfires, the research question was very important to solve and gain further insight into.
Step 3
Introduction
o
The objective of this study was to characterize the relationship between residential exposure to wildfires and the result of various cancer outcomes in a
national population-based cohort in Canada.
o
The title directly explains the subject of the study as it begins with the “long-
term exposure to wildfires and cancer incidence in Canada”.
o
The introduction is very coherent and sequential as it provides context on wildfires and the complex mixture of harmful pollutants they can release, and then it transitions into the various types of cancers that exist, which all ties back to the purpose of the study.
Methods
o
The methods in this study which consist of a cohort study with follow-ups is a
valid method to studying this problem of the long-term risks of exposure to wildfires in terms of cancer because it is able to provide sufficient and accurate information that can greatly help in solving the question.
o
The study could be duplicated from the methods and information given as it is
very detailed in terms of the timespan, geographical area, and other factors that were all considered when conducting this study, but because of how long the study is, it could time quite a bit of time.
o
The sample size is adequate as it consists of 3-6 million people which is quite sufficient for drawing conclusions, but there are flaws with a survey based study which applies to all studies of this type and that would be the possibility
of inaccurate information since the responses cannot be verified.
o
The sequence of events is clear and pertinent in the methods section as it begins with how the information was obtained and from who, where, when, and how, and then it was followed by the statistical models that were applied to this data to draw conclusions from.
o
The authors do not spend quite a bit of time on mentioning rigour in their research and whether how accurate the data truly is, but they do mention that the people in the study were followed-up with multiple times throughout the period of the study.
Results
o
There are numerous labels and column headings throughout the report which accurately describe the details of that section, but in terms of tables and figures, there is only one table and three figures in the report. Although there isn’t much data in these forms, the title for the table “Cohort characteristics at baseline” was accurate and directly described the table. The first figure displayed the area of forest burned in Canada from 1986 to 2015 and the title accurately depicted this. The other two figures also had accurate titles for the graphs that they were representing, and their legends were also descriptive.
o
The tables directly correlate and complement the results found by analyzing what they mean as the graphs and table are quite complex and may not be readily understandable to the common reader, the report dissects what these figures mean and how they contribute to solving the question of the study.
o
The researcher intended to discover a connection between long-term exposure to wildfires and an elevated risk to cancer, but the results were not conclusive enough to reveal this, and because of the complex variables associated with this study, there wasn’t enough evidence to prove this connection.
Discussion
o
The results from the statistical are slightly complex to understand but after analysis of the table and figures, it seems like the interpretation of the results arise logically from the data and makes an attempt to simplify these results for
the common reader. The results are not simply repeated but rather explained and understood. Flaws in the research are addressed and an example of this is when the dichotomous exposure terms, which compared risk between people unexposed to wildfires versus those exposed to the wildfires, was greater than 1, indicating a correlation, but the study stated that a “clear concentration-
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response relationship was not apparent in terms of area burned within a given buffer distance surrounding residences”.
o
The interpretation was supported by numerous other sources which were cited
in the study, amounting to about 35 other sources which aided in supporting various different parts of the study. One study commented on how wildfires are associated with elevated smoke and air pollution concentrations which are carcinogenic to humans. Another source indicated this can suggest elevated lung cancer risk due to biomass burning sources.
Critical Reflection
Embarking on the critical evaluation of the study that explored the potential risk of cancer
with wildfire exposure was a tremendous opportunity for learning that delved into the intricate landscapes of scientific inquiry. Each step taken in this evaluation process unveiled the layers of complexity inherent in deciphering the study's methodology, results, and their portrayal in the media. My experience began with a thorough dissection of the study's purpose and methodology, unravelling the depth of its approach. Reviewing the minute details of the research exhibited the quantitative data but also qualitative insights, shedding light on the possible connection between long-term exposures to wildfire and an increased risk of cancer. This detailed exploration underscored the importance of a holistic understanding, beyond mere statistical analyses, to shine
a light on the actual issue. Continuing to work through the critical appraisal and exploring the finer details of the study, the results seem to lead the way to the possibility of a connection between wildfire exposure and cancer incidences due to the results of the study. Despite these statistical analyses which could suggest a possible conclusion, the study was cautious in drawing a definitive connection and highlighted the challenges of establishing direct causality here because of the various complex variables. In this step, I was able to understand the numerous limitations inherent in epidemiological studies, which depicts the need for comprehensive research to ascertain a final conclusion. As I began completing my critical appraisal, I moved on
to discover that the media article which referenced the study agreed with its conclusion instead of utilizing it for some alternate narrative. Both these sources agreed on emphasizing the increased cancer risk that can be related to wildfire exposure but also explained that there is a necessity for further research on this topic. Oftentimes, the media will use sources that may imply one thing in an effort to directly bolster some point, but this media article reaffirmed the conclusions of the journal article. Moving past how I completed the critical appraisal and the media article’s usage of the study, reflecting on this journey has taught me about the importance of scientific literacy when studying such complex topics. It reinforced the need for constant research, rigorous analysis methodologies, and collaborative efforts to grasp the complex implications of environmental exposures on our health. My journey consisted of a significant learning curve because of the various scientific jargon that I had to decipher, while also grappling with the nuances contained within each facet of the study. This experience helped me comprehend the complexities of scientific research, depicting the conscientiousness required to scrutinize, analyze, and interpret results precisely. In essence, my critical evaluation journey of the study has strengthened my
comprehension of the study’s nuances but also highlighted the continuing difficulties in decoding
scientific research. It has reinforced the crucial role of critical thinking, constant exploration, and
effective communication in improving knowledge and promoting informed decision-making within science and society.