The smoke from forest fires is more terrible than you think

Wildfire smoke will be a persistent problem. As the climate continues to change, wildfires will become more frequent and more severe, with far greater impacts on human life than we currently realize. Current research focuses on the short-term effects of wildfire smoke, but there is a lack of data and information on the long-term health effects of wildfire smoke, such as long-term effects on lung function and potential effects on pregnant women and infants, which scientists and epidemiologists need to fill quickly.

Written by Zhu Yehua

In recent years, wildfires have occurred frequently around the world. Every summer, tens of millions of people live in the thick smoke of wildfires, which can even last for weeks in some places. Affected by weather, wind and dry bushes, wildfires cannot be controlled. They can burn nearly half a million hectares of land at a very fast speed, devouring everything along the way - trees, houses and humans. Frequent wildfires have brought devastating blows to the earth: releasing carbon stored in the land for many years, greatly losing the ability of trees to absorb carbon in the future, causing soil erosion in forests, and toxic particulate matter aggravating air pollution.

A dozen years ago, people thought that wildfire smoke was "natural" air pollution, and even if it was severe, it was only short-term, so it was not as worrying as pollution from chemical plants, refineries and car exhaust. But now, not only scientists and doctors, but also ordinary people have realized that wildfire smoke may have potential lasting effects on human health, and the longer the exposure to wildfire smoke, the more serious the effects may be.

Wildfires cause a surge in hospitalizations

In many Western countries, days of thick smoke are nothing new. Record-breaking wildfires occur almost every year. Human-caused climate change is increasing the intensity and duration of fires around the world. More people will be exposed to smoke more frequently in the future. Smoke from longer-lasting and more frequent wildfires can have serious health effects.

How to quantify this impact?

On September 8, 2021, the Lancet Planetary Health published two sister articles online, assessing the burden of wildfire smoke on human health [1-2].

The United States suffers from wildfire smoke every year. A 2021 study published in Nature Communications collected 14 years of hospital admission data in Southern California and compared it with peaks in air pollution during strong winds. The results found that fine particles in wildfire smoke led to a 10% increase in hospitalizations for respiratory problems compared to when there was no smoke. Although other sources of air pollution are also harmful, they only increased hospitalizations by about 1%. The study also sent a more worrying signal: the tiny particles released in wildfire smoke are 10 times more harmful to humans than particles released from other pollution sources (such as car exhaust) [3].

Why is wildfire smoke more harmful?

Wildfire smoke contains thousands of compounds, including carbon monoxide, volatile organic compounds, carbon dioxide, hydrocarbons, and nitrogen oxides. These components combine freely, and the resulting compounds are unique. Fine particles are the wildfire smoke component of greatest concern, and they can remain suspended in the air for long periods of time, traveling hundreds of kilometers.

Wildfire smoke is different from traffic exhaust. Its composition is more complex, and it will carry along any harmful substances it encounters during its spread. For example, wind will blow bacteria and fungi off the surfaces of farmland, deserts, lakes, oceans, etc. These microorganisms can rise into the atmosphere and travel around the world, and wildfires exacerbate the spread of microorganisms. In April 2020, scientists found traces of bacteria and fungi in smoke. According to the Centers for Disease Control and Prevention, the number of valley fever cases in Arizona and California increased more than sixfold from 1998 to 2018. Valley fever is a disease caused by Coccidioidomycosis, which causes coughing, fever, and chest pain, and can be fatal in severe cases. Coccidioidomycosis thrives in the soil of California and the southwestern deserts of the United States, and spreads into the air under dry and hot climate conditions. When the airborne Coccidioidomycosis is inhaled into the lungs, it may develop into valley fever. Firefighters involved in forest fire fighting are particularly susceptible to this disease [4].

How inhaled wildfire smoke affects the body

Fine particulate matter is one of the air pollutants of concern. It is small enough to penetrate the human respiratory system and penetrate deep into the lungs, irritating and exacerbating asthma and other respiratory diseases. It is also possible to bypass the body's defense mechanisms and enter the bloodstream, from where it reaches other organs, increasing the risk of stroke, heart attack and breathing problems.

According to a study in the Journal of the American Heart Association, wildfire smoke contains a wide variety of gases and particles from materials that support combustion, including ozone, carbon monoxide, polycyclic aromatic compounds, nitrogen dioxide, and particulate matter pollutants that have been linked to respiratory and cardiovascular disease.[5] What happens when a healthy person breathes smoky air for long periods of time each year?

When fine particulate matter enters the body, the human immune system quickly releases the same immune cells that attack viruses. But immune cells cannot break down particulate matter, so they can only work harder to try to defeat it, leading to more inflammation. There is also evidence that particles themselves can break through barriers in capillaries, enter the bloodstream, and cause an inflammatory response throughout the body. Inflammation can affect the lungs, kidneys, liver, and even the brain. It is worth mentioning that inflammation is particularly dangerous for people with asthma or chronic obstructive pulmonary disease, and persistent inflammation can make these diseases worse. According to a 2018 study in GeoHealth, wildfire smoke causes about 17,000 premature deaths in the United States each year, and this number is expected to double by 2100[6]. A 2016 report in Environmental Research Letters also pointed out that illegal land clearing fires and wildfires in Indonesia in 2015 caused an estimated 100,000 deaths in Southeast Asia. The culprit is particulate matter from the fire - organic and inorganic particles suspended in the air, including pollen, ash, and pollutants[7].

Respiratory problems are the most obvious response to smoke inhalation, but that doesn’t mean other hazards don’t exist. A 2016 study published in The Lancet looked at the effects of various pollutants in six cities in the United States and found a link between high levels of air pollution and coronary artery disease. The potential harm is particularly concerning when it comes to the damage that wildfire smoke can cause to the heart.[8]

Wildfire smoke will be a persistent problem. As the climate continues to change, wildfires will become more frequent and more severe, with far greater impacts on human life than we currently realize. Current research focuses on the short-term effects of wildfire smoke, but there is a lack of data and information on the long-term health effects of wildfire smoke, such as long-term effects on lung function and potential effects on pregnant women and infants, which scientists and epidemiologists need to fill quickly.

References

[1] https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(21)00200-X/fulltext

[2] https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(21)00173-X/fulltext

[3] https://www.nature.com/articles/s41467-021-21708-0

[4] https://www.cdc.gov/fungal/diseases/coccidioidomycosis/statistics.html

[5] https://www.ahajournals.org/doi/full/10.1161/jaha.117.007492

[6] https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GH000144#gh282-fig-0011

[7] https://iopscience.iop.org/article/10.1088/1748-9326/11/9/094023/pdf

[8] https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)00378-0/fulltext