Wildfire Smoke Can Pose Risks Months Later

Medscape

5 hours ago

The particulate matter from wildfire smoke may be difficult to spot — with the eyes — within days, but those dangerous particles continue to post health risks for up to 3 months after exposure, new research suggested.
A study published in Epidemiology in late May demonstrated that fine particulate matter in wildfire smoke represents a danger to human health considerably longer than a couple of days as previously thought. Researchers also found that exposure to the particulate matter can occur even after the fires have ended.
Because studies have shown that air pollution exposure can trigger heart attack within an hour, the duration of the effects of wildfire particulate matter surfaced by this new research is a key new insight.
The study, authored by researchers from the Icahn School of Medicine at Mount Sinai in New York City and Harvard T.H. Chan School of Public Health in Boston, highlighted increased risks for patients with cardiovascular disease (CVD) when exposed to smoke particulate matter, referred to as PM2.5, which by definition is 2.5 microns in diameter. To get an idea of how small the particles in wildfire smoke are, the average human hair is about 70 microns in diameter, meaning a 2.5-micron particle is about 28 times smaller than a human hair.
The study showed that this tiny irritant is dangerous to those with ischemic heart disease, arrhythmia, and hypertension, as well as people with a number of cardiorespiratory diseases.
Researchers made these conclusions by obtaining hospitalization records for the residents of 15 states between 2006 and 2016 from the State Inpatient Databases as well as daily smoke particulate matter estimates at 10 km2 cells across the contiguous US, and aggregating them using zip codes to match the spatial resolution of the hospital records. The 3-month exposure to smoke particulate matter was associated or marginally associated with increased hospitalization risks for most cardiorespiratory diseases, with hypertension showing the greatest susceptibility.
'Patients with CVD and the general public should be aware that wildfire smoke is a serious health risk, even if the fire is far away from your home. This is because the emissions can remain in the air and travel long distances for weeks or months after a wildfire has ended,' said Yaguang Wei, PhD, assistant professor at the Icahn School of Medicine at Mount Sinai and principal investigator of the study. 'Cardiologists and other healthcare providers should definitely discuss these risks with their patients, not only during wildfires but also in the following weeks, as the risk may persist.'
Wei said that ongoing studies show that the particulate matter in wildfire smoke is among the most toxic environmental pollutants and can do systemic damage, which can pose further complications for those battling CVD.
Yaguang Wei, PhD
'This is because smoke has smaller particles, which can more easily get into the body, and it has more carbonaceous compounds, which are thought to be especially toxic,' Wei said. 'They can enter the bloodstream and circulate throughout the body, which generates systematic effects. The emissions can remain in the air and travel long distances for weeks or months after a wildfire has ended.'
Loren Wold, PhD, a professor at the Ohio State University College of Medicine, Columbus, Ohio, said that this study is crucial, in that it is important to understand the health implications of this particulate matter given the increasing occurrence of wildfires worldwide, and that particulate matter is not very extensively studied.
'People with cardiovascular disease should be especially careful being outside during days when wildfire smoke is present, as exposure to particulate matter from wildfire smoke is especially dangerous for those with cardiovascular disease as it causes an increase in oxidative stress and inflammation, which can further worsen the disease,' Wold, who has been studying particulate matter himself for two decades, said. 'Wildfire smoke can also cause temporarily increased blood pressure and vascular inflammation, as well as changes in heart rate variability, which can further exacerbate cardiovascular disease.'
Loren Wold, PhD
Particulate matter this small can bypass the nose and throat and enter deep into the lungs, and 'penetrate the linings of blood vessels to gain entry to the circulation,' Wold said. It also contains higher concentrations of organic carbon and black carbon, or soot, and can travel thousands of miles and linger for weeks in the atmosphere, he said.
Plus, he said, the scale and unpredictability of exposure to wildfire particulate matter makes the health risks 'especially troublesome.'
Shahir Masri, ScD, an associate specialist in air pollution exposure assessment and epidemiology at the Irvine Joe C. Wen School of Population & Public Health, University of California, Irvine, California, said that the notable finding of this study is the duration of the effects posed by the wildfire smoke particulate matter. He pointed out this review paper from 2024 that highlighted its many negative effects, while arguing that the dangerous pollutants that come from wildfires come from other sources, too.
'Many pollutants originate from wildfires, such as carbon monoxide, nitrogen oxides, and polycyclic aromatic hydrocarbons. However, I should mention that these pollutants shouldn't be thought of as exclusively wildfire-related,' he said.
Instead, they're common byproducts from the combustion of organic matter, whether it be wildfires or vehicle exhaust, Masri said. 'Also, even acute, or short-term exposure, to wildfire pollution, is known to exacerbate the symptoms related to underlying health conditions, including cardiovascular disease, as well as asthma, COPD [ chronic obstructive pulmonary disease], and lung cancer, and others mentioned in the new Harvard study.'
At-Risk Individuals Should Take Care
The take-home from this study is that individuals suffering from CVD, as well as other underlying conditions, should protect themselves against the effects of wildfire smoke particulate matter when it's in the air. That includes both immediate, acute exposure as well as follow-on exposure, which this study shows can linger for up to 3 months after the event.
The first key is for impacted individuals to stay aware of when the particulate matter is in the air. The US government provides an air quality tool called Air Now, where users can look up their local air forecast with their zip code or city and state. The meter on this page displays the Air Quality Index (AQI). Government guidelines suggest that if results show that if the AQI is between 101 and 150, those with CVD or other underlying conditions should reduce prolonged or heavy outdoor exertion; if it's over 201, all outdoor exertion should be avoided; and if over 301, all physical activity outdoors should be avoided.
Shahir Masri, ScD
Wei said that the first thing individuals with CVD should use to protect against the complications from wildfire particulate matter is an air purifier with a high efficiency particulate air filter and noted that these are becoming more inexpensive. Masri agreed that air purifiers are essential to help with indoor air quality and provided some tips on successful use.
'Running an air purifier can be very effective at reducing levels of PM2.5 in the home and workspace by 50% or more. Air purifiers, however, come with different flow rates and (effective) sizes. One must be sure to read the label of the air purifier to understand the size of the room it is capable of cleaning,' Masri said. 'If you only have one air purifier, to ensure the cleanest air I suggest placing it in the room where you sleep or work during the day and closing the doors and windows to that room. This reduces intrusion of dirty outdoor air during a wildfire, for instance, and therefore enables the device to do its job more effectively.'
Masking is also an option, Masri said, but only when it's the right mask, worn properly.
'One can also opt to wear an N95 mask or respirator around the face to help reduce particulate matter exposure, but the mask must be secured tightly to the face,' he added. 'Those with facial hair will not achieve the tight seal needed to keep air pollution out of your lungs. Lastly, avoidance of outdoor exercise and other outdoor activities is important during major air pollution events like wildfires.'