Fine particulate matter (PM2.5) generated by wildfires can increase the risk of death for lung cancer patients more significantly than the same amount of PM2.5 from general air pollution sources, a study showed.

Dr. Min Zhang's research team at the Icahn School of Medicine at Mount Sinai reported in the medical journal Lancet Oncology on the 18th that an analysis of the relationship between long-term exposure to wildfire-related PM2.5 and survival among approximately 410,000 lung cancer patients revealed that wildfire PM2.5 is associated with greater toxicity per unit of exposure compared to non-wildfire PM2.5.

The research team stated that these findings indicate a need to treat wildfire smoke as a distinct environmental health hazard rather than simply a part of overall air pollution, emphasizing the urgency of developing new strategies to manage wildfires and mitigate their impacts.

Fine particulate matter (PM2.5) is known as a major risk factor for the development of and survival from lung cancer. In the United States, as climate change increases the frequency of wildfires, the proportion of total PM2.5 attributable to wildfires is growing.

The research team pointed out that while wildfire-related PM2.5 may have higher toxicity than non-wildfire PM2.5 due to smaller particle sizes and higher toxic substance content, the exact impact of wildfire PM2.5 on the overall survival of lung cancer patients remains unclear.

The research team estimated exposure levels to wildfire-related and non-wildfire PM2.5 based on the residential zip codes of lung cancer patients from 2008 to 2019, tracking the patients until they died after their lung cancer diagnosis, were lost to follow-up, or until the study concluded.

The study included a total of 1,211,490 person-years of follow-up data for 414,016 lung cancer patients aged 65 and older, with a median follow-up period of 2 years per individual patient.

The median PM2.5 concentrations to which patients were exposed were 0.28 micrograms per cubic meter for wildfire-related PM2.5 and 8.11 micrograms per cubic meter for non-wildfire PM2.5, showing that the absolute concentration of wildfire-related PM2.5 was much lower.

However, for every 1 microgram per cubic meter increase in atmospheric concentration, the risk of death associated with wildfire-related PM2.5 increased by about 7.8%, whereas non-wildfire PM2.5 increased the risk by about 1.7%.

The research team explained that this means wildfire-related PM2.5 has a stronger association with mortality risk when evaluated based on the same concentration increase, suggesting that the source of atmospheric PM2.5 can be just as important as its quantity when assessing health impacts.

Additionally, among the lung cancer patients included in the study, an estimated average of 696 excess deaths per year (95% confidence interval, 576 to 814 deaths) were attributed to wildfire-related PM2.5, and 3,465 deaths (3,061 to 3,864 deaths) to non-wildfire PM2.5.

In particular, a higher number of days with wildfire smoke or longer durations of smoke exposure were found to be associated with worse survival outcomes for lung cancer patients.

The research team explained that wildfire PM2.5 likely has higher toxicity than non-wildfire PM2.5, noting that while wildfire PM2.5 accounts for only about 4% of total PM2.5 mass, it accounts for approximately 17% of total PM2.5 exposure-related deaths.

They added that climate change is causing more frequent and intense wildfires, increasing the contribution of wildfire smoke to total PM2.5 in the United States, and warned that wildfire smoke is no longer a problem confined only to wildfire-prone regions.

However, they noted that the study estimated PM2.5 exposure based on residential zip codes rather than individual actual exposure, and the study subjects were lung cancer patients aged 65 and older, meaning the results should not be directly applied to all age groups or the general public.

The research team added that further research is needed to identify which chemical components of wildfire smoke increase toxicity and to understand the biological mechanisms through which wildfire-related PM2.5 affects cardiovascular, respiratory, and cancer-related health outcomes.