Ground-level ozone increasingly linked to cancer deaths, study finds

• Experts warn rising exposure poses systemic health risks beyond lungs

Ozone in the upper atmosphere protects Earth, but at ground level it acts as a harmful pollutant increasingly linked to cancer-related deaths, experts say.

“While the ozone layer in the stratosphere serves as a protective shield for Earth, ozone at breathing level is an extremely reactive and destructive molecule for living tissues,” said Prof. Dr. Mustafa Ozdogan, head of the Memorial Cancer Center in Istanbul.

A study published in the Journal of Hazardous Materials analyzed 9,223,332 cancer-related deaths across Australia, Brazil, Canada, Chile, South Korea, Mexico, New Zealand and Thailand, examining links between short-term ozone exposure and mortality.

It found ozone-related deaths rose 80% from 261,270 in 2000 to 469,860 in 2023, with traffic emissions and wildfires identified as the main contributors.

Annual ozone concentrations were measured at 11 micrograms per cubic meter from traffic, 4.8 from wildfires and 2.66 from industrial activity. Wildfires were the dominant source in parts of Australia and Brazil.

Ozone exposure tied to higher cancer mortality

The study found that every 10-microgram-per-cubic-meter increase in ozone exposure was associated with a 0.84% rise in deaths across 24 common cancer types.

The impact varied by cancer type, with a 0.42% increase in liver cancer deaths and a 1.43% rise in thyroid cancer deaths linked to the same increase in exposure.

Short-term ozone exposure accounted for 6.37% of all cancer-related deaths, with the highest shares in Brazil (10.8%), Chile (6.3%) and Thailand (6%).

System-wide effects beyond respiratory damage

Ozdogan said the findings show ozone acts not only on the respiratory system but as a systemic carcinogenic factor affecting the entire body.

“It has been proven that ozone affects the entire body,” he said.

He explained that tropospheric ozone is a secondary pollutant formed through photochemical reactions involving nitrogen oxides and volatile organic compounds in sunlight.

Repeated or chronic exposure suppresses antioxidant defenses, leading to persistent oxidative stress, DNA damage, telomere shortening and genetic alterations that can accelerate cancer progression.

He also cited research from China’s Fudan University indicating ozone effects extend through a “lung-liver axis,” disrupting lung microbiota, triggering systemic inflammation, impairing liver metabolism and activating cell death pathways.

Rising air pollution risks in Türkiye

Ozdogan said Türkiye is also facing increasing air pollution risks.

Average PM2.5 levels rose from 15.3 micrograms per cubic meter in 2024 to 19.2 in 2025, while ozone pollution in major cities such as Istanbul increased by 10% in 2024 compared with the previous year.

He noted Türkiye’s legal ozone limit is 120 micrograms per cubic meter over an eight-hour average, higher than the World Health Organization’s recommended 100 micrograms.

Ozdogan said reducing ozone exposure is critical for cancer patients and at-risk groups, advising limits on outdoor activity during peak hours, regular air quality monitoring, antioxidant-rich diets and improved indoor air safety.

*Writing by Fatma Zehra Solmaz