- PM2.5 was linked to 8.82 million cancer cases from 2000 to 2020.
- The study examined 109 million cancer cases across 952 locations.
- PM2.5 was associated with higher risks of several cancers beyond lung cancer.
- Women showed higher attributable risks for most cancers.
- Researchers say the findings underline the need for stronger air quality policies.
Air pollution is often discussed in terms of coughing, breathing difficulties and lung disease. A new global study suggests its impact may reach much further, with long-term exposure to fine particulate matter linked to millions of cancer cases worldwide.
Researchers analysed cancer and air pollution data from 952 locations between 2000 and 2020, covering a total of 109 million cancer cases. The study, published in Nature Health, looked at three common pollutants: fine particulate matter known as PM2.5, ozone and nitrogen dioxide.
PM2.5 emerged as the largest contributor. The researchers estimated that exposure to the tiny particles was associated with about 8.82 million cancer cases during the study period. Nitrogen dioxide was linked to approximately 6.67 million cases, while ozone was associated with about 2.59 million.
Why PM2.5 is such a concern
PM2.5 refers to particles measuring 2.5 micrometres or less in diameter. They are small enough to travel deep into the lungs and can enter the bloodstream.
The latest study found that every 10 micrograms per cubic metre increase in long-term PM2.5 exposure was associated with a 16 per cent increase in the risk of all cancers. For nitrogen dioxide and ozone, the corresponding increases were 11.7 per cent and 4.23 per cent.
The strongest concern remains cancer of the respiratory system. Researchers estimated that around 17.9 per cent of tracheal, bronchial and lung cancer cases could potentially be prevented if PM2.5 exposure were removed or addressed.
The findings also reinforce the International Agency for Research on Cancer's classification of outdoor air pollution and particulate matter as carcinogenic to humans, particularly in relation to lung cancer.
But the study suggests the story does not end with the lungs.
The cancer risks may go beyond the lungs
Researchers found associations between PM2.5 exposure and cancers affecting several other parts of the body, including the thyroid, oesophagus, colon and rectum, and breast.
The study also reported particularly high increases in risk for kidney and bladder cancer. A 10 micrograms per cubic metre increase in PM2.5 was associated with a 17.9 per cent higher risk of kidney cancer and a 21.1 per cent higher risk of bladder cancer.
The researchers said several biological mechanisms may explain the wider effects. Because the particles are so small, they may trigger processes such as oxidative stress, DNA damage and disruption of immune responses.
The study also found that women had consistently higher attributable risks and burdens for most cancers examined.
The authors wrote: "This study evaluated the effects of long-term exposure to PM2.5, O3 (ozone) and NO2 (nitrous oxide) on cancer incidence and quantified their attributable burdens worldwide, encompassing 109 million cases from 952 locations between 2000 and 2020."
They added: "PM2.5 emerged as the dominant contributor to the global cancer burden, accounting for approximately 8.82 million attributable cases during the study period."
A global problem with unequal exposure
The findings are particularly significant because exposure to air pollution is not evenly distributed around the world.
The researchers noted that 99 per cent of the global population breathes air containing pollutant levels above the World Health Organisation's air quality guidelines, with the highest exposures found in low- and middle-income countries.
For countries and cities struggling with traffic emissions, industrial pollution, construction dust and other sources of fine particles, the findings add to the growing evidence that cleaner air is not simply an environmental goal. It is also a long-term public health issue.
The researchers stressed that the study used globally representative cancer data covering low-, middle- and high-income countries. They said the results could help inform air quality policies aimed at reducing the cancer burden.
The findings do not mean that air pollution is responsible for every cancer case, nor that exposure guarantees an individual will develop cancer. Rather, the study estimates the population-level cancer burden associated with long-term exposure.
But its message is difficult to ignore: the air people breathe may play a much larger role in cancer prevention than previously appreciated.
