PM2.5 could be dominant contributor to air pollution-induced global cancer burden: Study

NEW DELHI: A study that analysed global cancer burden with a long-term exposure to common air pollutants across 952 locations found that PM2.5 is the dominant contributor.

Particulate matter sized under 2.5 microns or 0.0025 millimetres (PM2.5) accounted for 8.82 million cases of the total 109 million cases identified between 2000 and 2020, according to findings published in the journal Nature Health.

Highest preventable fraction of cancers in the population due to PM2.5 exposure was observed for cancers of the respiratory, reproductive and endocrine systems.

Researchers, including those from the Chinese Academy of Sciences, also found that globally, each 10 microgram per cubic metre increase in PM2.5, ozone and nitrous oxide levels was associated with an increased risk of cancer by 16 per cent, 4.23 per cent and 11.7 per cent, respectively.

Exposure to nitrous oxide was attributable to 6.67 million incident cases, while exposure to ozone was attributable to about 2.6 million incident cases during the study period. Women were found to be consistently more vulnerable for most malignancies.

Almost the entire global population (99 per cent) breathes air containing pollutant levels exceeding the World Health Organization's air quality guidelines, with the highest exposures seen in low and middle-income countries, the researchers said.

Air pollution adversely affects nearly every organ system in the body, they said.

"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," the authors wrote.

"PM2.5 emerged as the dominant contributor to the global cancer burden, accounting for approximately 8.82 million attributable cases during the study period," they said.

About 17.9 per cent of tracheal, bronchial and lung cancer cases could be prevented if exposure to PM2.5 was removed or addressed, the study found.

The results reinforce the International Agency for Research on Cancer's (IARC) -- the United Nations' cancer agency -- group 1 classification of PM2.5 as a carcinogen, particularly for lung cancer, signifying the existence of definitive, sufficient evidence of PM2.5's carcinogenic properties, the researchers said.

However, the study also showed that PM2.5's cancer-inducing gene mutations extend beyond the respiratory system, particularly cancers of the thyroid, oesophagus, colon and rectal, and breast.

Further, each 10 microgram per cubic metre increase in PM2.5 was found to correspond with a 17.9 per cent higher risk of kidney cancer and a 21.1 per cent higher risk of bladder cancer.

Biologically, PM2.5 exerts broad cancer-related impacts, possibly due to its small size and driving multiple processes, including systemic oxidative stress, DNA damage and immune dysregulation, the researchers said.

The study uses high-quality, globally representative cancer datasets involving populations from low, middle and high-income countries and therefore, ensures a generalisability of the findings, they said.

The findings provide critical evidence to inform air quality policies, the team added.