Air Pollutant Exposure Associated with Numerous Cancer Types

Long-term exposure to particulate matter air pollutants was associated with an increased risk of mortality for numerous types of cancer in the elderly Hong Kong population.

A study published in Cancer Epidemiology, Biomarkers & Prevention focused on ambient fine particulate matter — matter with an aerodynamic diameter less than 2.5 micrometers (PM2.5).

“Long-term exposure to particulate matter has been associated with mortality mainly from cardiopulmonary causes and lung cancer, but there have been few studies showing an association with mortality from other cancers,” said researcher Thuan Quoc Thach. “We suspected that these particulates could have an equivalent effect on cancers elsewhere in the body.”

For the study, researchers recruited 66,280 people age 65 or older between 1998 and 2001. Participants were followed until 2011 and the exact causes of death were gathered from Hong Kong registrations.

Researchers used satellite data and fixed-site monitors to estimate the annual concentrations of PM2.5 at the participants’ homes. The data was adjusted for smoking status and excluded deaths that occurred within 3 years of baseline to control for competing diseases.

The results of the study showed that for every 10 microgram per cubic meter (µg/m³) of increased exposure to PM2.5, the risk of cancer mortality increased by 22%. These increases were associated with a 42% increased risk of dying from cancer in the upper digestive track and 35% from accessory digestive organs, including bile ducts, gall bladder, liver, and pancreas.

In women, the study results revealed that for every 10 µg/m³ of increased exposure to PM2.5, there was an 80% increased risk of mortality from breast cancer. For men, there was a 36% increased risk of mortality from lung cancer.

According to the researchers, some possible explanations for the association include defects in DNA repair function, alterations in the body’s immune response, or inflammation that triggers angiogenesis.

For digestive organs, heavy metal pollution may affect gut microbiota, influencing the development of cancer.

“The implications for other similar cities around the world are that PM2.5 must be reduced to reduce the health burden,” said researcher Neil Thomas. “Air pollution remains a clear, modifiable public health concern."

Some limitations to the study included the focus on PM2.5 solely. Although new research is starting to study the effects of exposure to different pollutants on human health, study authors caution that pollution is only one risk factor for cancer, and that other factors like diet and exercise could have more significant and modifiable risk factors.

“The next step is to determine whether other countries experience similar associations between PM2.5 and cancer deaths,” Thomas said. “This study, combined with existing research, suggests that other urban populations may carry the same risks but we'd be keen to look into this further.”