Air Particle Pollution Exposure Linked To Higher Cancer Death Risk

Woman Takes Pictures in Shanghai Smog
A woman wears a mask to keep from inhaling smog as she takes pictures in Shanghai in March. Researchers have found that death rates from various types of cancer surge with increased exposure to pollution from microscopic particles invisible to the naked eye. Aly Song/Reuters

Air pollution doesn't just increase the risk of lung cancer, new research shows. A study of thousands of elderly people living in Hong Kong showed that long-term exposure to pollution from tiny but toxic air particles increased their risk of dying from any cancer by 22 percent.

Particle pollution is made up of microscopic solids or liquid droplets so small they can get into the lungs or bloodstream. These particles consist of substances that include hydrocarbons, nitrates, sulfates and heavy metals and are pervasive in cities, where the burning of fossil fuels for transportation or to generate power takes its toll. Some particle pollutants, like soot, dust and smoke, are large or dark enough to be visible to the naked eye, according to the U.S. Environmental Protection Agency. Even the largest fine particles, however, are 30 times smaller in diameter than a single strand of human hair.

For the study, published April 29 in Cancer Epidemiology, Biomarkers & Prevention, researchers recruited 66,280 people 65 or older between 1998 and 2001 and followed them until 2011. Using five monitoring stations around Hong Kong over that period, the team was able to measure hourly concentrations of ambient particulate matter less than 2.5 micrometers in diameter.

Linking those measurements to satellite data provided by NASA allowed the scientists to determine the amount of particulate pollutants per square kilometer. Next they estimated particulate concentration using a model that took into account the height of residential locations above mean sea level. Hong Kong buildings range from three stories to well over 70 in modern buildings. Incorporating the levels of each residential building into their model helped the team members more accurately assess the exposure to air particle pollution at each address once they digitally located each participant on the map.

Hong Kong death records showed that for every 10 micrograms per cubic meter of increased pollutant exposure, the risk of dying from any cancer rose by 22 percent. That level of exposure caused a 42 percent rise in the risk of dying from cancer of the upper digestive tract and a 35 percent greater risk of death from cancer of accessory digestive organs—the liver, bile ducts, gallbladder and pancreas. For women, the risk of dying from breast cancer rose by 80 percent for every 10-microgram increase, and men were 36 percent more likely to die of lung cancer at that level of exposure.

Study author Dr. Neil Thomas, who is with the Institute of Applied Health at the University of Birmingham, says some of the results were expected. Those not anticipated underscore the significance of studies evaluating air pollution's effects on cancers of organs outside of the pulmonary and respiratory systems.

"We have looked at lung cancer in other studies and were also expecting an association with upper digestive tract cancers which come into direct contact with the particles," Thomas says. "We knew there was a potential for a systemic effect and that ultrafine particles—those less than 1 microgram—can enter the bloodstream. The breast tissue has fine capillary beds to nourish the tissue as part of milk production, so it's not too surprising that these particulates enter and then cause cancer."

The researchers believe that increased exposure to these minuscule pollutants could trigger defects in the body's ability to repair DNA, alter its immune response or breed inflammation that spawns the growth of new blood vessels, which in turn allows tumors to spread. In the case of digestive organ cancer, heavy metal pollution could affect the gut microbiome to influence cancer proliferation.

Although there's no way to prove that particle pollution is any more to blame for the increase in cancer deaths than other pollutants, Thomas says the results of this study indicate it is a very likely suspect.

"What the study does show," he says, "is that contaminants, most likely in this case the fine particulates, in the air we breathe are causing us harm, and we should obviously try to minimize that."

Smoking cigarettes, he points out, is a risk factor only for those who smoke and those around them. "In contrast, everyone in the population is exposed to air pollution, so although the individual risk is much smaller, it can have a much broader impact on the population."