Researchers have long known that long-term exposure to fine-particle air pollution is implicated in lung cancer and heart disease, but a new study shows it is also associated with sharply higher mortality rates from cancers of the breast, the upper digestive tract and other organs.
Between 1998 and 2011, scientists followed more than 66,000 Hong Kong residents, who were at least 65 years old at the time of enrollment, and their exposure to particulate matter with a diameter of 2.5 micrometers or less. Such pollution typically forms when gases are emitted from cars, trucks, power plants and other industrial sources. Using fixed-site monitors and satellites, the researchers measured the concentration of particle pollution.
They found that every increased exposure of 10 micrograms per cubic meter was associated with a 22 percent higher risk of dying from any cancer. For some cancers, the greater mortality risk was much more: 42 percent for the upper digestive tract and 80 percent for breast cancer.
"The implications for other similar cities around the world are that [particulate pollution] must be reduced as much and as fast as possible," said G. Neil Thomas, a researcher at the University of Birmingham in England and one of the co-authors of the study.
John Groopman, an environmental-health expert at Johns Hopkins Bloomberg School of Public Health and who was not involved in the study, agreed that the results of the study could be extrapolated to similar urban areas in high-functioning economies, such as Singapore, New York and Los Angeles. "We really need the research to understand what it is about the nature of these particles that is contributing to this."
Besides Thomas, the other main co-author was Thuan Quoc Thach, a scientific officer of the University of Hong Kong's School of Public Health. The study was published Friday in the journal Cancer Epidemiology, Biomarkers & Prevention.
The researchers said that the association between the fine particulate matter and cancer could be the result of damage to the body's DNA-repair function, changes in the immune response or inflammation that triggers the growth of new blood vessels fueling the spread of tumors.
Particulate matter is a complicated mixture of extremely small particles and liquid droplets, according to the Environmental Protection Agency. Once inhaled, the particles can cause lung, heart and other problems.
A separate study by the Bloomberg School released Wednesday showed that even small amounts of air pollution appear to raise the risk of a condition in pregnant women linked to premature births.
Researchers, in a study conducted in Boston, found that fine particles from car exhaust and other industrial sources can end up in the placentas of pregnant women. The greater the maternal exposure to pollution, the more likely that the women would have a condition called intrauterine inflammation, a leading cause of premature birth.
The scientists said the study, reported online in Environmental Health Perspectives, suggested that EPA air-pollution standards may not be stringent enough to protect developing fetuses. "We found biological effects in women exposed to air pollution levels below the EPA standard," said lead author Rebecca Massa Nachman, who is a postdoctoral fellow at the Bloomberg School.