Landmark study of elderly Hongkongers ties air pollution to multiple types of cancer

Every 10 micrograms per cubic metre of increased exposure to tiny particulates in the air increases the risk of elderly Hongkongers dying from some kind of cancer by 22 per cent, a decade-long study by British and Hong Kong researchers has found.

While the links between particulate pollution and cardiopulmonary disease and lung cancer have been well-documented, the joint study was one of few to be published that highlighted an association with mortality from other cancers.

Researchers at the University of Birmingham in the UK and the University of Hong Kong recruited 66,280 people aged 65 or older between 1998 and 2001, and followed their mortality outcomes up to 2011. Causes of death were ascertained based on Hong Kong registrations.

Annual concentrations of fine particulates in their area of residence were estimated using data from satellites and fixed-site monitors.

Fine particulates, or PM2.5, are hazardous airborne particles measuring less than 2.5 microns in diameter and small enough to enter the lungs.

About 4,740 tonnes of PM2.5 are emitted annually into the city’s air. Around half comes from marine or road transport and about a tenth from power generation.

The study found that every 10 micrograms per cubic metre of PM2.5 was associated with a 42 per cent higher risk of dying from cancer of the upper digestive tract and a 35 per cent higher risk of dying from cancers of accessory digestive organs such as the liver, bile ducts, gall bladder, and pancreas.

The risks were found to differ between men and women. For women, the stated increase in PM2.5 exposure heightened their risk of dying from breast cancer by 80 per cent; in men, the same PM increase corresponded to a 36 per cent higher risk of dying of lung cancer.

The study was recently published in Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research, and deepened growing concern around the health risks of long-term PM2.5 exposure.

Dr Neil Thomas of the University of Birmingham’s Institute of Applied Health called air pollution a clear and modifiable public health concern. “The implications for other similar cities around the world are that PM2.5 must be reduced as much and as fast as possible,” he said.

He said the next step was  to determine whether other countries experience similar associations between PM2.5 and cancer deaths. “This study ... suggests that other urban populations may carry the same risks,” he said.

Researcher Dr Thuan Quoc Thach of HKU’s school of public health reiterated that pollution was just one risk factor for cancer. Others such as diet and exercise were “more significant and modifiable risk factors”, he noted.

The Environmental Protection Department said the city’s overall air quality had been improving the past few years with ambient PM2.5 concentrations dropping by 24 per cent between 2011 and last year. It said roadside concentrations dropped over the same period by 21 per cent.

It also said improvements stemmed from effective local air quality measures targeting vehicles, marine vessels and power plants as well as the gradual enhancement of air quality in the Pearl River Delta region.

The World Health Organisation stipulated 25 and 10 micrograms per cubic metre as the respective safe limits for 24-hour and annual concentrations. However, Hong Kong’s limits were less stringent at 75 and 35, respectively.

Clean Air Network chief executive Patrick Fung Kin-wai said the report highlighted the need to pull Hong Kong’s air quality objectives closer to Who standards to safeguard public health.

“A major source of PM2.5 is traffic, but as we can see, the number of private cars continues to grow,” he said. “While Hong Kong faces an ageing population, there have not been any major breakthroughs in transport policy or planning that can keep up.”

The department has commenced a review of its Air Quality Objectives, but any changes to them would not be seen until 2019, according to the department’s timeline.

Public policy think tank Civic Exchange welcomed the study and urged the government to consider other urban planning options to improve wind circulation and to provide more urban open space. Tailpipe solutions, it said, were only practical quick fixes.

A joint-study by the think tank and Hong Kong University of Science and Technology last year showed that PM2.5 concentrations and their associated health risks were highest in poorly ventilated urban street canyons of Hong Kong.

Dr Stephen Chan-lam, an associate professor of oncology at Chinese University of Hong Kong, described the findings as highly significant, saying they finally provided sound evidence linking air pollution to multiple cancers.

“There’s enough evidence for the government to seriously tackle air pollution,” Chan said.