Cancer Mortality Risks from Long-Term Exposure to Ambient Particulates in a Cohort of Older Population in Hong Kong

Background The World Health Organization has recently declared air pollution as carcinogenic. Very few studies have assessed the long-term effects of particulate matter (PM) on cancer mortality for different causes using the same population, but none are characterized by densely populated high-rise buildings, which are typical in metropolitan cities. Methods We recruited 66,820 persons who aged =65 in 1998-2001 and followed up till 2011. Annual mean concentrations of residential ambient PM were estimated using fixed-site pollutant-monitors, geospatial heights and satellite data. We used Cox regression model to assess the mortality hazard ratio (HR) of different cancer causes per 10µg/m3 increase of PM2.5 (aerodynamic diameter<2.5µm) or PM10 (<10µm). Results PM2.5 was associated with increased risk of all-cause (HR 1.13 [95%CI: 1.08,1.19] ) and all-cancer (1.22 [1.11, 1.34]) mortality, and for specific cancers of upper digestive tract, digestive accessory organs, brain and endocrine glands in all subjects; breast and ovary in females; lung and skin-and-structural tissues in males; lympho-hematopoietic in those aged=71. Compared with PM10, excess risks for PM2.5 were all at least two times as high. Cancer mortality of head-and-neck, lower digestive tract or urinary organs were not associated with PM2.5 or PM10. Conclusion Long-term particulate exposures are associated with elevated risks of death due to different types of cancers, indicating high public health relevance. This cohort study is particularly timely in China where compelling evidence is needed to support pollution control policy to counter the health damages associated with the rapid economic development.