Spatial Analysis of Ambient PM2.5 Exposure and Bladder Cancer Mortality in Taiwan

1. Introduction

Particulate matter (PM) is microscopic solid or liquid matter suspended in the atmosphere. Subtypes of atmospheric particulate matter include suspended particulate matter (SPM), thoracic and respirable particles [1], inhalable coarse particles, which are particles with a diameter between 2.5 and 10 micrometers (μm), fine particles with a diameter of 2.5 μm or less [2] (PM_2.5), ultrafine particles (PM₁₀), and soot. PM_2.5 is found in secondary production through photochemical reactions from hydrocarbons and oxides of nitrogen in the air [2] or in the emission of motor vehicles [3]. PM_2.5 also has been confirmed to be associated with health risks including elevated morbidity [4,5,6,7,8] in human populations around the world. Numerous epidemiological studies have shown associations between PM_2.5 exposure and respiratory-related mortality, and cardiovascular-related diseases [9,10]. Few studies have explored the effect of air pollution on bladder cancer specifically. A study in Spain pointed out that long-term exposure to polycyclic aromatic hydrocarbons (PAHs) and diesel engine emissions from industries near residential areas was associated with higher risk of bladder cancer [11]. In Taiwan, one matched case-control study found a dose-dependent effect of exposure to NO₂, SO₂, and PM₁₀ on bladder cancer mortality [12]. In Brazil, a correlation was observed between PM₁₀ exposure and bladder cancer incidence [13]. In the United States, air pollution ozone days were positively associated with increased bladder cancer mortality [14]. Increased health risks of bladder cancer from exposure to PM₁₀ in air were found in most of these studies. However, no report has yet found an association between exposure to the smaller PM_2.5 and bladder cancer mortality, although in the field of occupation medicine, an association was found between bladder cancer incidence and PAH exposure [15,16], and the concentration of PAHs in air was found to be correlated to PM_2.5. Thus, PM_2.5 might play a role in the etiology of bladder cancer.

Previous studies indicated that risk factors associated with bladder cancer include cigarette smoking, occupational exposure in the textile industry [17], arsenic in drinking water, environmental pollution, sex, and socioeconomic status [18,19]. The age-adjusted bladder cancer mortality in Taiwan ranged from 2.18 to 2.73 per 100,000 population during 2000-2012, and the age-adjusted...