Relationship between long-term exposure to fine particulate air pollution and colorectal cancer mortality in Taiwan

The International Agency for Research on Cancer classified fine particulate matter (PM_2.5) air pollution as carcinogenic to humans (Group I). Although PM_2.5 exposure has been associated with lung cancer occurrence, few studies investigated this association with non-lung cancer. Colorectal cancer (CRC) is the third leading cause of cancer deaths both among men and women. In Taiwan, deaths attributed to CRC vary considerably across townships, suggesting involvement of the environment. The aim of this study was to examine the association between long-term ambient PM_2.5 exposure and deaths attributed to CRC in 66 municipal areas across Taiwan. Annual PM_2.5 levels were compared against age-standardized CRC mortality rates in male and female residents of these municipalities from 2012 to 2021. Annual PM_2.5 levels of different municipalities were sub-divided into tertiles. Adjusted risk ratio (RR) was calculated by multiple regression analyses, controlling for municipal lung cancer deaths, urbanization level, annual average household income, and density of physicians in the municipal areas. For males, adjusted RRs for CRC death were 1.1 (95% CI = 1.05-1.15) for municipalities with PM_2.5 levels ranging from 18.96 to 25.19 µg/m³and 1.15 (95% CI = 1.1-1.21) for levels ranging from 25.2 to 29.48 µg/m³, respectively, compared to those areas belonging to the lowest tertiles. Our analysis of trend suggested that risk of CRC-related death paralleled increases PM_2.5 levels in males. For females, adjusted RRs were 1.18 (95% CI = 1.12-1.25) and 1.12 (95% CI = 1.06-1.19), respectively. Evidence indicated that long-term exposure to PM_2.5 may elevate the risk of CRC-related death in both men and women in Taiwan.