Specifying the Associations\nbetween PM<sub>2.5</sub> Constituents and Gastrointestinal Cancer\nIncidence: Findings from\na Prospective Cohort Study in Beijing, China

This study aimed to test the association between PM<sub>2.5</sub> and the incidence of gastrointestinal (GI) cancer, and\nfurther to\ndetect the primary constituents on this association. A sum of 142,982\nparticipants without GI cancer at baseline were derived from the National\nUrban Cancer Screening Program in Beijing (2013–2019). The\n5 year averaged concentrations of PM<sub>2.5</sub> mass and its five\nconstituents, namely, black carbon (BC), ammonium (NH<sub>4</sub><sup>+</sup>), nitrate (NO<sub>3</sub><sup>–</sup>), organic matter\n(OM), and inorganic sulfate (SO<sub>4</sub><sup>2–</sup>),\nwere estimated by using a hybrid machine learning model. The Cox proportional\nhazard model with fixed effects was used to explore the associations\nbetween PM<sub>2.5</sub> mass and its constituents with the incidence\nof GI cancer. The double-exposure linear model, the mixture exposure\nmodel of quantile-based g-computation, and an explainable machine\nlearning model were utilized to evaluate the importance of different\nPM<sub>2.5</sub> constituents. Long-term exposure to PM<sub>2.5</sub> mass and its constituents was linearly associated with GI cancer;\nthe estimated hazard ratio and 95% confidence interval (95% CI) of\nper standard deviation increment were 1.367 (95% CI: 1.257 to 1.487)\nfor PM<sub>2.5</sub> mass, 1.434 (95% CI: 1.307 to 1.574) for BC,\n1.255 (95% CI: 1.169 to 1.349) for NH<sub>4</sub><sup>+</sup>, 1.217\n(95% CI: 1.139 to 1.301) for NO<sub>3</sub><sup>–</sup>, 1.410\n(95% CI: 1.287 to 1.546) for OM, and 1.410 (95% CI: 1.288 to 1.542)\nfor SO<sub>4</sub><sup>2–</sup>. By using multiple methods,\nresults indicated that SO<sub>4</sub><sup>2–</sup> and BC were\nthe most important constituents. Results indicated that long-term\nexposure to PM<sub>2.5</sub> was associated with a high incidence\nof GI cancer, and BC and SO<sub>4</sub><sup>2–</sup> were robustly\nidentified as the primary constituents.