Long-term ambient hydrocarbon exposure and incidence of urinary bladder cancer

Abstract

Particulate matter and volatile organic compounds, including total hydrocarbons (THCs), are major ambient air pollutants. Primary nonmethane hydrocarbons (NMHCs) originate from vehicle emissions. The association between air pollution and urinary bladder cancer (UBC) is debatable. We investigated whether long-term exposure to ambient hydrocarbons increases UBC risk among people aged ≥ 20 years in Taiwan. Linkage dataset research with longitudinal design was conducted among 589,135 initially cancer-free individuals during 2000-2013; 12 airborne pollutants were identified. Several Cox models considering potential confounders were employed. The study outcomes were invasive or in situ UBC incidence over time. The targeted pollutant concentration was divided into three tertiles: T1/T2/T3. The mean age of individuals at risk was 42.5 (SD 15.7), and 50.5% of the individuals were men. The mean daily average over 10 years of airborne THC concentration was 2.25 ppm (SD 0.13), and NMHC was 0.29 ppm (SD 0.09). Both pollutants show long-term monotonic downward trend over time using the Mann-Kendall test. There was a dose-dependent increase in UBC at follow-up. UBC incidence per 100,000 enrollees according to T1/T2/T3 exposure to THC was 60.9, 221.2, and 651.8, respectively; it was 170.0/349.5/426.7 per 100,000 enrollees, corresponding to T1/T2/T3 exposure to NMHC, respectively. Without controlling for confounding air pollutants, the adjusted hazard ratio (adj.HR) was 1.83 (95% CI 1.75-1.91) per 0.13-ppm increase in THC; after controlling for PM_2.5, adj.HR was even higher at 2.09 (95% CI 1.99-2.19). The adj.HR was 1.37 (95% CI 1.32-1.43) per 0.09-ppm increase in ambient NMHC concentration. After controlling for SO₂ and CH₄, the adj.HR was 1.10 (95% CI 1.06-1.15). Sensitivity analyses showed that UBC development risk was not sex-specific or influenced by diabetes status. Long-term exposure to THC and NMHC may be a risk factor for UBC development. Acknowledging pollutant sources can inform risk management strategies.

Figure 1

The study flow diagram.

Figure 2

The log minus log survival plot by ambient air THC and NMHC pollutants, and the cumulative incidence of urinary bladder cancer in individuals among THC and NMHC pollutants’ tertile. Upper panel: To evaluate the proportional hazards (PH) assumption involving the comparison of estimated − ln (− ln) survival curves over different THC and NMHC tertiles, the plot of log (− log [survival function]) versus survival time in THC and NMHC air pollutants was constructed. The graphical approach showing parallel curves over time provides support of the PH assumption. Lower panel: Cumulative incidence of urinary bladder cancer for individuals among tertiles of THC and NMHC pollutants. The tertile values, in ppm (THC, NMHC), are as follows: THC (lowest tertile, T1: < 2.10; medium tertile, T2: ≥ 2.10 and < 2.25; and highest tertile, T3: ≥ 2.25); NMHC (lowest tertile, T1: < 0.26; medium tertile, T2: ≥ 0.26 and < 0.34; and highest tertile, T3: ≥ 0.34).

Figure 3

A schematic diagram summarizing the study results of the risk of developing urinary bladder cancer associated with long-term exposure to different tertiles of airborne THC or NMHC concentration. The magnitudes of risk show a significant exposure–response relationship.