Association between exposure to multiple air pollutants, transportation noise and cause-specific mortality in adults in Switzerland

BACKGROUND: Long-term exposure to air pollution and noise is detrimental to health; but studies that evaluated both remain limited. This study explores associations with natural and cause-specific mortality for a range of air pollutants and transportation noise. METHODS: Over 4 million adults in Switzerland were followed from 2000 to 2014. Exposure to PM(2.5), PM(2.5) components (Cu, Fe, S and Zn), NO(2), black carbon (BC) and ozone (O(3)) from European models, and transportation noise from source-specific Swiss models, were assigned at baseline home addresses. Cox proportional hazards models, adjusted for individual and area-level covariates, were used to evaluate associations with each exposure and death from natural, cardiovascular (CVD) or non-malignant respiratory disease. Analyses included single and two exposure models, and subset analysis to study lower exposure ranges. RESULTS: During follow-up, 661,534 individuals died of natural causes (36.6% CVD, 6.6% respiratory). All exposures including the PM(2.5) components were associated with natural mortality, with hazard ratios (95% confidence intervals) of 1.026 (1.015, 1.038) per 5 microg/m(3) PM(2.5), 1.050 (1.041, 1.059) per 10 microg/m(3) NO(2), 1.057 (1.048, 1.067) per 0.5 x 10(-5)/m BC and 1.045 (1.040, 1.049) per 10 dB Lden total transportation noise. NO(2), BC, Cu, Fe and noise were consistently associated with CVD and respiratory mortality, whereas PM(2.5) was only associated with CVD mortality. Natural mortality associations persisted < 20 microg/m(3) for PM(2.5) and NO(2), < 1.5 10(-5)/m BC and < 53 dB Lden total transportation noise. The O(3) association was inverse for all outcomes. Including noise attenuated all outcome associations, though many remained significant. Across outcomes, noise was robust to adjustment to air pollutants (e.g. natural mortality 1.037 (1.033, 1.042) per 10 dB Lden total transportation noise, after including BC). CONCLUSION: Long-term exposure to air pollution and transportation noise in Switzerland contribute to premature mortality. Considering co-exposures revealed the importance of local traffic-related pollutants such as NO(2), BC and transportation noise.