Long-term exposure to ultrafine particles and natural and cause-specific mortality

BACKGROUND: Health implications of long-term exposure to ubiquitously present ultrafine particles (UFP) are uncertain. The aim of this study was to investigate the associations between long-term UFP exposure and natural and cause-specific mortality (including cardiovascular disease (CVD), respiratory disease, and lung cancer) in the Netherlands. METHODS: A Dutch national cohort of 10.8 million adults aged >/= 30 years was followed from 2013 until 2019. Annual average UFP concentrations were estimated at the home address at baseline, using land-use regression models based on a nationwide mobile monitoring campaign performed at the midpoint of the follow-up period. Cox proportional hazard models were applied, adjusting for individual and area-level socio-economic status covariates. Two-pollutant models with the major regulated pollutants nitrogen dioxide (NO(2)) and fine particles (PM(2)(.)(5) and PM(10)), and the health relevant combustion aerosol pollutant (elemental carbon (EC)) were assessed based on dispersion modelling. RESULTS: A total of 945,615 natural deaths occurred during 71,008,209 person-years of follow-up. The correlation of UFP concentration with other pollutants ranged from moderate (0.59 (PM(2)(.)(5))) to high (0.81 (NO(2))). We found a significant association between annual average UFP exposure and natural mortality [HR 1.012 (95 % CI 1.010-1.015), per interquartile range (IQR) (2723 particles/cm(3)) increment]. Associations were stronger for respiratory disease mortality [HR 1.022 (1.013-1.032)] and lung cancer mortality [HR 1.038 (1.028-1.048)] and weaker for CVD mortality [HR 1.005 (1.000-1.011)]. The associations of UFP with natural and lung cancer mortality attenuated but remained significant in all two-pollutant models, whereas the associations with CVD and respiratory mortality attenuated to the null. CONCLUSION: Long-term UFP exposure was associated with natural and lung cancer mortality among adults independently from other regulated air pollutants.