Effects of long-term exposure to traffic-related air pollution on mortality and lung cancer

Abstract

We assessed the association between long-term exposure to air pollution and cause-specific mortality and lung cancer incidence using data from an ongoing cohort study: the Netherlands Cohort Study on Diet and Cancer (NLCS). The NLCS study was initiated in September 1986 with the enrollment of 120,852 subjects aged 55-69 years living in 204 municipalities located throughout the Netherlands. Long-term exposure to nitrogen dioxide (NO2), black smoke (BS), fine particles less than 2.5 ?m (PM2.5) and sulfur dioxide (SO2) was estimated. Exposure at each home address was considered as a function of a regional, an urban and a local component. The regional component was estimated using inverse distance weighed interpolation of measurement data from regional background sites in the national monitoring network. The urban component was estimated using regression models with urban concentrations as dependent variables, and number of inhabitants in different buffers and land use variables, derived with a Geographic Information System (GIS), as predictor variables. The local component was assessed using a GIS and a digital road network with linked traffic intensities. Traffic intensity on the nearest road and the total traffic intensity in a 100 m buffer around each home address were assessed. The methods that were developed explained a relatively large percentage of the spatial variance of the air pollution components. Air pollution and several traffic exposure variables were associated with mortality, but the relative risks were generally small. Statistically significant associations between NO2 and black smoke exposure and natural cause and respiratory mortality were found. The highest relative risks were found for respiratory mortality. We found suggestive evidence for larger effects of black smoke exposure in those with low education and in those with low fruit consumption. We found no association between air pollution concentrations, traffic variables and lung cancer incidence in the full study population. In never smokers, associations between black smoke concentrations and traffic variables with lung cancer incidence were (borderline) significant, however. This is the first time that the effects of air pollution, traffic intensity and traffic noise on cardiovascular mortality have been studied together. We observed an association between traffic intensity on the nearest road and overall cardiovascular mortality, which was driven by an association with ischemic heart disease mortality. Relative risks for background black smoke concentrations were elevated for cerebrovascular and heart failure mortality. These associations were not affected by adjustment for traffic noise. There was an indication of an effect of traffic noise in the highest noise exposure category (> 65 dB(A)), which was largely restricted to heart failure mortality. The relative risk for the association between ischemic heart disease mortality and high traffic noise was reduced to unity after adjustment for background black smoke concentrations and traffic intensity. The associations between traffic intensity on the nearest road with overall cardiovascular mortality and ischemic heart disease mortality were not explained by traffic noise. Overall, the results provide evidence that exposure to background and to traffic-related air pollution increases the risk of cardiovascular, respiratory and lung cancer mortality.