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Rob Beelen,¹ Gerard Hoek,¹ Piet A. van den Brandt,² R. Alexandra Goldbohm,³ Paul Fischer,⁴ Leo J. Schouten,² Michael Jerrett,⁵ Edward Hughes,⁶ Ben Armstrong,⁷ and Bert Brunekreef^1,8

¹Institute for Risk Assessment Sciences, Division Environmental Epidemiology, Utrecht University, Utrecht, the Netherlands; ²Department of Epidemiology, Maastricht University, Maastricht, the Netherlands; ³TNO Quality of Life, Department of Prevention and Health, Leiden, the Netherlands; ⁴Centre for Environmental Health Research, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands; ⁵School of Public Health, University of California, Berkeley, California, USA; ⁶Edward Hughes Consulting, Ottawa, Ontario, Canada; ⁷Public and Environmental Research Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom; ⁸Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, the Netherlands

Abstract
Background: Several studies have found an effect on mortality of between-city contrasts in long-term exposure to air pollution. The effect of within-city contrasts is still poorly understood.

Objectives: We studied the association between long-term exposure to traffic-related air pollution and mortality in a Dutch cohort.

Methods: We used data from an ongoing cohort study on diet and cancer with 120,852 subjects who were followed from 1987 to 1996. Exposure to black smoke (BS) , nitrogen dioxide, sulfur dioxide, and particulate matter ≤ 2.5 µm (PM_2.5) , as well as various exposure variables related to traffic, were estimated at the home address. We conducted Cox analyses in the full cohort adjusting for age, sex, smoking, and area-level socioeconomic status.

Results: Traffic intensity on the nearest road was independently associated with mortality. Relative risks (95% confidence intervals) for a 10-µg/m³ increase in BS concentrations (difference between 5th and 95th percentile) were 1.05 (1.00–1.11) for natural cause, 1.04 (0.95–1.13) for cardiovascular, 1.22 (0.99–1.50) for respiratory, 1.03 (0.88–1.20) for lung cancer, and 1.04 (0.97–1.12) for mortality other than cardiovascular, respiratory, or lung cancer. Results were similar for NO₂ and PM_2.5, but no associations were found for SO₂.

Conclusions: Traffic-related air pollution and several traffic exposure variables were associated with mortality in the full cohort. Relative risks were generally small. Associations between natural-cause and respiratory mortality were statistically significant for NO₂ and BS. These results add to the evidence that long-term exposure to ambient air pollution is associated with increased mortality.

Key words: air pollution, cohort, mortality, traffic. Environ Health Perspect 116:196–202 (2008) . doi:10.1289/ehp.10767 available via http://dx.doi.org/ [Online 19 November 2007]

Address correspondence to B. Brunekreef, Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80178, 3508 TD Utrecht, the Netherlands. Telephone: 31 30 2539490/94. Fax: 31 30 2539499. E-mail: b.brunekreef@uu.nl

Supplemental Material is available online at http://www.ehponline.org/members/2007/10767/suppl.pdf

We are indebted to the participants of this study and further thank the Dutch Central Bureau of Genealogy and the Dutch Central Bureau of Statistics for providing data. We thank S. van de Crommert, H. Brants, J. Nelissen, C. de Zwart, W. van Dijk, M. Moll, A. Pisters, M. Jansen, H. van Montfort, T. van Moergastel, L. van den Bosch, and R. Schmeitz for assistance ; C. van Wiechen (National Institute of Public Health and the Environment) for advice on geographic information system calculations ; the National Institute of Public Health and the Environment for providing air pollution data monitored by the National Air Quality Monitoring Network in the Netherlands.

The research described in this article was conducted under contract to the Health Effects Institute (HEI) (research grant 01-2) , an organization jointly funded by the U.S. Environmental Protection Agency (EPA) and certain motor vehicle and engine manufacturers. The Netherlands Cohort Study on Diet and Cancer was supported by the Dutch Cancer Society.

The contents of this article do not necessarily reflect the views of HEI, or its sponsors, nor do they necessarily reflect the views and policies of the U.S. EPA or motor vehicle and engine manufacturers.

The authors declare they have no competing financial interests.

Received 15 August 2007 ; accepted 9 November 2007.