Effects of long-term exposure to outdoor air pollution

1. Effects of long-term exposure to outdoor air pollution Gerard Hoek

2. Background • Many studies have found associations between daily variability of air pollution and mortality / hospital admissions (time series studies) • Fewer studies on long-term exposures • Public health impact even more important than of the short-term exposures • Use contrast in space

3. Ecological studies • Early studies were ecological • Both health and exposure data were at the area level, not the indivdual

4. Early ecological studies • Risk Anal. 1987 Dec;7(4):449-61. Associations between 1980 U.S. mortality rates and alternative measures of airborne particle concentration. • We analyzed the 1980 U.S. vital statistics and available ambient air pollution data bases for sulfates and fine, inhalable, and total suspended particles. Using multiple regression analyses, • we conducted a cross-sectional analysis of the association between various particle measures and total mortality. Results from the various analyses indicated the importance of considering particle size, composition, and source information in modeling of particle pollution health effects. • Of the independent mortality predictors considered, particle exposure measures related to the respirable and/or toxic fraction of the aerosols, such as fine particles and sulfates, were most consistently and significantly associated with the reported SMSA-specific total annual mortality rates. On the other hand, particle mass measures that included coarse particles (e.g., total suspended particles and inhalable particles) were often found to be nonsignificant predictors of total mortality. Furthermore, based on the application of fine particle source apportionment, particles from industrial sources (e.g., from iron/steel emissions) and from coal combustion were suggested to be more significant contributors to human mortality than soil-derived particles.

5. Issues with ecological studies • No individual confounders e.g. smoking • Individualized exposure not possible • Ecological fallacy

6. Mortality cohort studies

7. Harvard 6 cities study • Dockery DW, Pope CA, Xu X, Spengler JD, Ware JH, Fay ME, Ferris BG, Speizer FE. N Engl J Med. 1993;329:1753-9. • Prospective cohort study • Individual confounders • 9,000 subjects living in 6 U.S. cities • Followed for 15 years • Cities varied in long-term concentrations of sulfur oxides and particles

9. Dockery, NEJM 1993; 329: 1753-9

10. Pope, JAMA 2002

11. Exposure variability within communities

13. Lancet, 2002

14. Assessed the ACS cohort (~23,000 subjects) in Los Angeles area • Spatial interpolation of monitoring data

17. Land use regression • Dutch birth cohort (3000, spread over NL) • Measurements impossible • Measurements at 40 sites locations of NO2, PM2.5 and ‘soot’. Four 2-week periods spread over one year. • Geographic Information Systems information in specific circles around each site of • Traffic intensity (r= 50, 250 and 1000 m) • Address density (r=300, 1000, 5000 m) • Population density (r=300, 1000, 5000 m)

18. Land use regression • Pollution concentrations at 40 sites linked to GIS predictors, using linear regression models • Model was used to predict concentrations at the home address of the children

19. Prediction model PM2.5 (g/m3)R2= 0.73

20. Odds ratios for a 10 g/m3 change of PM2.5 for symptoms at age four, adjusted for confounders

21. Cardiovascular disease

25. Respiratory disease

27. Living near a major road and wheeze.Venn. AJRCCM 2002;164:2177-80.

28. Brunekreef, Epidemiology 1997; 8: 298-303

29. Traffic: noise or air pollution? • Correlations traffic noise: • 0.24 with background BS • 0.30 with traffic intensity nearest road • 0.38 with traffic intensity 100 m buffer.

30. Traffic noise and APTraffic noise only

31. Traffic noise and air pollution in one model

32. Overall BS Traffic intensity on nearest road Lung cancer incidence – Smoker subgroups Living near a major road Traffic intensity in a 100 m buffer

33. Black Smoke RR, education and fruit intake

34. Conclusions • Long-term exposure to outdoor air pollution is associated with • increased mortality rates • respiratory disease • possibly cardiovascular disease • (Traffic / combustion) PM important • Developments in exposure assessment have strengthened long-term studies (GIS; geostatistical methods; land use regression)

35. Conclusions • Uncertainties remain with respect to • Causal agent(s) • Biological mechanism • Sensitive groups • Differences between locations