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The Public Health Significance of Air Pollution Steve Clarkson A Brief History • 1930s-60s: severe air pollution episodes: Meuse Valley, Belgium, Donora, Pennsylvania, London, U.K. • 1960s-70s: introduction of clean air legislation • 1970s-80s: significant reduction in ambient concentrations of many pollutants • 1980s, early 1990s: studies demonstrating adverse effects even at lower levels of exposure • Mid to late 1990s: large number of studies replicated findings worldwide • Late 1990s-present: evaluation of nuances of associations observed in epidemiological studies, effects of specific sources, biological mechanisms, long term effects http://www.epa.gov/airnow//health-prof/EPA_poster-final_lo-res.pdf Health Effects of Air Pollution : Key Findings I Know more about short term effects: • More people die and are admitted to hospital for heart and lung problems on days with elevated levels of air pollution • These effects are the “tip of the iceberg” relative to other, milder effects • A variety of biological mechanisms have been identified for these effects • Effects found at levels previously thought to be safe • Effects observed using widely varying study designs: large scale population studies to controlled laboratory studies in humans/ animals Recent Highlights – Short-term Effects • Activity diaries from patients who had suffered heart attacks • Exposure to traffic in hour prior to heart attack appeared to be trigger CONTROLLED HUMAN EXPOSURE FACILITY AND PARTICLE CONCENTRATOR Gage Occupational & Environmental Health Unit • Statistical problem identified affecting time-series studies (mortality, hospital admissions) • Numerous studies affected • Suggested effects could be smaller and less certain than previously thought • Impact of statistical problem varied from study to study • In many cases size of effect smaller and less precise • Significant associations persisted in most studies Health Effects of Air Pollution : Key Findings II Know less about long term effects • People do not live as long in cities with high air pollution • Air pollution may contribute to – Adverse pregnancy outcomes – atherosclerosis – the development of lung cancer and chronic lung disease Recent Highlights – Long-term Effects • Sample of 5,000 subjects from Netherlands Study on Diet and Cancer • Mapped 1986 address to proximity to major roads • Follow-up 1986-1994 • Those living near major roads twice as likely to die from cardiopulmonary causes • Used data from two clinical trials on atherosclerosis prevention • Mapped study subjects to PM2.5 exposure • Exposure was associated with atherosclerosis in carotid artery • evidence of link with birth outcomes • Evidence strong enough to suggest causal link with low birth weight • Link with preterm birth, IUGR, congenital anomalies is weaker • Variety of possible biological mechanisms Policy Initiatives • • • • • Low sulphur gasoline Canada Wide Standards Canada-U.S. Air Quality Agreement Kyoto Protocol Health-risk based Air Quality Index Key points • There is a very large and growing evidence base linking air pollution at current levels with adverse health effects • There is more evidence about short term effects, but more evidence is now appearing on long term effects • The latest research focuses on effects on the cardiovascular system and of specific pollution sources like traffic • A number of policy initiatives have been undertaken to reduce the health burden from air pollution Extra slides • From a study of air pollution and mortality in Europe • 30 cities • Applied variety of models • Best fit from linear model • Similar evidence from 20 largest US cities (NMMAPS) Bob Dales, Ling Liu, Mieczyslaw Szyszkowicz, Jeff Willey, Ryan Kulka, Neil Ballack Health Canada Terrence Ruddy, Mary Dalipaj University of Ottawa Heart Institute PM2.5, PM1, NO2, weather Traffic count Recruitment: • Healthy subjects (n=35) • 18-50 yr • No heart & lung conditions • Nonsmoker Downtown Ultrasound for vascular reactivity Heart Rate Blood pressure Tunney’s Pasture Serum for ET-1 MORNING SLATER STREET, OTTAWA N Engl J Med 2005;352:1276-a • 4000 subjects from prevention and incidence of asthma and mite allergy study • At 2 years of age, some evidence of associations of modelled exposures to NO2, PM2.5 and “soot” with respiratory outcomes • Need for extended follow-up Do interventions to control air pollution have a measurable impact on health? Unusual Opportunity: • Natural experiment • Dramatic (70%) reduction in pollutant concentration over short period • Control communities readily available • Death rates decreased measurably – by 15.5% in case of deaths from respiratory causes