A new study published online in Environmental Health Perspectives ought to catch the attention of policy makers. It finds not only a strong link between fine particle soot and lung cancer, but it argues that cleaning up this stuff further would prevent many thousands of premature deaths a year.
Meanwhile, the Obama administration continues to delay its formal action to update national air quality standards for fine particle soot.
Chronic Exposure to Fine Particles and Mortality: An Extended Follow-Up of the Harvard Six Cities Study from 1974 to 2009
Johanna Lepeule, Francine Laden, Douglas Dockery, Joel Schwartz
Background: Epidemiologic studies have reported associations between fine particles (aerodynamic diameter ≤2.5µm, PM2.5) and mortality. However, concerns have been raised regarding the sensitivity of the results to model specifications, lower exposures, and averaging time.
Objectives: We addressed these issues using eleven additional years of follow-up of the Harvard Six Cities study, incorporating recent lower exposures.
Methods: We replicated the previously applied Cox regression, and examined different time lags, the shape of the concentration-response relationship using penalized splines, and changes in the slope of the relation over time. We then conducted Poisson survival analysis with time-varying effects for smoking, sex, and education.
Results: Since 2001, average PM2.5 levels, for all six cities, were below 18µg/m3. Each increase in PM2.5 (10µg/m3) was associated with an adjusted increased risk of all-cause mortality (PM2.5 average on previous year) of 14% (95% confidence interval (CI): 7, 22), and with 26% (95%CI: 14, 40) and 37% (95%CI: 7, 75) increases in cardiovascular and lung cancer mortality (PM2.5 average of three previous years), respectively. The concentration-response relationship was linear down to PM2.5 concentrations of 8µg/m3. Mortality rate ratios for PM2.5 fluctuated over time, but without clear trends, despite a substantial drop in the sulfate fraction. Poisson models produced similar results.
Conclusions: These results suggest that further public policy efforts that reduce fine particulate matter air pollution are likely to have continuing public health benefits.
Citation: Lepeule J, Laden F, Dockery D, Schwartz J 2012. Chronic Exposure to Fine Particles and Mortality: An Extended Follow-Up of the Harvard Six Cities Study from 1974 to 2009. Environ Health Perspect :-. http://dx.doi.org/10.1289/ehp.1104660
Received: 25 October 2011; Accepted: 28 March 2012; Online: 28 March 2012
Excerpts from the article:
The previous extended follow-up of the Harvard Six Cities study showed an elevated, but not statistically significant risk of lung cancer mortality (Laden et al. 2006), while the present extended follow-up estimated a statistically significant 37% increase in lung cancer mortality (for each 10μg/m3 increase in PM2.5), which is greater than that estimated for both the ACS cohort (14%) (Pope et al. 2002) and a Japanese cohort (27%) (Katanoda et al. 2011). Lungs are one of the organs that are most directly impacted by particulate air pollution. Fine particles, which may also carry toxic chemicals of carcinogenic potential (Laden et al. 2000), can reach lung alveoli where the clearance is slow (Pinkerton et al. 1995) and induce durable pulmonary and systemic inflammation (Riva et al. 2011).
These results agree with the literature (Gehring et al. 2006; Krewski et al. 2009; Puett et al. 2009; Schwartz et al. 2008) and suggest that health improvements can be expected almost immediately after a reduction in air pollution.
our estimated association between PM2.5 and all-cause mortality implies that a decrease by 1μg/m3 in population average PM2.5 would result in 33,932 fewer deaths per year.