Estimating Causal Effects of Long-Term PM _2.5 Exposure on Mortality in New Jersey

Abstract

Background:Many studies have reported the associations between long-term exposure to PM2.5 and increased risk of death. However, to our knowledge, none has used a causal modeling approach or controlled for long-term temperature exposure, and few have used a general population sample.Objective:We estimated the causal effects of long-term PM2.5 exposure on mortality and tested the effect modifications by seasonal temperatures, census tract–level socioeconomic variables, and county-level health conditions.Methods:We applied a variant of the difference-in-differences approach, which serves to approximate random assignment of exposure across the population and hence estimate a causal effect. Specifically, we estimated the association between long-term exposure to PM2.5 and mortality while controlling for geographical differences using dummy variables for each census tract in New Jersey, a state-wide time trend using dummy variables for each year from 2004 to 2009, and mean summer and winter temperatures for each tract in each year. This approach assumed that no variable changing differentially over time across space other than seasonal temperatures confounded the association.Results:For each interquartile range (2 μg/m3) increase in annual PM2.5, there was a 3.0% [95% confidence interval (CI): 0.2, 5.9%] increase in all natural-cause mortality for the whole population, with similar results for people > 65 years old [3.5% (95% CI: 0.1, 6.9%)] and people ≤ 65 years old [3.1% (95% CI: –1.8, 8.2%)]. The mean summer temperature and the mean winter temperature in a census tract significantly modified the effects of long-term exposure to PM2.5 on mortality. We observed a higher percentage increase in mortality associated with PM2.5 in census tracts with more blacks, lower home value, or lower median income.Conclusions:Under the assumption of the difference-in-differences approach, we identified a causal effect of long-term PM2.5 exposure on mortality that was modified by seasonal temperatures and ecological socioeconomic status.Citation:Wang Y, Kloog I, Coull BA, Kosheleva A, Zanobetti A, Schwartz JD. 2016. Estimating causal effects of long-term PM2.5 exposure on mortality in New Jersey. Environ Health Perspect 124:1182–1188; http://dx.doi.org/10.1289/ehp.1409671

Long-term Exposure to PM2.5 and Mortality Among Older Adults in the Southeastern US

“…11 A study in New Jersey also estimated that the effect increased with the percentage of black residents in each census tract. 32 However, they did not analyze race on an individual level and instead used the percentage of black residents as an ecologic surrogate.…”

“…11 Consistently, a recent study in New Jersey also found that the risks are higher among individuals living in a census tract with lower median income. 32 …”

“…The model for the northeast has been applied to estimate the causal effects of long-term PM 2.5 exposure on mortality in New Jersey during 2004-2009. 32 The present study made use of the hybrid PM 2.5 predictions for the southeastern US to estimate the association between long-term exposure to PM 2.5 and mortality among a large cohort of older adults (age ≥65) and test a wide range of effect modifiers including individual-level variables, neighborhood-level variables, seasonal temperature, and PM 2.5 components.…”

Air Pollution and Mortality in the Medicare Population

“…Finally, we found that our results were consistent with others published in the literature (Section 6 in the Supplementary Appendix). 5,17,[24][25][26][27][28] There was a significant association between PM 2.5 exposure and mortality when the analysis was restricted to concentrations below 12 μg per cubic meter, with a steeper slope below that level. This association indicated that the health-benefit-per-unit decrease in the concentration of PM 2.5 is larger for PM 2.5 concentrations that are below the current annual NAAQS than the health benefit of decreases in PM 2.5 concentrations that are above that level.…”

“…1,2 Studies suggest that fine particles (particles with a mass median aerodynamic diameter of less than 2.5 μm [PM 2.5 ]) are a public health concern, 3 with exposure linked to decreased life expectancy. [4][5][6] Long-term exposure to ozone has also been associated with reduced survival in several recent studies, although evidence is sparse. 4,[7][8][9] Studies with large cohorts have investigated the relationship between long-term exposures to PM 2.5 and ozone and mortality 4,[9][10][11][12][13] ; others have estimated the health effects of fine particles at low concentrations (e.g., below 12 μg per cubic meter for PM 2.5 ).…”