Individual and joint exposures to PM2.5 constituents and mortality risk among the oldest-old in China.

Abstract

Cohort evidence linking long-term survival of older adults with exposure to fine particulate matter (PM_2.5) constituents remains scarce in China. By constructing a dynamic cohort based on the Chinese Longitudinal Healthy Longevity Study, we aimed to assess the individual and joint associations of major PM_2.5 constituents with all-cause death in Chinese oldest-old (.80 years) adults. Time-dependent Cox proportional hazards models were adopted to estimate death risks of long-term exposure to PM_2.5 constituents. Among 14,884 participants, totaling 56,342 person-years of follow-up, 12,346 deaths were identified. The highest mortality risk associated with an interquartile range (IQR) increase in exposure was 1.081 (95% confidence interval [CI]: 1.055-1.108) for sulfate (IQR=4.1 μg m^-3), followed by 1.078 (95% CI: 1.056-1.101) for black carbon (IQR=1.6 μg m^-3), 1.056 (95% CI: 1.028-1.084) for ammonium (IQR=3.2 μg m^-3), 1.050 (95% CI: 1.021-1.080) for nitrate (IQR=5.8 μg m^-3), and 1.049 (95% CI: 1.024-1.074) for organic matter (IQR=10.3 μg m^-3). In joint exposure, each IQRequivalent rise of all five PM_2.5 constituents was associated with an 8.2% (95% CI: 4.0%-12.6%) increase in mortality risk. The weight analysis indicated the predominant role of sulfate and black carbon in driving PM_2.5-related mortality. Octogenarians (aged 80-89 years) and rural dwellers were at significantly greater risk of mortality from individual and joint exposures to PM_2.5 constituents. This study suggests that later-life exposure to PM_2.5 constituents, particularly sulfate and black carbon, may curtail long-term survival of the oldest-old in China.