Ultrafine particle exposure heightens risk for respiratory mortality
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Key takeaways:
- The risk for respiratory death went up following exposure to particles with an aerodynamic diameter of 0.1 m or smaller.
- These particles did not impact natural or cardiovascular mortality risk.
Individuals faced a high risk for respiratory mortality 5 to 7 days after being exposed to ultrafine particle pollution, according to results published in American Journal of Respiratory and Critical Care Medicine.
“The pooled results of our time-series study indicated an increased risk for respiratory mortality after exposure to [ultrafine particles],” Maximilian Schwarz, MSc, of the Institute of Epidemiology at Helmholtz Zentrum München-German Research Center for Environmental Health, and colleagues wrote. “In particular, delayed effects were seen for multiday averages and corroborated findings from high-pollution settings. No consistent associations were found for cardiovascular or natural mortality.”
With measures of ultrafine particles (10 nm-100 nm) and particle number concentrations (10 nm-800 nm) at six different sites within Dresden, Leipzig and Augsburg, Germany, Schwarz and colleagues sought to determine how these exposures impacted 2010 to 2017 natural, cardiovascular and respiratory mortality rates.
For each site, researchers assessed how ultrafine particle exposure influenced the risk for mortality using confounder-adjusted Poisson regression models that considered aggregated lags (0-1, 2-4, 5-7 and 0-7 days) following exposure. Data from the six sites were brought together using a multilevel meta-analytical method.
Notably, the two traffic-related stations had higher median concentrations of ultrafine particles (8,637 particles/cm3 and 10,123 particles/cm3) than urban background stations (range: 4,520 particles/cm3 to 5,655 particles/cm3).
Researchers did not observe any significant links between the air pollutants and cardiovascular or natural mortality, but they did find a link to respiratory mortality.
Five to 7 days following exposure to ultrafine particles, the relative risk for respiratory mortality went up by 4.46% (95% CI, 1.52%-7.48%) with an interquartile range elevation of 3,223 particles/cm3. This lag time demonstrated the strongest effect with ultrafine particles, according to researchers.
Notably, the impact of fine particulate matter (PM2.5) plus ultrafine particles on respiratory mortality 5 to 7 days after exposure (4.07%; 95% CI, 0.93%-7.3%) was not different from the relationship observed above between just ultrafine particles and respiratory mortality, according to researchers.
For particle number concentrations, researchers observed that the smallest particle size (10 nm-30 nm) demonstrated the highest relative risk for respiratory mortality 5 to 7 days after exposure with an increased risk by 4.49% (95% CI, 1.91%-7.14%).
Unlike ultrafine particles and particle number concentrations, both PM2.5 and nitrogen dioxide did not significantly impact respiratory mortality.
When further evaluating the relationship between respiratory mortality and ultrafine particles 5 to 7 days after exposure, researchers did not find differences in mortality risk among subgroups based on age or season but did find a heightened risk when comparing women with men (9.57%; 95% CI, 5.35%-13.97% vs. 0.45%; 95% CI, –3.1% to 4.13%).
“The study highlights that longer time series with more monitors per city of high-quality [ultrafine particle] measurements are needed to overcome the inconsistency in the available evidence,” Schwarz and colleagues wrote. “It also highlights that multiple measurements with a classification of particle size fractions, chemical composition and emission source are needed to further substantiate the impact of [ultrafine particles] as called for by the good practice statements for [ultrafine particles] published by the WHO in 2021. In general, focusing our policies on eliminating combustion might be the most health-protective air pollution mitigation approach.”
This study by Schwarz and colleagues demonstrates one impact of exposure to particles smaller than PM2.5. With more evidence on the risks linked to these particles, new pollution regulations could arise, according to an accompanying editorial by George D. Thurston, ScD, director of the program in exposure assessment and human health effects in the department of environmental medicine at NYU Grossman School of Medicine.
“To determine the most toxic PM2.5 components, we need the EPA and other monitoring networks around the world to expand their particulate matter sampling to include the more combustion-specific PM1 and [ultrafine particle] measurements and to perform compositional analyses of their constituents,” Thurston wrote. “This will allow more evaluations like those conducted by Schwartz and colleagues of these characteristics as potential additional or replacement particulate-matter air regulatory indices, based on which more efficient control of the particle pollution health risk might well be achieved.”