Higher levels of metal, sulfur in air linked to poor respiratory health in children
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Elevations in metal, sulfur and particle oxidative potential in the air strengthened the link between short-term exposure to outdoor pollution and respiratory hospitalizations among children, according to study results.
“Although Canada has some of the cleanest air in the world, health impacts of air pollution are still observed,” Jill Korsiak, MSc, PhD student in the department of epidemiology, biostatistics and occupational health at McGill University in Montreal, and colleagues wrote, adding that children are particularly vulnerable.
“Increasing evidence suggests that the health effects of fine particulate matter (PM2.5) vary depending on the source and chemical composition of particles, and traditional mass-based measures are unable to account for these potential differences in particle toxicity,” they wrote.
In a time-stratified case-crossover study published in American Journal of Respiratory and Critical Medicine, Korsiak and colleagues analyzed 10,534 children (median age, 5 years; 6,029 boys), ranging in age from birth to 17 years, hospitalized between June 2016 and December 2017 and discharged with a respiratory disease. Researchers sought to determine if particle constituents, specifically metals and sulfur, or oxidative potential changed the relationship between short-term fine particulate mass concentrations, oxidant gases (Ox) and respiratory hospitalizations.
Across 34 Canadian cities from June 2016 to December 2017, researchers gathered fine particle mass concentrations and oxidant gases — nitrogen dioxide (NO2) and ozone (O3) — from fixed-site monitors daily and measured estimates of fine particle constituents and oxidative potential monthly through integrated 2-week PM2.5 samples.
Researchers then evaluated relationships between respiratory hospitalizations and PM2.5 or Ox air pollution recorded the day prior to hospitalization (lag 1) with conditional logistic regression models.
Overall, researchers observed low mean concentrations of daily air pollutants (PM2.5 = 7.33 g/m3 ± 6.38; NO2 = 9.13 ppb ± 6.33; O3 = 22.76 ppb ± 8.37; Ox = 18.12 ppb ± 4.9), which they noted was typical for Canada.
In models that excluded particle constituents and oxidative potential, researchers found no association between lag 1 PM2.5 mass concentrations and respiratory hospitalizations (OR per 10 g/m3 increase in fine particulate matter = 1.004; 95% CI, 0.955-1.056). This finding persisted in sensitivity analysis performed in the warm and cold seasons separately.
They then conducted analyses above and below the median level of metals, sulfur and particle oxidative potential and found that levels above the median yielded positive associations. For instance, when copper was above the median, the odds ratio per a 10 g/m3 increase in fine particulate matter was 1.084 (1.007-1.167), whereas when copper was below the median, the OR was 0.97 (95% CI, 0.929-1.014).
Researchers also found lag 1 Ox was positively associated with respiratory hospitalizations (OR per 10 ppb increase in Ox = 1.088, 95% CI, 1.005-1.177).
When examining particle constituents and oxidative potential, levels of copper, iron, nickel, zinc, sulfur and glutathione oxidate potential above the median had stronger associations.
The effect of all metals, sulfur and oxidative potential appeared more pronounced in the warm season, with stronger associations observed between lag 1 PM2.5 and respiratory hospitalizations when all metals, sulfur and glutathione oxidate potential were above the median (P < .05).
“Our results suggest that the strength of associations between respiratory hospitalizations in children and short-term exposure to outdoor PM2.5 mass concentrations and Ox are influenced by the metal and sulfur content of PM2.5 and particle oxidative potential,” Korsiak and colleagues wrote. “These findings provide further support for efforts targeting specific sources of PM2.5 with high metal or sulfur content or oxidative potential as opposed to regulations targeting only PM2.5 mass. Additional work is needed, both in different populations and with different health outcomes, to evaluate whether similar trends emerge.”
This study by Korsiak and colleagues suggests the importance of evaluating PM elements, according to an accompanying editorial by Ana M. Rule, PhD, MHS, and Kirsten A. Koehler, PhD, both of the department of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health.
“The findings from the study by Korsiak and colleagues provide important insight into certain PM components and oxidative characteristics that may contribute to the differential toxicity of PM2.5 found across space and time,” Rule and Koehler wrote. “However, more work is needed to prioritize the metrics provided and incorporate additional components to understand the health effects of PM2.5 constituents, especially given common sources and correlations among components.”
They note that because Canada has low PM and ozone concentrations, the study results may not have been able to evaluate a large range of exposures.