Mortality-Air Pollution Associations in Low Exposure Environments (MAPLE): Phase 2
M Brauer1,2, J R Brook3, T Christidis4
1The University of British Columbia, Vancouver, British Columbia, Canada.
Research Report (Health Effects Institute)
|October 12, 2022
Summary
Long-term exposure to fine particulate matter (PM2.5) is linked to increased mortality, even at low concentrations. This study found adverse health effects associated with PM2.5 at levels as low as 2.5 μg/m³, with no clear safe threshold identified.
Area of Science:
- Environmental Health Sciences
- Epidemiology
- Air Pollution Research
Background:
- Long-term exposure to fine particulate matter (PM2.5) is a known risk factor for mortality.
- The precise concentration-response relationship and the lowest exposure levels associated with increased mortality risk remain poorly understood.
- Previous research indicated potential attenuation of PM2.5 associations with nonaccidental mortality when considering copollutants like ozone (O3).
Purpose of the Study:
- To characterize the shape of the concentration-response relationship between ambient PM2.5 and nonaccidental mortality at low exposure levels.
- To investigate associations between PM2.5 and specific causes of death.
- To evaluate the sensitivity of these associations to copollutants (O3, Ox) and regional variations.
Main Methods:
- Utilized refined PM2.5 exposure estimates at 1 km² resolution across large national Canadian cohorts (up to 7.1 million individuals).
- Employed Cox proportional hazard models, stratified and adjusted for numerous individual and ecological covariates.
- Investigated the concentration-response function shape using restricted cubic splines (RCS) and extended Shape Constrained Health Impact Function (eSCHIF) models.
Main Results:
- Consistent positive associations between PM2.5 and nonaccidental mortality were observed across all cohorts.
- The eSCHIF methodology indicated adverse effects on mortality at PM2.5 concentrations as low as 2.5 μg/m³, with no clear lower threshold.
- PM2.5 was also associated with increased mortality from ischemic heart disease, respiratory disease, cardiovascular disease, and diabetes.
Conclusions:
- Associations between PM2.5 exposure and nonaccidental mortality exist at low concentrations, challenging the notion of a safe threshold.
- The study highlights the importance of considering air pollutant mixtures, as ozone and oxidant capacity attenuated PM2.5 associations.
- Regional variations in PM2.5-mortality associations suggest the influence of uncharacterized air pollutant mixtures.
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