05 May Blog | Exposure to Ambient Air Pollution and Health Effects
by Evi Samoli & Maria-Iosifina Kasdagli | NKUA
Epidemiological studies have consistently documented the adverse health effects of long-term exposure to outdoor air pollution on a variety of morbidity and mortality outcomes. According to the World Health Organization (WHO), air pollution is responsible for approximately seven million deaths annually. Particulate matter (PM), compromising a mix of various components and sizes, has been classified as the second leading risk factor for death worldwide, as epidemiological studies have documented the health effects of PM with diameter less than 2.5 μm (PM2.5). Over the last decades, a growing body of literature has also assessed the association between exposure to nitrogen dioxide (NO2) – a toxic gas, primarily originating from fuel combustion and vehicle emissions – and several health endpoints. Additionally, ozone (O3), a highly reactive gas formed via atmospheric chemical processes including nitrogen oxides and volatile organic compounds, with its formation facilitated by solar radiation, has increasingly gained attention in scientific research for its potential health impacts.
In 2021, WHO issued the latest update of the “Air Quality Guidelines” (AQGs) providing guidance to stakeholders on the health effects of exposure to air pollution and proposing concentration levels per pollutant for public health protection, based on evidence so far. To develop these guidelines, the WHO Regional Office for Europe commissioned a series of systematic reviews for the evidence on selected health outcomes to quantify the health impacts related to the long- and short-term exposure to air pollutants. Two reviews published in 2020 assessed the effects of long-term exposure to particulate matter, NO2 and O3 on all-cause and cause-specific mortality.
Our team at the National and Kapodistrian University of Athens (ES and MIK), in collaboration with the National Technological University (UTN), San Nicolás Regional Faculty in Argentina (Pablo Orellano) and under the guidance of a WHO commissioned consulting group, undertook the update of these two systematic reviews that informed the 2021 AQGs. The results were reported in two scientific publications (one on particles and one on gases) and will be used to inform the Update of the Health Risks of Air Pollution in Europe (HRAPIE-2) project, coordinated by the WHO Regional Office for Europe’s European Centre for Environment and Health.
More specifically, the aim of these systematic reviews was to assess the association between long- term exposure to PM2.5, PM10, NO2 and O3 and all-cause and cause-specific mortality, including mortality from circulatory diseases, ischemic heart disease, cerebrovascular diseases, respiratory diseases, chronic obstructive pulmonary disease, acute lower respiratory infections and lung cancer. To achieve this goal, an extensive literature search was conducted to identify published studies addressing the research question published from September 2018 until May 2023. The final studies were selected according to pre-specified inclusion criteria related to the study design and target population. The results from the final studies were combined by applying meta-analytic statistical techniques that summarize the results of multiple studies.
The updated review included 84 studies on long-term exposure to PM2.5 and 47 for PM10 and mortality, while 83 studies reported on NO2 and 26 on O3. Exposure to air pollutants was associated with increased risks for mortality.
Indicatively:
• A 10 μg/m3 increase in ambient PM2.5 or PM10 was associated with 9.5% (95% Confidence Interval (CI): 6.4% – 12.7%) and 8% (95% CI: 5.2% – 11%) increased risk of all-cause mortality, respectively.
• Associations were reported for long-term exposure to particles and all analyzed cardiorespiratory mortality outcomes.
• Lon-term NO2 exposure was also associated with increased risk for mortality. For example, a 10 μg/m3 increase in NO2 was associated with 5% (95% CI: 3% – 5%) increased risk of mortality from all-causes and with 7% (95%CI: 4% – 10%) from lung cancer.
As the body of evidence is continuously growing, investigating diagnoses specific health outcomes as well as less studied and emerging air pollutants underscores the importance of updating reviews on air pollution epidemiology to provide accurate estimates to inform health risk assessments.
Within the MI-TRAP project we will assess the link between traffic-related pollution and its health impacts by conducting a systematic review of the health effects associated with short- and long-term exposure to traffic-related pollutants, following the same methodological approach of the systematic reviews conducted for the WHO.
More specifically, the exposures of interest include: black carbon, organic carbon, elemental carbon, or black smoke; ultrafine particles, i.e. particulate matter with a diameter of less than 100 nanometers; traffic-related noise; PM elements [Copper, Zinc, Lead and Iron]. The targeted health outcomes include: for long-term exposures mortality from all-causes, cardiovascular and respiratory disease; incidence of ischemic heart disease, chronic obstructive pulmonary disease, asthma and lung cancer in adults and asthma incidence and acute lower respiratory infections in children; for short- term exposures we focus on mortality from all-causes, cardiovascular and respiratory disease; cardiovascular and respiratory hospital admissions in adults and respiratory hospital admissions in children.
Building upon the findings from the review, we will apply scenarios for air quality informed by measurements within the MI-TRAP project to estimate the attributed number of cases. The continuing investigation of the impact of environmental risk factors on health is of public health significance, considering the involuntary nature of the exposure and the growing urban population in European cities.
About
Evi Samoli is a Professor of Epidemiology and Medical Statistics and Maria-Iosifina Kasdagli is a Postdoctoral Researcher at the Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens.