Traffic-Related Pollution Linked to New Pediatric Asthma Cases Every Year

The United States ranks highly in a global study examining traffic-related pollution and new cases of childhood asthma, and the authors suggest that pollution guidelines may need to be re-evaluated, since most affected children live in areas where pollution falls within current limits.

The United States has the 25th highest percentage of traffic pollution-attributable childhood asthma incidence in the world and ranks third in the world by number of cases of asthma related to traffic-related pollution. The report was published in The Lancet Planetary Health.

Researchers said that globally, traffic-related air pollution is associated with 4 million new cases of childhood asthma annually, with an estimated 170 new cases of traffic pollution-related asthma per 100,000 children every year; 13% of childhood asthma cases diagnosed each year are linked to traffic pollution.

The study contains estimates for 194 countries and 125 major cities. The authors said it is the first study to give a global estimate of the annual burden of pediatric asthma incidence attributable to ambient nitrogen dioxide (NO₂) pollution.

Pediatric asthma has been rising steadily since the 1950s. Previous epidemiological studies done worldwide have reported associations between traffic-related air pollution (TRAP) exposure and new-onset asthma in children; the associations are less clear in adults.

Last year, a study found that patients with asthma with certain genotype combinations demonstrated more intense symptoms when combined with a close proximity to roadways.

Pollutants are believed to damage the airways, leading to inflammation that triggers asthma in genetically predisposed children. Previous reviews by the Environmental Protection Agency and Health Canada suggest that a link is likely to between long-term NO₂ exposure and childhood asthma development, the study said.

N0₂ measures are used as a proxy because they are readily available in many countries, and the variability of TRAP mixture appears to be well characterized by NO_2. Traffic emissions can contribute up to 80% of ambient NO₂ in cities.

As might be expected, the top areas in the United States cited in the report were all urban cities. The worst incidence of new cases of asthma per 100,000 children to the least are:

• Los Angeles (530 cases)
• New York City (530 cases)
• Chicago (470 cases)
• San Francisco (460 cases)
• Dallas (430 cases)
• Philadelphia (420 cases)
• San Diego (410 cases)
• Houston (400 cases)
• Washington, DC (390 cases)
• Miami (320 cases)

South Korea ranked highest in the world for the proportion of traffic pollution-attributable childhood asthma incidence, while the United Kingdom ranked 24th, China 19th, and India 58th. Globally, 8 of the 10 cities with the highest proportion of cases were in China.

“Nitrogen dioxide pollution appears to be a substantial risk factor for childhood asthma incidence in both developed and developing countries, especially in urban areas,” senior author Susan Anenberg, PhD, of George Washington University, which funded the study, said in a statement. “Our findings suggest that the World Health Organization guideline for annual average NO₂ concentrations might need to be revisited, and that traffic emissions should be a target to mitigate exposure.”

Lead author Ploy Achakulwisut, PhD, also of George Washington University, added, “Our study indicates that policy initiatives to alleviate traffic-related air pollution can lead to improvements in children’s health and also reduce greenhouse gas emissions. Recent examples include Shenzhen’s electrification of its entire bus fleet and London’s Ultra-Low Emission Zone congestion charges.”

New York City, for example, plans to follow the other cities’ lead by implementing congestion pricing for vehicle traffic in 2021. The price for driving anywhere in Manhattan south of Central Park, however, has yet to be determined.

The authors combined a global dataset of ambient NO₂ (modelled from ground-level monitors, satellite data, and land use variables such as road networks) with data on population distribution and asthma incidence to estimate the number of new traffic pollution-related asthma cases in children aged 1 to 18 years.

“We also found that countries and cities with higher [carbon dioxide] emissions from fossil fuel combustion tend to have higher NO₂ exposures, providing further support that alignment of policy initiatives to mitigate air pollution and climate change can have multiple public health benefits. Traffic emissions should be a target for exposure-mitigation strategies,” the authors wrote.

Reference

Achakulwisut P, Brauer M, Hystad P, Anenberg SC. Global, national, and urban burdens of paediatric asthma incidence attributable to ambient NO₂ pollution: estimates from global datasets. [published online April 10, 2019]. Lancet Planet Health. doi: 10.1016/S2542-5196(19)30046-4.