Modified Diesel Exhaust May Be More Harmful for Lung Health

Chris Carlsten, MD, MPH

Particle depletion of diesel exhaust is actually associated with an increased rate of impaired lung function when combined with allergen exposure, according to a new study.

A team of investigators from the University of British Columbia (UBC) and Emory University have reported findings which show allergen-sensitized participants actually experience worsened lung function when exposed to particle-depleted diesel exhaust (PDDE) plus allergen than when exposed to diesel exhaust and allergen.

Diesel exhaust has been long established as a public health model for traffic-related air pollution, having been significantly associated with global asthma burden as well as allergen inhalation effects. As investigators noted, though, diesel particulate-filtering technologies may drive rates of nitrogen dioxide (NO₂) emissions.

Investigators sought to understand whether PDDE- or diesel exhaust-associated toxins would worsen an individual’s lung function.

“We previously demonstrated that diesel exhaust augmented allergic responses as well as airflow declines in those genetically susceptible, but we wondered if removing particles from the exhaust would lessen these effects,” senior study author Chris Carlsten, MD, MPH, head of respiratory medicine and Canada Research Chair in Occupational and Environmental Lung Disease at UBC, said in a statement.

Led by Denise J. Wooding, MSc, of the Air Pollution Exposure Laboratory, the team conducted a randomized, double-blind crossover trial involving 14 allergen-sensitized participants undergoing inhaled allergen challenge following exposures to differing forms of air. For 2 hours, participants were exposed to either diesel exhaust, PDDE, or filtered air.

Investigators conducted blood sampling and spirometry for 48 hours prior and following the air exposures. Airway responsiveness was evaluated at 24 hours. Inhaled saline following filtered air was used as the control condition. A majority of patients (n = 9) were identified as airway hyperresponsive, indicating them as being at greater lung impairment risk.

Participants reported more impaired lung function from PDDE plus allergen coexposure than from diesel exhaust and allergen exposure, particularly the more at-risk population. Both forms of altered air increased airway responsiveness in normally responsive patients, though diesel exhaust was associated with increased participant blood neutrophils and persistent eosinophil at 48 hours.

Both diesel exhaust and PDDE increased total peripheral leukocyte counts, which correlated with lung function decline.

Clinical discussion into the effect of pollutants on chronic respiratory health has been spurred by public health concerns surrounding climate change projections and major global urbanization. A report from last month showed associations between ambient air pollution and emphysema morbidity and mortality, and an even more recent global cohort analysis associated particulate matter exposure with cardiovascular and respiratory mortality.

An essay accompanying the latter study, written by Renee M. Salas, MD, MPH, of the Department of Emergency Medicine at Massachusetts General Hospital and Harvard Medical School, emphasized the urgency of action to follow these clinical findings.

“Neither the gravity and enormity of climate change nor the unfortunate politicization of this health emergency should cause us to shy away from action,” Salas wrote. “The timeline for action to avert some of the most catastrophic health outcomes of climate change has been estimated to be a little over a decade.”

Add to that portfolio of evidence the findings of the diesel exhaust assessment—which conluded that both diesel exhaust and particle-depleted exhaust are associated with impaired lung function, indicate investigators and public health leaders need to access other drivers of diesel exhaust’s harm than just particulates.

“The take-home message is that technologies that remove particulate matter from diesel exhaust cannot be simply assumed to be beneficial to health, especially in susceptible populations,” Carlsten said.

The study, "Particle Depletion Does Not Remediate Acute Effects of Traffic-related Air Pollution and Allergen. A Randomized, Double-Blind Crossover Study," was published online in American Journal of Respiratory and Critical Care Medicine.