Air Quality Study on 2023 Canadian Wildfires Reports New Bacterial Toxin Spread Throughout U.S. East Coast

The harmful, orange haze that clouded the New York City skyline and other East Coast cities at the peak of the 2023 Canadian wildfires, triggering air quality alerts in more than 20 states, might have carried more than an unpleasant smell.

A new University of Maryland air quality study conducted during and after the air pollution episode spanning June 6–8, 2023 found an airborne chemical associated with toxic blooms with potential health effects. Research led by Akua Asa-Awuku, chemical and biomolecular engineering professor and associate dean in the A. James Clark School of Engineering, documented the presence of “aeruginosin” in wildfire plumes for the first time—reported in a paper in the journal American Chemical Society ES&T Air.

Aeruginosins, the toxic “blooms” linked to health complications

Aeruginosins are a type of chemical compound emitted by cyanobacteria, which are algae-like microorganisms found in water bodies such as lakes, rivers, ponds, estuaries and marine water. When certain conditions are met, such as the combination of warm temperatures, sunlight and nutrient-rich water environments, cyanobacteria thrive, reproducing at quick rates and creating “blooms” often observable in the water surface. More specifically, aeruginosins blooms are a release of hepatotoxins that have been linked to adverse human health implications.

For one, inhalation of aeruginosin toxins has been linked to bronchitis, asthma, allergies, rhinitis, and dermatitis, and other forms of contact, such as accidental ingestion through contaminated water and recreational activities, has been found to cause gastrointestinal symptoms.

Although studies have not identified how wildfire plumes trigger bloom metabolite release into the air, the research found a connection between those two enabled the presence of airborne aeruginosins during the 2023 July event—one that impacted millions.

“It was surreal how the sky looked, so it’s important to understand what drives it and what’s actually in the air when these things happen,” said Asa-Awuku.

Canadian aeruginosins traveled thousands of miles to Maryland

Their findings raise new questions about the public health impact of wildfire smoke emissions, which have already been reported to cause or worsen respiratory conditions such as asthma, and pose even greater risks for vulnerable groups such as children, seniors, and those underlying health conditions.

The study reported that aeruginosin made up 12% of the air samples collected by the research team in College Park, MD, with majority of the composition made up of chemicals characteristic to biomass combustion already associated with wildfire emissions. Consistent with the Air Quality Index reported, which ranged from 157 to 50 (or “unhealthy” to “good”), the presence of aeruginosin was most prevalent during peak pollution, and decreased as air quality improved.

Due to the proximity of the 2023 Canadian wildfires, UMD researchers conducted a real-world study that characterized the chemical composition of the air during the event.

“There’s not much information about how emissions change over long distances,” said Asa-Awuku. “When you’re further away, how air mass ages can affect the toxicity and composition of what’s in the air.”

In College Park, the implications of the study reflect new ways that climate change could impact the area as wildfire activity may intensify in the future.

Published May 26, 2026