Study links timing of blue-green blooms, airborne particles

This story has been updated to include the link to the published report.

As spring gives way to summer and temperatures rise, the rivers and streams that are part of the Albemarle Sound Basin in northeastern North Carolina are home to an increasing number of algal blooms. New research draws a connection between the presence of these blooms and potentially hazardous fine particulate matter in the air.

In 2021, the Albemarle Resource Conservation and Development Council noted on its website that, “After an absence of 25-30 years, algal blooms have returned to parts of the Chowan River, Edenton Bay, Albemarle Sound, Little River, Perquimans River, and Pasquotank River. The summer blooms in 2015-2020 triggered state advisories for swimming and consuming fish.”

The algal blooms triggering the advisories are caused by cyanobacteria, a form of bacteria that produces its own food through photosynthesis. Cyanobacteria are responsible for the blue-green blooms in the waters of the Chowan River and its tributaries.

Although not all cyanobacteria are harmful, those that are have been shown to contain neurotoxins, hepatotoxins that cause liver damage, cytotoxins that cause cellular damage, and dermatoxins that potentially cause skin irritation, necrosis and damage to mucous membranes. 

Cyanobacteria blooms have become a global health concern. Writing in the introduction to their paper, the authors note, “Water security across the globe is threatened by the recent expansion of toxin-producing cyanobacterial harmful algal blooms (CHABs) in freshwater and estuarine ecosystems.”

The paper, which was posted as preprint access at SSRN, had not been peer reviewed, although final review was expected by the end of June. Update: The peer-reviewed final publication is at Science Direct. 

The release of toxins from cyanobacteria blooms into the air was an area of research that doctoral student and lead author of the paper Haley Plaas told Coastal Review had not been studied as extensively as the toxic effects of the bacteria in the water.

“What has been understudied is if their toxins and their cells have the potential to go airborne, and we know very little about what the health impacts might be for people and wildlife and pets,” she said. “These toxins have been studied quite a bit for their impact when it’s ingested via drinking water, or absorbed through the skin. We know a lot about those health impacts. But we know significantly less about what the health impacts might be if it’s inhaled.”

The ability of red tide algal blooms in the ocean to release their toxins into the air have been studied extensively. For Plaas, the red tide algal booms in Florida were what led to her work at the University of North Carolina Institute of Marine Sciences in Morehead City.

“I was studying the red tide and the Gulf of Mexico, which is another type of harmful algae whose toxin can easily get into the air, which will shut down beaches all across the west coast of Florida,” she said. “I became really fascinated by this. This microscopic organism having such a big impact on human health and the economy… how water quality can impact human health.”

Cyanobacteria have not been studied as much as the algae that causes red tides.

Colleen Karl, chair of the Chowan-Edenton Environmental Group and one of the co-authors of the paper, said not as much was known about blue-green algae. It was not until recently that environmental conditions had become more conducive to the freshwater blooms.

“Blue-green algae, the cyanobacteria, are pretty much a newcomer,” she said. “They’ve been around for eons. I mean, in the last 10 or 20 years, we’ve started talking about this more as they’re showing up more in local ecosystems.”

Compared to ocean algal blooms, there are relatively few studies looking at the effects cyanobacteria blooms have on air quality. The work by Plaas, Karl and their colleagues sheds new light.

“As far back as 2010, they started looking at the ability of the cyanobacteria toxins to get into the air, but there have been less than 10 studies that have really looked at this,” Plaas said. “Where our study is unique, we’ve actually found a correlation between increases of particulate matter, the PM2.5, and association with bloom periods.”

PM2.5 refers to particulate matter 2.5 microns in size or smaller, air pollutants that the Environmental Protection Agency considers to be of “the greatest risk to health.”

The Chowan River study does not specifically identify cyanobacteria toxins in the particulate matter. Rather, the authors were looking for toxins called microcystins. Microcystins, a family of the bacteria that the EPA considers a “a potent liver toxin and possible human carcinogen,” had previously been shown to be present in area waters “on numerous occasions,” according to the paper.

During the study period, however, microcystins were not the dominant blue-green algae found.

“In our study, we didn’t see a lot of microcystins,” Plaas said. Instead, the research found a lot of another type of cyanobacteria that is not as frequently associated with microcystins production.

Nonetheless, the researchers established what they say is a clear connection between different stages of cyanobacteria bloom and aerosol particulate matter. The authors found that more particulate matter was present early in the life cycle of a bloom, even though it’s at the end of the cycle when blooms can get pretty smelly and their presence is most readily apparent.

“It’s when they’re just beginning their lifecycle when they’re ramping everything up,” Plaas said. “What we are predicting in our preliminary findings, at that early stage, more toxins are being produced when you don’t have as much of the herald signs of a bloom. Toward the end, that’s when it’s potentially less toxic.”

Plaas was cautious about linking the increase in particulate matter specifically to airborne toxins, saying, “It’s not a smoking gun because we can’t say for a fact, ‘Yes, those PM 2.5 particles were made of cyanobacteria or something from the cyanobacteria.’ But we did a robust statistical analysis looking at that time period during the bloom versus not during the bloom and found a significant association.”

The study did not examine why more cyanobacteria blooms are occurring in freshwater bodies worldwide. For that, Dr. Hans Paerl, Kenan Distinguished Professor at UNC Institute of Marine Sciences and a co-author of the paper, pointed to nitrogen, especially in the Albemarle-Chowan River basin.

“Nitrogen ends up being kind of on the short end of the stick. So, any new nitrogen that’s coming into the system will help promote the growth of algae and blooms,” Paerl said.

He said there had been a steady increase in the potential for algal blooms in northeastern North Carolina for some time, as shown in North Carolina Department of Environmental Quality data.

“The thing that we’ve been doing … is analyzing data that’s been collected by DEQ on Albemarle Sound” he said. “The amount of chlorophyll in the water, which is indicative of how much algae is there has been steadily increasing since … back in the probably late ‘90s or so.”

What is causing the increase, however, may be a complex interaction of factors and global climate change may play a role. But Paerl cautioned against looking solely at rising temperatures as the driving factor.

“Temperature is definitely important, and during the summertime when the temperature is up, you have a greater potential for getting blooms of cyanobacteria, which are the problematic bloom organisms,” Paerl said. “But if you look at the long-term data from DEQ, it’s hard to see a signal that’s significantly different from the natural variability out there.”

Paerl said that even though temperatures in Albemarle Sound are rising, “it’s not the increase in temperature that’s responsible for the increase in blooms.”

That’s not to dismiss climate change as playing a significant role. Paerl noted that extreme weather — hurricanes and violent storms — flush lawn, farm and animal waste nutrients into the watershed.

“Climate change may play a role, not so much in terms of the increase in temperature, which is very subtle, but more extreme events,” Paerl said. “More major storm events and floods, and those, of course, would lead to more discharge of nutrients into the system.”