Toxins from freshwater algae blooms can go airborne

Each August, Lake Erie’s fishermen develop a cough. Residents who live along the body of water, one of the Great Lakes situated between the US and Canada, feel their asthma kick up. Some have such trouble breathing that they end up in the hospital.

The suspected culprit: the harmful algal blooms that turn the lake into a noxious green soup every summer. A combination of nutrient-rich runoff (such as nitrogen and pollution), warm temperatures, and lots of sunlight supercharges the lake’s algal growth.

Toxic particles from these blooms, scientists are discovering, can also go airborne—and likely into people’s lungs (Environ. Sci. Technol. 2018, DOI: acs.est.7b03609).

“What happens in the water doesn’t stay in the water,” says Greg Dick, a microbial biologist at the University of Michigan working to understand the public health threat posed by these transported toxins.

It’s a pervasive problem. About half of people worldwide live close to a freshwater system (PLOS One 2011, DOI: 10.1371/journal.pone.0020578), and blooms have occurred in every state and on every continent except Antarctica. In addition, warming temperatures caused by climate change are increasing the risk of both marine and freshwater blooms (Env. Sci. Technol. 2017, DOI: 10.1021/acs.est.7b01498).

Going beyond microcystins

Freshwater bloom research has largely centered on the common cyanobacteria Microcystis and theirtoxins, microcystins. In the 1990s, a bloom contaminated the water at a dialysis clinic in Brazil, and dozens of patients died from microcystin poisoning (Br. Med. Jr. 1996, DOI: 10.1136/bmj.312.7040.1183b). People who ingest the contaminated water can experience liver damage or neurological problems.

Yet in recent years, as researchers have begun looking beyond Microcystis, they’ve found a diverse collection of microbes.

“It’s this zoo of bacterial community composition,” Dick says. “We’re just beginning to understand . . . what toxins are being produced.”

Hundreds of other bacterial and cyanobacterial species can produce potentially toxic compounds in freshwater blooms, including saxitoxin-producing species (Environ. Sci. Technol. 2025, DOI: 10.1021/acs.est.4c10888), which are responsible for shellfish poisoning.

“Microcystin is the tip of the iceberg,” says Lauren Hart , a microbial ecologist who completed her PhD in Dick’s lab. The emphasis on microcystin “has led us to not really focus on all of the other biosynthesis properties of cyanobacteria,” she says.

That’s why in a recent study Hart drew on years of metabolomics and metagenomics data from Lake Erie to assess several different strains of cyanobacteria to see what other toxins they could make.

Her work revealed the presence of cyanopeptides, including anabaenopeptins, which fluctuated over time. The presence of microcystins had a synergistic effect on their potential toxicity, thus highlighting the importance of assessing many types of toxins (Environ. Toxicol. 2026, DOI: https://doi.org/10.1002/tox.70028).

“This just adds another layer of concern,” Hart says. Each species and its toxins could add a new set of interactions to the soup. Those interactions could vary throughout the bloom’s life cycle, creating a constantly shifting public health concern.

Toxins take to the air

Daunting as it may be, sorting out who’s who in the microbial zoo is just the first step.

For years, the idea that freshwater lakes could emit particles, including toxins, was “really overlooked,” says Andrew Ault, an atmospheric chemist at the University of Michigan. In 2017, he and his colleagues showed that particles in Lakes Erie and Michigan could be aerosolized. What’s more, some of these particles, detected up to 40 km away, were the perfect size to inhale.

They later uncovered another critical factor.

“What was in the air was different than what was in the water,” Ault says. “And what was in the air was dependent on its chemistry.” More hydrophobic toxins were more likely to be aerosolized (Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.9b07727). And, as it happened, those tended to be more toxic congeners of microcystin.

Ault and his colleagues are continuing this work, collecting water and air samples in the field and experimenting to determine which toxins migrate into the air and how.

Cassandra Gaston, an atmospheric chemist at the University of Miami, studies microcystins and other toxins in freshwater blooms, including those in Lake Okeechobee.

“There are a lot of unanswered questions” about the blooms’ health effects, Gaston says. Some Florida researchers are interested in the neurotoxin β methylamino-L-alanine, which is harder to –measure than microcystins but equally concerning.

Unlike the Great Lakes, Lake Okeechobee doesn’t get big waves, so Gaston is looking at other controls on toxin aerosolization, including salinity changes, temperature, and rainfall.

Gaston says that, ultimately, to get answers, “we need more monitoring.”

Tracking health impacts

Of course, the chemistry doesn’t stop once toxins enter the air.

The atmosphere is “a beaker for chemical reactions,” and “aerosols and droplets are chemical reactors,” says Eric Vejerano, an air quality scientist at the University of South Carolina. He researches freshwater airborne bloom toxins, which are less well studied than marine toxins like those produced by some dinoflagellates and diatoms.

Airborne toxins can break apart or combine with other molecules, which may affect their behavior and, ultimately, their degree of harm.

“We don’t know if toxins get more potent, less potent, or stay the same” once airborne, Vejerano says. Even for relatively well-known microcystins, he adds, “the knowledge we have is very limited when it comes to aerosolization.”

“The big knowledge gap is for chronic or low-dose exposure,” says David Kennedy, a professor of medicine at the University of Toledo. The lungs are a “gateway” to the bloodstream and every organ, he says. The potential damage from a lifetime of repeated exposures to toxic air could be significant—as suggested by studies of red tides—but he says the research simply isn’t there yet.

In collaboration with Michigan researchers through the Great Lakes Center for Fresh Waters and Human Health, Kennedy tracks regional patients’ symptoms. He also collects breath samples and nasal swabs to see which toxins may be present and at what concentrations. Similar work is ongoing in Florida.

Although each lake and bloom is unique, the researchers are optimistic that some of the major findings will apply to freshwater systems worldwide. A shift in perspective will need to come first.

“We have to study harmful algal blooms as water quality and air quality issues,” Vejerano says. “Then we can close this gap.”