When water sources are loaded with excess nutrients, often the result of agricultural runoff, harmful algal blooms can occur. An explosion of cyanobacterial populations can lead to contaminated seafood and drinking water and the death of marine life. However, the release of toxic compounds into the air is increasingly being recognised as a route of chronic exposure that can harm human health.

Certain species of cyanobacteria and algae produce toxins capable of affecting the liver, nervous system, and other organs. While these compounds are known to enter the body through contaminated food and water, evidence suggests aerosolised exposure can occur in areas distant from the water source. Understanding how often airborne droplets of toxins are generated, and at what concentrations this becomes a danger to human health, is essential for improving assessments of environmental and public health risks.

A new study, published in the Open Access journal Toxins, developed a portable air sampling system capable of detecting a range of airborne cyanobacterial toxins in Southwest Florida, USA. By comparing toxins present in both air and nearby water, the researchers provide new insights into an exposure pathway that has remained difficult to investigate.

How do toxins become airborne?

Many harmful cyanobacterial toxins are produced during algal blooms, when cyanobacteria multiply rapidly in freshwater environments. These blooms can release toxins into surrounding waters, particularly as cells begin to break down.

Once present in the water, toxins become incorporated into tiny aerosol droplets created by breaking waves or bursting bubbles at the surface. These droplets, known as lake spray aerosols (LSAs), can then be carried through the air, potentially exposing people who are near affected lakes, rivers, or coastlines through inhalation rather than direct contact with contaminated water.

Although previous studies have detected airborne cyanotoxins, relatively few have investigated multiple toxin classes simultaneously or developed practical methods that can be used routinely in the field. This has made it difficult to understand how common airborne exposure may be, or to compare findings between different locations.

Establishing a better way to monitor airborne toxins

To address this challenge, the researchers developed the Airborne Detection for Algae Monitoring (ADAM) system.

Designed as a portable and self-contained monitoring unit, ADAM combines a glass-fibre filter with a liquid impinger which allows it to collect both airborne particles and dissolved toxins carried within aerosol droplets (Figure 1A). The compact design enables researchers to transport the device easily between sampling locations while collecting samples under real-world environmental conditions (Figure 1B). Importantly, the device contained a collapsible monopole, allowing the device to detect air toxins at a height representative to a person’s breathing height (approximately 5–6 feet).

Figure 1: A) The ADAM shown with both filter and impinger, B) The self-contained pump set up which allows easy transportation between locations.

Importantly, the system was designed with future environmental monitoring in mind. Standardised sampling methods could allow researchers working across different geographical regions and seasons to compare airborne toxin concentrations more consistently. Building larger, comparable datasets could ultimately improve future environmental monitoring and health risk assessments.

Assessing airborne particles

The team deployed ADAM during 21 paired air and water sampling campaigns across Southwest Florida.

Although visible cyanobacterial blooms were absent from most sampling locations, analyses detected several cyanobacterial toxins in air samples at low concentrations. Among these, the neurotoxin BMAA and its related isomers were detected most frequently, while other cyanotoxins, including anatoxin-a and brevetoxins, were also identified on occasion.

Previous studies have also reported high concentrations of the BMAA isomer 2,4-DAB in the brains of stranded dolphins from Florida’s Indian River Lagoon. These dolphins also displayed pathological features associated with Alzheimer’s disease, highlighting why understanding long-term exposure to cyanobacterial neurotoxins remains an active and important area of research.

Dr. James Metcalf, lead scientist on the study, explains:

Data obtained from ADAM airborne detectors indicate that people may be chronically exposed to low concentrations of cyanobacterial toxins and that further assessment is required to help protect human health.

The most significant part of these findings was that airborne toxins were detected even when there was no visible blooms at sampling sites. This suggests that people may be exposed to low levels of airborne cyanobacterial toxins without the presence of the dense surface accumulations that are typically associated with harmful algal blooms.

An overlooked route of toxin exposure

These findings add to growing evidence that inhalation should be considered alongside drinking water and food consumption when assessing exposure to cyanobacterial toxins. However, this study did not investigate the health effects of inhaling these toxins or determine the concentrations required to cause harm. Instead, its findings provide an important foundation for future research aimed at understanding the risks associated with airborne cyanotoxin exposure and informing public health monitoring strategies.

Current monitoring programmes often focus on visible blooms or toxin concentrations in water. However, the ability to detect airborne toxins even during periods of limited bloom activity suggests that routine air monitoring could provide valuable additional information for environmental management and public health.

This study also highlights the importance of developing standardised monitoring methods. Reliable, portable sampling systems, such as ADAM, could enable researchers to build larger datasets, improve comparisons between studies, and better understand how conditions and seasonal changes influence airborne toxin concentrations.

Looking towards future monitoring of airborne toxins

Although questions remain about the long-term effects of chronic exposure to low concentrations of airborne cyanobacterial toxins, this study provides an important foundation for future research.

While improved monitoring will be key to understanding airborne exposure, preventing harmful algal blooms remains the most effective long-term strategy for reducing human health risks. Reducing nutrient pollution from agricultural runoff, wastewater and urban sources will be essential alongside advances in monitoring technology.

The authors suggest that combining portable air samplers with rapid field-based detection methods could enable environmental agencies to monitor airborne toxins more routinely and respond more effectively during bloom events. As these technologies develop, they could improve our understanding of this often-overlooked exposure pathway and help inform future public health guidance. as Dr. James Metcalf suggests:

Even though we can avoid contaminated food and water, preventing exposure through breathing is far more difficult.

Ultimately, this research highlights that the impacts of harmful algal blooms may extend beyond the water itself. By developing new tools to monitor airborne toxins, researchers are building a more complete understanding of how these environmental hazards may affect human health.

More studies on toxin detection and airborne microbial toxins can be found across the Open Access journals Sensors and Toxins. Alternatively, you can access the full MDPI journal list here.