U.S. Geological Survey scientists have detected toxins — known as microcystins — produced by various forms of algae in 39 percent of the small streams assessed throughout the southeastern United States. The recent study looked at 75 streams in portions of Alabama, Georgia, North Carolina, South Carolina and Virginia.

“This is the first systematic stream survey of algal toxins in the southeastern United States,” says Keith Loftin, the USGS research chemist who led the study. “It’s important, because it provides a better understanding of the occurrence of these microcystins in aquatic ecosystems with flowing waters.”

Microcystins are a well-known public health concern. Public health practitioners and medical researchers have observed a range of symptoms in humans after exposure to microcystins. Symptoms can include nausea, dermatitis and, in severe cases, liver failure. Toxicity issues have been reported for humans, companion animals, livestock and wildlife. 

Although the maximum microcystin concentration measured in this study (3.2 micrograms per liter) did not exceed World Health Organization moderate risk thresholds (10 micrograms per liter) in the streams sampled, further research is needed to understand the potential effects on water quality and related environmental health concerns in downstream aquatic ecosystems, lakes and drinking water reservoirs.   

Previous research indicated that cyanobacteria, a form of algae capable of producing microcystins, were found in 74 percent of the streams assessed throughout the southeastern United States. However, that research did not include the study of microcystins.

This is the first of several regional assessments of algal toxins, which will provide context for the design of future environmental health studies. These studies will investigate land-use and other factors that might influence or create new environmental pathways of exposures to cyanobacteria and associated toxins. Ongoing work by the USGS in the Pacific Northwest and planned work in the northeastern United States and California will expand the understanding of cyanobacteria and toxins in a wider variety of aquatic ecosystems. 

More information about this study can be found here. Support for this work was provided by the USGS’ Toxic Substances Hydrology Program and the National Water Quality Assessment Program (NAWQA).