Algal toxins found in many streams in the Southeast

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How safe is your local stream? @bberwyn photo.

Scientists gain better understanding of health risks associated with microsystins

Staff Report

Taking a swim in a cool, clear stream on a hot summer day always seems like a good idea, but if you’re in the southeastern U.S., you may want to stop and think. According to a new U.S. Geological Survey study, close to 40 percent of the streams in the region may be contaminated by algal toxins known as microsystins.

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.

The scientists 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,” said 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.”

The maximum microcystin concentrations measured in this study did not exceed World Health Organization moderate risk thresholds in the streams sampled, but 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.

The assessments of algal toxins will provide context for the design of future environmental health studies. These studies will investigate land-use and other factors that may 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 our understanding of cyanobacteria and toxins in a wider variety of aquatic ecosystems.

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