Toxins Found in 39% of U.S. Southeastern Streams

U.S. Geological Survey (USGS) scientists detected microcystin—an algal toxin—in 39 percent of 75 streams assessed in the southeastern United States. These results will inform and become part of a larger, systematic national survey of algal toxins in small streams of the United States.

Cyanobacteria are photosynthetic microorganisms that are present in streams, lakes, wetlands, and oceans worldwide. Cyanobacteria are known to intermittently produce toxins (cyanotoxins) that can have adverse effects on a wide range of organisms including bacteria, algae, insects, plants, bivalves, fish, and humans, but the factors that trigger toxin production are not well understood. Microcystins are among the most commonly reported and widely studied cyanotoxins, and concerns are growing due to apparent increases in the frequency and severity of human and ecological health effects.

As a first step toward designing a survey to advance our understanding of microcystin occurrence in smallstreams, USGS scientists utilized historical periphyton data (1993–2011) and identified cyanobacteria (including  Leptolyngbya ,  Phormidium ,  Pseudoanabaena , and  Anabaena  species) in 74 percent of headwater streams in Alabama, Georgia, South Carolina, and North Carolina during this time period. Although microcystins were not measured during that initial research, the presence of microcystin producing cyanobacteria provided critical evidence that enabled the scientists to prioritize and design subsequent research.

With that evidence in hand, USGS scientists then collected environmental samples from 75 targeted streams with varying urban and agricultural land use in the southeastern United States for microcystin analyses. Five sites representative of a land use gradient were resampled monthly in August, September, and October 2014 to provide additional insight into the persistence and temporal variability of microcystin occurrence within the study area. Overall, microcystins were detected in 39 percent of the streams with median detected concentrations of 0.29 micrograms per liter (µg/L) and a maximum concentration of 3.2 µg/L.

USGS scientists collecting microcystin samples from the Enoree River at Pelham, South Carolina. Photo Credit: Dianna Jarvis, USGS.

Although none of the microcystin concentrations exceeded the World Health Organization moderate risk threshold of 10 µg/L, this study is the first of several regional assessments of algal toxins, (including the Pacific Northwest, the northeastern U.S., and California) being planned and conducted now. Together, these studies will provide important baseline data across the United States to understand and document the extent, magnitude, and sources of algal toxins in the environment.

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Taxonomy

• Toxins
• Environment
• Algae