Environmental Health - Toxic Substances Hydrology Program
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 small streams, 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.
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.
The environmental health significance and causal factors controlling the distribution and magnitude of microcystin occurrence remains poorly understood. Baseline data from these regional studies are being used to inform new research designed to improve those understandings and will be focused on investigations of land use and other factors that may affect or create new environmental pathways of exposure to cyanobacteria and associated toxins.
Loftin, K.A., Clark, J.M., Journey, C.A., Kolpin, D.W., Van Metre, P.C., and Bradley, P.M., 2016, Spatial and temporal variation in microsystins occurrence in wadeable streams in the southeastern USA: Environmental Toxicology and Chemistry, v. 35, doi: 10.1002/etc.3391.