2012 Drought and HAB Reconnaissance Monitoring Effort

In late summer 2012, concerns arose in Illinois after reports of highly elevated concentrations of microcystin in several northern Illinois lakes. The microcystin concentration reported from one lake (31,500 µg/L) was an astounding 1,575 times greater than the 20 µg/L World Health Organization (WHO) guidance value indicating a “high” probability of acute health effects due to recreational exposure (see table below).

As a result of these reports, Illinois EPA and the U.S. Geological Survey (USGS) initiated reconnaissance monitoring during August through October 2012. The purpose of this monitoring effort was to assess the spatial extent and characteristics of blue-green algal blooms in Illinois during the drought and to verify the elevated microcystin concentration in certain lakes. Ten lakes and two rivers were sampled during the monitoring period. Samples were analyzed for microcystin, cylindrospermopsin, and saxitoxin. Microcystins were the most frequently detected toxin, found in 85% of the water bodies sampled. The highest microcystin concentration detected (4,800 µg/L) was 240 times the 20 µg/L WHO guidance value for a high probability of acute health effects. Based on this 20 µg/L guidance value, a total of four lakes had microcystin concentrations in the high probability range for adverse health effects. Lower concentrations of microcystin were found in five other lakes and one river. Virtually all of the water bodies sampled during the monitoring period had high or very high probabilities of associated health effects based on total cyanobacteria cell counts. More details of this effort are provided in a USGS Open-File Report.

Results from the 2012 monitoring clearly indicate that blue-green algal blooms and algal toxins, especially microcystin, can be cause for concern in Illinois surface waters. While drought conditions and hot temperatures present during much of the summer 2012 in Illinois may have contributed to the development of the blue-green algal blooms, it is still unclear how those conditions contributed to the production and persistence of algal toxins.

World Health Organization Guidance Values
Relative Probability of Acute Health Effects (Advisory Level)Microcystin-LR (ug/L)Total Cyanobacteria (cells/mL)
Low<10<20,000
Moderate10-2020,000-100,000
High20-2,000100,000-10,000,000
Very High>2,000>10,000,000

Reference: WHO guidance values for the relative probability of acute health effects during recreational exposure to microcystins, based on information presented in Chorus and Bartram, 1999, and Graham and others, 2009.