Environmental Health - Toxic Substances
Algal Blooms Consistently Produce Complex Mixtures of Cyanotoxins and Co-Occur with Taste-and-Odor Causing Compounds in 23 Midwestern Lakes
U.S. Geological Survey (USGS) scientists studying the effects of harmful algal blooms on lake water quality found that blooms of blue-green algae (cyanobacteria) in Midwestern lakes produced mixtures of cyanotoxins and taste-and-odor causing compounds, which co-occurred in lake water samples. Cyanotoxins can cause allergic and/or respiratory issues, attack the liver and kidneys, or affect the nervous system in mammals, including humans. The findings of this study are significant because studies assessing toxicity and risk of cyanotoxin exposure have historically focused on only one class of toxins (microcystins). The common presence of several types of cyanotoxins indicates that there is the potential for inaccurately quantifying hazards using current assessment methods. Additionally, these results suggest that odor (e.g. earthy, musty smells) may serve as an additional warning signal of the presence of cyanotoxins in water, albeit cyanotoxins may be present in the absence of taste-and-odor problems.
Samples were collected during 2006 from near-shore locations in 23 recreational lakes in the Midwestern United States; seven of the lakes are also water-supply reservoirs. All samples were analyzed for a mixture of six different types of cyanotoxins (anatoxins, cylindrospermopsins, lyngbyatoxins, microcystins, nodularins, and saxitoxins), taste-and-odor compounds (such as geosmin and 2-methylisoborneol (MIB)), chlorophyll, and phytoplankton. Five of 6 cyanotoxin classes were detected. Microcystins were detected in 100 percent of samples, anatoxin-a in 30 percent, saxitoxins in 17 percent, cylindrospermopsins in 9 percent, and nodularins in 9 percent. Toxins and taste-and-odor compounds co-occurred in 91 percent of 23 algal blooms.
Maximum total microcystin concentrations were measured at 19,000 micrograms per liter (µg/L), anatoxin-a (9.5 µg/L), saxitoxins (0.19 µg/L), cylindrospermopsin (0.14 µg/L), and nodularin-R (0.19 µg/L). The maximum microcystin concentration was 3 orders of magnitude larger than the World Health Organization recommended guideline for recreational activities (20 µg/L). Recreational guidelines have not been established for the other measured compounds individually or in mixtures because there currently is insufficient toxicological and epidemiological data.
This study is part of an ongoing effort by the USGS to characterize the sources, occurrence, transport and fate of cyanotoxin mixtures in various environmental settings. Scientists and managers can use these data to more fully understand and manage potential threats caused by cyanotoxin exposures to humans and animals.
Graham, J.L, Loftin, K.A., Meyer, M.T., Ziegler, A.C., 2010, Cyanotoxin mixtures and taste-and-odor compounds in cyanobacterial blooms from the Midwestern United States: Environmental Science and Technology, doi:10.1021/es1008938