Regional and Seasonal Variation of Cyanotoxins

GMU Center for Biomedical Science and Policy

Center for Biomedical Science and Policy Twitter/X

Author Information1

Aaravabhoomi, H.2; Field, D.3; Gibson, A.4; Kou, S.5; Schlueter, M.6; Shah, R.7

(Editor: Baxt, P.R.8)

1 All authors are listed in alphabetical order.

2 Maggie L. Walker Governor’s School, VA, 3 Los Altos High School, CA, 4 Yorktown High School, VA, 5 Cupertino High School, CA, 6 James Madison School, VA, 7 Poolesville High School, CA

8 George Mason University

Background: Harmful Algal Blooms (HABs) and their toxins thrive in warm, nutrient-rich freshwater conditions, and can produce harmful cyanotoxins. Typically, these cyanotoxins take the form of hepatotoxins, dermatoxins, or neurotoxins. Exposure to cyanotoxins can occur in various fashions, including skin-to-water contact, inhalation of fumes, ingestion of contaminated water, and indirect ingestion through contaminated water sources or aquatic animals [1]. Exposure to microcystins, a common hepatotoxin found in cyanobacteria blooms, has been linked to fatal liver damage in both humans and dogs [3]. Additional evidence connects cyanotoxin BMAA to neurodegenerative diseases, such as ALS and Parkinson’s disease [5]. Minimal treatment options are widely available. Government bodies therefore focus their efforts on cyanobacterial toxicosis prevention, commonly issuing public safety alerts and advisory warnings around peak HAB exposure areas [3].

Objective: This research examines how HAB blooms and cyanobacteria outbreaks vary both regionally and seasonally across the United States from 2008-2018.

Methods: A series of t-tests, chi-squared tests, and ANOVA specifications stratified by region and season underlie the reported results. Each utilizes the US EPA Cyanobacteria state reported events and recreation advisories data from 2008-2018. Additionally, we include QGIS data mapping to visualize seasonal and regional differences across our dataset. We define our analysis across three following dimensions: 1) Presence of HABs, 2) High cyanobacteria levels: any cell counts ≥ 20,000 to 80,000/mL and 3) High cyanotoxin levels: any detected concentration ≥ 4 to 20 μg/L.

Results: Findings suggest cyanobacteria outbreaks mostly occur in the West North Central region of the US and during the summer months. US. Iowa, Vermont, Ohio, and North Carolina contain most of the reported outbreaks. Bloom occurrences similarly often occur during the summer but are mostly found in the New England area. Single factor ANOVA testing confirmed this result, finding at least one region to statistically differ in mean bloom count compared to other regions, significant at the 1% level. T- and Chi-sq tests all report significant differences in HAB status between regions and seasons as well. Chi-Sq results find a difference between bloom status and region at the 1% level. Two-sample T-tests (i.e., comparing each region vs. all other regions) find statistically significant differences with the East North Central (p<0.001), New England (p=0.019), Pacific (p=0.02), South Atlantic (p=0.006), and West North Central (p<0.001) regions. All seasons outside of Fall (p=0.112) are found to be statistically significantly different from all other times of the year at the 1% level. Finally, QGIS data mapping reiterates these regional and seasonal HAB and cyanobacterial differences in our dataset. The Midwest year-round and Western states Winter-Spring HAB exposure are definitively displayed in our figures, as well as New England’s Fall and Summer peak HAB concentrations.

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Conclusion: Mitigating exposure to cyanobacterial toxicosis requires awareness of HAB regional and seasonal patterns. Our study finds HAB risks highest during the summer months, with regions following their own unique HAB seasonal patterns. We suggest government bodies incorporate these findings to better target their public awareness campaigns.


  1. Backer, Lorraine C., Deana Manassaram-Baptiste, Rebecca LePrell, and Birgit Bolton. “Cyanobacteria and algae blooms: review of health and environmental data from the harmful algal bloom-related illness surveillance system (HABISS) 2007–2011.” Toxins 7, no. 4 (2015): 1048-1064.
  2. Metcalf, J.S., Tischbein, M., Cox, P.A. and Stommel, E.W., 2021. Cyanotoxins and the nervous system. Toxins13(9), p.660.
  3. Rankin, K.A., Alroy, K.A., Kudela, R.M., Oates, S.C., Murray, M.J. and Miller, M.A., 2013. Treatment of cyanobacterial (microcystin) toxicosis using oral cholestyramine: case report of a dog from Montana. Toxins5(6), pp.1051-1063.
  4. Svirčev, Z., Lalić, D., Bojadžija Savić, G., Tokodi, N., Drobac Backović, D., Chen, L., Meriluoto, J. and Codd, G.A., 2019. Global geographical and historical overview of cyanotoxin distribution and cyanobacterial poisonings. Archives of toxicology93, pp.2429-2481.
  5. Trevino-Garrison, I., DeMent, J., Ahmed, F.S., Haines-Lieber, P., Langer, T., Ménager, H., Neff, J., Van der Merwe, D. and Carney, E., 2015. Human illnesses and animal deaths associated with freshwater harmful algal blooms—Kansas. Toxins7(2), pp.353-366.
  6. Zhang, F., Lee, J., Liang, S. and Shum, C.K., 2015. Cyanobacteria blooms and non-alcoholic liver disease: evidence from a county level ecological study in the United States. Environmental Health14(1), pp.1-11.
  7. “OHHABS Data | Harmful Algal Blooms (HABs).” Accessed: July 26, 2023. [Online]. Available: