Blue-Green Algal Blooms and Microcystin

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What is microcystin?
Algal blooms, often caused by the addition of nutrients to a water body, are sometimes made up of cyanobacteria, commonly called blue-green algae.  Some cyanobacteria can produce toxins, called cyanotoxins. Although many blooms contain non-toxic species of cyanobacteria, lab tests are needed to determine whether a bloom is toxic or nontoxic. Microcystin is the primary cyanotoxin identified in Minnesota lakes.

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Ways people are exposed to microcystin:

  • Swallowing of lake water while swimming, skin contact with lake water while swimming, and breathing in water spray while recreating on the lake.
  • Watering lawns and gardens with lake water – People can be exposed through eating produce from gardens, skin contact and breathing in water spray.
  • Fish consumption - Although there have been no confirmed reports of cyanotoxin-related health effects due to eating fish, it is uncertain whether enough toxins in fish can be consumed to pose a health risk.   
  • Private well water – It is unknown if microcystin will migrate into shallow wells, leading to exposure from ingestion, skin contact, and breathing water spray. 

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What are the possible health effects?
Individual health risk depends on many factors, including amount of exposures and how long a person is exposed, and age, occupation, and health history. Exposure can cause short-term health effects that commonly include nausea, vomiting, fever, rashes, and eye and ear irritation. Low level exposures to microcystins over time can cause liver toxicity.  A resident concerned about health problems associated with microcystin exposure should consult their physician. Children are at a higher risk from cyanotoxins than adults because their exposure is likely to be greater when adjusted for lower body weight. They are also more likely to swallow water during swimming/wading in water. 

Offensive odors can be generated during algal blooms. Concentrations of hydrogen sulfide may get high enough in the air that people can experience temporary symptoms such as eye and throat irritation, headaches, nausea, and dizziness.

Are there community health standards for microcystin?
There are no federal standards for microcystin in drinking water or recreational waters. Some states regularly monitor for cyanotoxins in surface water and have standards based on World Health Organization guidelines. In Minnesota, there is no formal cyanotoxin monitoring program. However, MDH has developed health-based guidance values (HBVs) for use in determining if the levels of microcystin in drinking water are safe. The value, derived in 2012, is 0.04 μg/L for all exposure durations. For more information about the guidance values, please see microcystin in the Human Health-Based Water Guidance Table and the Microcystin-LR in Drinking Water (PDF 130KB/2 pages) information sheet. People are encouraged to call the MPCA with concerns regarding a particular bloom or lake.

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Recommendations for what to do if you have a concern about lakes with algal blooms:

  • Avoid swallowing lake water, skin contact with lake water, and breathing in water spray from recreational activities. Contact with lake scum in or out of the water should be avoided. 
  • Fish caught from the lake should be eaten in moderation. To avoid the highest concentrations of toxins in fish, avoid eating the intestines and organs, especially the liver. 
  • If odors cause discomfort, leave the area if possible.
  • Pets should not be allowed to swim in or drink water from the lake.
  • Phosphorus loading should be decreased to reduce algal blooms frequency. Contact MPCA with water quality concerns.

If experiencing health effects, contact a medical professional. In addition, you are encouraged to report human health effects to MDH’s Foodborne Illness Hotline at 1-877-366-3455.

For health questions, contact MDH’s Acute Disease Investigation and Control group at 651-201-5414.

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Printable Information Sheet: Blue-Green Algal Blooms and Microcystin (PDF: 241KB/2 pages)

More information: 
There is still much to be learned about cyanotoxins and microcystin. MDH will work to update the community as new information becomes available. 

Microcystin at Little Rock Lake

Health Consultation for Little Rock Lake: Microcystin in Little Rock Lake (PDF: 458KB/23 pages)

For information about blue-green algal blooms, visit Blue-green Algae and Harmful Algal Blooms on the Minnesota Pollution Control Agency website.

For information about common illnesses associated with Minnesota beaches and recreational waters, visit How Safe is It? on the Minnesota Department of Health website.

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If you have questions or comments about this information, please contact us.

Updated Tuesday, August 05, 2014 at 06:56AM