Municipal Affairs and Environment

Blue-Green Algae: Frequently Asked Questions

Blue-Green Algae Toxins

  1. Are blue-green algae toxic?
  2. What are microcystins?
  3. Are all blue-green algae blooms harmful?

1. Are blue-green algae toxic?

Several types of blue-green algae are capable of producing toxins. People may be exposed to these toxins through contact with the skin (e.g., swimming), through inhalation (e.g., boating or water skiing), or by swallowing contaminated water. Types of toxins and their potential health effects include the following:

Hepatotoxins — these are the most commonly occurring blue-green algae toxins. Significant exposure can damage the liver and other internal organs, and can cause gastroenteritis, tissue damage, muscle weakness, paralysis, and respiratory failure (with acute exposure), tumors, and possibly liver cancer (with long-term, chronic exposure). Examples include microcystins and nodularins.

Neurotoxins — these toxins affect the central nervous system. Significant exposure can lead to seizures, paralysis, respiratory failure or cardiac arrest. Examples include anatoxin-a and saxitoxin. Saxitoxin is the toxin associated with red tide and paralytic shellfish poisoning in marine systems.

Cytotoxins — these toxins can affect the liver and other organs (though through a different mode of action than hepatotoxins) and can potentially cause malaise, headache, anorexia, vomiting, chromosome loss, DNA strand breakage, and damage to organs. An example is cylindrospermopsin.

Dermatotoxins and Gastrointestinal Toxins — these toxins can affect the skin and mucous membranes, and can cause allergy-type reactions such as rashes, eye/nose/throat irritation, and asthma, as well as headaches, fever, and gastroenteritis (nausea, stomach cramps, vomiting, diarrhea).

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2. What are microcystins?

Microcystins are one group of hepatotoxins produced and released by blue-green algae. Microcystin is the most common of the blue-green algal toxins found in water and is most often responsible for affecting animals and humans who come into contact with toxic blooms. Microcystins are extremely stable in water because of their chemical structure, can persist in both warm and cold water and can tolerate radical changes in water chemistry, including pH. To date, scientists have identified about 50 different kinds of microcystins. One of these, microcystin-LR, appears to be most commonly found in water supplies around the world. For this reason, most research in this area has focused on this toxin.

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3. Are all blue-green algae blooms harmful?

Researchers generally agree that 30 to 50 per cent of blue-green algae blooms are harmless because they contain only non-toxic species of freshwater blue-green algae. Blooms containing even one species of toxic blue-green algae will be poisonous and potentially dangerous. Because there's no obvious way to tell if a particular bloom is toxic, samples have to be analyzed in a laboratory before a body of water can be declared safe.

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