Microcystis in the Environment and Its Health Effects

Introduction

Microcystis,a genus of cyanobacteria, is a microscopic organism that is found naturally at low concentrations in freshwater systems such as lakes and streams. It occasionally  forms a harmful algal bloom (HAB).  Microcystis is also sometimes found in low salinity waters when it is washed out of a freshwater system. It has frequently been reported in both fresh and low salinity waters in Florida. Although often called a bluegreen algae, Microcystis is actually not an alga, but a simpler form of life more closely related to bacteria. It occurs globally, from Australia to South America to Europe, and to the United States.

Under optimal conditions (such as high light and calm weather, usually in summer), Microcystis occasionally forms a bloom, or dense aggregation of cells, that floats on the surface of the water forming a thick layer or 'mat'. At higher concentrations, Microcystis blooms are so dense that they resemble bright green paint that has been spilled in the water. These blooms  potentially affect water quality as well as the health of human and natural resources. Decomposition of large blooms can lower the concentration of dissolved oxygen in the water, resulting in hypoxia (low oxygen) or anoxia (no oxygen). Sometimes, this results in fish kills. The blooms can also be unsightly, often floating at the surface in a layer of decaying, odiferous, gelatinous scum.

Excessive nutrient inputs have often been cited as the cause of freshwater cyanobacteria blooms. Although nutrient enrichment, or eutrophication, contributes to bloom formation, the underlying factors leading to a cyanobacterial bloom are complex. They may include poor water flow (stagnant conditions) and alternations of the lake ecosystem such as land clearing, agricultural activities, and water management.

Of the more than 50 genera of freshwater cyanobacteria identified, approximately one third produce toxins. Microcystis is the most common of these toxic cyanobacteria and has been associated with human and livestock poisoning as well as fish kills. Consequently, considerable research has focused on this organism and its toxins. Not all Microcystis blooms are harmful or toxic. In fact, both toxic and nontoxic strains of Microcystis exist. Toxic strains can also regulate the gene for toxin expression, essentially 'turning on' or 'turning off' toxin production so that they may not be toxic under all conditions. Toxic strains of Microcystis produce a protein-based toxin called microcystin. Currently, more than 60 structural variants of microcystins have been identified. Some other cyanobacteria such as Anabaena flos-aquae also produce microcystins.

Health Effects

Microcystins are hepatotoxins (toxins that acts upon the liver) and known tumor promoters. If people drink water contaminated by microcystins, symptoms of exposure include nausea, vomiting and, in very rare but  severe cases, acute liver failure. Reported health effects from cyanobacteria in humans are highly uncommon in the United States.

Although the likelihood of people being affected by a Microcystis bloom is low, minor skin irritation can occur with contact, and gastrointestinal discomfort can also occur if water from a bloom is ingested. People recreationally exposed (e.g., personal watercraft operators) to microcystins have also reported minor skin irritation. Health problems may occur in animals if they are chronically exposed to fresh water with Microcystis present. Just as livestock and domestic animals can be poisoned by drinking contaminated water, fish and bird mortalities have been reported in water bodies with persistent Microcystis blooms.

To limit exposure to microcystin toxin:

• Avoid or limit exposure to water containing high concentrations of Microcystis.  This includes swimming and any activity resulting in accidental immersion.
• Do not allow children or pets to play in water containing a bloom.
• Never drink untreated water containing a Microcystis bloom, and do not let pets or livestock drink the water.
• Do not use herbicides to kill Microcystis cells because this will release the toxins directly into the water.

If exposed, wash the area thoroughly with clean water. Also thoroughly wash the fur of a pet that has been swimming in waters containing Microcystis.

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