Do you recognize this ancient, prolific organism?  Many people don’t.  However, public awareness of cyanobacteria is rising.  Many people have encountered warning signs posted at recreational areas detailing the adverse health effects of exposure to cyanobacteria when boating or swimming.  An even greater number of us drink water from reservoirs where the organism routinely grows.  Cyanobacteria is more commonly known as blue-green algae, or pond scum.

Cyanobacteria forms large masses called blooms, preferentially in warm, standing water.  They occur most often in the summer during periods of low rainfall.   It has long been known that the blooms are partly to blame for dead zones, areas of open water that no longer support life due to turbidity and lack of oxygen.  The blooms proliferate, in part, because of eutrophication, which is excessive plant growth and decay.  The explosive growth is primarily attributed to the presence of an abundance of agricultural chemical runoff, including nitrogen and phosphorus.   

Certain species of the organism produce toxins that attack the liver (hepatotoxins), the nervous system (neurotoxins), or simply irritate the skin.  When cells of the organism die or rupture, these toxins are released into the water.  Since many people depend on lakes and reservoirs for their drinking water, monitoring its presence is of particular concern for water treatment facilities worldwide.

There is a long, documented history of injury and death associated with acute exposure to these toxins.  Numerous cases of livestock fatalities have been reported in Australia, Finland, Argentina, England, and the United States.  In 1996 in Caruaru, Brazil, 117 dialysis patients were sickened by incompletely treated water used in routine dialysis.  The water was found to contain high levels of microcystin-LR, a particularly potent cyanotoxin.  One hundred of these patients developed acute liver failure, and fifty of them died.  Brazilian health authorities are monitoring the surviving patients to assess the long-term health effects of this acute exposure.  Specifically, the main concern will be cancer rates because microcystin-LR is known to be a strong liver tumor promoter in mammals.

In contrast, there is currently not enough data to predict the effects of long-term, low level exposure to cyanobacteria.  The World Health Organization (WHO) has adopted a provisional guideline for exposure of 0.001 mg/L.  The United States Environmental Protection Agency has had the organism on its Contaminant Candidate List (CCL) since 1998.  This lists tracks substances currently being investigated for inclusion on the list of regulated water contaminants.  While on the CCL list, prior and ongoing research for the substances is evaluated and published for public comment and review.   There has not been a formal, final determination made for cyanobacteria.