Toxic Cyanobacteria (formerly known as blue-green algae)

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What are Cyanobacteria?

Cyanobacteria, formerly called "blue-green algae", are simple, life-forms closely related to bacteria. Although they are similar to algae, they are not true algae. Cyanobacteria are found throughout the world in freshwater and marine habitats. However, cyanobacteria "blooms" typically only occur in freshwater. Nutrient-rich bodies of water such as eutrophic lakes, agricultural ponds, or catch basins, may support a rapid growth of cyanobacteria. When conditions are right, a "clear" body of water can become very turbid with a green, blue-green or reddish-brown growth within just a few days.

A close-up of cyanobacteria

Cyanobacteria Toxins

Sometimes cyanobacteria blooms may produce toxins that are potentially lethal to animals, including humans. Cyanotoxins include a diverse range of toxic mechanisms as illustrated in Table 1. Poisoning from nerve toxins can appear within 15-20 minutes after ingestion. In animals symptoms from neurotoxin exposure include weakness, staggering, difficulty in breathing, convulsions and death (DOH 2000). In people symptoms may include numbness of the lips, tingling in fingers and toes, and dizziness. Liver toxin poisoning may take hours or days for symptoms to appear. Symptoms of liver toxin exposure include pain, diarrhea and vomiting in humans and death in animals.

Microcystis magnified 100 times under a microscope

Two genera of cyanobacteria account for the vast majority of toxic blooms worldwide: Microcystis and Anabaena. Toxin producing versions of both genera have been documented in Washington State. Microcystis forms numerous small ball shaped cells that join together in groups as colonies that tend to float near the water surface. Anabaena is filamentous and often looks like a coil or necklace of beads. Visit Cyanosite to view a library of photos of various cyanobacteria.

Human health risk from exposure to cyanobacteria and their toxins during recreational water use arises through three routes of exposure (WHO):

• direct contact of exposed parts of the body, including sensitive areas such as the ears, eyes, mouth and throat, and the areas covered by a bathing suit (which may collect cell material);
• accidental uptake of water containing cells by swallowing; and
• uptake of water containing cells by aspiration (inhalation).

Not all cyanobacteria blooms are toxic, and even blooms caused by known toxin producers may not produce toxins or may produce toxins at undetectable levels. It is not known what triggers toxin production. Recent studies have shown the probability that an individual bloom containing Anabaena, Microcystis, and/or Aphanizomenon will be toxic could be between 45 and 75% (Toxic Cyanobacteria Blooms; A Field/Laboratory Guide, Dr. M. A. Crayton).

1. Many structural variants may be known for each toxin group.
2. Not produced by all species of a particular genus
3. Whole cells of toxic species elicit widespread tissue damage to kidney and lymphoid tissue.

Toxic Cyanobacteria Monitoring Program in King County

In 2003 King County began routine cyanobacteria toxicity testing on samples collected from Lake Sammamish, Lake Washington, and Lake Union. The program was revised in 2005 and now includes sample collection at 13 Routine Major Lake stations and 11 Swimming Beach Program stations. Samples are collected on alternating weeks from March through October (see sampling locator map).

The County’s sampling efforts are designed primarily to evaluate the presence of cyanobacterial toxins, and secondarily to estimate concentrations and geographic extent of the toxicity, should it be present. For more information about King County’s toxic cyanobacteria program see the 2007 Phase III Sampling and Analysis Plan for Toxic Cyanobacteria in Lake Washington, Lake Sammamish and Lake Union.

Click on map to view full size image

Methods

Because studies have shown that microcystins are more frequently detected than anatoxins in cyanobacterial bloom samples (Chorus 2001), King County routinely monitors for microcystins.

Microcystin analysis is done at the King County Environmental Lab using both the enzyme-linked immunosorbent assay (ELISA) and the protein phosphatase inhibition assay (PPIA). In order to get a close approximation to the total microcystin concentration in the ambient water (extra- and intracellular concentrations), sample preparation includes cell lysing prior to analysis. The resulting concentration (reported as Total Microcystin) is assumed to be representative of a recreational exposure in which a swimmer ingests ambient water and cells as a combined dose.

Results

The results of the County’s cyanobacteria sampling efforts can be viewed in Table 2 and Figures 1-4.

Table 2. Summary of King County DNRP Toxic Cyanobacteria Monitoring Results.

1. Total microcystin concentration (extra- and intracellular). Sample preparation includes cell lysing by freezing and sonication prior to analysis.
2. Both PPIA and ELISA analysis done on all samples. Method that resulted in maximum total microcystin value for the year is listed here.

From 2003 through 2006, only two of the 860 samples collected have had microcystin values greater than 1.0 µg/L, the threshold for drinking water recommended by the World Health Organization (WHO 1988). These two samples, measuring 1.35 and 52.6 µg/L total microcystin (by PPIA), were collected during a cyanobacteria bloom in the Matthews Beach area in Lake Washington on May 30, 2006. The higher sample was collected directly from a cyanobacterial scum north of the swimming beach and the other from the main swimming beach area.

Several toxic blooms have been documented in King County. The first toxic Microcystis bloom recorded in Lake Sammamish was in the fall of 1997. However, previous blooms not tested may have been toxic as well. A study conducted on Lake Sammamish during the summer and fall of 1999 revealed a toxin-producing bloom during late August and early September despite the absence of visible cyanobacterial biomass (B. Kenworthy, masters thesis University of Washington, 2000). In addition, a prolonged toxic Microcystis bloom occurred in Green Lake from early August 2002 through January 2003 (Jacoby 2003).

We cannot predict if future blooms of cyanobacteria will be toxic, or what the long-term effects might be. We do know that if nutrients entering the lakes increase, blooms will occur more frequently; and based on probability, toxic blooms could occur more frequently as well.

Risks Levels for Exposure to Toxic Cyanobacteria

Currently there are no state or federal guidelines for issuing cyanobacteria bloom advisories. The WHO has recommended that microcystin concentrations should not exceed 1 µg/L in drinking waters. This level may be overly protective for lakes that are not being used for drinking water (Jacoby and Kann 2007). Some agencies are developing guidelines based on the number of cells/ml of potential toxic cyanobacteria rather than measured toxins. For example, the Oregon Department of Health issues advisories in recreational waters if cell density of potentially toxic cyanobacteria is equal to or greater than 100,000 cells/ml.

The Washington State Department of Ecology (Ecology) recently received funding to develop an Algae Control Program and will be working with the State Department of Human Services (ODHS) to set up statewide guidelines for cyanobacterial blooms/toxins. In the meantime, King County will continue sampling for toxins throughout the three large lakes and will deal with toxic blooms on a case by case basis.

References

• Chorus, I. (ed.). 2001. Cyanotoxins. Springer-Verlag, Berlin, Germany, 357 pp.
• Chorus, I. and J. Bartrum (eds.) 1999. Toxic Cyanobacteria in Water: A Guide to their Public Health Consequences, Monitoring and Management. London: E & FN Spon (published on behalf of the World Health Organization).
• Jacoby, J. 2003. Toxic blooms of cyanobacteria: a new challenge for recreational lakes. LakeLine 23(2):23-26.
• Jacoby, J. and J. Kann. 2007. The occurrence and response to toxic cyanobacteria in the Pacific Northwest, North America. Lake and Reservoir Management 23:123-143.
• King County Department of Natural Resources and Parks. 2007. Phase III Sampling and Analysis Plan for Toxic Cyanobacteria in Lake Washington, Lake Sammamish, and Lake Union.
• Oregon Department of Human Services (ODHS). 2005. Public Health Advisory Guidance for Toxigenic Cyanobacteria in Recreational Waters. Oregon State Public Health. Portland, OR.
• Washington State Department of Health (DOH). Toxic Blue Green Algae Blooms. DOH Pub 333-006 6/2000.
• World Health Organization (WHO). 1998. Guidelines for Drinking-Water Quality. 2nd ed. Addendum to Vol 2, Health Criteria and other Supporting Information. WHO, Geneva.

Other Web Sites

• Lake Sammamish 1997 toxic bloom.
• The Factors Associated with Cyanobacterial Toxin Production in Lake Sammamish During the Summers of 1997 and 1999. (Masters Thesis by Bernadette Rae Kenworthy)
• Washington State Department of Ecology
• Washington State Departm
• ent of Health
• Oregon State Department of Health
• Photo library of Cyanobacteria
• World Health Organization (WHO)

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