What they are:

• Blue-green algae, or cyanobacteria, and other algae include a number of species of microscopic aquatic organisms that perform photosynthesis to produce energy and oxygen. Produced Earth’s earliest fossils.
• Exist as single cells, or as groups of cells in visible “pond scum,” filaments or sheath-covered masses.
• Some species are important food sources, but others release toxic compounds, called cyanotoxins, that harm humans and animals.
• Water can have an earthy, musty odor due to cyanobacteria species producing two organic compounds: geosmin and MIB (2-methylisoborneol).

Occurrence:
• Invisible in surface water in low numbers, multiply rapidly into raft-like “blooms” where water is warm, shallow and undisturbed. Blooms can look green, blue-green, yellow, brown or red.
• Reports of algae-caused unpleasant taste and odor in drinking water are common. US Environmental Protection Agency (EPA) is funding research to improve detection of cyanotoxins. Detection now must be performed in an analytical laboratory.

Health effects:
Algae-containing water can be swallowed, can contact the skin or is inhaled in aerosol-like droplets while swimming or showering. Cyanotoxins can cause gastrointestinal and lung ailments; allergic responses; skin and eye irritation; liver damage; tumor growth; and neurotoxic (nerve) reactions. Effects of long-term consumption uncertain.

Regulation:
• No state or federal standards for cyanotoxins in US drinking water. Canada, Australia, Brazil and Japan are among nations that have standards. Some US drinking water systems voluntarily test for cyanotoxins.
• EPA has added cyanobacteria to its Drinking Water Contaminant Candidate List (CCL). They are among EPA’s unregulated contaminants for which monitoring is required.
• World Health Organization guideline for the cyanotoxin microcystin LR in drinking water is 1 microgram per liter.

Water treatment:
• Activated carbon is effective and can resolve cyanobacteria-caused taste and odor issues.
• Reverse osmosis (RO), nanofiltration and ultrafiltration will remove/reduce single-cell cyanobacteria, may also help reduce cyanotoxins.
• Disinfection methods (such as chlorination) may kill cyanobacteria but not eliminate the cyanotoxins they release.

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Sources: US EPA, US Centers for Disease Control and Prevention, New York State Department of Health, California Department of Public Health, University of California.
Photos by New York State Department of Health