Blue Green Algae

Blue green algae are really a type of bacteria known as Cyanobacteria. There are similar to algae to look at and have the same requirements for light, nutrients and carbon dioxide.

Oxygen-producing cyanobacteria have been found from 2.8 billion years ago in fossilized stromatolites. It is thought that the ability of cyanobacteria to perform photosynthesis converted our early reducing atmosphere into an oxidizing one. This changed dramatically the composition of life forms on Earth and generated an explosion biodiversity.

Aquatic cyanobacteria are probably best known for the extensive and highly visible blooms (including red tides) that can form in both freshwater and the marine environment and can have the appearance of blue-green paint or scum. In large concentrations they can produce chemicals that taint drinking water with musty or earthy tastes and odours. These bad tastes and odours often require a combination of flocculation, filtration, chlorination and activated carbon to remove and in bad cases the water is undrinkable. Worse still some species can be hazardous to animals and people as they produce toxins that if ingested, inhaled or even come in contact with the skin may cause illness.

The Cooperative Research Centre (CRC) for Water Quality and Treatment in Australia advises that blue-green algae produce three main types of toxin:

Hepatotoxins damage the liver and may also increase the risk of certain types of cancer.
Neurotoxins damage nerves and can cause muscle tremors, especially in the muscles animals and people need to breathe.
Allergens are thought to produce a range of reactions including skin rashes, irritation of the eyes, and possibly gastroenteritis.

To put the toxicity of blue-green algae in perspective, the potency of pure saxitoxin (one of the common cyanobacterial toxins in Australia) is similar to the toxins of the common tiger snake, taipan and common brown snake when injected into mice.

However it is not all bad news about blue green alage. In some parts of Asia it is used as a biofertilizer and grown amongst rice crops to supplement nitrogenous fertilizers. The organisms fix nitrogen from the atmosphere and it then becomes available to the plant.

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