What are cyanobacteria?

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Cyanobacteria is the scientific name for blue-green algae, or "pond scum." The first recognized species were blue-green in colour, which is how the algae got their name. Species identified since range in colour from olive-green to red.

Cyanobacteria form in shallow, warm, slow-moving or still water. They are made up of cells, which can house poisons called cyanobacterial toxins. A mass of cyanobacteria in a body of water is called a bloom. When this mass rises to the surface of the water, it is known as surface scum or a surface water bloom. Although we don't know the extent to which cyanobacterial blooms occur across Canada, we do know they mostly appear in the hot summer months and are quite prevalent in the prairies.

What are cyanobacterial toxins?

Cyanobacterial toxins are the naturally produced poisons stored in the cells of certain species of cyanobacteria. These toxins fall into various categories. Some are known to attack the liver (hepatotoxins) or the nervous system (neurotoxins); others simply irritate the skin. These toxins are usually released into water when the cells rupture or die. Health Canada scientists are more concerned about hepatotoxins than neurotoxins, because neurotoxins are not considered to be as widespread as hepatotoxins in water supplies. Very few cyanobacterial toxins have actually been isolated and characterized to date. Better methods of detection are being developed to help us learn more about them, especially to find out which toxins are a problem in Canada and what conditions encourage their production.

What are microcystins?

One group of toxins produced and released by cyanobacteria are called microcystins because they were isolated from a cyanobacterium called Microcystis aeruginosa. Microcystins are the most common of the cyanobacterial toxins found in water, as well as being the ones most often responsible for poisoning animals and humans who come into contact with toxic blooms. Microcystins are extremely stable in water because of their chemical structure, which means they can survive in both warm and cold water and can tolerate radical changes in water chemistry, including pH. So far, scientists have found about 50 different kinds of microcystins. One of them, microcystin-LR, appears to be one of the microcystins most commonly found in water supplies around the world. For this reason, most research in this area has focused on this particular toxin.

Does the presence of a cyanobacterial bloom always mean the water is contaminated?

No. Researchers generally agree that between 30 and 50 per cent of cyanobacterial blooms are harmless because they contain only non-toxic species of freshwater cyanobacteria. Blooms containing even one species of toxic cyanobacteria will be poisonous and potentially dangerous. Because there's no obvious way to tell if a particular bloom is toxic, samples have to be analysed in a laboratory before a body of water can be declared safe.

Why do blooms sometimes appear overnight?

Even if you can't see a cyanobacterial bloom floating on the surface of the water, that doesn't mean one isn't present in the water - the bloom could be suspended at various depths in the water where you can't see it.

The depth at which cyanobacterial blooms float depends on a number of factors. The most important of these are light, phosphorus and nitrogen, which cyanobacteria need in order to survive. As the availability of these elements can change quickly with the time of day and the weather, most cyanobacteria have evolved to be able to control their buoyancy. By being able to sink and rise at will, they are able to move to where nutrient and light levels are at their highest.

In order to activate the mechanism that allows them to move, cyanobacteria need light. At night, when there is no light, cells are unable to adjust their buoyancy and often float to the surface, forming a surface scum. This scum literally appears overnight and lingers until the wind and waves scatter the cells throughout the water.

Are cyanobacterial blooms a new problem?

No. The earliest reliable account of a cyanobacterial bloom dates back to the 12th century; the toxic effects of cyanobacteria on livestock have been recognized for more than 100 years. Since cyanobacterial bloom formation seems to be linked to nutrient-rich water bodies (for example, water that contains a lot of phosphates from detergents and phosphate fertilizers), the problem is not likely to go away in the near future.


Effects on Humans and Animals

Can cyanobacterial toxins kill me?

Although many people have become ill from exposure to freshwater cyanobacterial toxins, death from algal-contaminated drinking water is unlikely to occur given that water resources are usually effectively managed to control taste, odour and other algae-related problems. It's possible that extended exposure to low levels of cyanobacterial hepatotoxins could have long-term or chronic effects in humans.

How will I know if I've accidentally come into contact with cyanobacterial toxins?

If you ingest water, fish or blue-green algal products containing elevated levels of toxins, you may experience headaches, fever, diarrhoea, abdominal pain, nausea and vomiting. If you swim in contaminated water, you may get itchy and irritated eyes and skin, as well as other hay fever-like allergic reactions. If you suspect you might have come into contact with cyanobacterial toxins and are experiencing any of these symptoms, rinse any scum off your body and consult your physician immediately.

Are children more vulnerable than adults?

Yes. Children are at greater risk than adults of developing serious liver damage should they ingest high levels of microcystins, because of their comparatively lower body weight.

Should I let my pets or my livestock drink water containing cyanobacterial blooms?

No. The animals could become extremely ill and even die. The first recorded episode of animal poisoning attributable to cyanobacteria occurred in Australia in 1878. Since then, there have been many widespread incidents of poisoning, affecting a variety of both wild and domestic animals. Animals are not more sensitive than people to the effects of the toxins; they are simply not as concerned with the way water looks or smells before they drink it.

Death is usually caused by damage to the liver or to the nervous system, depending on which toxins were predominant in the water. Treatments to counteract the effects of cyanobacterial toxins in animals have not been extensively investigated to date.