Information About Blue-green Algae: Background, potential impacts to human health and safety of drinking water (part 2)

Note: This information is taken from the Ministry of the Environment factsheet "Information about blue-green algae: Background, potential impacts to human health and safety of drinking water," produced in 2005. To view the factsheet as a pdf file, click here.

What are the potential health effects associated with blue-green algae toxins?

The severity of symptoms and level of risk to health is dependant on the mode of exposure to the cyanobacteria toxins. Human health effects from contact with these toxins may include:

itchy, irritated eyes and skin that may result from direct external contact through recreational activities, such as swimming and water skiing; and
if the toxins are swallowed, symptoms such as headaches, fever, diarrhea, abdominal pain, nausea and vomiting.

Higher levels of risk to human health are linked to ingestion of large quantities of cyanobacteria toxins in water. Drinking contaminated water is the most common route of toxin consumption.

Can drinking water be contaminated with toxins from blue-green algae?

If drinking water is obtained from a surface water source during a blue-green algae bloom then it is possible that the water may become contaminated with toxins released during decomposition of the algae cells. Usually people won’t drink water contaminated with blue-green algae blooms because of its unsightly pea soup appearance and foul smell. However, sometimes it is hard to tell if the drinking water has been contaminated unless confirmed by laboratory tests specifically for measuring microcystin levels.

How much microcystin is allowable in drinking water under the Ontario Drinking Water Quality Standards

Although appreciable levels are extremely rare in treated water, due to the potential health risk microcystin-LR has been identified as a toxin parameter of interest in drinking water. The Ontario Drinking Water
Quality Standard for the cyanobacteria toxin microcystin-LR is a maximum acceptable concentration (MAC) of 0.0015 mg/L (O.Reg 169/03, schedule 2).

Can water containing cyanobacteria be treated to make it safe to drink?

Treatment of drinking water containing algae may be effective when the cyanobacteria have been removed through specialized filtration systems. These systems remove whole cyanobacteria cells early in the treatment process thereby reducing the potential for toxin release. Some treatment processes have also been found effective for removing toxins; these include particular oxidation processes, activated carbon, and membrane filtration. For the most part, large drinking water treatment systems are more likely to have the specialized treatment facilities that are capable of dealing with the effects of cyanobacteria blooms.

What about smaller treatment systems and private supplies?

Small drinking water systems with modest treatment facilities and private supplies with either no treatment or minimal water treatment systems are less likely to have the specialized equipment to effectively filter and
treat water during cyanobacteria blooms. The treatment methods most commonly used by these sectors are for the most part ineffective against cyanobacterial contamination because they can potentially rupture the algae cell wall and release the toxins to the water. For example:

Countertop jug filtration systems do not provide reliable treatment because they do not properly filter the water of algae and toxins;
Boiling the water may break the cell wall releasing more toxins into the water; moreover boiling does not remove or neutralize any microcystin present in the water; and
Some disinfection techniques, such as using chlorine (bleach), are ineffective as the treatment may chemically corrode the cell wall thereby releasing more toxins into the water.

For more information:

For information on the health related risks and what to do to safeguard human health during a blue-green algae bloom, contact your local Health Unit. For information about your health unit, call the Ministry of Health INFOline at 1-800-268-1154.

Take a cautious approach. If you suspect a blue-green algae bloom, assume toxins are present and call the Ministry of the Environment Spills Action Centre at 1-800-268-6060. Reduce the likelihood of health risks by
avoiding activities that increase exposure to these toxins during algae blooms; call the local Health Unit for information and follow their advice. If you are unsure about the safety of water for drinking during an algae bloom, then use alternative water sources such as bottled, carted or tanked water. You can also call a water treatment service provider for help.

For more information on blue-green algae contact the Ministry of the Environment’s Public Information Centre at 1-800-565-4923.

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