BLUE-GREEN ALGAE (CYANOBACTERIA) and their toxins
This It's Your Health document covers a wide
range of topics related to cyanobacteria, their toxins, and your health:
What are cyanobacteria?
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.
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
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
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.
DRINKING WATER and WATER USED FOR DIALYSIS TREATMENT
How likely am I to drink water contaminated with cyanobacteria and/or its
Not very likely. Relatively few incidents of human poisoning have been
reported. People don't usually drink water contaminated with cyanobacteria because
of the scum and the accompanying smell (fresh blooms smell like newly mown grass;
older blooms smell like rotting garbage). However, people could unknowingly
drink water containing cyanobacterial toxins released from blooms that have
If your water comes from a source that is prone to blue-green algal contamination
(dugouts, for example), you should monitor the water for bloom formation.
If you detect a bloom in your water supply, contact your local health authorities
Can I cook using water with blue-green algae in it?
No! Boiling water does not remove toxins from the water. As it is impossible
to detect the presence of toxins in the water by taste, odour or appearance,
you must assume that they are present until testing is completed.
What about using contaminated water for washing?
If there is a safe source of water available, don't use contaminated water
for washing clothes or dishes. If no alternative supply is available, use rubber
gloves to avoid direct contact with the water. Bathing or showering in contaminated
water should be avoided, as skin contact with the algae can lead to skin irritation
Are cyanobacteria a year-round problem in water supplies?
No. Canadian water supplies are unlikely to contain cyanobacteria during
the winter, although some hepatotoxins may linger.
How do water treatment plants deal with cyanobacteria?
Most municipal water treatment plants do not regularly look for cyanobacterial
toxins in the water supply. However, because cyanobacteria have strong smells
and tastes and interfere with certain water treatment processes, most municipalities
with a history of blooms monitor their surface water supplies for cyanobacteria.
Once cyanobacteria are detected in the water supply, treatment plants can
remove them in a number of ways. Conventional water treatment facilities can
remove the cells by adding chemicals that bind them together. As the cells
clump together, they become heavier and fall to the bottom of the reservoir
or tank, where they can be easily filtered out.
While this method will remove cells, it will not remove potentially harmful
cyanobacterial toxins. These can be removed using certain oxidation procedures
or activated charcoal. Further research in this area is required.
Generally speaking, chemicals (such as copper sulphate) or any other treatment
method that causes the cells to break down and release their toxins should
not be used.
The best way to avoid the problems associated with cyanobacterial blooms
is to prevent blooms from forming. This can be done by reducing the input
of nutrients, such as phosphates, into the water source or by mixing the water
in a reservoir.
Can I treat my water at home to remove blue-green algae and their toxins?
Although results vary, treatment options are available for the homeowner.
However, devices for household treatment can be very expensive. As well, it
is difficult to assess the performance and ensure the quality of these household
devices. More research in this area is needed and is under way.
What is Health Canada doing to make sure our drinking water is safe?
Health Canada works with the provinces and territories to establish drinking
water quality guidelines. The guidelines often take the form of maximum acceptable
concentrations for substances found in drinking water supplies. A consultation
document on microcystins prepared by the Secretariat of the Federal-Provincial-Territorial
Subcommittee on Drinking Water recommends a maximum acceptable concentration
of 0.0015 mg/L for total microcystins in drinking water, based on the toxicity
of microcystin-LR. This proposed guideline is believed to be conservative, as
it is based on a lifetime of daily exposure via the oral route, even though
toxins will probably not be present in Canadian water supplies more than four
or five months each year because of climatic conditions.
The Subcommittee has decided that it will not adopt this guideline until
a practical analytical method for microcystins is available to all jurisdictions.
Health Canada is currently developing such a method, and it should soon be
available. Once the guideline is approved, some municipal water treatment
plants may be required to monitor for the presence of microcystin-LR in their
water supplies, especially if the source is prone to cyanobacterial blooms.
Monitoring strategies will vary between provinces.
To obtain a copy of the consultation document on microcystin-LR or to learn
more about Health Canada's drinking water program, please refer to either our
English web site at http://www.hc-sc.gc.ca/waterquality
or our French web site at http://www.hc-sc.gc.ca/eauqualite.
I am undergoing renal dialysis treatment. Am I more at risk than others?
While the proposed level of microcystins allowed for drinking purposes
will not adversely affect the health of most people, patients undergoing renal
dialysis treatment may be more susceptible to the associated health risks. Because
dialysis patients receive dialysis two or three times per week (exposure to
more than 300L of water per week), there is potential for dialysis patients
to be exposed to elevated levels of these toxins.
Conventional surface water treatment processes are usually effective in
removing the algal cells, but are not very effective at removing or destroying
dissolved toxins, particularly from supplies that contain high levels of organic
material. Specialized surface water treatment processes can reduce the toxin
levels to below the drinking water guideline, but these levels (0.1-0.5 µg/L)
are still of concern for dialysis patients.
As a dialysis patient, what can I do to reduce my risk of exposure?
If you think your water supply comes from surface water, you or your dialysis
treatment provider, should ask your local treatment plant if this source water
is prone to blue-green algae blooms. If, after contacting your source water
supplier, you discover there may be microcystins in your water, sampling should
be done to determine whether the toxins are in the dialysate (hospitals and
treatment centres may already have additional treatment capacity in place to
eliminate all toxins of this nature). Additional treatment of the water may
be necessary. These treatments can range from granular activated carbon filtration
followed by reverse osmosis to much more complex membrane filtration systems
(e.g., ultrafiltration). The extent of additional treatment will depend entirely
on the quality of the municipal water supply.
Can water containing cyanobacterial blooms be used for recreational activities?
Unlike controls available with a drinking water source contaminated with
cyanobacteria, there are very few options available once these algae accumulate
in water used for recreational activities, such as swimming, boating, wind surfing
and fishing. Blooms in recreational bodies of water are usually associated with
unpleasant odours and offensive appearance on shorelines as the scum accumulates
and decays. Although cyanobacterial toxins are probably not absorbed through
the skin, they can cause skin irritation. The toxins, if present, can be absorbed
from the water via ingestion or can become airborne and be absorbed via inhalation.
Individuals should avoid swimming and other water-related activities in areas
with dense blooms.
What should I do if I suspect water has been contaminated by toxic cyanobacteria?
Because all cyanobacterial blooms are potentially toxic, it's always best
to stay away from contaminated water until it has been tested and declared safe.
Even after the bloom is gone, it's a good idea to wait until health authorities
declare the water safe before swimming in it. For example, in one study in which
a bloom was treated with algicide, the toxins released by the dead cells took
more than three weeks to disappear.
What is Health Canada doing to ensure the quality of recreational water?
The drinking water guideline for microcystins will not apply to recreational
water. To ensure public safety, Health Canada is developing a separate guideline
for microcystin-LR in recreational water.
Can I eat fish from contaminated water?
Microcystins can accumulate in the tissues of fish, particularly in the viscera
(liver, kidney, etc.), and in shellfish. Levels in the tissues depend upon
the severity of the bloom in the area where the fish or shellfish are caught
or collected. In general, caution should be taken when considering the consumption
of fish caught in areas of a water body where major blue-green algal blooms
occur; in particular, the viscera of the fish should not be eaten.
BLUE-GREEN ALGAL PRODUCTS
Where do the blue-green algae used in food supplements come from?
Historically, large-scale harvesting of blue-green algae masses was done
for research purposes, to study their properties, their possible use as therapeutic
and antibiotic agents, and their potential as agricultural commodities. Today,
the algae used to manufacture blue-green algal products are harvested from controlled
ponds or natural lakes. Before or during harvest, some types of algae will naturally
produce chemicals such as microcystins, and these toxins could be retained in
the blue-green algal products.
What is Health Canada doing about this situation?
A broad sampling and testing of blue-green algal products was recently
performed by Health Canada to measure the levels of microcystins in blue-green
algal products available on the Canadian market and to determine the level of
risk to Canadian consumers. Results of the testing, conducted at three separate
laboratories, indicate that no microcystins were detected in blue-green algal
products containing only the blue-green algae Spirulina. However, for
many non-Spirulina blue-green algal products, particularly those harvested
from natural lakes, when consumed according to manufacturers' directions, the
resulting daily intake of microcystins was above that considered acceptable
by Health Canada and the World Health Organization.
Health Canada's Food Directorate has communicated the test results and their
health significance to the Canadian Food Inspection Agency (CFIA), and has
indicated that products on the Canadian market, when consumed according to
the manufacturers' directions, should not exceed the daily intake of microcystins
considered acceptable by the World Health Organization and Health Canada.
Subsequent compliance measures are the responsibility of the CFIA.
Should I stop taking my blue-green algal supplements?
Blue-green algal products are sold in some pharmacies and health food stores
as food supplements, often in tablet or caplet form. Health Canada is advising
consumers to apply caution in their use of the products until evidence of their
safety can be firmly established. In particular, adult consumers who choose
to use products containing non-Spirulina blue-green algae should do so
for short periods of time only. However, consumers can safely use products made
only from Spirulina blue-green algae as these were found to be free of
What about my child, who takes these tablets as a treatment for Attention
Health Canada has not received adequate scientific evidence that supports
the claim for use of blue-green algae as an effective treatment for Attention
Deficit Disorder in children and has not authorized the marketing of any blue-green
algal products for any therapeutic purpose. Most of the blue-green algal products
in Canada are sold as foods, and Health Canada does not allow therapeutic claims
for substances sold as foods. Meanwhile, because of their lower body weights,
there is a potential risk of children being exposed to harmful levels of toxins
if they ingest blue-green algal products, particularly if they ingest the products
for an extended period of time.
As a precaution, Health Canada is recommending that the use of non-Spirulina
blue-green algae by children be discontinued until follow-up measures have
Where can I get more information?
For more information on Health Canada's drinking water guideline related
to blue-green (cyanobacterial) toxins see http://www.hc-sc.gc.ca/waterquality'
or send an e-mail to email@example.com'
. Information related to blue-green algal products can be found at: http://www.hc-sc.gc.ca/food-aliment/'.
It's Your Health (formerly Issues) is one of a series of information sheets produced
by the Healthy Environments and Consumer Safety Branch of Health Canada for the
public, media and special interest groups. No changes permitted. Reprint permission
not required. Aussi disponible en français.
September 14, 2001