United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-92/079 September 1992
EPA Project Summary
A Status Report: on Planktonic
Cyanobacteria (Blue-Green
Algae) and their Toxins
W.W. Carmichael
While several groups of algae can
cause dense waterblooms, blue-green
algae are the most common offenders.
Blue-green algae — also called
cyanobacteria — are minute, single-
celled microorganisms that lack a dis-
tinct, membrane-bound nucleus but, be-
cause they contain chlorophyll, can
photosynthesize.
Surface blooms or scums of
cyanobacteria commonly occur during
the warm, windless days of late sum-
mer and fall when water can stagnate
and when there are sufficient concen-
trations of such nutrients as nitrogen
and phosphorus. Nutrient levels that
contribute to water-bloom formation
can result from runoff of fertilizers or
livestock or human wastes.
While cyanobacterial blooms can af-
fect the water's taste, odor, and ap-
pearance, they also pose a more seri-
ous problem. Most, if not all, of the
common bloom-forming cyanobacteria
can produce potent biotoxins. These
toxins, formed at all stages of the or-
ganisms' growth, generally remain in-
side the cell until age or stress causes
their release into the surrounding wa-
ter. The main toxic genera include fila-
mentous Anabaena, Aphanizomenon,
Nodularia, Nostoc, Oscillatoria, and uni-
cellular Microcystis. More than one
species within these genera can be
toxic, and all toxic species can form
waterblooms.
Toxic waterblooms can take place in
many eutrophic (nutrient rich) to
hypereutrophic lakes and ponds at tem-
perate latitudes worldwide. They are
responsible for sporadic but recurrent
episodes of illness and death among
wild and domestic animals. Algal tox-
ins have also been implicated in hu-
man poisonings from certain municipal
and recreational -water supplies. This
implication is important for public
health officials and water management
personnel who need to be aware of the
significance of the threat to health from
these water-based toxins. The full re-
port provides a comprehensive assess-
ment of toxins from cyanobacteria and
a directory to the literature published
on this subject.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Toxic waterblooms of cyanobacteria can
be found in many eutrophic to
hypereutrophic lakes, ponds and rivers
throughout the world (Table 1). The pri-
mary toxicoses that result from ingesting
toxic cyanobacteria or their toxins include
acute liver toxicosis, rapid neurotoxicosis,
and gastrointestinal disturbances. Most
cases, known from wild and domestic ani-
mal poisonings, involve the first two types.
They result from ingesting lethal or suble-
thal numbers of toxic cells from a toxic
waterbloom.
Most cyanobacterial poisonings result
in hepatotoxicosis. The algal hepatotoxins
are a related family of low-molecular-weight
cyclic hepta- and pentapeptides called
Printed on Recycled Paper
-------
T«W» 1. Know Occurrences of Toxic Cyanobacteria in Frssh or Marine Water
Argentina
Austrialia
Chite
Bangladesh
Bermuda
Brail
Canada
Alberta
British Columbia
Manitoba
Ontario
Saskatchewan
Europe
Czechoslovakia
Denmark
Finland
France
Germany
Greece
Hungary
Italy
Netherlands
Norway
Poland
Portugal
Russia
Sweden
Ukraine
United Kingdom
India
Israel
Japan
New Zealand
Okinawa (marine only)
Peoples Republic of China
South Africa
Thailand
U.S.A.
California
Colorado
Florida
Hawaii (marine only)
Idaho
Illinois
Indiana
Iowa
—-^—Michigan
Minnesota
Mississippi
Montana
Nebraska
Nevada
New Hampshire
New Mexico
New York
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
South Dakota
Texas
Washington
Wisconsin
Wyoming
microcystins and nodularins (Table 2). Of
the peptide-toxin producing genera,
Mkrocystls is the main offender world-
wide. Animals affected by these
hepatotoxins may display weakness,
anorexia, and pallor of the extremities and
mucous membranes. Since all animals in
a herd or flock usually drink from the same
water supply, most members will be af-
fected within the same time. Death oc-
curs after liver cell architecture loss, which
leads to destruction of the parenchyma)
cells and sinusoids of the liver. This
causes lethal intrahepatic hemorrhage
within minutes to hours or hepatic insuffi-
ciency within several hours to a few days.
Cyanobacterial neurotoxicosis results
from ingestion of toxic Anabaena,
Aphanizomanon or Oscillatoria. While
these genera can produce peptide
hepatotoxins as well as neurotoxins, the
neurotoxins act more rapidly and domi-
nate the field and clinical syndrome. The
neurotoxins comprise two groups: ana-
toxins and saxttoxins (Table 2). There are
two known anatoxins: anatoxin-a and ana-
toxin-a(s). Anatoxin-a is a bicyclic sec-
ondary amine that blocks the postsynaptic
transmission of nerve impulses by depo-
larizing (stimulating) the neurons that re-
ceive the signal. The mechanism is simi-
lar to what the natural chemical transmit-
ter, acetylcholine, does in stimulating
muscle contraction. However, unlike ace-
tylcholine, anatoxin-a is not physiologically
regulated and causes continuous depolar-
ization that leads to muscle fatigue and
paralysis. Anatoxin-a(s), is an organo-
phosphate (OP) cholinesterase inhibitor
that acts like an OP pesticide overdose.
Here, the toxin inhibits the natural en-
zyme, acetylcholinesterase, from recycling
the transmitter, acetylcholine. Both toxins
produce symptoms that include muscle
twitching and contraction, reduced move-
ment, gasping respiration, cyanosis (blu-
ish color from poorly oxygenated blood),
convulsions, and death. Neuromuscular
blockage of the muscles used in breath-
ing is the most likely cause of death.
Although both toxins are respiratory neu-
rotoxins, anatoxin-a produces a rigid neck
contracture in birds as a result of its depo-
larizing activity, while anatoxin-a(s) causes
intense salivation and mucous nasal dis-
charge as a result of its anticholinest-
erase activity. Investigators can use these
two very different signs of poisoning in
avian species to differentiate the two tox-
ins, either in field poisonings or in labora-
tory assays.
Aphanizomenon has been shown in
some cases to produce the potent sodium
channel neuromuscular blocking agents,
saxitoxin and neosaxitoxin. These two
neurotoxins are better known from being
produced by marine dinoflagellate algae
responsible for the red tide poisoning phe-
•• nomenon, paralytic shellfish poisoning
(PSP).
Potential for Human Poisoning
All cyanotoxins could cause death or
illnesses in humans as well as in wild and
domestic animals. Yet many officials re-
main unconvinced of the need to monitor
or regulate these toxins in municipal or
recreational water supplies. The skepti-
cism seems to arise from the fact that,
despite the presence of cyanobacteria in
many bodies of water there are no con-
firmed cases of human death or illness
from their toxins.
Several factors, which probably act in
combination, may explain the lack of re-
ported human toxicity:
• Mollusks that concentrate toxins the
way shellfish concentrate marine PSP
toxins are uncommon in freshwater.
Where they do exist, as in Europe,
people tend not to eat freshwater
shellfish, except locally.
• Cyanotoxins induce lethal toxicity at
a very low concentration, but they
have_a_jsteep .dose-response curye.
In other words, animals must swallow
a lethal or nearly lethal dose before
signs of poisoning are observable.
Such high concentrations of toxin oc-
cur only when waterblooms accumu-
late on the water's surface, especially
on the downwind shore. While this is
certainly the most dangerous for wa-
tering animals, humans often find the
waterblooms' sight and smell repul-
sive.
• Most water supplies in North America
and Europe don't support high con-
centrations of toxic cyanobacteria year
round, largely because of better wa-
ter quality management and colder
winters. While toxic waterblooms do
occur in some drinking water sup-
plies, filtration and dilution reduce lev-
-------
Table 2. Comparison of Toxicities of Some Biological Toxins
Toxin
Botulinum Toxin
Tetanus Toxin
Ricin
Diphtheria Toxin
Kokoi Toxin
Tetrodotoxin
Saxitoxin
Cobra Toxin
Anatoxin-a(s)
Nodularin
Microcystin
Source
Clostridium botulinum
Clostridium tetani
Ricinus communis
Corynebacterium diphtheriae
Phyllobates bicolor
Arothron meleagris
Aphanizomenon flos-aquae
Naja na]a
Anabaena flos-aquae
Nodularia spumigena
Microcystis, Anabaena,
Common Name
(Bacterium)
(Bacterium)
(Castor Bean Plant)
(Bacterium)
(Poison Arrow Frog)
(Puffer fish)
(Cyariobacteria)
•*-- - fDirtrtflanallatAV
* ^u/u t\ft ici^Qiiciioy
(Cobra Snake)
(Cyariobacteria)
(Cyariobacteria)
(Cyariobacteria)
Lethal Dose*
0-Dso)
0.00003
0.0001
0.02
0.3
2.7
8
9
20
20
50
50-500
Anatoxin-a
Amatoxin
Curare
Strychnine
Muscarin
Phallotoxin
Oscillatoria, Nostoc
Anabaena flos-aquae
Amanita sp.
Chrondodendron tomentosum
Strychnos nox-vomica
Amanita muscaria
Amanita sp.
(Cyariobacteria)
(Fungus)
(Brazilian Poison
Arrow Plant)
(Plant)
(Fungus)
(Fungus)
200
200-500
500
500
1100
1500-2000
Sodium Cyanide
10000
*The acute LD in u.g per kg bodyweight: intra-peritoneal injection; some with mice, some with rats.
els in the finished water below those
that cause acute toxicosis. Further,
without sensitive detection methods
it's difficult to determine how much is
in the finished drinking water, and
without a clear understanding of the
toxins' mechanisms of action it's diffi-
cult to determine whether they are
causing subacute or chronic toxicosis
in humans.
Effects of Low-Level Exposure
The most likely threat to human health
from cyanobacterial toxins is subacute and
chronic toxicity. We know from research
over the past 20 years what the most
likely mode of death will be from a lethal
dose. What we don't know is the mecha-
nism of action for a nonlethal dose,
whether from a single exposure or from
chronic exposure to a drinking water sup-
ply containing a persistent toxic
waterbloom. There is indirect evidence
that low-level concentrations of peptide
hepatotoxins in drinking water affect the
liver and intestine. Recent research shows
that the peptide toxins are potent inhibi-
tors of protein phosphatases type 1 and
2A. This means that they are tumor pro-
moters similar in action to okadaic acid,
the causative agent of diarrhetic shellfish
'U.S. Government Printing Office: 1992— 648-080/60109
-------
poisoning. Research currently underway C.
at the National Cancer Research Institute
In Tokyo shows these peptide toxins can
produce liver tumors in laboratory rodents. rj
Thus, the continuous low-dose exposure
that would occur during a summertime
waterbloom could possibly promote liver
tumor formation in humans.
Recommendations for E.
Research and Development
A. Continue efforts to develop predic-
tive models to quantify the forma-
tion of cyanobacterial blooms. F.
These models should be developed
with thought toward their use for
devising management plans for vari-
ous water bodies.
B. Further research to develop mea-
sures to control eutrophication and
minimize development of cyanc—
bacteria waterblooms and scums.
Support development of sensitive,
rapid and accurate methods for the
detection of cyanotoxins.
Support efforts to adopt standard
procedures for characterization of
the cyanotoxins that would in turn
support efforts to make toxin stan-
dards available for research.
Support research leading to an un-
derstanding of the transport, fate,
and ecological role of cyanotoxins
in aquatic environments.
Support studies of the physiologi-
cal and genetic mechanisms in-
volved in toxin production.
Cyanobacteria can be genetically
manipulated and studied with many
of the, same, techniques^-ayailable.
to study molecular and cellular ge-
netics of other prokaryotes.
G. Support studies on the taxonomy
and classification of cyanobacteria.
This information is critical to effec-
tive communication about toxic
cyanobacteria and their toxins.
H. Develop USEPA support to carry
out several aspects of the work on
cyanobacterial toxins. These in-
clude:
1. Educate and advise Federal, State
and local public health workers and
the general public on toxic cyano-
bacteria.
2. Link work on cyanotoxins with ap-
propriate authorities in other parts
of the world so that information can
be exchanged and collaborative re-
se_arcb_project.s. can _be, developed,
and supported.
Wayne W. Carmtchael is with the Wright State University, Dayton, OH 45435.
Roberts. Safferman is the EPA Project Officer (see below).
The complete report, entitled "A Status Report on Planktonic Cyanobacteria (Blue-
Green Algae) and Their Toxins," (Order No. PB92- 206 259/AS; Cost: $25.00;
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty fqr Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-92/079
------- |