_EPA Project Summclry

United States

Environmental Protection

Agency

Research and Development

Environmental Monitoring

Systems Laboratory

Cincinnati, OH 45268

EPAl600/SR-921079 September 1992

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, singlecelled microorganisms that lack a distinct, membrane-bound nucleus but, because they contain chlorophyll, can

photosynthesize.

Surface blooms or scums of

cyanobacteria commonly occur during

the warm, windless days of late summer and fall when water can stagnate

and when there are sufficient concentrations 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 affect the water's taste, odor, and appearance, they also pose a more serious problem. Most, if not all, of the

common bloom-forming cyanobacteria

can produce potent biotoxins. These

toxins, formed at all stages of the organisms' growth, generally remain inside the cell until age or stress causes

their release into the surrounding water. The main toxic genera include fila- .

mentous Anabaena, Aphanizomenon, ,

Nodularia, Nostoc, Oscil/atoria, and unicellular 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 temperate latitudes worldwide. They are

responsible for sporadic but recurrent

episodes of illness and death among

wild and domestic animals. Algal toxins have also been implicated in human 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 fuJI report provides a comprehensive assessment 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 primary 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 animal poisonings, involve the first two types.

They result from ingesting lethal or sublethal 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

@ Printedon RecycledPaper
r.bhl1. Known OccurrrmcBs of Toxic Cyanobacteria in Fresh or Marine Water

U.S.A.

Califomia

Colorado

Florida

Hawaii (marineonly)

Idaho

Illinois

Indiana

Iowa - ,,-~ .._.._..~~. MichiganMinnesota

Mississippi

Montana

Nebraska

Nevada

New Hampshire

New Mexico

New York

North Dakota

Ohio

Oklahoma

Oregon

Pennsylvania

South Dakota

Texas

Washington

Wisconsin

Wyoming

two known anatoxins: anatoxin-aand anatoxin-a(s). Anatoxin-a is a bicyclic secondary amine that blocks the postsynaptic

transmission of nerve impulses by depolarizing (stimulating) the neurons that receive the signal. The mechanism is similar to what the natural chemical transmitter, acetylcholine, does in stimUlating

muscle contraction. However, unlike acetylcholine, anatoxin-a is not physiologically

regulated and causes continuous depolarization that leads to muscle fatigue and

paralysis. Anatoxin-a(s), is an organophosphate (OP) cholinesterase inhibitor

that acts like an OP pesticide overdose.

Here, the toxin inhibits' the natural enzyme, acetylcholinesterase, from recycling

the transmitter, acetylcholine. Both toxins

produce symptoms that include muscle

twitching and contraction, reduced movement, gasping respiration, cyanosis (bluish color from poorly oxygenated blood),

convulsions, and death. Neuromuscular

blockage of the muscles used in breathing is the most likely cause of death.

Argentina

Austrialia

Chilo

Bangladesh

B'lnnuda

Bmil

Canada

Alberta

British Columbia

Manitoba.

Ontario

Saskatchowan

Europg

CzGChoslovakia

Denmark

Finland

France

Germany

GrGQC8

HungalY

Italy

Netherlands

Norway

Poland

Portugal

Russia

SWllden

Ukraine

United Kingdom

mlcrocystlns and nodularins (Table 2). Of

the peptide-toxin producing genera,

Microcystls Is the main offender worldwide. Animals affected by these

hepatotoxlns 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 affected within the same time. Death occurs after liver cell architecture loss, which

leads to destruction of the parenchymal

cells and slnusolds of the liver. This

causes lethal intrahepatic hemorrhage

within minutes to hours or hepatic insufficiency within several hours to a few days.

Cyanobacterial neurotoxicosis results

from Ingestion of toxic Anabaena,

Aphanlzomenon or Oscillatoria. While

these genera can produce peptide

hepatotoxlns as well as neurotoxins, the

neurotoxins act more rapidly and dominate the field and clinical syndrome. The

neurotoxins comprise two groups: anatoxins and saxitoxlns (Table 2). There are

India

Israel

Japan

New Zealand

Okinawa (marineonly)

PeoplesRepublic of China

South Africa

Thailand

Althoughboth toxins are respiratory neurotoxins, anatoxin-a produces a rigid neck

contracture in birds as a result of its depolarizing activity, while anatoxin-a(s) causes

intense salivation and mucous nasal discharge as a result of its anticholinesterase activity. Investigatorscan use these

two very different signs of poisoning in

avian species to differentiate the two toxins, either in field poisonings or in laboratory 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 remain unconvinced of the need to monitor

or regulate these toxins in municipal or

recreational water supplies. The skepticism seems to arise from the fact that,

despite the presence of cyanobacteria in

many bodies of water there are no confirmed cases of human death or illness

from their toxins.

Several factors, which probably act in

combination, may explain the lack of reported 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

_bave._a_.sil3el'c1Q§e__re§pol1se Cwye.,__ .,...

In other words, animals must swallow

a lethal or nearly lethal dose before

signs of poisoning are observable.

Such high concentrations of toxin occur only when waterblooms accumulate on the water's surface, especially

on the downwind shore. While this is

certainly the most dangerous for watering animals, humans often find the

waterblooms' sight and smell repulsive.

• Most water supplies in North America

and Europe don't support high concentrationsof toxic cyanobacteria year

round, largely because of better water quality management and colder

winters. While toxic waterblooms do

occur in some drinking water supplies, filtration and dilution reduce lev2
Table 2. Comparison of Toxicities of Some Biological Toxins

Saxitoxin Aphanizomenon flos-aquae .,.". ,." ." , .... " .• ,"~ ., "i''''.~'; .•,~,,=,.& Alexandrium sp.

Toxin

Botulinum Toxin

Tetanus Toxin

Ricin

Diphtheria Toxin

Kokoi Toxin

Tetrodotoxin

Cobra Toxin

Anatoxin-a(s)

Nodularin

Microcystin

Anatoxin-a

Amatoxin

Curare

Strychnine

Muscarin

Phallotoxin

Sodium Cyanide

Source

Clostridium botulinum

Clostridium tetani

Ricinus communis

Corynebacterium diphtheriee

Phy/lobates bicolor

Arothron me/sagris

Naja naja

Anabaena flos-aquae

Nodularia spumigena

Microcystis, Anabaena,

Oscil/atoria, Nostoc

Anabaena flos-aquae

Amanita sp.

Chrondodendron tomentosum

Strychnos nox-vomlce

Amanita muscaria

Amanita sp.

Common Name

(Bactlarium)

(Bacterium)

(Castor Bean Plant)

(Bac~terium)

(Poison Arrow Frog)

(PuffElr fish)

(Cyanobacteria)

(Dinclflagellate)

(Cobra Snake)

(Cyanobacteria)

(Cyanobacteria)

(Cyanobacteria)

(Cyanobacteria)

(Fungus)

(Brazilian Poison

Arrow Plant)

(Plant)

(Fungus)

(Fungus)

Lethal Dose'

(LDso)

0.00003

0.0001

0.02

0.3

2.7

8

9

20

20

50

50-500

200

200-500

500

500

1100

1500-2000

10000

*The acute LDso in f.lg 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 difficult 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 mechanism of action for a nonlethal dose,

whether from a single exposure or from

chronic exposure to a drinking water sup3

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 researchshows

that the peptide toxins are potent inhibitors of protein phosphatases type 1 and

2A. This means that they are tumor promoters 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

at the National Cancer Research Institute

In Tokyo shows these peptide toxins can

produce liver tumors In laboratory rodents.

Thus, the continuous low-dose exposure

that would occur during a summertime

waterbloom could possibly promote liver

tumor formation in humans.

Recommendations for

Research and Development

A. Continue efforts to develop predictive models to quantify the formation of cyanobacterial blooms.

Thesa models should be developed

with thought toward their use for

devisingmanagementplansfor various water bodies.

B. Further research to develop measures to control eutrophication and

minimize development of cyanobacteria waterblooms and scums.

C. Support development of sensitive, G. Support studies on the taxonomy

rapid and accurate methods for the and classification of cyanobacteria.

detection of cyanotoxins. This information is critical to effecD. Support efforts to adopt standard tive communication about toxic

procedures for characterization of cyanobacteria and their toxins.

the cyanotoxins that would in turn H. Develop USEPA support to carry

support efforts to make toxin stan- out several aspects of the work on

dards available for research. cyanobacterial toxins. These inE. Support research leading to an un- elude:

derstanding of the transport, fate, 1. Educate and advise Federal, State

and ecological role of cyanotoxins and local public health workers and

in aquatic environments. the general public on toxic cyanoF. Support studies of the physiologi- bacteria.

cal and genetic mechanisms in- 2. Link work on cyanotoxins with apvolved in toxin production. propriate authorities in other parts

Cyanobacteria can be genetically of the world so that informationcan

manipulated and studied with many be exchanged and collaborative re-

.ot the-same techniques..availabJe_.__~-,__ ,__ s_E;l_aLcb_Rr.Qj~cJl;L c_~m_b~.cl§)feJoREl,q __ ._.

to study molecular and cellular ge- and supported.

netics of other prokaryotes.

Wayne Carmichael is with the Wright State University, Dayton, OH 45435.

RobertS. Safferman is the EPA Project Officer (see below).

The complete report, entitled'~ Status Report on Planktonic Cyanobacteria (BlueGreen Algae) and Their Toxins," (Order No. PB92- 206 259/AS; Cost: $25.00;

subject to change) will be available only from:

National Technical Information SeNice

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

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