A PEAC user called AristaTek, Inc.,
and asked why the chemical “ricin” was not listed under
the PEAC classification of biological warfare agents.
Ricin is a very toxic chemical derived from the castor
bean and has the potential to be “weaponized”, that is,
a toxic aerosol of the chemical can be prepared which
can be inhaled. The PEAC tool listed “ricin” under the
broad classification of chemical warfare agents and not
biological warfare agents because it is basically a
chemical and not an agent which causes disease. However
the PEAC user pointed out that the U.S. Military lists
biotoxins under the broad classification of bioterrorist
agents along with smallpox, pneumonic plague, and
anthrax. Chemicals such as VX, Sarin, and mustard gas
are classified under chemical warfare agents. We have a
problem with definition.
A “biotoxin” is a poison produced
by living organisms. The living organisms might be
plants, an animal, fungi, microbes, algae, etc.. Over
400 biotoxins have been identified and many more exist
in nature. The list includes ricin produced from the
castor bean plant, snake venom, various toxins produced
by bacteria, tetrodotoxin isolated from the livers of
globe fish, aflatoxin produced by certain molds,
cicutoxin from water hemlock, histrionicotoxin from the
skin of the poison arrow frog, etc., ; the list is long.
However the list is shortened to perhaps 15 or 20
biotoxins if we limit ourselves to those poisons which
can be potentially used as a weapon of mass destruction.
Only a few biotoxins produced in nature can be mass
produced and dispersed in the form of an aerosol which
can be inhaled or sprayed onto surfaces and absorbed
through the skin. Poisoning of food and water supplies
is possible, but the poison would have to be mass
produced and added to the food source or water supply.
Many biotoxins (but not all) are destroyed by cooking or
by normal water chlorination.
Biotoxins which enter the human body
do not replicate. Disease-causing microorganisms do
replicate themselves. The PEAC tool listings for
biological warfare agents are limited to diseases that
might be spread by a terrorist or used in warfare. Many
disease-causing microorganisms produce biotoxins in the
human body. If the disease-causing microorganisms can be
grown in the laboratory or mass-produced and a poisonous
but non-infectious material isolated, we have listed
this material under the classification of a biotoxin.
The disease or microorganism causing the disease is
classified under biological warfare agents. For example,
botulism is listed in the PEAC tool under “biological
warfare agents”. Botulism is a disease caused by a
microorganism (a spore-forming bacterium called
Clostridium botulinum). The microorganism
produces the very toxic botulinum toxin. The bacteria
can be grown in fermentors and the toxin harvested.
Therefore the PEAC tool also has a listing under
chemical warfare agents as “botulinum toxin”. The next
PEAC tool release will have botulinum toxin listed under
the classification of “biotoxin”.
How Toxic Are Biotoxins?
Table 1, below, lists LD50
values for laboratory mice inhaling selected biotoxins.
The LD50 value is the dose in units of
micrograms per kilogram of body weight that results in
50% kill of the test animal. The information was
obtained from David R. Franz, 1997 (revised), “Defense
Against Toxin Weapons”, U.S. Army Medical Research
Institute, Fort Detrick, MD.
Table 1. Comparative Lethality of
Selected Toxins in Laboratory
Rosay Pea Plant
0.04 by inhalation
20 by ingestion
Arrow poison frog
Castor bean (plant)
2.0 by inhalation
10 by ingestion
Incapacitation as well as lethality
must be considered. Some toxins such as the T-2 toxin
cause illness at doses many times less than the
concentration required to kill.
By comparison, the LD50
value (mice) for the chemical warfare agent Sarin is 100
mg/kg. For the
chemical warfare agent VX, LD50 is 15 mg/kg. For Soman,
LD50 is 64 mg/kg. On a per unit
weight basis, some biotoxins are more potent than any of
the synthetic chemical warfare agents.
How do Biotoxins Act on the Human
Toxins can be classified by the
mechanism of toxicity. The two broad classifications are
cytotoxins and neurotoxins.
Cytotoxins cause cellular destruction
Neurotoxins affect the central nervous
system. Neurotoxins may be further classified into (1)
presynaptic and postsynaptic neurotoxins, (2)
ion-channel and sodium-ion binding toxin, and (3)
Neurotoxins block nerve conduction
and cause death by paralyzing muscles of respiration.
Ricin is an example of a cytotoxin.
T-2 Toxin is a hermorrhagic cytotoxin which causes
bleeding. Botulinum toxin and saxitoxin are examples of
presynaptic and postsynaptic neurotoxins. Tetrodotoxin
is an example of an ion-channel neurotoxin. Ciguatoxin
(from fish contaminated with a dinoflagellate) is a
sodium-ion binding toxin.
How might a Terrorist Deliver a
The most likely method an aggressor
might target military troops and civilian populations is
as a respirable aerosol, which allow the toxin to
contact the inner surface of the lung. There are major
technological problems that the aggressor must overcome.
None of the biotoxins form gases or liquids that
vaporize. All of them are solids (or powders) which must
be delivered as an aerosol. To be most effective, the
aerosol particle should be between 0.5 and 5 microns
diameter to be captured by the lung surface. Particles
larger than about 20 microns fall harmlessly to the
ground. Particles between 5 and 20 microns may lodge in
the nasal passages and trachea and therefore are not as
effective as when lodged in the lungs. A substantial
portion of particles less than 0.5 microns in diameter
will be exhaled and not retained in the lungs.
Consider ricin which has a
LD50 toxicity of 3 mg/kg. Assuming the
data obtained from mice also apply to man, a 70 kg man
receiving a 3(70)/1000 = 0.21 milligram dose would have
a 50% chance of surviving. The amount of ricin required
to achieve this dose over a one kilometer square area is
estimated to be about 80 kilograms. This assumes that
the ricin is emitted as a respirable aerosol near the
ground. Even though ricin is very toxic, there are
technological problems in covering a large surface area
with the toxin.
With botulinum toxin, less quantity
is required. Botulinum has a LD50 of 0.001
mg/kg. We are
now talking of 32 grams of botulinum toxin to cover a
one square kilometer area. Again, this is assuming that
the right-sized aerosol diameter is produced, the
aerosol is delivered uniformly over the area, and
meteorological conditions are ideal.
Again, these are idealized,
theoretical calculations. Because of inefficiencies in
the aerosol delivery system, larger quantities would
have to be delivered to achieve an LC50
Some biotoxins result in
incapacitating illnesses at levels much below the
LC50 dose. An example is staphylococcal
enterotoxin B which causes illness at very low dosages
(vomiting and diarrhea). The LD50 by
inhalation is 0.027 mg/kg. Staphylococcal
enterotoxin B is a cytotoxin that causes the body to
release large amounts of its own chemicals and fluids.
Thichothecene mycotoxins in low
dosages cause skin lesions and systemic illness without
being inhaled and absorbed through the respiratory
system. The most likely route of exposure is through the
skin. A dose of one-billionth of a gram per square
centimeter of skin is sufficient to cause irritation of
the skin. A dose of one-millionth of a gram causes
destruction of skin cells (necrosis). Microgram dosages
can cause irreversible injury to the eye. The
LD50 dose for one of the mycotoxins (T-2
Toxin) is 1210 mg/kg.
An assassin could target an
individual by injecting a biotoxin-contaminated pellet.
An example is Bulgarian exile Georgi Markov who was
apparently killed by a ricin-containing pellet injected
in his thigh in London in 1978.
What about Contamination of Food
and Water Supplies?
Fortunately, there are a number of
factors that work against massive contamination of
public food and water supplies. Normal water
chlorination will destroy bacterial toxins, for example,
5 parts per million of chlorine for 30 minutes destroys
botulinum toxin. Water chlorination at these
concentrations is ineffective against ricin, saxitoxin,
T-2 toxin, or microcystin. Cooking food will also
inactivate most biotoxins. Coagulation/floculation at a
water treatment plant will remove the higher molecular
weight compounds/proteins but is ineffective against
ricin, saxitoxin, or other lower molecular weight
compounds. Carbon adsorption or reverse osmosis water
treatment removes biotoxins, even the lower molecular
weight compounds. Ingestion of most biotoxins is less
toxic than inhalation.
Responders and health care
providers ask whether they may tell the difference
between a chemical warfare attack, a biotoxin attack, or
a biological warfare attack using infectious agents.
Radiation detection equipment is essential for detecting
a dirty bomb attack.
The onset of incapacitating symptoms
in a chemical warfare attack is almost immediate (within
minutes). The onset may be a little longer if the
chemical agent is absorbed through the skin. Chemical
nerve agent poisoning is a violent illness resulting in
respiratory failure, airway constriction, and increased
body secretions (saliva and airway secretions), pinpoint
pupils, perhaps also convulsions and muscle spasms.
Symptoms are delayed in the case of a
biotoxin attack or a biological warfare attack. There
may be a delay of several days, even a week, from the
time of exposure to an infectious agent to the time
symptoms first occur. The delay may be on the order of
minutes to two or three days in the case of a biotoxin
attack depending upon the toxin and route of exposure.
As expected, the delay is less if the toxin is inhaled.
It is difficult, in general, to distinguish between a
biotoxin and biological warfare agent attack. Diagnosis
is based on specific symptoms and conformation by
Each toxin must be considered
individually. Some toxins incapacitate so quickly that
there would be little time for therapy after an attack.
Fortunately, the potent bacterial protein toxins (e.g.
botulinum toxin) act slower, and therapy is usually
successful if started within about 12 hours after
exposure providing the toxin is identified.
Biotoxins are solids, usually a
powder, which when weaponized is dissolved or slurried
in a liquid (usually a water or weak alcohol solution)
and then an aerosol created. Tight-fitting face masks
can protect emergency response personnel. Eventually the
aerosol will settle on the ground or on surfaces.
Because toxins are not volatile, they should not pose a
further threat (providing they are not ingested). An
exception is the situation where the biotoxin also
contains an infectious agent such as anthrax spores.
Another exception is some mycotoxins (e.g. T-2 toxin)
which are absorbed through the skin.
If the toxin contaminates skin and
clothing, ordinary soap and water should remove almost
all of the toxin.
Description: Ricin is a
cytotoxin derived from the beans of the castor plant.
Although it is roughly a 1000 times less toxic than the
most potent of the bacterial toxins on a per unit weight
basis, the widespread availability of castor beans and
the ease of production make ricin a potential biological
weapon. Ricin acts on the human body by preventing
Symptoms of ricin poisoning:
This depends upon whether ricin is ingested or inhaled.
Inhalation of an aerosol toxin results in upper airway
and pulmonary symptoms which may occur from minutes to
about 6 hours after exposure depending upon the dose.
Symptoms may include nasal and airway congestion, nausea
and vomiting, itching of the eyes, urticaria, and
tightness of the chest. After 12 to 24 hours, depending
upon the dose, pulmonary manifestations include airway
lesions and edema (lungs fill with fluid). Death occurs
36 to 48 hours after exposure. From mice studies,
LD50 = 3 mg/kg. Ricin is less
toxic by ingestion, but ingestion of two castor beans
will kill a human. Ingestion results in nausea,
vomiting, abdominal pain and cramping, diarrhea, fever
and chills, hematochezia, a drop in blood pressure,
shock and vascular collapse, but no lung damage. Autopsy
findings have found significant hepatic, splenic, and
Diagnosis of ricin poisoning:
Diagnosis is based on clinical and epidemiologic
factors. Conformation of ricin exposure by inhalation
can be made by ELISA analysis of a swab sample from
nasal mucous taken less than 24 hours after exposure.
Treatment: Treatment is
supportive. Inhalation injury may require treatment of
pulmonary edema with respiratory support. Early
following ingestion, patients should undergo GI
decontamination, with administration of activated
charcoal. Intravenous crystalloid infusion and pressor
support may be necessary for patients with hypotension.
Description: Botulinum toxin
is a neurotoxin produced by the microbe Clostridium
botulinum. This anaerobic, spore-forming bacillus
produces on of the most lethal toxins known, the
estimated lethal dose to humans LD50 = 0.001
micrograms/kg. The toxin can be mass-produced in
fermentors and can be aerosolized. Botulism food
poisoning can occur by ingestion of food containing the
toxin or bacterial spores. The toxin acts on the human
body by preventing the presynaptic release of
acetylcholine blocking neurotransmission; the result is
muscular weakness and paralysis. Several toxin types are
known (designated A through G) with type A being the
Symptoms: Symptom onset for
inhalation typically occurs between 24 to 36 hours after
exposure but could be less if the dose is high. Initial
symptoms include headache, queasiness, blurred vision,
muscle weakness, mydriasis (dilatation of eye pupil),
ptosis (drooping of upper eyelid), dysphagia (difficulty
in swallowing), and dysphonia (slurred speech). This
progresses to increased muscle weakness and eventual
respiratory paralysis. Deep tendon reflexes may be
depressed or absent on physical examination. Patients
may become cyanotic (skin appears bluish because of
carbon dioxide buildup in the blood) secondary to
respiratory failure. Ingestion may also result in
vomiting and involuntary defecation.
Diagnosis: Diagnosis is based
on clinical and epidemiologic factors (see symptoms
described above). Confirmation of inhalation
intoxication can be made using ELISA analysis of nasal
swabs taken less than 24 hours after exposure. Ingestion
exposure can be detected by analyzing serum or gastric
fluids with a mouse neutralization assay.
Treatment: Treatment is
supportive. As most serious complication is respiratory
failure, ventilation assistance is necessary. An
antitoxin is available for administration in confirmed
cases. There are risks associated with administrating
antitoxins developed from serum products (e.g. horse
Staphylococcal Enterotoxin B
enterotoxin B is one of the most common causes of food
poisoning. Nausea, vomiting, and diarrhea follow
ingestion of contaminated food. It is listed in the PEAC
tool as a biotoxin because of the toxin can be
mass-produced and is stable as an aerosol which can be
inhaled. The inhaled dose necessary to incapacitate
individuals is small, about 0.004 micrograms/kg.
Individuals usually recover. In severe cases of
inhalation exposure, death may occur due to pulmonary
edema and toxic shock. The LD50 value (by
inhalation) is 0.027 micrograms/kg.
Symptoms: Symptoms begin to
occur in 2 to 12 hours after exposure. In more severe
inhalation cases, symptoms may occur 1 hour after
exposure. Mild to moderate inhalation exposure produces
nonspecific systemic illness characterized by fever,
chills, headache, chest pain, myalgias (muscle pain),
and a non-productive cough. Ingestion produces vomiting
and diarrhea. More severe exposure results in pulmonary
edema and toxic shock. The duration of the illness is 3
to 10 days.
Diagnosis: Diagnosis is based
on clinical and epidemiologic factors. Laboratory
studies may show a nonspecific neutrophilic leukocytosis
and an elevated erthrocyte sedimentation rate. A
radiograph may show interstitial edema in patients with
significant pulmonary symptoms. The toxin accumulates in
the urine and can be detected for several hours after
exposure. If the toxin is inhaled, it may be isolated
from nasal swabs taken less than 12 hours after
Treatment: Treatment is
supportive, with close attention paid to oxygenation and
hydration. Patients with severe toxin exposure may need
ventilator support and diuretics.
Collection of Biological Samples
(blood, urine, nasal swabs, saliva)
Identifying toxins or their
metabolites in biological samples is very difficult
because only a very small amount of toxin is required to
cause illness. Therefore extremely sensitive assays are
required. Furthermore, the biological samples must be
collected soon after exposure or the molecules will be
lost. The samples must be kept refrigerated until they
can be analyzed as the toxin will be destroyed if stored
at room temperature. Enzyme-linked immunosorbent assays
(ELISA) of nasal swabs are definitive diagnostic tests
for inhalation of biotoxins. They are sensitive to about
1 to 10 nanograms per millimeter and require about four
hours to complete. The polymerase chain reaction
technique provides a very sensitive means of detecting
and identifying the genetic material of any living
organism that might remain in the crude, impure toxin
collected in the field.