MECHANISM OF TOXICITY
TIME COURSE OF EFFECTS
RETURN TO DUTY
Riot control agents, also called irritants, lacrimators, and
tear gas, produce transient discomfort and eye closure to render
the recipient temporarily incapable of fighting or resisting. Law
enforcement agencies use them for riot control and military
forces use them for training and in combat (see below). They have
a high LCt50 and a low effective Ct50, and
therefore have a high safety ratio. Their major activity is to
cause pain, burning, or discomfort on exposed mucous membranes
and skin; these effects occur within seconds of exposure, but
seldom persist more than a few minutes after exposure has ended.
Paris police used riot control agents to dispel rioters before
World War I, and these compounds were the first chemical agents
deployed during that war; French soldiers used them with limited
success in small skirmishes. About 30 riot control agents were
developed and used, but their use decreased following the advent
of more potent compounds.
After WWI, military and law enforcement agencies used CN for
various purposes until CS, a more potent and less toxic compound
synthesized by Corson and Stoughton (hence the nomenclature) in
1928, replaced it in about 1959. Today CN is in commercially
available devices for selfprotection (MaceR), but CS
is the agent otherwise used. The military forces of most
countries use it in training as a confidence builder for the
protective mask (the "gas chamber exercise"), and the
United States used it extensively in Viet Nam, primarily for
tunnel denial. Worldwide, police forces of many countries, e.g.,
Ireland, France, Russia, and the U.S., use it for crowd control
or during riots.
The United States excludes these agents from international
treaty provisions. They may be used in military situations by
The agents in use today are CS and CN. CA is outmoded, CR is a
British agent, and DM is neither used nor stockpiled.
Unlike most agents, which are liquids under temperate
conditions, riot control agents are solids with low vapor
pressures and are dispersed as fine particles or in solution.
Dispersion devices include small hand held spray cans, large
spray tanks, grenades, and larger weapons.
MECHANISM OF TOXICITY
The mechanism of biological activity is less well characterized for riot control agents than for most other agents; fortunately a detailed knowledge of the mechansim of action is not a prequisite for appropriate medical management.
CS and CN are SN2 alkylating agents (mustard, in
contrast, is an SN1 alkylator) and react readily at
nucleophilic sites. Prime targets include sulfhydryl-containing
enzymes, such as lactic dehydrogenase. In particular, CS reacts
rapidly with the disulfhydryl form of lipoic acid, a coenzyme in
the pyruvate decarboxylase system. It has been suggested that
tissue injury may be related to inactivation of certain of these
Pain can occur without tissue injury and may be bradykinin
mediated. CS causes bradykinin release in vivo and in
vitro, and elimination of bradykininogen in vivo
abolishes the systemic response to CS.
The initial response to aerosolized CS is an increase in blood
pressure and irregular respiration, suggestive of the Sherrington
pseudoaffective response. Bypassing the pain receptors of the
nose and upper airway by endotracheal administration of CS leads
to the same decrease in blood pressure and in respiration seen
after intravenous injection and suggests that the initial pressor
effect and irregular respiration are responses to a noxious
stimulus rather than pharmacologic effects of CS.
The main effects of riot control agents are pain, burning, and
irritation of exposed mucous membranes and skin. These effects do
not differ appreciably from one agent to another except in the
case of DM, which will be discussed in a separate section.
Eye: The eye is the most sensitive organ to riot
control agents. Contact with agent produces a sensation of
conjunctival and corneal burning and leads to tearing,
blepharospasm, and conjunctival injection. The severe
blepharospasm causes the lids to close tightly and produces
transient "blindness," an effect that could inhibit the
recipient's ability to fight or resist. However, if the recipient
opens his eyes, his vision is near normal even if a significant
concentration of the agent persists.
Because these compounds are solids it is possible for a
particle or clump to become embedded in the cornea or conjunctiva
to cause tissue damage. With the caveat noted below, there is no
evidence that this complication has ever occurred. However, a
recipient seeking medical care for eye pain after exposure should
have his eyes thoroughly decontaminated and a undergo thorough
ophthalmic examination. It could be necessary to pick out the
particles of agent from tissue.
Reviewers examined the evidence for permanent eye damage from
riot control agents. In each instance, the damage was from a
weapon fired from close range (about 50% were selfinflicted).
The reviewers concluded that the blast force driving the agent
deep into tissue (with or without the wadding of the weapon) was
major cause of the permanent injuries. This should not happen
under normal use.
Nose and mouth: Contact with the delicate
mucous membranes of the nose produces a burning sensation,
rhinorrhea, and sneezing; a similar burning sensation accompanied
by increased salivation occurs after contact with the mouth.
Airways: Inhalation causes burning and
irritation of the airways with bronchorrhea, coughing, and a
perception of a "tight chest" or an inability to
breathe. However, pulmonary function studies done immediately
after exposure have shown minimal alterations.
An inhaled irritating compound might be expected to exacerbate
a chronic pulmonary disease such as asthma, emphysema, or
bronchitis, but this appears not to happen after CS or CN even
though these agents have been used widely in mixed populations.
The medical care provider should nevertheless anticipate airway
problems in individuals with lung disease, particularly if they
are exposed to higher than the average field use concentrations.
There is no evidence that CS causes permanent lung damage
after one or several exposures to field concentrations. Following
inhalation of lethal amounts animals died from severe airway
damage 12-24 hours post-exposure, but survivors from large
exposures had minimal or no pulmonary abnormalities. After
multiple (50 or more) daily exposures to smaller amounts animals
developed laryngitis and tracheitis.
Skin: Contact with skin causes a tingling or
burning sensation and may cause erythema, particularly if the
skin is raw or freshly abraded (e.g., shortly after shaving). The
erythema begins several minutes after exposure and generally
subsides 4560 minutes after termination of exposure.
Under conditions of high temperature, high humidity, and high concentration of agent there may be more severe dermatitis starting with erythema hours after exposure and followed by vesication. Generally these are second-degree burns not unlike, but more severe than, sunburn. Firemen who entered contaminated buildings after summer riots several decades ago developed these lesions. After stirring up the contaminating particles, they later developed erythema and blisters on their exposed skin.
Hypersensitivity may develop. In one instance, an individual
developed generalized vesication and high fever after an
uneventful exposure to CS more than 20 years after his only and
equally uneventful previous exposure.
Gastrointestinal tract: Gastrointestinal effects
usually do not occur with most riot control agents (DM is an
exception), although there may be retching or vomiting if the
agent concentration is high, if the exposure is prolonged, or if
the individual is sensitive.
Cardiovascular: A transient increase in heart
rate and blood pressure has occurred in people immediately prior
to an exposure to a riot control agent or immediately after onset
of exposure. The heart rate and blood pressure returned
essentially to pre-test ranges while exposure continued and may
have been caused by the anxiety or the initial pain rather than
to a pharmacological effect of these agents. This "alarm
reaction" may cause adverse effects in one with preexistent
Oral ingestion: Children occasionally eat CS and
several adults have swallowed CS pellets. Aside from bouts of
diarrhea and abdominal cramps (which might have been from the
cathartics and antacids used as therapy) their courses have been
uneventful. In animals, the LD50 is about 200 mg/kg
(which is about 14 grams/70-kg person), an amount unlikely to be
ingested even deliberately. A few animals fed lethal amounts (or
greater) had gastric irritation or erosions, and several had
signs of intestinal perforation. Recommended therapy after
ingestion consists of cathartics, antacids, and surgical
Lethality: CN, occasionally in combination with
DM, has caused deaths in people who refused to exit a confined
space. In each case the agent was used in excess. Death generally
occured hours after initial exposure, and postmortem findings
were those of severe airway damage similar to that seen in
Metabolism: Animals given lethal amounts of CS
by intravenous or intraperitoneal administration developed
increased blood thiocyanate concentrations hours later,
indicating that the malononitrile portion of CS had been
metabolized to cyanide. Cyanide was not a factor in causing death
(lung damage was). A significant increase in blood concentration
of thiocyanate has not been noted after aerosol administration of
CS. Several popular data bases mention this cyanogenic potential
of CS and suggest that treatment of a CS casualty might require
therapy for cyanide poisoning (this recommendation is apparently
based on the i.v. or i.p administration data). After receiving
lethal amounts of CS by inhalation animals died 12-24 hours later
from severe airway damage; cyanide was not implicated in their
The effects of usual field concentrations of DM (Adamsite) are
similar to those of the other riot control agents, except that DM
has little irritancy to the skin. However, at higher
concentrations, DM causes nausea, vomiting, and a feeling of
generalized malaise. For this reason it is called a vomiting
TIME COURSE OF EFFECTS
Except for those produced by DM, the biological effects from
these agents begin seconds after exposure and continue for 15
minutes or so after one exits the contamination to fresh, clean
air. The effects from DM begin 34 minutes after the onset of
exposure and may last an hour or two. (This is advantageous
militarily as an individual, unaware of the agent, will continue
to inhale it for several minutes and absorb a larger dose. He may
then vomit, requiring mask removal, which leads to continued
inhalation of agent.)
Usually the circumstances of exposure make the diagnosis
obvious. The history and the few physical signs (conjunctival
injection with normal pupils, tearing, etc.) are usually
adequate. On a battlefield, the sudden onset of burning pain and
irritation might lead one to consider Lewisite or phosgene oxime
exposure, but the signs and symptoms of riot control agents
gradually recede, whereas those from the vesicants worsen.
There are no specific laboratory tests that will confirm the
diagnosis. Complications, e.g., infection of a skin lesion, will
produce the laboratory findings characteristic of the
The effects of exposure to these agents under the usual field
conditions usually are self limiting and require no specific
therapy. Most will disappear in 15-30 minutes, although erythema
may persist for an hour or longer.
The following section discusses potential complications
occurring only under exceptional circumstances, such as exposure
to a very large amount of agent (as in an enclosed space),
exposure in adverse weather, or experimental studies in humans or
animals. They are not to be expected with normal use of these
Fewer than 1% of exposed people will have effects severe or
prolonged enough to cause them to seek medical care. Those who do
probably will have eye, airway, or skin complaints. Because there
is no antidote for these agents, treatment consists of
Eye: The eye should be carefully flushed with
water or saline and impacted particles should be sought. General
care consists of a topical solution (many are available) to
relieve the irritation and topical antibiotics. An
ophthalomologist should be consulted for further evaluation and
Pulmonary: These agents may exacerbate chronic
disease or unmask latent disease (although there is little
evidence of this). Bronchospasm with wheezing and mild distress
hours continuing after exposure may occur in a latent asthmatic
and more severe effects and respiratory distress may occur in one
with chronic bronchitis or emphysema. Management includes oxygen
administration (with assisted ventilation, if necessary),
bronchodilators if bronchospasm is present, and specific
antibiotics dictated by the results of sputum studies (Gram
stains of smears followed by culture). A specialist skilled in
the treatment of inhalational injury should be consulted early.
Animal studies and very limited human data indicate that maximal
effects occur 12 hours after exposure.
Skin: The early erythema requires reassurance,
but no specific therapy unless severe and prolonged more than an
hour or two. The later-onset erythema, precipitated by a larger
exposure in a hot and humid atmosphere, is usually more severe
and less likely to resolve quickly; it may require the use of
soothing compounds such as calamine, camphor, and mentholated
creams. Small vesicles should be left intact, but larger ones
will ultimately break and should be drained. Irrigation of
denuded areas several times a day should be followed by the
application of a topical antibiotic. Large oozing areas have
responded to compresses containing substances such as colloidal
oatmeal, Burow's solution, and other dermatologic preparations.
A person exposed to the usual field concentrations of riot
control agents will probably not be seen at a triage area. Those
presenting with complications should be triaged according to the
nature of their injuries.
RETURN TO DUTY
Because the effects of field concentrations clear within minutes, the casualty should be returned to duty as soon as possible. Casualties with complications may require evacuation and further medical treatment before returning to duty.