Tear Gas - Harassing Agent or Toxic Chemical Weapon?
August 4, 1989, Volumne 262, the Journal of the American Medical Association,
Howard Hu, MD, MPH; Jonathan Fine, MD; Paul Epstein, MD, MPH; Karl
Kelsey, MD, MOH; Preston Reynolds, MD, PhD; Bailus Walker, PhD, MPH
Use of Tear Gas in Seoul, South Korea
CS and Other Tear Gas Agents
Toxicology of CS
Potential for Genotoxicity
Toxicity of CN
Tear gas has gained widespread acceptance as a means of controlling civilian
crowds and subduing barricaded criminals. The most widely used forms of tear
gas have been 0-chlorobenzylidenemalononitrile and w-chloroacetophenone.
Proponents of their use claim, that if used correctly, the noxious effects of
exposure are transient and of no long-term consequences. The use of tear gas in
recent situations of civil unrest, however, demonstrates that exposure to the
weapon is difficult to control and indiscriminate, and the weapon is often not used
correctly. Severe traumatic injury from exploding tear gas bombs as well as lethal
toxic injury have been documented. Moreover, available toxicological data are
deficient as to the potential of tear gas agents to cause long-term pulmonary,
carcinogenic, and reproductive effects. Published and recent unpublished in vitro
tests have shown o-chlorobenzylidenemalononitrile to be both clastogenic and
mutagenic. Sadly, the nature of its use renders analytic epidemiologic
investigation of exposed persons difficult. In 1969, eighty countries voted to
include tear gas agents among chemical weapons banned under the Geneva
Protocol. There is an ongoing need for investigation into the full toxicological
potential of tear gas chemicals and renewed debate on whether their use can be
condoned under any circumstances.
Tear gas is a weapon that has become familiar to the world. Hardly a week goes
by without press reports of tear gas being used in a public setting, typically the
dispersal of demonstrators or the subdual of a barricaded criminal. Recent years
have seen the use of large amounts of tear gas in several countries, including
Chile; Panama; South Korea; and the Gaza Strip and West Bank, Israel.
Tear gas is actually the common term for a family of chemical compounds that
have been otherwise referred to as "harassing agents" because of their ability to
cause temporary disablement. Some 15 chemicals have been used worldwide as
tear gas agents. Four of these--w-chloroacetophenone (CN), o-
chlorobenzylidenemalononitrile (CS), 10-chloro-5, 10-dihydrophenarsazine, and
x-bromo-x-tolunitrile-have been used extensively (1). In the United States,
Britain, and Europe, CN and CS have been employed most widely. O-
Chlorobenzylidenemalononitrile, in particualr, is a weapon that has gained
widespread acceptance as a means of controlling civilian populations during
The widespread use of tear gas agents naturally raises the question of their safety.
Relatively little, however, has appeared in the mainstream medical literature
regarding their toxicology. In general, authors of review articles have averred
that, if used correctly, the noxious effects of exposure are transient and of no
long-term consequence. (2-4). Much emphasis has been given to the findings of
the Himsworth Report (5), the results of an inquiry by a committee appointed by
the British Secretary of State for the Home Department following the use of CS in
Londonderry, Northern Ireland, in 1969. In addition, to investigating the use of
CS in Londonderry, the committee reviewed a wide range of scientific data. Its
main conclusion was that while exposure to CS can be lethal, most likely in the
form of toxic pulmonary edema, such an occurrence would only be at
concentrations that were several hundred times greater than the exposure dosage
that produces intolerable symptoms.
Many questions remain, however. Epidemiologic inquiry following the use of tear
gas under actual field conditions has been almost completely absent.
The Use of Tear Gas in Seoul, South Korea
This lack of information became apparent to us during a July 1987 visit to Seoul,
South Korea, during the course of which we gathered information on the use and
effects of tear gas. Political demonstrations resulting in the use of tear gas had
taken place in Seoul, Pusan, Taegu, Kwangju, Taejon, and Inchon--almost every
major city in South Korea--during the month of June. By its own account, the
government had used 351,200 tear gas canisters and grenades against civilian
demonstrators in that month (New York Times, July 1, 1987; section 1:8). We
interviewed more than a hundred people, including hospital and medical school
staff, medical and other university students, individuals who had been exposed to
tear gas, bystanders, religious and community leaders, and officials of the US
Embassy in Seoul.
A compilation of our findings, including interviews, results of physical
examinations, and a community epidemiology survey, was summarized in
monograph form. (6). We were able to obtain a sample of tear gas chemical that
represented the typical compound being used by the South Korean government.
Mass spectrometry analysis identified the substance as pure CS. We were struck
by the indiscriminate use and effects of tear gas on bystanders and others in
proximity to the demonstrators being teargassed. We heard pervasive accounts of
police firing canisters and throwing tear gas grenades directly into crowd
gatherings and enclosed spaces, such as rooms, motor vehicles, and subway
corridors. Persons who were close to the exploding tear gas grendades and
canisters commonly sustained penetrating trauma from plastic fragments that was
exacerbated by the presence of tear gas chemcial. Many individuals sustained
blistering skin burns from direct contact with the tear gas powder. There were
several accounts of people who were alleged to have experienced more severe
toxic injuries requiring hospitalization. Our community survey of small
shopkeepers close to university campuses where student demonstrations were
common uncovered some symptoms, including cough and shortness of breath,
among the interviewees and their children that persisted for weeks up to the time
of the survey. Physicians noted that patients with asthma and chronic obstructive
lung disease who were exposed to tear gas waftign into hospital wards through
open windows experienced deterioration in lung function, some to a serious
degree requiring a lengthened hospital stay.
We were especially struck by the lack of information available to the Korean
medical community on tear gas. According to Korean scientists we interviewed,
the government withheld the chemical composition of agents employed. Local
laboratories apparently refused to perform chemical analyses on tear gas
substances for fear of government reprisal. No guidelines had been issued to the
public or health authorities on methods of treating injuries or toxic effects of tear
gas weapons. Hospital authorities would not share with us medical records data,
citing fear of persecution. Senior and junior physicians, without exception,
confirmed that no one dared to undertake laboratory, clinical, and epidemiologic
studies of tear gas effects for fear of serious government reprisals.
Similar findings have been reported in inquiries into the use of tear gas in Gaza
and the West Bank of Israel. Of particular concern are allegations that exposure to
tear gas has been associated with increases in miscarriages and stillbirths (7,8).
CS and Other Tear Gas Agents
While poisonous gases have been used sporadically in military history as early as
428 B.C., when burning wax, pitch, and sulfur were used in wars between the
Athenians and Spartans, it took the birth of the modern chemical industry and the
circumstances of World War I for the invention of chemical warfare agents to
begin in earnest. Agents that could temporarily incapacitate victims were among
the first to be developed and were deemed "harassing agents." Of these, chemicals
that produce lacrimation and uncontrollable blepharospasm, otherwise known as
tear gas agents became the most popular.
Harassing agents are capable of a number of immediately perceived effects:
intense irritation of the eyes, causing crying or temporary blindness; irritation of
the mucous membranes of the nose, trachea, or lungs, causing coughing, irritation
of the throat and stomach, with the induction of vomiting and possibly diarrhea;
and irritation of the skin. Most harassing agents will cause several or all of these
reactaions to a greater or lesser extent.
For many years, CN was the most widely used agent by civil and military
authorities. It is the active ingredient in Mace and is still used in many parts of the
world. Dissatisfaction with its potency and chemical instability, however, led
military scientists to search for alternative agents.
In the 1950s, the Chemical Defence Experimental Establishment (Porton,
England), developed CS. O-Chlorobenzylidenemalononitrile is a white crystalline
substance that is usually mixed with a pyrotechnic compound in a grenade or
canister for use. Its useful form is intended to be a smoke or fog of suspended
particles. Effectiveness in crowd control derives from its properites as an
extremely severe skin and mucous membrane irritant and lacrimator, even at
minute doses. Instantaneous conjunctivitis with concomitant blepharospasm,
burning and pain are characteristic. These symptoms are exacerbated in hot or
humid weather. O-Chlorobenzylidenemalononitrile that has been micronized and
mixed with an antiagglomerant or treated with a silicone water repellant
(formulations known as CS1 and CS2, respectively) can remain active for days to
weeks when dusted on the ground.
Since its introduction, CS has virtually replaced CN as the riot control agent of
choice in England and the United States. During the Vietnam War, the United
States developed an array of delivery vehicles for CS, including small pocket
grenades, the "Mighty Mite" (a continuous spray device used in caves and tunnel
systems) and 58-kg cluster bombs dropped from helicopters and planes.
Toxicology of CS
Military studies among volunteers have noted that, in most cases, removal from
exposure to CS results in fairly rapid recovery with cessation of all symptoms
within minutes (9). Proponents of the use of CS believe that, when used properly,
high or prolonged exposure to the substance would be precluded by an
individual's natural aversion to remaining in an area where the substance is
present (United Kingdom patent specification 967 66; 1960). Its popularity among
military and police authorities stems partly from comparisons with the other tear
gas agents, which suggests that CS is a more potent lacrimator and seems to cause
less long-term injury, particularly with respect to the eye.
Inhalation toxicology studies (10-12) at high levels of CS exposure, however,
have demonstrated its ability to cause chemical pneumonitis and fatal pulmonary
edema. In situations in which high levels of exposures have occurred, the same
effects, as well as heart failure, hepatocellular damage, and death, have been
reported in adults (5(p23), 8, 13). An infant exposed to CS in a house into which
police fired CS canisters to subdue a mentally disturbed adult developed severe
pneumonitis requiring therap with steroids, oxygen, antibiotics, and 29 days of
The respiratory concentration of CS that would be lethal for 50% of healthy adults
has ben estimated to be 25,000 to 150,000 mg/m 3 per minute, based on animal
studies (15). When detonated outside, a CS grenade generates a cloud 6 to 9 m in
diameter, at the center of which a concentration of 2,000 to 5,000 mg/m 3 can be
produced, with concentrations rapidly tapering off at the periphery. (16)
If detonated in an enclosed space or in clusters, however, much higher levels of
exposure could be expected. Moreover, chemical weapons have generally been
noted to be notoriously uneven in their dispersal. (17).
Oral toxicology studies (18,19) have noted the ability of CS to cause severe
gastroenteritis with perforation. Metabolic studies (20, 21) indicate that absorbed
CS is metabolized to cyanide in peripheral tissues.
The potential for CS exposure at levels seen in the field to result in significant
generation of cyanide at the tissue level is controversial. (21, 22). Authors who
downplay this possibility reason that one would have to inhale massive quantities
that could only occur if the gas were used improperly, and that severe pulmonary
injury would overshadow the effects of cyanide generation. (2). However, this
argument ignores the ingestion of tear gas chemical that can occur with pharyngeal
deposition of incompletely dispersed CS compound and swallowing of respiratory
Contact burns and the development of skin sensitization with contact dermatitis
have been described in a number of experimental and observational studies on
animals and humans (16,23-25). This is in keeping with the many skin burns
encountered during our inquiry.
Studies have not adequately examined the possibility that CS at less than high
concentrations can cause lasting pulmonary effects. One study (11) of CS
exposure on volunteers showed no increase in airway resistance following several
exposures. However, only seven healthy military recruits were examined and
volunteers with a history of asthma were excluded. Previous studies have shown
that single exposures to high levels of respiratory irritants similar to CS have been
associated with the development of reactive airways disease syndrome in some
individuals. (26). The symptoms of prolonged cough and shortness of breath that
were reported in our community survey suggest that such an effect may have
occurred as a result of CS exposure in South Korea.
Only one study (27) has assessed the effect of CS on pregnancy in animals and it
found no significant effect. The Himsworth committee (5) found no signficant
increase in abortions, stillbirths, or congenital abnormalities in geographic districts
of tear gas use, comparing a 9-month period of heavy tear gas exposure to a
previous 9-month period. More sophisticated epidemiologic studies do not exist.
Potential for Genotoxicity
The agent CS can alkylate sulfhydryl groups, and, possibly, DNA. (28-30). As
such, it is potentially genotoxic. The agent has not, however, been well studied for
its genetic effect in vitro or in vivo. Some researchers have shown CS to be
mutagenic in both Ames Salmonella assays (30) and in the L5178Y tk + /tk-
mouse lymphoma forward mutation essay. (31). Zeiger et al (32) reported CS to
be questionably mutagenic in the Ames assay, testing lower doses than Von
Daniken et al. (30). When Von Daniken et al accounted for the toxicity of CS, its
mutagenic effects increased by a factor of 2. Thus, the toxicity of this agent can
make it difficult to study in vitro. Cytogenetic testing done by the National
Toxicology Program (unpublished data, 1988) and the National Institute of
Environmental Health Sciences has shown CS to be clastogenic in Chinese
hamster ovary cells and to induce sister chromatid exchanges in these same
mammalian cells. Other researchers (33, 34) have reported negative results in
testing CS for mutagenicity on the Ames test. A single study (27) of animal
embryos did not reveal any teratogenic effects of CS.
The agent CS has been found to suppress nonspecific esterase activity in mouse
skin sebaceous gland (35, 36). This property has been suggested for use as a
screening test for the carcinogenic potential of suspected chemicals (36). A study
(37) of the carcinogenicity of CS in A/J strain mice and Sprague-Dawley-Wistar
rats done at the Edgewood Arsenal reported CS to induce more pulmonary tumors
in exposed animals after 4-week inhalation experiments, conducted at 0, 50, and
500 mg/m 3 per minute. The increase, however, was not strictly dose related and
of borderline statistical significance. This report concluded that CS was not
significantly tumorigenic in these animals, but observed that chronic exposure to
very low concentrations of CS is of greater concern and should be further studied.
In addition, Marrs et all (38) studied the inhalation toxicity of CS in rodents.
Owing to the limited number of animals studied, they were also unable to draw a
firm conclusion concerning the tumorigenicity of CS.
Toxicity of CN
Although CS has been the most widely used and well studied of the tear gas
agents, other agents are still available. Of particular importance is CN, which is
still being produced in the United States (39) and was reported to have been used
in the West Bank and Gaza Strip (Jerusalem Post, May 6, 1988:1). (8,40). w-
Chloroacetophenone is generally acknowledged to be of greater toxicity than CS,
being more likely to cause permanent corneal damage on contact with the eye (19)
and primary and allergic contact dermatitis. (41,42). The maximum safe inhaled
dose has been estimated to be several times lower than than of CS (3) and at least
five deaths have been reported following the use of CN grenades in confined
spaces (2,43,44). Little is known regarding its potential for chronic pulmonary or
genotoxic effects or for potentional effects on reproduction.
Most exposures to CS and CN typically cause immediate and severe irritation of
the eyes and respiratory tract, accompanied by blepharospasm, lacrimation,
coughing, sneezing, and rhinorrhea, followed rapidly by a burning sensation of
exposed skin surfaces and the mouth. Some persons also experience nausea and
vomiting, photophobia, and headache. These symptoms usually disappear within
a few hours after removal from exposure.
Clinically, signs of exposure consists of blepharospasm, conjunctival injection,
palpebral edema, and lacrimation. Management is conservative, beginning with
aeration and the disposal of all contaminated clothing in plastic bags. Skin should
be washed, although contact with water can briefly exacerbate skin symptoms
from CS exposure, and a mild alkaline solution (6% sodium bicarbonate, 3%
sodium carbonate, and 1% benzalkonium chloride) has been recommended to
hastend decontamination of CS (16). Persistent eye irritation can be relieved with
application of a local anesthetic preparation and a patch. Contact dermatitis may
respond to corticosteroid creams and antipruritics.
Exposure of high concentrations of tear gas by inhalation or ingestion, as may
occur in an enclosed space or in proximity to an exploding tear gas device, should
be treated cautiously. Pulmonary injury with edema can be delayed and the patient
should be kept under observation for several days. Initial treatment may begin
with humidified oxygen; bronchodilators and ventilator therapy may be
necessary. Prophylactic antibiotics have been suggested. (2) We believe a
thiocynate assay should be considered in cases of ingestion or extremely high
Persons with preexisting lung disease such as asthma or emphysema should be
observed carefully for exacerbation of their condition.
From a toxicological perspective, there is a great need for epidemiologic and
more laboratory research that would illuminate the full health consequences of
exposure to tear gas compounds such as CS. The possibility of long-term health
consequences such as tumor formation, reproductive effects, and pulmonary
disease is especially disturbing in view of the multiple exposures sustained by
demonstrators and nondemonstators alike in some areas of civilian unrest. The
development of tolerance to CS, a phenomenon that has been confirmed in studies
of human volunteers, (45), has likely increased the length and intensity of
exposure sustained by some individuals. Unfortunately, the same social conditions
that accompany political unrest and the use of tear gas make epidemiologic
research difficult, if not impossible.
We also believe, however, that the evidence already assembled regarding the
pattern of use of tear gas, as well as its toxicology, raises the question of whether
its further use can be condoned under any conditions. Fact-finding missions to
areas of civil unrest in addition to South Korea have frequently observed security
forces using tear gas against peaceful demonstrators and not uncommonly against
civilians in no way involved in protest. (7,46).
We recognize it is not adequate for health professionals simply to study and reject
as "medically unacceptable" every modality of riot control. As with many
hazards--for example, asbestos, industrial toxic emissions, or radiation--there is
an important role for the independent professional: to study , document, analyze,
and report on such hazards and to advise government on what does and does not
carry an acceptable risk. If a weapon is found to present too serious a risk, it is
then the responsibility of those in charge of public safety to decide on alternatives.
In doing so, active consultants should be sought with medical and public health
specialists who are independent of law enforcement agencies, and, ideally, drawn
from both governmental and nongovernmental agencies and institutions. In the
United States, for example, health specialists might be recruited from medical
school faculties, state and local health departments, the Public Health Service, and
the Centers for Disease Control.
At a time when the world has recently seen the recurrence of the use of mustard
gas, this time in the Middle East, it is also worthy to note that in 1969, at the
United Nations General Assembly, 80 countries voted to ban the use of any
chemical in war, including tear gas, under the Geneva Protocol. (47)
Finally, we have been persuaded that in many instances in which harassing agents
have been used, dialogue and negotiation could have been pursued. Often, public
order might be better served if riot police are not called immediately to duty. It is
the hallmark of repressive regimes to equate the voicing of dissent with disorder
and to deny opponents the freedom of assembly, and speech, rights guaranteed
universally among signatories to the Universal Declaration of Human Rights (48).
For full list of references for this article, please see JAMA, August 4, 1989 Vol.
262, No. 5