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© by PSP Volume 26 – No. 1/2017, pages 151-155 Fresenius Environmental Bulletin
151
TOXICITY AND HEALTH EFFECTS OF ORTHO-
CHLORO-BENZYLIDENE-MALONONITRILE (CS GAS)
Massimo Zucchetti*, Raffaella Testoni
Dipartimento di Energia, Politecnico di Torino Corso Duca degli Abruzzi, 24, 10129 Torino, Italy
ABSTRACT
The CS gas has repeatedly been used as a tear
gas by police forces during manifestations and riots,
in Europe, in the United States and elsewhere. Our
study is aimed to examine toxicity and health
effects on humans of CS gas, following the people
exposure to CS gas in Valsusa (Italy), during the
2011-2015 period. The claims that the CS gas is not
toxic are counterbalanced by many findings by
recent studies, showing many toxic effects,
especially in case of misuse of the gas, or in weak
and sensitive subjects. Adoption of the precaution
principle seems, in this case, recommendable. The
use of CS gas by police forces for riot control
should therefore be abandoned, substituted by other
countermeasures.
KEYWORDS:
CS gas, toxicity, health effects, tear gas.
INTRODUCTION
The chemical product ortho-chloro-
benzylidene-malononitrile (the so-called CS gas), is
chemically synthesized by reacting two chemicals
compounds: 2-clorobenzaldeide and malononitrile.
CS gas has repeatedly been used as a tear gas by
police forces during manifestations and riots, in
Europe, in the United States and elsewhere.
Our study is aimed to examine toxicity and
health effects on humans of CS gas, given our
observation of side effects cases due to exposure of
Italian people participating to manifestations since
2001 up to the present days.
The immediate effects of the gas on humans
occur at low concentrations and depend on the
irritating action to the skin and mucous membranes.
The first target organs are represented by eyes:
intense tearing due to irritation of the mucous
membrane, blepharospasm, conjunctivitis,
periorbital edema, burning, and pain. CS is
commonly classified as a non-lethal weapon to
control the riots. However, CS gas has proven to
have toxic side effects, which are currently studied
in toxicology.
According to Amnesty International, after
exposure in riots in Genoa 2001 (Italy), many
persons have filed a formal complaint,
accompanied by medical reports, claiming to suffer
long-term effects (damage to lungs, throat and skin)
due to exposure to gas CS. Similar reports are
available from other exposed people in Valsusa
(Italy) manifestations during 2011-2015.
In weak subjects, literature reports damage to
the lungs, and in some cases, effects on heart and
liver have been reported too. The potential damage
to internal organs, as well as gastrointestinal
symptoms, was evidenced by accidental exposures
reported in literature. Concerning the eyes, the
increase in intraocular pressure may onset acute
glaucoma in susceptible individuals.
As far as respiratory apparatus is concerned,
usual effects are represented by irritation of the
upper airways that are clinically manifested as nasal
congestion and runny nose: those effects are usually
reversible and disappear within a short time if the
exposed person moves to breath clean air and
washes himself and his/her clothes with fresh water.
In some cases, irritating effects may extend distally
and cause laryngitis, tracheitis, bronchial irritation
and cough with copious phlegm. In severe cases
laryngitis may result in laryngospasm and irritation
of the lower airways, namely ARDS (Acute
Respiratory Distress Syndrome). In medical
literature, numerous cases of prolonged cough and
breathing difficulties for several months are also
reported. Concerning skin, contact with the gas skin
causes burning sensation that usually subsides
quickly: the contamination of the clothes can
prolong the effects and, in case of prolonged
exposure, can lead to real burns. For
gastrointestinal tract, effects usually stem from the
contamination of food and beverage, and depend on
the irritation of the mucous membranes and lead to
symptoms such as nausea, vomiting, loss of
appetite, diarrhea, and abdominal pain. More
serious effects, such as acute liver disease
(hepatitis), have also been reported occasionally.
Finally, there is some – however disputed -
evidence from recent studies of carcinogenic and
mutagenic effects of CS. They identify the
mechanism that underlies the toxic action of CS,
namely the formation of cyanides. The carcinogenic
© by PSP Volume 26 – No. 1/2017, pages 151-155 Fresenius Environmental Bulletin
152
mechanism of CS is not based on the interaction of
the compound with DNA, but directly on the
apparatus of mitotic cells, causing chromosomal
aberrations.
MATERIALS AND METHODS
The effectiveness of CS in crowd control
comes from its property as a skin and mucous
membrane irritant and extremely serious tear
maker, even at low doses. Conjunctivitis and
concomitant blepharospasm, burning and pain are
typical. These symptoms are exacerbated in hot or
humid environment. CS is commonly micronized
and mixed with an antiagglomerant or treated with
a water repellent silicone (known formulations as
CS1 and CS2, respectively): in those cases, it can
remain active for days or weeks when dusted on the
ground.
The use of tear gas in recent situations of civil
unrest shows that exposure to the weapon is
difficult to control and this weapon is seldom
incorrectly used. Severe traumatic injuries from
exploding tear gas grenades and toxic damage were
documented. In addition, the available toxicological
data are still uncertain regarding this agent’s
possibility to cause long-term pulmonary,
carcinogenic and reproductive effects. However,
published in vitro tests showed o-
chlorobenzylidenemalononitrile to be both
mutagenic and clastogenic.
The widespread use of tear gas agents
naturally raises the question of their safety.
Unfortunately, the nature of its application makes
analytical epidemiological investigation of exposed
persons difficult. In general, the authors of early
(70’s and 80’s) review articles have found out that,
if used properly, the harmful effects are transient
and of no consequence in the long run [1-3].
The question arises on the effects of tear gas
when improperly used. In our community survey,
performed in the recent years (2011-2015) in
Valsusa (Italy) [4], we had repeated accounts of
police forces firing tear gas directly into crowd
gatherings and enclosed spaces such as rooms and
shops.
People who find themselves close to
exploding tear gas grenades, may not unfrequently
sustain penetrating trauma from plastic fragments,
which is exacerbated by the presence of chemical
tear gas. Many individuals sustain blistering skin
burns from direct contact with the tear gas powder.
There have been several stories of people that
experienced more severe toxic injuries requiring
medical care and, in some cases, hospitalization.
Our survey on the Val Susa community
discovered some common symptoms, including
coughing and shortness of breath, among
respondents and their children, which persisted for
weeks after the exposure. The medical doctors
noted that patients with asthma and chronic
obstructive pulmonary disease who were exposed to
tear gas seldom showed deterioration of lung
function, some in a serious degree that required
medical treatment and hospitalization. We were
particularly impressed by the lack of information
available to the local community on the effects of
tear gas.
TOXICOLOGY OF CS
As reported above, many studies between
volunteers have noted that, in most cases, the
removal from exposure to the CS determines fairly
rapid recovery with cessation of all symptoms
within a short time.
Toxicology studies by inhalation [5, 6] at high
levels of exposure CS, however, have demonstrated
its ability to cause fatal chemical pneumonitis and
pulmonary edema. In situations where high levels
of exposure have occurred, those effects, as well as
heart failure, hepatocellular damage and death, have
been reported in adults. [5-8]. A child exposed to
CS in a house where police fired CS containers to
subdue a mentally disturbed adult developed severe
pneumonia requiring steroid therapy, oxygen,
antibiotics, and 29 days of hospitalization [9].
The concentration of the respiratory tract of
CS that would be lethal to 50% of healthy adults
was estimated to be of 25000-150000 mg/m3 per
minute, based on animal studies [10]. When
detonated outdoors, a CS grenade generates a cloud
of 6 to 9 m in diameter, in the center of which a
concentration of 2000-5000 mg / m3 can be
produced, with concentrations quickly decreasing
with distance [11]
If detonated in an enclosed space or in groups,
however, you could expect much higher levels of
exposure. In addition, chemical weapons are
generally been noted to be notoriously uneven in
their dispersion [12].
Oral toxicology studies [13-14] have noted the
ability of CS to cause severe gastroenteritis with
perforation. Metabolic studies indicate that CS
absorbed is metabolized to cyanide in peripheral
tissues. However, the actual possibility of exposure
to CS levels causing significant generation of
cyanide at the tissue level is controversial: to
breathe the massive quantities, necessary to
generate cyanide, serious lung injury may prevent
this occurrence. However, this argument ignores the
ingestion of chemical tear gas that can occur with
pharyngeal deposition of compounds CS, not
completely dispersed and swallowing of respiratory
secretions.
© by PSP Volume 26 – No. 1/2017, pages 151-155 Fresenius Environmental Bulletin
153
Burns due to contact and the development of
skin sensitization with allergic contact dermatitis
have been described in a series of experimental and
observational studies on animals and humans [15-
19]. This is in line with many skin burns
encountered during our investigation in Val Susa.
Symptoms of prolonged cough and shortness
of breath that were reported in our survey of the Val
Susa community: they suggest that this effect may
have occurred because of exposure to CS.
The potential damage to internal organs, as
well as gastrointestinal symptoms, was evidenced
by an accidental exposure reported in [20]. The
laryngeal and bronchial obstruction is demonstrated
for example in [21]. Some studies have associated
exposure to the CS with miscarriages, see for
instance [22].
POTENTIAL GENOTOXICITY
In the study [23], it was established that the
CS chemical agent had no carcinogenic effects
mediated by DNA damage. However, the study in
[24] affirms that the carcinogenic mechanism of CS
is not based on the interaction of the compound
with DNA, but directly on the apparatus of mitotic
cells, causing chromosomal aberrations. The agent
CS can alkylate sulfhydryl groups and, possibly,
DNA [25-26]. As such, it is potentially genotoxic.
Some researchers have shown CS to be mutagenic
on salmonella cells [26] and mice [27]. The CS
agent has been found to suppress the non-specific
esterase activity in mouse skin sebaceous glands
[28-29]: this property was suggested to be used as a
screening test for the carcinogenic potential of
chemicals [29]. A study [30] showed the
carcinogenicity of CS in mice.
RESULTS AND DISCUSSION
From the toxicological point of view, there is
a great need for more epidemiological and
laboratory research that illuminate the health
consequences of exposure to full tear gas
compounds such as CS. The possibility of health
consequences in the long term, such as the
formation of cancer, reproductive effects, and lung
disease is particularly worrying in view of the
multiple exposures suffered by demonstrators and
non-demonstrators too in some areas of civil unrest.
The development of tolerance of CS, a
phenomenon that has been confirmed in studies on
human volunteers [31] has probably increased the
length and intensity of the exposure held by some
individuals.
We also believe, however, that the evidence
already assembled on the misuse of tear gas, as well
as its toxicology, arise the question whether its
further use may be tolerated under any conditions.
We recognize that it is not enough for health
professionals to study and simply refuse as
"clinically unacceptable" any mode of riot control.
As with many dangers, for example, asbestos, toxic
industrial emissions, radiation, there is an important
role for scientists: study, document, analyze and
report on these risks and to advise the government
on what is acceptable and what does not lead to an
acceptable risk.
At a time when the world has recently seen
the recurrence of the use of CS, this time in the
Middle East, it is also noteworthy that, in 1969, on
the occasion of the General Assembly of the United
Nations, 80 countries voted for prohibit the use of
any chemical warfare, including tear gas, by
applying the Protocol of Geneva.
The technical paper presented at the Public
Prosecutor's Office Court of Genoa , as informative
part and attached to the file - complaint "Syndrome
Genoa " June 15, 2002 , titled "Malononitrile - CS :
mutagenicity data" , signed by Prof. Nicola Lopresti
(University of Pisa) and other researches, shows, on
a scientific basis and based on experimental data,
that a substance like CS could be classified by the
European Commission (Dangerous Substances
Directive 675/148/CEE) in Class 3, namely:
"substances presenting positive results in the most
revealing mutagenicity assays , for which no
relevant in vivo data are available”. Substances of
this type represent a danger to humans because of
their possible mutagenic effects.
Exposure to Genoa in 2001 was massive but
single. Instead, two exposure situations are
particularly dangerous as regards Valsusa:
- For operators of the police forces, CS gas
is a working tool and the contact could have
continued, long-term effects unknown today,
especially in those backside officials and agents not
wearing masks.
- For the protesters of the Susa Valley, there
is the same scenario of repeated exposure.
Exposures in the 2011-2016 five-year period have
been some tens.
Prolonged exposure could transform both the
police agents and the protesters in a group of
highly-exposed subjects to CS gas, potentially
causing unexpected effects due to repeated
exposure.
CONCLUSIONS
Concerning legal aspects, the Italian Law is
actually not clearly treating this case. Under the bill
April 18, 1975, # 110 (Supplementary to the current
regulations for the control of small arms,
ammunition and explosives), Article 1 states that
© by PSP Volume 26 – No. 1/2017, pages 151-155 Fresenius Environmental Bulletin
154
"For the purposes of criminal laws, the public
security and other laws or regulations on weapons
are weapons of war of every kind that , by their
strong potential for offense, are or may be intended
for the modern armament of the troops at home or
abroad for the use of war and the bombs of any type
or parts of them , aggressive chemicals, deadly
contraptions of war of any kind , bottles or
wrappers explosive or incendiary". This ranks the
CS gas as weapons of war in the third category, i.e.
"chemical weapons".
As for its use in war, the "Convention on the
Prohibition of the Development, Production,
Storage and Use of Chemical Weapons and on their
Destruction" signed at European Union level, in
Paris January 13th , 1993, and adopted in Italy in
1995 and entered into force on April 29th 1997,
prohibits the use of CS gas in any war scenario.
Unfortunately, no explicit statement about the use
of CS gas for riot control by police forces is added
to this prohibition. CS gas is part of the equipment
of the Italian police forces since 1991.
In conclusion, the claims that the CS gas is not
toxic are counterbalanced by many findings by
recent studies, showing many toxic effects,
especially in case of misuse of the gas, or in weak
and sensitive subjects. Adoption of the precaution
principle seems, in this case, recommendable. The
use of CS gas by police forces for riot control
should therefore be abandoned, substituted by other
countermeasures.
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© by PSP Volume 26 – No. 1/2017, pages 151-155 Fresenius Environmental Bulletin
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Received: 29.06.2016
Accepted: 26.09.2016
CORRESPONDING AUTHOR
Massimo Zucchetti
Dipartimento di Energia, Politecnico di Torino
Corso Duca degli Abruzzi, 24 – 10129 Torino, Italy
Email:zucchetti@polito.it
