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An Associate Laboratory of
National Environmental Research Center-Corvallis

Ibrahim Joseph Hindawi, Ph.D.
National Ecological Research Laboratory
CorvalVis, Oregon 97330
To be Presented at the Meeting in-the
Dalles, Oregon, February 20, 1975

Chlorine (CI2)» a greenish-yellow gas with a sharp odor is 2.5
times as heavy as air and 20 times as toxic as hydrogen chloride gas.
During World War I, chlorine became notorious as a poisonous gas. When
chlorine reaches the lung tissue, it combines with the hydrogen of water
to form the highly corrosive hydrochloric acid (HC1). During this
process, traces of ozone, another strong irritant, and free oxygen also
are liberated according to the formulas:
Cl2 + H2) 	~ HC1 + HOC!
8 HOC! 	~ 6 HC1 + 2 HC102 + 02
(In sunlight or bright light, H0C1 decomposes mainly as:
2 H0C1 	~ 2 HC1 + 02.)
Uses of Chlorine
The largest consumer of chlorine is the chemical industry. The gas
is used for preparation of organic and inorganic agents such as vinyl
chloride plastics, pesticides and herbicides (e.g., DDT). The pulp and
paper industry uses chlorine in bleaching operations*. Approximately 4%
of all chlorine is used for water and sewage treatment (Tables 1 and 2).
In addition, a variety of inorganic chemicals is prepared with chlorine,
namely the chlorine salts, metals and other compounds; paint coatings;
silicates (glass making); and phosphates.
Hydrochloric acid 1s emitted mainly from combustion of coal and oil
(Table II). Between 0.01% and 0.5% of domestic coal is chlorine by
weight, and 95% of that reaches the atmosphere as hydrochloric acid. It
has been estimated that the average chlorine content of coal is 0.2% and
that 95% of this is converted to hydrochloric acid. 3

Lapalucci and coworkers (4) estimated on a similar basis (i.e.,
0.2% chlorine coal) that the stack of an 800-mw power plant will emit
11,300 cubic feet of hydrogen chloride each hour or 4560 tons each year.
Near incineration dumps where poly-vinylchloride (vinyl plastics) is
burned, hydrochloric acid is a major contaminant.
Chlorine usually is shipped in liquified form. During the liquifi-
cation process it can become an important source of atmospheric contami-
nation. When in contact with moisture, chlorine reacts to form hypo-
chlorite, the active ingredient in liquid household bleaches, and hydro-
chloric acid, a strong corrosive irriting to the eyes and to the whole
respiratory tract. In the United States, the industrial threshold limit
value (TLV) for chlorine is 3 mg/meter (1 ppm) for an 8-hour day,
whereas Russia has adopted a more stringent limit of 1 mg/meter .
Chlorine Effects on Vegetation
The deleterious effects of chlorine compounds on plant life have
been known and documented for well over a hundred years. In a 1951
report, Moyers (5) recounted a classic case in 19th centry England:
In the early days of the Leblanc soda process, most of the hydrogen
chloride from the treatment of salt with sulfuric acid was washed
into the atmosphere causing extensive damage to plants near the
factory. Between 1836 and 1863 scrubbers were installed at the
various alkali works In England to remove at least 95 percent of
the hydrogen chloride in the stack gases and in 1874 the con-
centration in these gases was limited to 0.45 mg per cubic meter,
which eliminated crop damage. Hydrogen chloride 1s less toxic to
plants than sulfur dioxide. The lesions are found principally on
the margins or tips of the leaves, but sometimes between the veins
as well.

Whereas SOg and flouride pose region-wide pollution problems,
chlorine is found only where it is being used or where it is a byproduct
of a manufacturing process. In recent years the localized damage from
chlorine has been noted near swimming pools and sewage disposal plants.
In one case, leaking cylinders used in water chlorination caused the
damage. In another case at an industrial plant in Cincinnati, Ohio, (6)
an accidental release caused severe damage in the immediate neighbor-
hood. On the day after the release, leaves began to fall from tomato
plants and trees in nearby yards. Silver maple trees had markings
similar to those caused by S02. Extensive privet hedges in the area
were almost bare. Plants reportedly have been defoliated with high
level short-term field fumigations. The concentration of chlorine
caused plant damage is greater than that reported for hydrogen fluoride
and less than that reported for sulfur dioxide (7). Choride also can
cause the type of marginal and tip necrosis induced by fluoride.
In 1955, Zimmerman (7) of Boyce Thompson Institute exposed 19
species of plants to chlorine at concentrations between 0.46 and 4.67
ppm, and 16 species experienced leaf spotting. Brennan, et al., (8)
exposed tomato plants to three different CIg levels for two and three
hour periods, periodically spraying half of the plants with water and
leaving the other half unsprayed. Wet and dry plants responded similarly:
Whereas a concentration of 0.31 ppm caused no damage, 0.61 ppm caused
slight injury and 1.38 ppm caused severe damage.
Chlorine in water exists partly 1n true solution and partly as HC1
and the relatively unstable HOC!. Stanford Research Institute has
reported Injury to alfalfa and radishes after exposure to 0.10 ppm Clg
for two hours (7).
As with sulfur dioxide, the middle-aged leaves are most susceptible
to chlorine injury, followed by the oldest and then the youngest leaves.

The injury by the Clg resembles that induced by flouride, but frequently
the effects more nearly resemble those of sulfur dioxide gas.
Hydrochloric Acid Mist and Chlorine Effects Observations
On August 14, 1969, vegetation injury from chlorine and acid mist
was observed in Washington, West Virginia at a farm 3/4 mile northeast
of the Amax specialty metals plant, producer of metals such as zirconium
and hafnium. Such production involves complex metallurgical and chemical
processes that can result in injurious emissions. For example, chlorine
emission reportedly reached as much as 45 pounds per hour.
The farm's apple trees, grape vines, red buds, corn, and hibiscus
all evidenced severe injury. The leaf tissue of broad leaf plants was
discolored brownish-orange, and necrotic spots had formed on leaf
surfaces. Injured apple and maple trees showed defoliation. Typical of
chlorine damage, middle-aged and old leaves were most readily injured.
In October 1966, Hindawi (6) visited an eastern community to
examine vegetation because residents had complained of acid mist smell
and damage to trees, shrubs, and ornamental plants. Severe air pollution
damage was evident on specimens of maple, cherry, red bud, rose bush,
and begonia, accompanied by early leaf abscission. This damage re-
sembles injury by hydrogen fluoride and sulfur dioxide.
Local emissions of hydrochloric acid mist and chlorine came from a
glass manufacturing company, where the basic process reduces SICl^ in
high-temperature ovens to produce fused silica glass. The company
exhausted the waste gases through four stacks, two 125 feet high and two
105 feet high. Although HC1 and Cl2 were the main pollutants in the
effluent, some silicon dioxide and silica gel also carried over, giving
the effluent a bluish cast as it left the stack.

Table 3 shows HC1 and Cl2 emissions from three samples taken in
each stack taken when, according to the company, the plant was operating
at approximately 50% of its capacity. Total loading of HC1 and Clg at
these conditions was 220 pounds per hour.
During night and early morning hours when winds are light and
temperatures are cool, meteorological estimates of ground-level HC1
concentrations indicate that about 0.5 ppm should be experienced about a
mile downwind of the plant. Similar concentrations should occur on
cloudy or mostly cloudy days with gentle winds. On bright sunny days
with low wind speeds, concentrations should be much greater and the
maximum concentrations should occur within a mile of the plant. How-
ever, because of terrain variations in the vicinity of the manufacturing
plant, large variations from these estimates may be expected.
Hydrogen chloride gas has a high affinity for water, and once
absorbed into water it becomes hydrochloric acid. In this instance, the
plant damage, orange-brown in color and mainly marginal or in the
necrotic area, could have been caused by chlorine diffusing through the
margin of the leaves as droplets of acid.
However, chemical analyses of the tissue of injured silver maples
showed a chloride content of 4700 ppm, compared to 3800 ppm for un-
injured silver maple trees.
Health Effects
Chlorine concentrations of 3 to 6 ppm (9 to 18 mg/meter ) cause
stinging and burning in the eyes (10). Exposures to concentrations of
14 to 21 ppm for 30 to 60 minutes cause pulmonary edema, emphysema, and
bronchitis, usually accompanied by marked muscular soreness and headache
\ ...
(11). Long term (up to 9 months) exposure of rabbits to chlorine concen*
tratlons of 0.7 to 1.7 ppm resulted 1n weight loss and a high incidence

Acute epidemics have repeatedly resulted in accidents while handling
or emptying liquid chlorine containers. On January 31, 1961 (13) for
instance, 6000 gallons of liquid chlorine spilled from a tank car torn
open in a train wreck in the rural community of LaBarre, Louisiana. The
gas cloud covered approximately six square miles and 1000 people had to
be evacuated. Seven hours later the chlorine gas concentrations were
still 400 ppm at a distance of 75 yards (about 70 meters) from the site
of the accident and 10 ppm at the fringe of the cloud. As a result of
this accident, about 100 people were treated for varying degrees of
respiratory illness, and some developed congestive heart failure. An
11-month old infant died, as well as 500 animals including dogs, cats,
horses, mules, chickens, hogs, cows, and ducks.
Only two months later in March (14), another accident occurred in
Maryland. Supposedly empty liquid chlorine cylinders were being un-
loaded from a freighter in the Baltimore harbor. The main valve of a
cylinder snapped off, immediately afflicting 156 persons with hemorrhages
from the lungs or asthma-like wheezing and pneumonia-like lung infil-
tration. Some injuries persisted for 19 to 35 months and resulted in
long-term pulmonary impairment.
More recently (15), 27 persons were treated in St. Luke's Hospital
in Cleveland after a leak occurred in a liquid chlorine storage tank on
May 9, 1969. Eighteen of them subsequently underwent a series of
pulmonary function studies up to 14 months after the exposure. Although
obstruction and hypoxemia (low oxygen levels in blood) cleared within
three months, five persons still had persistently reduced air inflow
after 14 months.
These experiences have prompted health authorities to enact strict
precautionary rules for handling liquid chlorine cylinders, rules
including plans for evacuating populations near threatened areas.

Chronic Effects
The numerous reports of acute poisoning by chlorine gas contrast
with the great paucity of information on the chronic effect of minute
amounts. Most observations have been made in factories producing the
chemical. As early as 1909, Ronzani (16) observed that men working with
chlorine aged prematurely, suffered from bronchial trouble, and were
predisposed to tuberculosis. Corrosion of teeth was widespread because
of the hydrochloric acid formed when chlorine combined with moisture of
the mouth.
Veterans of World War I, hospitalized after gassing with chlorine,
developed permanent lung damage and emphysema. Dr. Walbott (17) observed
several individuals with advanced emphysema initiated by exposure to
chlorine gas in World War I. In some he was able to pinpoint a specific
area of the lungs showing a localized process, suggestive of a primary
corrosion of bronchial and pulmonary tissue at the site of impact. This
so-called asthma resists treatment that usually benefits allergic asthma.
When chlorine is combined with hydrochloric acid, a higher concen-
tration is required for detection of the odor than for each gas in-
dividually (17).
Effect of Hydrochloric Acid and Chlorine Gas on Materials
In the literature reviewed, no information was found describing
corrosion or damage to material from exposure to environmental concen-
trations of the hydrochloric acid and chlorine. However, 1t 1s well-
known that hydrochloric acid and solutions are extremely corrosive to
most metals and alloys (18, 19). Mellor (20) has summarized 24 studies
on hydrochloric acid corrosion of various hard and mild steels and cast
iron. He noted that corrosion of cast iron and steel Increases regularly

as the concentration of acid increases. This suggests that chlorine in
sufficiently high concentrations would corrode metals, discolor and
damage painted material, and damage textile and fibers.

Summary and Conclusion
Chlorine, an odorous gas, is 2.5 times as heavy as air and
more toxic than hydrogen chloride gas.
Chlorine is used in bleaching operations, purification of
water and preparation of organic and inorganic agents.
Chlorine pollution is not a widespread problem like sulfur
dioxide. Chlorine gas damage on vegetation has been noticed
near swimming pools, sewage disposal plants, and other localized
sources of chlorine.
An accidental release of chlorine causes severe vegetation
damage in the immediate neighborhood.
The concentration of chlorine required for plant damage is
greater than that reported for hydrogen flouride and less than
that reported for sulfur dioxide.
Chlorine irritates mucosal membranes such as the eyes and
respiratory tract because Cl2 combines with moisture to form
Acute epidemics have repeatedly resulted from accidents
associated with the handling or emptying of liquid chlorine
Chlorine and hydrochloric acid mist and solutions are extremely
corrosive to most metals and alloys.
Hydrochloric acid 1s produced when water absorbs the hydrogen
chloride gas. Hydrogen chloride 1s produced by the add salt

process, by direct synthesis, and from chlorination of organic
The burning of coal and/or chlorinated plastics and paper is
another source of hydrochloric acid pollution.

1.	Stahl, Q. R. Air pollution aspects of chlorine gas, Litton Systems
Inc., Bethesda, Maryland for U. S. Department of Commerce, National
Bureau of Standards Publication 188-087. 1969.
2.	Gerstle, R. W. and T. W. Devitt, Chlorine and hydrogen chloride
emissions and their control. Presented in Atlantic City, New
Jersey, at the Sixty-fourth Annual Meeting of the Air Pollution
Control Association. 1971.
3.	Bureau of the Census. Current industrial reports. Inorganic
chemical and gases. U. S. Department of Commerce, Washington, D,C.
1962, 1966, 1967.
4.	Lapalucci, T. A., R. J. Demski, and D. Bienstock. Chlorine in coal
combustion. Pittsburgh Coal Research Center, U. S. Bureau of
5.	Thomas, M. D. Gas damage to plants. Ann. Rev. of Plant Phys. 11:
6.	Ibrahim Joseph Hindawi. Injury by sulfur dioxide, hydrogen flouride
and chlorine as observed and reflected on vegetation in the field.
APCA Jour. 18:5 May 1968.
7.	Zimmerman, P. W. Proceedings of the First National Air Pollution
Symposium. Conducted in Los Angeles by Stanford Reserch Institute,
Stanford University, Stanford, CA. 1949.
8.	Brennan, E., I. A. Leone, and R. H. Daines. Chlorine as a phytotoxic
air pollutant. Int. J. Air-Water Poll., 9:791-797. 1965.

9.	Ibrahim J. Hindawi. Survey of air pollution damage to vegetation,
Chap. IV. In: Parkershueg, West Virginia-Marietta, Ohio. Air
Pollution Abatement Activity. U. S. Deparment of Health Education
and Welfare, Public Health Service, 1969. p. 25-31.
10.	Heyroth, F. F. Chlorine, Clg. In: (F. A. Patty, editor,) Industrial
Hygiene and Toxicology, Vol. II, Ed. 2, New York: Interscience.
11.	Kramer, C. G. Chlorine. J. Occup. Med. 9:193, 1967.
12.	Skljanskaja, R. M. and J. L. Rappoport. Chronic chlorine poisoning
of rabbits with small doses of chlorine and the development of the
fetus in chlorine-poisoned rabbits. Arch. Exp. Path. Pharmacol.
117:276, 1935.
13.	Joyner, R. E. and E. 6. Durel. Accidental liquid spill in a rural
community J. Occup. Med. 4:152, 1962.
14.	Kowitz, T. A., R. C. Reba, R. T. Parker, and others. Effects of
chlorine gas upon respiratory function. Arch. Environ. Health
14:545. 1967.
15.	Kaufman, J. and D. Burkons. Clinical roentgenologic and physiologic
effects of acute chlorine exposure Arch. Environ. Health 23:29-34,
16.	Ronzani, E. Uber den Einfluss der Einatmungen von reizenden Gasen
der Indstrien auf die Schutzkrafte des Organismus gegenuber den
infektiven, Arch Hyg. 70:217, 1909.

17.	George C. Waldbott Health Effects of Environmental Pollutants. The
C. V. Mosby Co. Saint Louis. 1973.
18.	Stayzhkin, V. M. Hygenic determination of limits o.f allowable
concentrations of chlorine and hydrochloric gases simultaneously
present in atmospheric air. U.S.S.R. Literature on Air Pollution
and Related Occupational Diseases 9:55. 1962.
19.	Manufacturing Chemists Association. Hydrochloric acid, aqueous and
hydrogen chloride, anhydrous. Chemical safety data sheet, SP-39.
Manufacturing Chemists Association, Washington, D.C. 1951.
20. Mel 1or, J. W. Inorganic and Theoretical Chemistry — Suppl. 11,
Part 1. New York: Longmans, Green and Co., 1956.

Table I. Uses of chlorine and hydrochloric acid in 1969 in the United States
Chlorine	Percent Hydrochloric Acid	Percent
Organic chlorinations	78.5
Pulp, paper bleaching	15.0
Water, sewage treatment	3.5
Manufacturing bleaches	2.0
Metallurgical processes	1.0
Organic chlorinations	50.0
Treatment of oil wells	17.0
Metallurgical processes	17.0
Metal pickling	7.0
Food processing	4.0
Miscellaneous inorganic chemicals 5.0
Table II. Estimated United States emissions of chlorine and hydrochloric acid
in 1969 (tons/year)^
c ~	Estimated Emissions*
SourC€	Chlorine	Hydrochloric acid
Chlorine manufacture	47,000	0
Hydrochloric Acid manufacture	800	5,700
Chemical and industrial processes	30,400	27,400
Combustion	0	874,500
Total	78,200	907,600

Table III. Stack Emissions from Glass Manufacturing Plant (ppm)
1	119	0.91
2	473	0.56
3	302	0.52
4	421	0.92

Chlorine injury lo silver maple leaves is similar to sulfu.
dioxide injury.
Figure 7. Injury or. begon e scves ceu»td bv ch'ori-e and hydro-
chloric cc'd rpisr.
. Cucumber leaf exposed to 0.75 ppm Cl2tor 4 hours shows
injury similar to sulfur dioxide injury.
Figure 6. Irlury (r -edbud feev«s csottd 6* tWortie o"d Svrfro
~ch!oric QS'd mist.

Chlorine injury to mustard leaves
observed in the field. The middle
aged and the old leaves severley
injured. Photo courtesy of
O.C. Taylor. (California).
Chlorine injury to white pine
observed in the field. Photo
courtesy of A.C. Hill. (Utah).