The following information has been extracted from our CHEMINFO database, which also contains hazard control and regulatory information. [More about...] [Sample Record]

Access the complete CHEMINFO database by contacting CCOHS Client Services.

 
SECTION 1. CHEMICAL IDENTIFICATION

CHEMINFO Record Number: 568
CCOHS Chemical Name: Chlorine dioxide

Synonyms:
ClO2
Chlorine peroxide
Chlorine oxide
Chlorine(IV) oxide
Chloroperoxyl
Chloroperoxide
Anthium dioxide

Chemical Name French: Dioxyde de chlore
Chemical Name Spanish: Dióxido de cloro
CAS Registry Number: 10049-04-4
RTECS Number(s): FO3000000
EU EINECS/ELINCS Number: 233-162-8
Chemical Family: Inorganic halogen oxide / inorganic halogen dioxide / chlorine oxide / chlorine dioxide / inorganic gas
Molecular Formula: Cl-O2
Structural Formula: O=Cl=O

SECTION 2. DESCRIPTION

Appearance and Odour:
Yellowish-green to orange gas.(1,9,16) The pungent odour has been described as chlorine-like (1) or resembling a mixture of chlorine or ozone.(9,16)

Odour Threshold:
Reported odour threshold values (9.4 ppm (method not specified) (15) and 15 ppm (method not specified) (13)) have not been evaluated. A detection level of 0.1 ppm though widely reported (14) is not considered correct.

Warning Properties:
POOR - odour threshold is above the TLV.

Composition/Purity:
Chlorine dioxide gas is very unstable and poses a high risk of rapid decomposition. Therefore, the gas is always produced on site and used immediately.(27) It is mixed with air or nitrogen so that the chlorine dioxide concentration does not exceed 10%. Chlorine dioxide may be temporarily stored as a dilute solution in water. These solutions are acidic, which leads to decomposition. Therefore, the solutions are usually stabilized using sodium hydrogen carbonate, sodium carbonate or sodium chloride. These compounds react with chlorine dioxide such that the solutions are actually of sodium chlorite and sodium chlorate rather than chlorine dioxide.(1) Therefore, this CHEMINFO review does not address the potential hazards of chlorine dioxide in solution. For information on potential hazards and control measures for sodium chlorite and sodium chlorate, refer to the relevant CHEMINFO review. Solid chlorine dioxide is technically feasible but is rarely produced because of its instability and risk of explosion. Therefore, this review does not address the potential hazards and control measures for solid chlorine dioxide.

Uses and Occurrences:
Chlorine dioxide is mainly used in the pulp and paper industry for wood pulp bleaching. It is also used as a disinfectant or biocide in municipal water treatment for purification and for taste, odour and colour control; in industrial water treatment (e.g. cooling systems/towers); in wastewater treatment; in ammonia plants; in pulp mills (slime control and paper machines); in scrubbing systems; in the meat, dairy, beverage, fruit and vegetable and other food processing applications; in the electronics industry; as a bleaching agent in the textile industry and for bleaching leather, fats, oils, and beeswax; in sterilizing manufacturing and laboratory equipment, environmental surfaces, tools and clean rooms; in the oil and gas industry for downhole applications; and in the manufacture of chlorite salts. Chlorine dioxide is also applied to medical wastes.(1,9,16,27)


SECTION 3. HAZARDS IDENTIFICATION

EMERGENCY OVERVIEW:
Yellowish-green to orange gas. The pungent odour has been described as chlorine-like or resembling that of a mixture of chlorine or ozone. Will not burn. POWERFUL OXIDIZER. Promotes combustion. Contact with combustible materials may cause a fire and/or explosion. DANGEROUSLY REACTIVE. Thermally unstable. Explodes violently at concentrations greater than 10% by volume in air at pressures above 10.1 kPa (76 mm Hg). May be initiated by light, shock, electrical discharge including static electricity, hot surfaces, open flames or contact with a variety of materials. VERY TOXIC. May be fatal if inhaled. Irritating to the respiratory tract at very low concentrations. Causes lung injury-effects may be delayed. CORROSIVE to the eyes, skin and respiratory tract. Can cause a visual disturbance called halo vision where eyesight becomes foggy or blurred and it appears as though there are halos around lights. Long-term lung injury may result from a severe short-term exposure.



POTENTIAL HEALTH EFFECTS

Effects of Short-Term (Acute) Exposure

Inhalation:
Chlorine dioxide is a very toxic, corrosive gas that poses a very serious inhalation hazard. It is unstable and highly reactive at concentrations above 10% in air, and is a strong oxidizing agent.(1) In many cases, exposure is not to chlorine dioxide alone, but to a mixture of chemicals that can include toxic and corrosive chlorine and/or sulfur dioxide.
Chlorine dioxide irritates the nose, throat, trachea and bronchi at very low concentrations (less than 5 ppm) resulting in breathlessness, wheezing and coughing. Higher concentrations can cause inflammation in the upper respiratory tract, bronchial spasms and difficulty in breathing. A potentially fatal accumulation of fluid in the lungs (pulmonary edema) could occur. Symptoms of pulmonary edema (chest pain and shortness of breath) can be delayed for up to 24 or 48 hours after exposure. Long-term respiratory effects (e.g. sensitivity to respiratory irritants, chronic nasal inflammation, asthma, pulmonary emphysema and spastic bronchitis) have been noted in workers accidentally exposed to unspecified concentrations for a short time.

There are several case reports of accidental inhalation exposure to chlorine dioxide.
Workers in a bottling plant were accidentally exposed to less than 0.3-0.37 ppm chlorine dioxide aerosol (as sampled during and after exposure) for 30 minutes to 12 hours. Symptoms were pain and irritation of the throat and sinuses, tearing and burning of the eyes, nasal discharge, chest irritation, coughing, headache and fatigue. Symptoms persisted and progressed in some workers for several days following exposure. Six workers who showed the most symptoms were followed up to determine if they had developed irritant/induced asthma. None of these workers showed signs of asthma, as determined by bronchial challenge tests.(3) A bleach tank worker who was exposed to a reported concentration of 19 ppm (sampling information not provided) for an unspecified time died. Exposure to 5 ppm (sampling information not provided) for an unspecified time caused respiratory irritation.(5)
Thirteen people were examined 5 years after exposure (duration not reported) to unspecified concentrations of chlorine dioxide from a leak in a water purification system. Long-term effects included sensitivity to respiratory irritants (13/13), disability with loss of employment (11/13), chronic fatigue (11/13), nasal abnormalities (13/13), chronic nasal inflammation (11/13) and asthma (6/13).(22) This study is limited by the lack of exposure information. A historical report describes a chemist with three accidental exposures to chlorine dioxide. He developed irreversible and progressive pulmonary emphysema with spastic bronchitis and respiratory insufficiency.(23)

Skin Contact:
The gas is corrosive and may irritate or burn the skin if sufficient airborne concentrations are achieved. Any skin contact will also involve significant inhalation exposure. There is no human or animal information available.
The gas is not expected to be absorbed through the skin.(7)

Eye Contact:
Chlorine dioxide gas is corrosive and is expected to produce severe eye irritation if sufficient airborne concentrations are achieved. Any eye contact will also involve significant inhalation exposure.
Eye irritation and a visual disturbance called halo vision were reported in workers at a sulfite-cellulose production plant when equipment failures resulted in exposure to relatively high, but unknown, concentrations of chlorine dioxide gas.(8 ) This study is limited by concurrent exposures to chlorine and sulfur dioxide and the lack of exposure information. With halo vision, eyesight becomes foggy or blurred and it appears as though there are halos around lights. Affected persons may not experience eye discomfort or pain. This effect normally clears up within a day and causes no permanent injury, but could contribute to accidents. In animal studies, exposure to 10 ppm and greater has resulted in eye irritation.

Ingestion:
Ingestion is not an applicable route of exposure for gases.

Effects of Long-Term (Chronic) Exposure

There is little human information on the effects from long-term exposure to chlorine dioxide gas. Studies with limitations (e.g. mixed exposures, lack of exposure information and potential self-reporting biases) indicate that long-term occupational exposure to corrosive gases including chlorine dioxide may cause respiratory effects such as wheezing and decreased lung function. However, these effects probably result from short-term incidents of high exposures ("gassing" episodes) to chlorine and chlorine dioxide.

Lungs/Respiratory System:
Limited studies suggest that occupational exposure to corrosive gases including chlorine dioxide may cause wheezing and decreased lung function. However, these effects are probably due to short-term incidents of high exposures ("gassing" episodes) to chlorine and chlorine dioxide, rather than long-term exposure to low concentrations of these gases.
Ninety-nine workers in the bleaching department of a pulp mill were exposed to chlorine, chlorine dioxide and sulfur dioxide. The health of these workers was compared to 286 unexposed workers. The exposed group worked in the bleaching-department for an average of 18 years. In this group, 90% were exposed to chlorine/chlorine dioxide and 73% to sulfur dioxide. There was a significant increase in the incidence of self-reported, physician-diagnosed, adult-onset asthma in the exposed workers compared to the unexposed group. These workers also reported a high incidence of "gassing" episodes. The incidence of wheezing was also increased in workers who reported gassing episodes.(24) This study is limited by mixed exposures, lack of exposure data and by self-reporting.
In another study, 321 pulp mill workers exposed to chlorine dioxide, chlorine, hydrogen sulfide, sulfur dioxide and methyl mercaptan were compared to 237 unexposed railway workers. The average employment time in the pulp mill was 7.8 years. Measured exposures of chlorine/chlorine dioxide in the workplace air at the time of the study were less than 0.1 ppm. There was a significant increase in respiratory symptoms reported by pulp mill workers. Workers reporting incidents of "gassing" with chlorine/chlorine dioxide reported significantly more wheezing and missed work because of chest illness. Lung function testing suggested there was more airflow obstruction in workers who had been gassed. However, there were no significant differences in overall lung function when the exposed group was compared to the unexposed group.(25) This study is limited by multiple exposures and by self-reporting of symptoms and gassing episodes.
A significant decrease in pulmonary function was not observed in 147 workers from a pulp mill with exposure to sulfur dioxide, chlorine, and chlorine dioxide compared to 124 controls from a paper mill. The average employment time in the pulp mill was 23 years. Workers exposed mainly to chlorine/chlorine dioxide reported significantly more shortness of breath than those exposed mainly to sulfur dioxide. The control group included many workers who had formerly worked in the pulp mill, many of whom left because they disliked the odours. The control group may therefore have included a group with respiratory tracts more sensitive to irritants.(26) This study is also limited by mixed exposures and by self-reporting of symptoms.

Respiratory Sensitization:
There is insufficient information to conclude that chlorine dioxide is an occupational respiratory sensitizer. Limited studies suggest that some workers develop asthma following short- or long-term exposure to chlorine dioxide. This effect is most likely due to severe irritation of the respiratory tract, which occurs following "gassing" incidents. A review of these studies is included under "Short-Term Effects - Inhalation" or "Long-term Effects - Respiratory".

INGESTION STUDIES: No significant effects were observed in studies where volunteers ingested water treated with chlorine dioxide.

Carcinogenicity:

There is no human or animal information available.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has not assigned a carcinogenicity designation to this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
The limited information available does not suggest that chlorine dioxide causes developmental toxicity.
Human studies have focused on populations exposed to chlorine dioxide-treated drinking water. In this situation, there would be concurrent exposure to other chemicals including disinfection byproducts. Therefore, these studies are not considered relevant to assessing the effects of occupational exposure to chlorine dioxide gas. All of the available animal studies involved exposure to chlorine dioxide in drinking water at concentrations that result in decreased water intake, making it difficult to draw conclusions. Many of these studies had design limitations (e.g. use of a single dose) or the observed effects did not reach statistical significance.

Reproductive Toxicity:
The limited information available does not suggest that chlorine dioxide causes reproductive toxicity. There is no human information available. In the only animal study located, rats orally dosed with chlorine dioxide in water showed no reproductive effects.

Mutagenicity:
There is insufficient information available to conclude that chlorine dioxide is mutagenic. There is no human information available. Negative results were obtained in tests using live animals exposed to chlorine dioxide in water. Positive and negative results were obtained in tests with cultured mammalian cells.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Chlorine dioxide does not accumulate in the body.(27,28)


SECTION 4. FIRST AID MEASURES

Inhalation:
This chemical is very toxic. Take proper precautions to ensure your own safety before attempting rescue (e.g. wear appropriate protective equipment, use the buddy system). Remove source of contamination or move victim to fresh air. If breathing is difficult, oxygen may be beneficial if administered by trained personnel, preferably on a doctor's advice. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately transport victim to an emergency care facility.

Skin Contact:
If irritation occurs, flush with lukewarm, gently flowing water for 5 minutes or until the chemical is removed. Obtain medical attention immediately. Note: Any skin contact will also involve significant inhalation exposure.

Eye Contact:
If irritation occurs, remove source of contamination or move victim to fresh air. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 5 minutes or until the chemical is removed, while holding the eyelid(s) open. Obtain medical attention immediately. Note: any eye contact will also involve significant inhalation exposure.

Ingestion:
Ingestion is not an applicable route of exposure for gases.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures.
Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation of authority obtained, as required.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.



SECTION 5. FIRE FIGHTING MEASURES

Flash Point:
Not combustible (does not burn)

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Pure liquid chlorine dioxide is unstable and extremely shock sensitive which can initiate detonation and decomposition to chlorine and oxygen.(10) The solid is explosive by impact at -100 deg C.(10)

Sensitivity to Static Charge:
Concentrated mixtures with air (greater than 10%) are readily detonated by electrostatic discharge.(10)

Minimum Ignition Energy:
Not applicable

Potential for Dust Explosions:
Not applicable

Combustion and Thermal Decomposition Products:
Chlorine dioxide may explode on heating. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, hydrogen chloride, chloric acid and perchloric acid.(16)

Fire Hazard Summary:
Chlorine dioxide is not combustible (does not burn). However, it is a powerful oxidizing agent (enhances the combustion of other substances) and is a serious fire and explosion risk, especially when contaminated with, or if it comes into contact with, oxidizable, combustible materials (e.g. cloth, grease, leather, oil and solvents, paper, sawdust, rubber, plastics and wood). In these situations, there may be spontaneous ignition and explosion. May react explosively with hydrocarbons (fuels). Thermally unstable. At concentrations greater than 10% in air and pressures greater than 10.1 kPa, there is a risk of explosion as a result of decomposition. Explosion may be caused by any source of initiation energy, such as sunlight, heat or electrostatic discharge, or contamination. Decomposes explosively under intense fire conditions to form corrosive and highly toxic chlorine and hydrogen chloride gases. Closed containers may rupture violently due to rapid decomposition, if exposed to fire or excessive heat for a sufficient period of time.

Extinguishing Media:
Chlorine dioxide does not burn. Extinguish fire using extinguishing agents suitable for the surrounding fire and not contraindicated for use with chlorine dioxide. Chlorine dioxide is an oxidizing agent. Therefore, flooding quantities of water spray or fog should be used to fight fires involving chlorine dioxide.

Extinguishing Media to be Avoided:
DO NOT use dry chemical fire extinguishing agents containing ammonium compounds (such as some A:B:C agents) on oxidizers that contain chlorine, since an explosive compound (nitrogen trichloride) can be formed. DO NOT use Halon extinguishers or halocarbon extinguishers, because they can react with chlorine dioxide. DO NOT use carbon dioxide, dry chemical powder or other extinguishing agents that smother flames, since they are not effective in extinguishing fires involving oxidizers.(12)

Fire Fighting Instructions:
Extreme caution is required in a fire situation. Evacuate area and fight fire from a protected, explosion-resistant location or maximum possible distance. Approach fire from upwind to avoid hazardous decomposition products, such as chlorine, hydrogen chloride, chloric acid and perchloric acid. Wear full protective gear if exposure is possible. See Protection of Firefighters.
If possible, isolate materials not involved in the fire, if this can be done without risk, and protect personnel. If chlorine dioxide is not involved in the fire, move containers from the fire area only if they have not been exposed to heat. Chlorine dioxide may be ignited by friction, heat, or contamination. Use extreme caution since containers of chlorine dioxide may explode in the heat of the fire. Otherwise, apply water from as far a distance as possible, in flooding quantities as a spray or fog streams to keep fire-exposed containers or equipment cool and absorb heat, until well after the fire is out. Water spray or fog may also be used to knock down irritating/toxic combustion products which may be produced in a fire. Dike fire control water for appropriate disposal. DO NOT get water inside containers, since a violent reaction may occur.
Chlorine dioxide is an oxidizer. Remove all flammable and combustible materials from the vicinity, especially oil and grease. Stay away from ends of tanks, but realize that shrapnel may travel in any direction. Withdraw immediately in case of rising sound from venting safety device or any discolouration of tanks due to fire. In an advanced or massive fire, the area should be evacuated. Use unmanned hoseholders or monitor nozzles.
Tanks or drums should not be approached directly after they have been involved in a fire or heated by exposure, until they have been completely cooled down. Clean-up or salvage operations should not be attempted until the chlorine dioxide is cooled.

Protection of Fire Fighters:
Chlorine dioxide and its decomposition products (e.g. chlorine and hydrogen chloride) are extremely hazardous to health. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective equipment (Bunker Gear) will not provide adequate protection. Chemical protective clothing (e.g. chemical splash suit) and positive pressure self- contained breathing apparatus (NIOSH approved or equivalent) may be necessary.



NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) HAZARD IDENTIFICATION

NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


SECTION 9. PHYSICAL AND CHEMICAL PROPERTIES

Molecular Weight: 67.45

Conversion Factor:
1 ppm = 2.75 mg/m3; 1 mg/m3 = 0.36 ppm at 25 deg C (calculated)

Physical State: Gas
Melting Point: -59.6 deg C (-75.3 deg F) (16,18)
Boiling Point: 10.9 deg C (51.6 deg F) (16,18)
Relative Density (Specific Gravity): Not applicable (gas)
Solubility in Water: Very soluble (concentration depends on temperature and gas pressure; 3.01 g/L at 25 deg C and 4.6 kPa (34.5 mm Hg)).(9,27)
Solubility in Other Liquids: Soluble in carbon tetrachloride, sulfuric acid and acetic acid.(9) Reacts with many organic solvents.
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = -3.22 (estimated) (29)
pH Value: Forms acidic solutions in water. However, acid decomposes chlorine dioxide, which make the solutions unstable.
Viscosity-Dynamic: Not applicable (gas)
Surface Tension: Not applicable (gas)
Vapour Density: 2.33 (air = 1) (calculated)
Vapour Pressure: 142.13 kPa (1066 mm Hg ) at 20 deg C; 168.84 kPa (1266.3 mm Hg ) at 25 deg C (calculated) (18)
Saturation Vapour Concentration: Not applicable (gas)
Evaporation Rate: Not applicable (gas)
Henry's Law Constant: Not available
Critical Temperature: 192 deg C (377.6 deg F) (16)
Critical Pressure: 8621.6 kPa (85.11 atm) (16)

SECTION 10. STABILITY AND REACTIVITY

Stability:
Unstable. Chlorine dioxide is thermally unstable, even with mild heating. It is pressure sensitive and decomposes in the presence of air and at high concentrations.(9,16,36)

Explosive Properties:
Explosive decomposition occurs above 45 deg C at concentrations greater than 10% by volume in air at pressures above 10.1 kPa (76 mm Hg). Decomposition can be caused by light, sparking, electrical discharge including static electricity, rapid heating, hot surfaces or open flames, and by contact with most flammable organic solvents, oxidizable materials, or inorganic substances, e.g. mercury and sulfur.(16,30,31) Chlorine dioxide is pressure sensitive and will decompose violently if it is compressed for storage or shipping.(36) The transfer of chlorine dioxide from one container to another can cause an explosion.(32)

Oxidizing Properties:
Chlorine dioxide is a powerful oxidizing agent.(1,16,31) Chlorine dioxide has an "available chlorine" content of 263% and therefore has an oxidizing power that is theoretically more than 2.5 times that of chlorine.(32) It is an inorganic gas containing both oxygen and chlorine atoms.

Hazardous Polymerization:
Does not polymerize.

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.


COMBUSTIBLE MATERIALS (e.g. hydrocarbons (e.g. butadiene, ethane, ethylene, methane or propane), rubber, cork, sulfur, or sugar) - ignite on contact and may cause explosion.(10,36)
CARBON MONOXIDE - explode on mixing.(10)
NON-METALS (e.g. phosphorus) - ignite on contact and may cause explosion.(10)
DIFLUORAMINE or TRIFLUORAMINE - interaction in the gas phase is explosive.(10,33)
FLUORINE - reaction is explosive.(33)
HYDROGEN - mixtures detonate on sparking, or on contact with platinum sponge.(10)
MERCURY - chlorine dioxide gas explodes upon shaking with mercury.(10)
PHOSPHORUS PENTACHLORIDE and CHLORINE - mixture causes explosion.(10)
POTASSIUM HYDROXIDE - explodes in contact with solid potassium hydroxide or its concentrated solutions.(10)

Hazardous Decomposition Products:
Chlorine

Conditions to Avoid:
Light, shock, electrical discharge including static electricity, hot surfaces, open flames, and other ignition sources.

Corrosivity to Metals:
There is no information available on the corrosivity of chlorine dioxide gas to metals.

Corrosivity to Non-Metals:
Chlorine dioxide gas attacks plastics, like polyvinylidene chloride, polypropylene, nylon, polyurethane, high-density polyethylene, thermoset isophthalic acid polyester, and thermoset epoxy. It does not attack Teflon, acrylonitrile-butadiene-styrene (ABS), polyvinylidene fluoride, chlorinated polyvinyl chloride (CPVC), polyvinyl chloride (PVC) and vinyl ester.(35)

Stability and Reactivity Comments:
It has been reported that sparking produces decomposition of gaseous chlorine dioxide at concentrations as low as 2%, but it is not violent. The rate of decomposition at concentrations in the range of 7-8% becomes rapid enough to be considered hazardous. At 10% concentration, the explosion is violent.(34)


SECTION 11. TOXICOLOGICAL INFORMATION

Note: This review is for chlorine dioxide gas, which is unstable, and highly reactive. Much of the animal toxicity information for chlorine dioxide involves exposure to chlorine dioxide solutions, which are rarely used in occupational settings. These studies are not reviewed here. However, relevant conclusions are summarized, as appropriate. Review information on chlorine dioxide solutions is available from CCOHS upon request.

LC50 (rat): 32 ppm (4-hour exposure; nose-only) (1*, unconfirmed)
*Note: The original report is unpublished and unavailable. However, the study was conducted according to OECD Guidelines and has been peer reviewed.

Effects of Short-Term (Acute) Exposure:

Inhalation:
Chlorine dioxide gas is a very severe respiratory irritant at very low concentrations. In an LC50 study, rats were exposed to 0, 16, 25, 38 or 46 ppm chlorine dioxide gas for 4 hours. At 16 ppm, there were no deaths. Deaths were observed at higher concentrations. Respiratory distress was observed and autopsy showed pulmonary edema and emphysema in all exposed groups.(1, unconfirmed) This study is unpublished and unavailable, but was conducted according to OECD guidelines. Rats were exposed to 0, 5, 10 or 15 ppm for 15 minutes, 2 or 4 times/day, for 1 month. At 15 ppm, 1 animal in each exposure group died and there was a marked decrease in body weight, inflammation of the mucous membranes of the eyes and nose, bronchitis, and inflammation of the alveoli. For animals exposed 4 times/day, effects were more severe. Recovery from the respiratory tract lesions was noted 15 days after exposure. At 10 ppm, bronchitis and alveolar irritation were less marked. At 5 ppm, there were no harmful effects noted.(11) In a limited study, rats and/or rabbits were exposed to 5 or 10 ppm (2 hr/d) or to 2.5 ppm (7 hr/d) for 30 days. Rats exposed to 10 ppm had decreased body weights, red eyes, nasal discharge, bronchopneumonia and increased red and white blood cell counts. Rats and rabbits exposed to 5 ppm had similar but less severe effects. Rats and rabbits exposed to 2.5 ppm had bronchial inflammation, alveolar inflammation, congestion and bleeding. Recovery was noted 15 days after exposure in both rats and rabbits (exposure groups not specified).(6) This study is limited by poor reporting and statistical evaluation of the data was not conducted. A series of studies, which are limited by low animal numbers, poor reporting and by concurrent respiratory infections in some controls, were carried out on rats. A single exposure of 4 rats to 260 ppm for 2 hours resulted in discharge from the eyes, bleeding from the nose and pulmonary edema. One rat died after 1 hour of exposure, the others were killed at the end of the 2 hours. In the same study, 3-minute exposures, once/week for 3 weeks to decreasing concentrations from 3400-800 ppm caused respiratory distress and bronchopneumonia in 2/3 rats. Exposure to 10 ppm (4 hr/d, 9/13 days) resulted in death in 5/5 rats by day 13, a decrease in body weight (significance not reported), respiratory distress, discharge from the nose and eyes, severe bronchitis, and bronchopneumonia.(2)

Effects of Long-Term (Chronic) Exposure:

Inhalation:
In a limited study, rabbits exposed to 2.5 ppm for 45 days (4 hr/d) had alveolar congestion and bleeding. Recovery was noted 15 days after exposure stopped.(6) This study is limited by poor reporting. Rats exposed whole-body to an average of 0 or 0.1 ppm for 10 weeks (5 h/d, 7 d/wk) showed no signs of toxicity. No information on nasal effects was reported.(2) This study is limited by low animal numbers, poor reporting and by concurrent respiratory infections in some controls.

Ingestion:
Ingestion studies have involved the exposure of animals to chlorine dioxide in drinking water. Typically, there is decreased water intake due to the taste of the water, making it difficult to draw conclusions. In general, decreased body weight has been observed in rats exposed to 0.1 mg/kg/day for 1 year or to 10 mg/kg/day for 8 weeks or more. Other effects include significant decreases in organ weight in rats at 2.4 mg/kg/day and higher for 90 days, decreased osmotic fragility of red blood cells in rats at 0.1 mg/kg/day and higher for 1 year and decreased hemoglobin in rats at 10 mg/kg/day and higher for 1 year. Reversible reductions in the thyroid hormone T4 were reported in rats at 10 mg/kg/day for 8 weeks and in monkeys at 9 mg/kg/day for 4 weeks.

Teratogenicity, Embryotoxicity and/or Fetotoxicity:
There is insufficient evidence to conclude that chlorine dioxide is a developmental toxin. All of the studies available exposed animals to chlorine dioxide in drinking water at concentrations that other studies have shown to result in decreased water intake because of decreased palatability, making it difficult to draw conclusions. Many of the studies had design limitations (e.g. use of a single dose) or the observed effects did not reach statistical significance. One study showed signs of thyroid depression in rat offspring, but reversibility was not assessed.

Reproductive Toxicity:
There is insufficient information available to conclude that chlorine dioxide causes reproductive toxicity. No reproductive effects were noted in rats exposed to up to 10 mg/kg/day chlorine dioxide in drinking water in one study.

Mutagenicity:
There is insufficient information available to conclude that chlorine dioxide is mutagenic. A negative result was obtained in a test in live mice orally exposed to chlorine dioxide in water and in mice and rats exposed by intraperitoneal injection. Positive and negative results were obtained in cultured mammalian cells.
Mice were given 0, 7.6, 15.2 or 30.4 mg/kg/day chlorine dioxide (cited as 1 mL of solution containing 100, 200, or 400 mg equivalents of chlorine/L/mouse/day) in water orally for 1 or 5 days. There were no increases in bone marrow chromosome aberrations or micronuclei and no increase in sperm head abnormalities.(4) Negative results were obtained for chromosomal aberrations and sister chromatid exchanges in mice and a dominant lethal test in rats exposed by intraperitoneal injection to water solutions of chlorine dioxide.(1, unconfirmed) This route of exposure is not relevant to occupational situations.
In unpublished studies, cultured mammalian cells were exposed to a buffered solution of chlorine dioxide. There were dose-related, significant increases in chromosome aberrations and in gene mutations, with and without metabolic activation. Negative results were obtained for cell transformation.(1, unconfirmed) No conclusions can be drawn from a study that tested a product containing stabilized chlorine dioxide in mammalian cells and bacteria.(17) This product is a water solution of sodium chlorite and only contained a trace of chlorine dioxide.(7)


SECTION 16. OTHER INFORMATION

Selected Bibliography:
(1) International Programme on Chemical Safety. Chlorine dioxide (gas). Concise International Chemical Assessment Document 37. World Health Organization, 2002
(2) Dalhamn, T. Chlorine dioxide: toxicity in animal experiments and industrial risks. AMA Archives of Industrial Health. Vol. 15, no. 2 (Feb. 1957). p. 101-107
(3) Hickmann, M.A., et al. Are high-dose toxic exposures always associated with reactive airways dysfunction syndrome (RADS). Archives of Environmental Health. Vol. 56, no. 5 (Sept. 2001). p. 439-442
(4) Meier, J.R., et al. Evaluation of chemicals used for drinking water disinfection for production of chromosomal damage and sperm-head abnormalities in mice. Environmental Mutagenesis. Vol. 7 (1985). p. 201-211
(5) Elkins, H.B. Chlorine dioxide. In: The Chemistry of Industrial Toxicology. 2nd ed. Wiley and Sons, 1959. p. 89-90
(6) Paulet, G., et al. De l'action du bioxyde de chlore (ClO2) à faible concentration sur les animaux de laboratoire. Archives des Maladies Professionnelles, de Mèdecine du Travail et de Sècuritè Sociale. Vol. 31, no. 3 (Mars 1970). p. 97-106
(7) Chlorine dioxide. Risk Assessment Document. EH72/14. Health and Safety Executive (HSE) Books, 2000
(8) Gloemme, J., et al. Health hazards from chlorine dioxide. AMA Archives of Industrial Health. Vol. 16 (1957). p. 169-176
(9) Vogt, H., et al. Chlorine oxides and chlorine oxygen acids: chlorine dioxide. In: Ullmann's encyclopedia of industrial chemistry. 7th ed. John Wiley and Sons, 2002. Also available at: <www.mrw.interscience.wiley.com/ueic/ueic_search_fs.html> (Subscription required)
(10) Urben, P.G., ed. Bretherick's reactive chemical hazards database. [CD-ROM]. 6th ed. Version 3.0. Butterworth-Heinemann Ltd., 1999
(11) Paulet, G., et al. Action du bioxyde de chlore (ClO2) sur le rat en exposition discontinue. Archives des Maladies Professionnelles, de Mèdecine du Travail et de Sècuritè Sociale. Vol. 35, no. 9 (Sept. 1974). p. 797-804
(12) NFPA 430. Code for the storage of liquid and solid oxidizers. 2004 ed. National Protection Association, 2004
(13) Odor thresholds for chemicals with established occupational health standards. American Industrial Hygiene Association, 1989. p. 15, 51
(14) Ruth, J.H. Odor thresholds and irritation levels of several chemical substances: a review. American Industrial Hygiene Association Journal. Vol. 47 (Mar. 1986). p. A-142 to A-144
(15) Amoore, J.E., et al. Odor as an aid to chemical safety : odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology. Vol. 3, no. 6 (1983). p. 272-275
(16) Kaczur, J.J., et al. Chlorine oxygen acids and salts, chlorous acid, chlorites, and chlorine dioxide: chlorine dioxide. Kirk-Othmer encyclopedia of chemical technology. John Wiley and Sons, 1993. Available at: <www.mrw.interscience.wiley.com/kirk/kirk_search_fs.html> (Subscription required)
(17) Ishidate, M., et al. Primary mutagenicity screening of food additives currently used in Japan. Food Chemistry and Toxicology. Vol. 22, no. 8 (1983). p. 623-636
(18) Dean, J.A. Lange's handbook of chemistry. 15th ed. McGraw-Hill, Inc., 1999. p. 3.25, 5.32
(19) Chlorine dioxide. In: NIOSH pocket guide to chemical hazards. National Institute for Occupational Safety and Health, June 1997. p. 58-59
(20) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002, p. 98
(21) European Communities (EC). Commission Directive 2004/73/EC. Apr. 29, 2004
(22) Meggs, W.J., et al. Nasal pathology and utrastructure in patients with chronic airway inflammation (RADS and RUDS) following an irritant exposure. Clinical Toxicology. Vol. 34, no. 4 (1996). p. 383-396
(23) Petry, H. Chlorine dioxide: a hazardous irritant gas. (English Translation; HSE Translation No. 15844A). Archiv fur Gewerbepathologie und Gewerbehygiene. Vol. 13 (1954). p. 363-369
(24) Andersson, E., et al. Adult-onset asthma and wheeze among irritant-exposed bleachery workers. American Journal of Industrial Medicine. Vol. 43, no. 5 (2003). p. 523-538
(25) Kennedy, S.M., et al. Lung health consequences of reported accidental chlorine gas exposures among pulp mill workers. American Review of Respiratory Diseases. Vol. 143 (1991). p. 74-79
(26) Ferris, B.G., et al. Prevalence of chronic respiratory disease in a pulp and paper mill in the United States. British Journal of Industrial Medicine. Vol. 24, no. 1 (1967). p. 26-37
(27) Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for chlorine dioxide and chlorite. Draft for Public Comment. US Department of Health and Human Services, 2003
(28) Toxicological review of chlorine dioxide and chlorite (CAS Nos. 10049-04-4 and 7758-19-2). In support of summary information on the Integrated Risk Information System (IRIS). EPA/635/R-00-007. US Environmental Protection Agency, 2000
(29) Syracuse Research Corporation. Interactive LogKow (KowWin) Database Demo. Date unknown. Available at: <syrres.com/esc/kowdemo.htm>
(30) McHale, E.T. et al. The explosive decomposition of chlorine dioxide. Journal of Physical Chemistry. Vol. 72, no. 6 (June 145, 1968). p. 1849-1856
(31) Masschelein, W. J., et al. Chlorine dioxide: chemistry and environmental impact of oxychlorine compounds. Ann Arbor Science Publishers, Inc., 1979. p. 1-34
(32) Stanley Associates Engineering Ltd. Chlorine dioxide study: final report . Alberta Environment, Sept. 1985
(33) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 491
(34) Stedman, R.F. Exploding ClO2. Letter. Chemical and Engineering News. Vol. 29, no. 44 (1951). p. 5030
(35) Pruett, K.M. Chemical resistance guide for plastics: a guide to chemical resistance of engineering thermoplastics, fluoroplastics, fibers and thermoset resins. Compass Publications, 2000. p. 98-109
(36) Gates, D.J. The chlorine dioxide handbook. Water disinfection series; v. 2. American Water Works Association, 1998. p. 8
(37) Occupational Safety and Health Administration (OSHA). Chlorine Dioxide in Workplace Atmospheres. In: OSHA Analytical Methods Manual. Revision Date: Oct. 31, 2001. Available at: <www.osha-slc.gov/dts/sltc/methods/toc.html>

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.


Review/Preparation Date: 2005-03-29



©2007 Canadian  Centre  for  Occupational  Health  &  Safety  
www.ccohs.ca  E-mail: clientservices@ccohs.ca  Fax: (905) 572-2206  Phone: (905) 572-2981  
Mail:  250  Main  Street  East,  Hamilton  Ontario  L8N  1H6