Hazardous substance assessment: Sodium hypochlorite (in liquid solutions)

Identification

Chemical name:

Sodium hypochlorite

CAS #:

7681-52-9

Chemical composition:

NaOCl

Synonyms:

Hypochlorous acid, sodium salt
Hypochlorite sodium
Household bleach
Sodium oxychloride

UN #:

UN 1791

Pictogram(s):

Figure 1. - Text Equivalent

The symbol within the pictogram is an exclamation mark. This symbol indicates that hazardous products with this pictogram can cause certain health effects for example:

• skin irritation
• eye irritation
• skin sensitization

Figure 2. - Text Equivalent

The symbol within the pictogram, which applies only to 5% or above aqueous solutions of sodium hypochlorite, shows a container dripping liquid onto a piece of metal and another container dripping liquid onto a hand. This symbol indicates that hazardous products with this pictogram can:

• damage or destroy metal
• cause irreversible damage to the skin (for example, burns, blisters, scarring)
• produce tissue damage in the eye or vision loss that is irreversible or not fully reversible within 21 days

WHMIS classification

Health hazards:

• Acute Toxicity (Oral) – Category 4
• Skin Irritation – Category 2 (for 2% or above aqueous solutions)
• Serious Eye Damage – Category 1 (for a 5% or above aqueous solution); Eye Irritation – Category 2A (for an aqueous solution at or above 3.6% but less than 5%)

Physical hazards:

Solutions of sodium hypochlorite do not meet the criteria for classification.

Health hazards

Acute Toxicity (Oral):

Category 4

Oral median lethal dose (LD₅₀): 654 milligrams of available chlorine per kilogram of body weight (mg/kg-bw) (rat) ^{Footnote 1}.

A study equivalent or similar in design to the Organisation for Economic Co-operation and Development (OECD) Test Guideline 401 (Acute Oral Toxicity) was conducted in male Wistar rats (10 per dose) gavaged once with an aqueous solution of sodium hypochlorite (12.5% available chlorine) at a dose of 5.01, 7.94, 8.64, 9.3 or 10.0 grams of solution per kilogram of body weight (g/kg-bw). Clinical signs of ungroomed fur, light to moderate sedation, diarrhea, ataxia, and increased breathing of differing severity were reported at varying degrees depending on the dose. As the LD₅₀ of the 12.5% solution was 8.83 g/kg-bw, the LD₅₀ of sodium hypochlorite was 1 100 mg/kg-bw of available chlorine ^{Footnote 1}. The LD₅₀ of this study meets the classification criteria for Acute Toxicity (Oral) – Category 4.

Another study similar in design to OECD TG 401 conducted in male albino rats (5 per dose) administered "undiluted" sodium hypochlorite at a dose of 4.64, 6.81, 10.00 or 14.70 g/kg-bw (method of oral administration presumed to be gavage) reported an LD₅₀ of 8 910 mg/kg-bw. Clinical signs of hypoactivity, muscular weakness, haemorrhagic rhinitis and emaciation were reported at all doses tested and no gross pathological effects were reported ^{Footnote 1}. The study summary noted the sodium hypochlorite administered to be "undiluted"; however, as pure sodium hypochlorite is an unstable solid, it is more likely an aqueous solution, of unspecified concentration, had been administered.

Another study similar in design to OECD TG 401 conducted in Sprague-Dawley rats (5 per sex and dose) gavaged once with an aqueous solution of sodium hypochlorite (12.5% available chlorine) at a dose of solution of 3.5, 4.66, 6.20, 8.26 or 11.0 g/kg-bw reported an LD₅₀ of solution of 5.23 g/kg-bw based on combined-sex mortality rates. The principal clinical signs observed were decreased activity, ataxia, urinary incontinence, bloody nasal discharge, diarrhea, rales, salivation and chromodacryorrhea. The main necropsy findings were discolouration of the lungs, liver, spleen and kidneys, vascularization of the stomach and pylorus, distention of the intestines and presence of a dark substance in the cecum ^{Footnote 1}. As the LD₅₀ of the 12.5% solution was 5.23 g/kg-bw, the LD₅₀ of sodium hypochlorite was 654 mg/kg-bw of available chlorine. The LD₅₀ of this study meets the classification criteria for Acute Toxicity (Oral) – Category 4.

A non-guideline study in male albino mice (9 or 10 per dose) with limited study information provided reported an oral LD₅₀ for sodium hypochlorite of 880 mg/kg-bw ^{Footnote 1}.

The available data meet the classification criteria for Acute Toxicity (Oral) – Category 4 [subsection 8.1.1(1) of the HPR].

Acute Toxicity (Dermal):

Does not meet criteria

Dermal LD₅₀: >2 500 mg/kg-bw (rabbit) ^{Footnote 1}.

A study similar in design to OECD TG 402 (Acute Dermal Toxicity) was conducted in male and female albino rabbits (4 per sex and dose) exposed to a 12.5% aqueous solution of sodium hypochlorite at a dose of 7.5, 10.4, 14.42 or 20.0 g/kg-bw of solution. No mortality was reported with an LD₅₀ of the solution greater than 20 000 mg/kg-bw (or greater than 2 500 mg/kg-bw of available chlorine). Decreased activity, very red and very swollen backs, nasal discharge, soft stools, ataxia, mouth sores, bloody saliva and urinary incontinence were observed at the lowest dose and above. Gross pathological findings included pale lungs, kidneys and intestines, dark and mottled liver, dark and granular spleen, full bladder and stomach, and bloody liquid in the chest cavity ^{Footnote 1}.

Acute dermal toxicity in rats was reported to be greater than 2 000 mg/kg bw of a 5.25 % available chlorine solution (or greater than 105 mg/kg-bw of available chlorine). No further details of the study are available ^{Footnote 2}.

The available data do not meet the classification criteria for a category of Acute Toxicity (Dermal).

Acute Toxicity (Inhalation – Gases):

Not applicable

While aqueous solutions of sodium hypochlorite can react with some other substances to generate chlorine gas, they are not gases themselves. The classification criteria for Acute Toxicity (Inhalation – Gases) do not apply to aqueous solutions of sodium hypochlorite.

Acute Toxicity (Inhalation – Vapours):

Not applicable

A study equivalent or similar in design to OECD TG 403 (Acute Inhalation Toxicity) was conducted in male albino rats (n=6) exposed to a concentration of 10.5 milligrams per litre (mg/L) of sodium hypochlorite, identified to be in vapour, for 1 hour. No mortality was observed. Clinical signs of inactivity and lacrimation were observed. There were no significant gross pathological findings. The median lethal concentration (LC₅₀) was greater than 10.5 mg/L for a 1-hour exposure, which converts to an LC₅₀ greater than 5.25 mg/L for a 4-hour exposure ^{Footnote 1}.

The study is considered to have limited relevance to the classification evaluation. The vehicle of administration is not provided. Although sodium hypochlorite can react to produce chlorine gas in the presence of some substances, it is not volatile itself. Inhalation exposure to sodium hypochlorite in aqueous solution can only occur via aerosols.

Acute Toxicity (Inhalation – Dusts and Mists):

No data available

No data are available to determine whether sodium hypochlorite in aqueous solutions meets the classification criteria for a category of Acute Toxicity (Inhalation – Dusts and Mists).

Skin Corrosion / Irritation:

Category 2 (for 2% or above aqueous solutions)

Humans: Exposure to a sodium hypochlorite solution at a concentration of 5 to 5.25% of available chlorine (pH of 10.7) was found to be severely irritating to intact human skin in 4 of 7 test subjects, including weeping and eschar formation on the application site, after a 4-hour exposure under occluded patch conditions. Application of a 2% sodium hypochlorite solution in a 48-hour patch test was found to cause weak to moderate irritation in 15 out of 69 dermatitis patients; in 20 of these patients, further testing of 1% and 0.5% solutions did not result in irritation ^{Footnote 2}.

Animals: A study similar in design to OECD TG 404 (Acute Dermal Irritation/Corrosion) was conducted in albino rabbits (n=6) exposed to 0.5 millilitre (mL) of a 12.5% solution of sodium hypochlorite for 24 hours under semi-occlusive conditions. Mean scores across the exposed animals over 24- and 72-hours post-exposure for exposure via intact skin were 2.16 out of 4 for erythema and 1.04 out of 4 for edema. Mean scores across the exposed animals over 24- and 72-hours post-exposure for exposure via abraded skin were 3.63 out of 4 for erythema and 1.13 out of 4 for edema. Exposure to a 12.5% solution of sodium hypochlorite was irritating to the rabbits' skin ^{Footnote 1}. Although mean scores per animal were not reported nor was scoring conducted at 48 hours post-exposure, the erythema result for abraded skin is considered to meet classification criteria for Skin Irritation – Category 2.

An OECD TG 404-compliant study was conducted in albino rabbits and Hartley guinea pigs (6 per species) exposed to a 5.0 to 5.25 % by weight solution of sodium hypochlorite for 4 hours under semi-occlusive conditions. The sum of mean erythema and edema scores, that were scored on a scale of 0 to 4, over 4-, 24- and 48-hours post-exposure across the exposed rabbits were 1.0 and 1.3 for exposure via intact and abraded skin, respectively; the mean primary irritation index was 1.2 out of 8. The sum of mean erythema and edema scores, also scored on a scale of 0 to 4, over 4-, 24- and 48-hours post-exposure across the exposed guinea pigs were 0.3 and 1.2 for exposure via intact and abraded skin, respectively; the mean primary irritation index was 0.8 out of 8. The mean scores for erythema and edema were not provided nor were mean scores per animal provided. All effects observed were fully reversible (times for reversibility within the 1-month observation period were not provided) ^{Footnote 1}. The results of the study do not meet classification criteria.

A non-guideline study in rabbits with no study details available, reported that exposure to sodium hypochlorite was severely irritating at a concentration of available chlorine of 6.4%, as irritating at 3.2% and as slightly irritating at 1.6%. No other information was available. A couple of other studies with limited information also reported that solutions of 4.74% or 5.25% of sodium hypochlorite were not irritating in rabbits ^{Footnote 1}. Due to the limited information, these studies were not used to determine a classification.

The available data meet the classification criteria for Skin Irritation – Category 2 for solutions of sodium hypochlorite at a concentration of 2% or higher [subsection 8.2.2(3) of the HPR].

Serious Eye Damage / Eye Irritation:

Category 1 (for a 5% or above aqueous solution); Category 2A (for an aqueous solution at or above 3.6% but less than 5%)

Humans: An accidental exposure to the eye of 1 female patient with a commercial sodium hypochlorite solution (0.5% sodium hypochlorite) caused burning discomfort and slight superficial disturbance of the corneal epithelium (the eye was washed for several minutes after the exposure). The effects cleared completely within 2 days without additional treatment ^{Footnote 1}. In 2 other cases where Clorox (containing 5.25% sodium hypochlorite) was accidentally splashed into the eyes, a burning sensation and slight damage to the cornea was reported. Rinsing of the eyes with water led to complete recovery within 48 hours ^{Footnote 3}.

Animals: A study similar in design to OECD TG 405 (Acute Eye Irritation/Corrosion) was conducted in New Zealand White rabbits (3 animals with eye wash, 6 animals without eye wash) exposed ocularly to 0.1 gram (g) of undiluted sodium hypochlorite (specific concentration was not clear). In the unwashed group, mean scores over 24-, 48- and 72-hours post-instillation across the 6 animals exposed were 0.83 out of 4 for corneal opacity, 0.94 out of 2 for iritis, 3 out of 3 for conjunctival redness and 3.72 out of 4 for chemosis. The corneal and iridial effects were observed in 5 of the 6 animals, while the conjunctival effects were observed in all 6 animals. Effects were not fully reversible within 7 days. In the group of washed animals, mean scores over 24-, 48- and 72-hours post-instillation across the 3 animals exposed were 0 out of 4 for corneal opacity, 0.11 out of 2 for iritis, 3 out of 3 for conjunctival redness and 2.77 out of 4 for chemosis. The iridial effects were observed in 1 of the 3 animals, while conjunctival effects were observed in all 3 animals. The iridial effects were fully reversible within 48 hours but the other effects were not reversible within 7 days. While reversibility information past 7 days was not provided, the available data meet classification criteria for at least Eye Irritation - Category 2A ^{Footnote 1}.

A Draize study in rabbits exposed ocularly to a 5% solution of sodium hypochlorite demonstrated slight to moderate eye irritation scored at 24-, 48- and 72-hours post-instillation in groups of animals with and without an eye wash. In the rinsed group, effects were reversible by day 14 post-instillation. However, in the unrinsed group, pronounced injury to the cornea and conjunctiva was reported and the effects had not fully reversed by day 21 post-instillation. No scores or additional details were available ^{Footnote 3}. Since effects were not fully reversible within 21 days, the results meet classification criteria for Serious Eye Damage – Category 1.

Another Draize study was conducted in rabbits exposed ocularly to a 12.5% commercial solution of sodium hypochlorite or to dilutions thereof (1.85, 3.6, or 6.25%). Animals exposed to a sodium hypochlorite concentration of 12.5% or 6.25% experienced severe eye irritation, with Draize maximum average scores (MAS) of 60 and 49 out of 110, respectively. Complete recovery was observed only by week 10 post-instillation for the 12.5% solution and by week 4 for the 6.25% solution. Exposure to the 3.6% solution was moderately irritating, with a Draize MAS of 11 out of 110, and complete reversal of effects was observed by day 15 post-instillation. Exposure to the 1.85% solution was slightly irritating, with a Draize MAS of 1 out of 110, and complete reversal of effects was observed by day 4 post-instillation ^{Footnote 3}. For sodium hypochlorite concentrations of 6.25% and higher, since effects were not fully reversible within 21 days, the results meet classification criteria for Serious Eye Damage - Category 1. At a sodium hypochlorite concentration of 3.6%, the results meet classification criteria for Eye Irritation - Category 2A since effects were reversible by day 21 post-instillation (but not by day 7). At a sodium hypochlorite concentration of 1.85%, the results did not meet classification criteria for a category or subcategory of this hazard class.

A number of other in vivo studies in rabbits and in vitro studies are available that indicate that exposure to sodium hypochlorite is irritating to the eye; however, most are non-guideline studies with limited study details available to inform classification.

The available data meet the classification criteria for Serious Eye Damage – Category 1 [subsection 8.3.2(1) of the HPR] at exposure concentrations of 5% or higher and for Eye Irritation – Category 2A [subsection 8.3.2(3) of the HPR] at exposure concentrations less than 5% but at or above 3.6%.

Respiratory Sensitization:

No data available

No data are available to determine whether solutions of sodium hypochlorite meet the classification criteria for a category or subcategory of Respiratory Sensitization.

Skin Sensitization:

Does not meet criteria

Humans: A human patch test study in a group of 40 individuals reported 2 of these individuals as experiencing a positive skin reaction following exposure to a 1% sodium hypochlorite solution. No other study details were available ^{Footnote 1}. The results do not meet classification criteria. A patch test study in 50 volunteers exposed to a 1% sodium hypochlorite solution reported no signs of sensitization in the volunteers ^{Footnote 1}. However, 2 cases of dermatitis in the hands from occupational exposure to sodium hypochlorite, with positive patch test reactions for sodium hypochlorite at concentrations of 0.1 to 2%, have been reported ^{Footnote 1}. A handful of other positive single-person patch test reactions have been reported; however, the test substance used in most of these cases is a household cleaner for which exact composition information was not reported ^{Footnote 1}.

Repeated insult patch tests conducted on healthy human volunteers with sodium hypochlorite formulations have shown no evidence of development of allergic contact dermatitis. In tests performed with 0.034% and 0.076% sodium hypochlorite solutions on 86 and 90 volunteers respectively, 1 subject in the latter exposure group demonstrated some evidence of skin sensitization, which may have been attributable to another test substance patched at a nearby site ^{Footnote 2}.

Animals: A study similar in design to OECD TG 406 (Skin Sensitisation) was conducted in Dunkin-Hartley guinea pigs (10 exposed per sex) induced via 3 epicutaneous applications of an undiluted test material containing sodium hypochlorite at an unspecified concentration under occlusive conditions. The animals were subsequently challenged with a solution containing a 40% by volume dilution of the test material in distilled water. Of the 20 animals exposed, 0 demonstrated positive reactions at 24 and 48 hours following challenge. The test substance was considered to be non-sensitizing to the skin ^{Footnote 1}.

A couple of other studies similar in design to OECD TG 406 (Skin Sensitisation) were conducted in guinea pigs (10 exposed per sex) induced and challenged with a 25% or a 50% dilution of a sodium hypochlorite-containing test material in water. Of the 20 animals exposed in each study, 0 demonstrated positive reactions at 24 and 48 hours following challenge. The test substance was considered not sensitizing to the skin ^{Footnote 1}.

The available data do not meet the classification criteria for a category or subcategory of Skin Sensitization.

Germ Cell Mutagenicity:

Does not meet criteria

In vivo:

A study similar in design to OECD TG 474 (Mammalian Erythrocyte Micronucleus Test) conducted in male ddY mice (6 per dose) injected intraperitoneally with a single dose of up to 2 500 mg/kg-bw of sodium hypochlorite (from a 6.6% solution) in saline solution, or with 4 doses of 300 mg/kg-bw each spaced over 24-hour intervals, provided negative results for genotoxicity ^{Footnote 1}.

A non-guideline DNA damage assay was conducted in male Fischer 344 rats gavaged once with 900 mg/kg-bw of sodium hypochlorite (vehicle unspecified). Negative genotoxic effects were reported up to 48 hours post-administration, as no significant increase in 8-hydroxydeoxyguanosine levels in the liver and kidneys was observed ^{Footnote 1}.

A non-guideline in vivo mouse sperm head abnormality assay conducted in male B6C3F₁ mice (10 per dose) gavaged once per day with a dose of 0, 1.6, 4 or 8 mg/kg-bw of sodium hypochlorite in distilled water for 5 days reported ambiguous results for genotoxicity. Observations of increased sperm-head abnormalities at 3 weeks following treatment (at all 3 treatment doses tested), but not at 1 or 5 weeks, suggested that the abnormalities may be specific to late primary spermatocytes. The increases observed were small, demonstrated a shallow dose-response relationship, were only slightly outside the historical control range and were subject to significant inter-reader variability ^{Footnote 1}. In light of these considerations, the study was not used for classification.

A study similar in design to OECD TG 474 in CD-1 mice (5 per sex and dose) gavaged once per day with a dose of 0, 1.6, 4.0 or 8.0 mg/kg-bw of available chlorine on 5 consecutive days reported negative clastogenic activity, with no significant increase in the number of micronucleated erythrocytes observed in the bone marrow ^{Footnote 1}.

A study similar in design to OECD TG 475 (Mammalian Bone Marrow Chromosomal Aberration Test) conducted in CD-1 mice (4 per sex and dose) gavaged with a dose of 0, 1.6, 4.0 or 8.0 mg/kg-bw of available chlorine in distilled water, either once or 5 times over 24-hour intervals, reported negative clastogenic activity, with no increase in the number of chromosomal aberrations observed in the bone marrow ^{Footnote 1}.

In vitro:

A study similar in design to OECD TG 471 (Bacterial Reverse Mutation Test) in S. typhimurium strains TA 100 and TA 98 was positive with S9-mix metabolic activation in TA 100, negative with activation in TA 98 and negative without activation in both strains ^{Footnote 1}. A study similar in design to OECD TG 471 in S. typhimurium strains TA 98, TA 100 and TA 102 was negative without metabolic activation ^{Footnote 1}. A non-guideline bacterial reverse mutation assay in S. typhimurium strains TA 97 and TA 102 was negative with and without S9-mix metabolic activation ^{Footnote 1}. In contrast, a non-guideline bacterial reverse mutation assay in S. typhimurium strains TA 98, TA 100 and TA 1537 was positive with metabolic activation ^{Footnote 1}.

A study similar in design to OECD TG 473 (In Vitro Mammalian Chromosomal Aberration Test) in Chinese hamster lung cells showed some positive results at 48 hours but negative results at 24 hours with and without metabolic activation. Test results were equivocal ^{Footnote 1}. Another study similar in design to OECD TG 473 in Chinese hamster lung cells indicated weak clastogenicity with S9-mix metabolic activation at the concentration of sodium hypochlorite tested and provided no result without activation due to the cytotoxicity observed ^{Footnote 1}. Another study similar in design to OECD TG 473 in human HE2144 fibroblasts exposed without metabolic activation to 2 concentrations of sodium hypochlorite reported an increased number of sister chromatid exchanges per cell at both test concentrations, slightly exceeding the target threshold response above controls only at the high concentration. Given the minimal exceedance and the lack of chromosomal breakages and micronuclei formation, the clastogenicity result was considered ambiguous ^{Footnote 1}.

Several additional genotoxicity studies in bacteria and in vitro mammalian chromosomal aberration tests are available with conflicting positive and negative results depending on bacterial strains used, concentrations of sodium hypochlorite tested, or presence or absence of metabolic activation. In many cases, cytotoxicity at the concentrations tested may have been excessive ^{Footnote 1}.

Despite some positive genotoxicity results in in vitro studies, possibly associated with excessive cytotoxicity, the classification criteria for a category or subcategory of Germ Cell Mutagenicity are not considered to be met in consideration of the negative results in in vivo studies.

Carcinogenicity:

Does not meet criteria

Sodium hypochlorite has not been reviewed by the National Toxicology Program (NTP) nor the American Conference of Governmental Industrial Hygienists (ACGIH). The International Agency for Research on Cancer (IARC) assessed hypochlorite salts, including sodium hypochlorite, and classified them as Group 3 (not classifiable as to their carcinogenicity to humans) based on inadequate evidence of carcinogenicity in experimental animals and a lack of data on carcinogenicity in human studies ^{Footnote 4}.

A study similar in design to OECD TG 453 (Combined Chronic Toxicity/Carcinogenicity Studies) was conducted in Fischer 344 rats (50 per sex and dose) exposed daily to sodium hypochlorite in drinking water at a concentration of 0, 0.05 or 0.1% (males) or of 0, 0.1 or 0.2% (females) for 104 weeks. The corresponding nominal doses of sodium hypochlorite were 0, 25 and 50 milligrams per kilogram of body weight per day (mg/kg-bw/day) in males and 0, 57.2 and 114.4 mg/kg-bw/day in females. Body weight was reduced in males and females in a dose-dependent manner, reaching statistical significance at a dose of 114.4 mg/kg-bw/day in females. There were no treatment-related increases in non-neoplastic lesions or in the incidences of tumours ^{Footnote 1}. Another study similar in design to OECD TG 453 conducted in Fischer 344 rats and in B6C3F₁ mice (70 per sex, dose and species) exposed daily to sodium hypochlorite in drinking water for 103 to 104 weeks at doses of available atomic chlorine up to 13.75 and 15.7 mg/kg-bw/day for male and female rats, respectively, and up to 45.8 and 55 mg/kg-bw/day in male and female mice, respectively, also reported no evidence of treatment-related carcinogenicity ^{Footnote 1}.

A study similar in design to OECD TG 451 (Carcinogenicity Studies) was conducted in Fischer 344 rats and B6C3F₁ mice (50 per sex, dose and species) exposed to sodium hypochlorite in drinking water for 104 and 103 weeks, respectively. The nominal dose to which animals were exposed was 25 or 50 mg/kg-bw/day for male rats, 57.1 or 114.3 mg/kg-bw/day for female rats, 83.3 or 166.7 mg/kg-bw/day for male mice or 100 or 200 mg/kg-bw/day for female mice. No evidence of carcinogenicity was observed ^{Footnote 1}. A OECD TG 451-compliant study conducted in Sprague-Dawley rats (50 per sex and dose) exposed to sodium hypochlorite in drinking water for 104 weeks at an active chlorine dose of up to 37.5 or 42.9 mg/kg-bw/day in male and females, respectively, reported some increased incidences of lymphomas and leukemias and tumours of the stomach and the lungs; however, the effects were not clearly dose dependent and the authors concluded that the study results were ambiguous ^{Footnote 1}.

A non-guideline study in which a commercial solution of sodium hypochlorite at an effective chlorine concentration exceeding 10% was applied 60 times to the skin of female ddN mice over a period of 300 days reported no skin tumours or leukemia ^{Footnote 1}. Another non-guideline study in female Sencar mice exposed dermally to 0.2 mL of a 1% solution of sodium hypochlorite 2 times per week for 51 weeks also reported no skin tumours nor epidermal hyperplasia ^{Footnote 1}. A third non-guideline study in female NMRI mice exposed dermally to a 1% sodium hypochlorite solution 2 times per week for 10 weeks, with a post-exposure observation until week 124, also reported no evidence of carcinogenicity ^{Footnote 1}.

The available data do not meet the classification criteria for a category or subcategory of Carcinogenicity.

Reproductive Toxicity:

Does not meet criteria

A study similar in design to OECD TG 414 (Prenatal Developmental Toxicity Study) was conducted in female Sprague-Dawley rats (6 per dose) exposed to hypochlorite, from hypochlorous acid, in drinking water at a dose of available chlorine of 0, 0.057, 0.57 or 5.7 mg/kg-bw/day for 2.5 months prior to and throughout gestation. Maternal toxicity was not evaluated in the study. There were no treatment-related changes in viability, fetal weights nor external appearance for fetuses in all dose groups. The frequencies of skeletal and soft-tissue defects were in the normal range for all dose groups ^{Footnote 1}.

The available data do not meet the classification criteria for a category or subcategory of Reproductive Toxicity.

Specific Target Organ Toxicity – Single Exposure:

Does not meet criteria

Oral Route of Exposure:

Humans:

A case of stomach constriction due to scarring and fibrosis after a suicidal ingestion of Clorox (5.25 % of sodium hypochlorite; pH of 10.8) was reported ^{Footnote 1}.

A case study in children reported caustic esophageal burns and esophageal strictures after accidental chlorine bleach ingestion in 80 children due to the irritating and corrosive potential of sodium hypochlorite ^{Footnote 1}.

A review of 27 cases of accidental ingestion of sodium hypochlorite reported that it did not cause severe damage in any of the 27 patients involved. Vomiting and visible reddening in the mouth and throat were observed in a few cases, while a single case, where contrast radiography had been performed, revealed superficial burns in the esophagus ^{Footnote 1}. Another study reviewed 129 cases of Clorox ingestion for the period of 1954 to 1962 at the Children´s Hospital of Washington, DC. Only 2 cases showed any evidence of mild esophageal injury ^{Footnote 1}.

A 66-year-old woman reportedly died of cardiac arrest 4.5 hours after ingesting an unknown quantity of bleach. The autopsy revealed oesophageal and gastric mucosal erosions, perforations at the gastro-oesophageal junction and extensive necrosis of adjacent soft tissue ^{Footnote 2}. In consideration of the severity of the gastrointestinal effects, the cardiac arrest may have been a secondary effect.

Although the gastrointestinal effects were not invariably lethal, the deaths observed may be attributable to alkaline corrosion of the gastrointestinal tract. As sodium hypochlorite meets the classification criteria of Acute Toxicity (Oral) - Category 4, further classification of these acute effects is superfluous.

Animals:

A study similar in design to OECD TG Guideline 401 was conducted in male Wistar rats (10 per dose) gavaged once with an aqueous solution of sodium hypochlorite (12.5% available chlorine) at a dose of 5.01, 7.94, 8.64, 9.3 or 10.0 g/kg-bw. Clinical signs of ungroomed fur, light to moderate sedation, diarrhea, ataxia, and increased breathing of differing severity were reported at varying degrees depending on the dose. The LD₅₀ of sodium hypochlorite was 1 100 mg/kg-bw as available chlorine ^{Footnote 1}.

Another study similar in design to OECD TG 401 conducted in male albino rats (5 per dose) administered undiluted sodium hypochlorite at a dose of 4.64, 6.81, 10.00 or 14.70 g/kg-bw reported an LD₅₀ of 8 910 mg/kg-bw. Clinical signs of hypoactivity, muscular weakness, haemorrhagic rhinitis and emaciation were reported at all doses tested and no gross pathological effects were reported ^{Footnote 1}.

Dermal Route of Exposure: A study similar in design to OECD TG 402 was conducted in male and female albino rabbits (4 per sex and dose) exposed to a 12.5% aqueous solution of sodium hypochlorite at a dose of 7.5, 10.4, 14.42 or 20.0 g/kg-bw of solution. No mortality was reported with an LD₅₀ greater than 2 500 mg/kg-bw of available chlorine. Decreased activity, very red and very swollen backs, nasal discharge, soft stools, ataxia, mouth sores, bloody saliva and urinary incontinence were observed at the lowest dose and above. Gross pathological findings included pale lungs, kidneys and intestines, dark and mottled liver, dark and granular spleen, full bladder and stomach, and bloody liquid in the chest cavity ^{Footnote 1}.

Inhalation Route of Exposure: A study equivalent or similar in design to OECD TG 403 was conducted in male albino rats (n=6) exposed to a concentration of 10.5 mg/L of sodium hypochlorite, identified to be in vapour, for 1 hour. No mortality was observed. Clinical signs of inactivity and lacrimation were observed. There were no significant gross pathological findings. The LC₅₀, converted to a 4-hour exposure, is greater than 5.25 mg/L ^{Footnote 1}. The study is considered to have limited relevance for the classification evaluation.

The available data do not meet the classification criteria for a category of Specific Target Organ Toxicity – Single Exposure.

Specific Target Organ Toxicity – Repeated Exposure:

Does not meet criteria

Oral Route of Exposure: A study similar in design to OECD TG 453 was conducted in Fischer 344 rats (50 per sex and dose) exposed daily to sodium hypochlorite in drinking water for 104 weeks at a nominal dose of 0, 25 or 50 mg/kg-bw/day in males or of 0, 57.2 or 114.4 mg/kg-bw/day in females. Body weight was reduced in males and females in a dose-dependent manner, reaching statistical significance at a dose of 114.4 mg/kg-bw/day in females ^{Footnote 1}. This dose is outside the guidance values for a category of this hazard class.

An OECD TG 408-compliant (Repeated Dose 90-Day Oral Toxicity Study in Rodents) study was conducted in Sprague-Dawley rats (10 per sex and dose) exposed for 90 days to a chlorine solution in drinking water at a dose of available chlorine of 0, 2.1, 7.5, 12.8 or 16.7 mg/kg-bw/day for males or of 0, 3.5, 12.6, 19.5 or 24.9 mg/kg-bw/day for females. No treatment-related toxicity was reported ^{Footnote 1}.

An OECD TG 408-compliant study was conducted in B6C3F₁ mice (9 or 10 per sex and dose) exposed for 90 days to chlorine in drinking water at a dose of available chlorine of 0, 2.7, 5.1, 10.3, 19.8 or 34.4 mg/kg-bw/day for males or of 0, 2.8, 5.8, 11.7, 21.2 or 39.2 mg/kg-bw/day for females. Male mice in the 2 highest dose groups exhibited decreased body weight gain whereas in female mice of the 2 highest dose groups a dose-dependent decrease in drinking water consumption was observed. Furthermore, changes in red and white blood cell counts, haematocrit, and activities of some enzymes were observed, along with decreases in the absolute and relative weights of some organs. The effects observed were considered to be mild, not dose-related or secondary to nutritional deficiencies resulting from poor palatability of the drinking water ^{Footnote 1}.

Several other guideline-compliant repeated-dose oral studies in rodents have also reported no significant signs of toxicity at the doses tested ^{Footnote 1}.

Dermal Route of Exposure: No data available

Inhalation Route of Exposure: No data available

The available data do not meet the classification criteria for a category of Specific Target Organ Toxicity – Repeated Exposure.

Aspiration Hazard:

No data available

No human data are available and sodium hypochlorite is not a liquid hydrocarbon.

Biohazardous Infectious Materials:

Not applicable

Sodium hypochlorite is not a microorganism, protein, or nucleic acid.

Physical hazards

Explosives:

Not evaluated*

* Explosives are excluded from the HPAand its regulations. Explosives are regulated under the Explosives Act. For more information, visit Natural Resources Canada.

Flammable Gases:

Not applicable

Sodium hypochlorite is not a gas. The classification criteria for Flammable Gases do not apply to this substance.

Aerosols:

Not evaluated

Classification of a hazardous product in the Aerosols hazard class is product dependent.

Oxidizing Gases:

Not applicable

Sodium hypochlorite is not a gas. The classification criteria for Oxidizing Gases do not apply to this substance.

Gases Under Pressure:

Not applicable

Sodium hypochlorite is not a gas. The classification criteria for Gases Under Pressure do not apply to this substance.

Flammable Liquids:

Does not meet criteria

A guideline-compliant test that used the rapid equilibrium closed-cup method determined the flash point of sodium hypochlorite at a concentration of available chlorine of 24.3% to be greater than 111°C at standard atmospheric pressure ^{Footnote 1}.

The tested sodium hypochlorite solution does not have a flash point equal to or below 93°C and therefore does not meet the definition of a flammable liquid [section 7.6 of the HPR].

Flammable Solids:

Not applicable

Sodium hypochlorite as a solution is not a solid. The classification criteria for Flammable Solids do not apply to this substance.

Self-reactive Substances and Mixtures:

No data available

No data are available to determine whether solutions of sodium hypochlorite meet the classification criteria for a category of Self-reactive Substances and Mixtures.

Pyrophoric Liquids:

No data available

No data are available to determine whether solutions of sodium hypochlorite meet the classification criteria for a category of Pyrophoric Liquids.

Pyrophoric Solids:

Not applicable

Sodium hypochlorite as a solution is not a solid. The classification criteria for Pyrophoric Solids do not apply to this substance.

Self-heating Substances and Mixtures:

No data available

No data are available to determine whether solutions of sodium hypochlorite meet the classification criteria for a category of Self-heating Substances and Mixtures.

Substances and Mixtures Which, in Contact with Water, Emit Flammable Gases:

Excluded from classification

Sodium hypochlorite forms stable aqueous solutions. The solubility in water is 79.9 g of substance per 100 g of water at a temperature of 25°C^{Footnote 5}.

Sodium hypochlorite is accordingly excluded from classification in a category of this hazard class [paragraph 7.12.1(1)(c) of the HPR].

Oxidizing Liquids:

Does not meet classification criteria

In a test on oxidizing properties of liquids, the mean time for the pressure in a heated vessel to rise from 690 to 2 070 kilopascals above atmospheric pressure for powdered cellulose mixed in a 1:1 ratio by mass with an unspecified reference substance or with a sodium hypochlorite solution containing a concentration of available chlorine of 24% was 5 150 or 34 666 milliseconds, respectively.

As the mean pressure rise time for cellulose mixed with the sodium hypochlorite solution was longer than that when mixed with the reference substance, the sodium hypochlorite solution was not considered to be oxidizing^{Footnote 1}.

Oxidizing Solids:

Not applicable

Sodium hypochlorite as a solution is not a solid. The classification criteria for Oxidizing Solids do not apply to this substance.

Organic Peroxides:

Not applicable

Sodium hypochlorite is not an organic peroxide. The classification criteria for Organic Peroxides do not apply to this substance.

Corrosive to Metals:

No data available

No data are available to determine whether solutions of sodium hypochlorite meet the classification criteria for a category of Corrosive to Metals.

Combustible Dusts:

Not applicable

Sodium hypochlorite as a solution is not a solid. The classification criteria for Combustible Dusts do not apply to this substance.

Simple Asphyxiants:

Not applicable

Sodium hypochlorite is not a gas. The classification criteria for Simple Asphyxiants do not apply to this substance.

Chemicals Under Pressure:

Not evaluated

Classification of a hazardous product in the Chemicals Under Pressure hazard class is product dependent.

Regulatory and other information

Regulatory information:

Hazardous substance assessments are prepared by Health Canada as educational and information resources. Under the HPA, suppliers of hazardous products must, upon the sale or importation of a hazardous product, provide a safety data sheet and label that meet the requirements set out in the HPR.

Other information:

The information and classifications contained in these hazardous substance assessments are based on publicly available sources, such as peer-reviewed literature or reports by international bodies. New information, including proprietary information, could have an impact on the classification of substances or hazardous products containing them. It is the responsibility of the supplier to ensure the accuracy, sufficiency and reliability of their hazardous product classifications.

Last updated:

2025

Prepared by:

Workplace Hazardous Materials Bureau, Health Canada