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EC number: 233-162-8
CAS number: 10049-04-4
Chlorine dioxide should not be considered as a substance with a carcinogenic potential.
of the Initiation/Promotion assay
No. of animals with tumour, %
Negative control (2% Emulphor)
Positive control (Urethane 500 mg/kg)
Water disinfected with Chlorine dioxide
a carcinogenicity study, Chlorine dioxide was administered to Sencar
mice in drinking water at dose levels of 0.5
mL three times a week for the first two weeks as part of the
“initiation” phase of the assay. Two weeks after the final initiating
dose, 1.0 µg of 12-tetradecanylphorbal-13-acetate (TPA, a known cancer
promoter) in 0.2 mL acetone was administered by topical application to
the dorsal skin of half of the experimental animals three times per week
for 20 weeks, whereas the remaining animals received acetone only (0.2
mL/mouse) for the same duration. This was part of the “promotion” phase
of the assay.
Tumor incidence was observed at 30
Concurrent vehicle (2% Emulphor) animals
were used as a negative control and 500 mg/kg urethane was used as a
positive control. The results obtained with these controls were
considered as acceptable. Indeed, the treatment with vehicle control (2%
Emulphor) yielded 0.09 tumor per animal, 9% of the animals presented
tumors. The positive control group (500 mg/kg urethane) gave 0.9 tumours
per animal, 65 % of the animals presented skin tumors.
Under the test conditions, skin tumours were
not observed in the mice dosed by chlorine dioxide via drinking water
followed by promoter skin administration. Therefore, Chlorine dioxide
should not be considered as an initiator in the carcinogenic process.
of Carcinogenicity study
Number of animals
Mean ± SD no. of GGT-foci/cm3
21.0 ± 21.0
Positive control (DENA 50 mg/kg)
383 ± 97
carcinogenicity study, Chlorine dioxide was administered to
hepatectomised rats (2/3 partial hepatectomy) by oral route. This is
part of the “initiation” phase of the assay. One week later (day 7), the
rats started to received 500 ppm sodium Phenobarbital (a known cancer
promoter) in their drinking water for a total of 56 days. This is part
of the “promotion” phase of the assay. All animals were sacrificed at
day 70. Then, frozen liver sections were prepared for the histochemical
detection and quantification of γ-glutamyltranspeptidase-positive foci,
which are an indicator of preneoplatic liver changes.
vehicle (2% Emulphor) animals were used as a negative control and 50
mg/kg Diethylnitrosamine (DENA) was used as a positive control. The
results obtained with these controls were considered as acceptable.
Indeed, the treatment with vehicle control (2% Emulphor) yielded 0.00
foci/cm3,whereas the positive control group gave 383 (+/- 97)
Under the test conditions, GGT foci in the
liver were not observed in the rats dosed by chlorine dioxide via
drinking water followed by the promoter administration. Therefore,
Chlorine dioxide should not be considered as an initiator in the
of Carcinogenicity study
2000 X concentrate
4000 X concentrate
Animals with tumor
Tumors per animal
Chlorine dioxide treated water
Vehicle control (2% Emulphor)
Positive control (10 mg Urethane)
carcinogenicity study, 0.25 mL of Chlorine dioxide water sample in 2%
Emulphor was administered to male and female mice by oral route 3 times
per week for 8 weeks at 2 concentrations: 2000 and 4000 X concentrate.
After a 16 week post-exposure period, animals were sacrificed and
examined for lung adenoma. 20 animals/dose/sex were used for this study.
vehicle (2% Emulphor) animals were used as a vehicle control and 10 mg
of urethane was used as a positive control. The results obtained with
these controls were considered as acceptable. Indeed, the treatment with
vehicle control (2% Emulphor) yielded 1 female/20 with tumors and 2
males/15 with tumors,whereas the positive control group gave all animals
Under the test conditions, lung adenoma was
not observed in the mice dosed by chlorine dioxide via drinking water.
The classification entered in the Annex VI to the CLP Regulation for Chlorine dioxide is not harmonised for the carcinogenicity category.
No self-classification is proposed.
There is no concern for carcinogenicity resulting from exposure to chlorine dioxide based on:
- the three studies used as a weight of evidence approach showing that the chlorine dioxide was not an initiator of the carcinogenesis and didn't induce lung adenoma. Therefore, chlorine dioxide is not implicated in the first step of the carcinogenesis.
- Chlorine dioxide has not a widespread dispersive use or there is no evidence of frequent or long-term human exposure and,
- the substance is not classified as mutagen, as chlorine dioxide has no mutagenic potential (see § 7.6).
Therefore, chlorine dioxide should not be considered as a substance with a carcinogenic potential.
Moreover, regarding the chlorine dioxide classification as corrosive and fatal by inhalation, the workers wear appropriate Protective Personal Equipments (mask and gloves) at the workplace. Hence, the workers are not exposed to the chlorine dioxide frequently or for a long period of time. Therefore, it is not deemed useful to perform a carcinogenicity study on the chlorine dioxide.
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