Chlorine dioxide

Carcinogenicity

Description of key information

Chlorine dioxide  should not be considered as a substance with a carcinogenic potential.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

No data

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: No guideline or GLP compliance specified but the study is well conducted. No details on the animals conditions and the study is performed with water disinfected with chlorine dioxide.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Chlorine dioxide was administered orally at 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. Tumour incidence was observed at 30 experimental weeks.

GLP compliance:

not specified

Species:

mouse

Strain:

Sencar

Sex:

not specified

Details on test animals or test system and environmental conditions:

No data

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

No data

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No data

Duration of treatment / exposure:

2 weeks initiation with the test material (ClO2 by oral route) 3 times/week followed by 20 weeks of topical administration of TPA in acetone or acetone alone.

Frequency of treatment:

Initiation phase: 3 times a week
Promotion phase: 3 times a week

Post exposure period:

8 weeks (the animals were observed for skin tumor incidence at 30 experimental weeks).

Remarks:

Doses / Concentrations:
Total volume applied = 0.5 mL
Basis:

No. of animals per sex per dose:

34 animals for the initiation and promotion (the full assay), 14 animals only for the initiation step.

Control animals:

yes, concurrent vehicle

Details on study design:

No data

Positive control:

Positive control: 500mg/kg urethane

Observations and examinations performed and frequency:

No data

Sacrifice and pathology:

no data

Other examinations:

After the sacrifice of the animals, skin tumor incidence on the back of the mouse was determined

Statistics:

No data

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Details on results:

Pathology: The treatment with vehicle control (2% Emulphor) yielded 0.09/9 tumors per animal/animals with tumor. The positive control group (500 mg/kg urethane) had 0.9 tumors per animal. Chlorine dioxide treated water did not induce tumors on the back of the mice (see table 7.7/1).

Relevance of carcinogenic effects / potential:

Chlorine dioxide was not considered as an initiator.Therefore, chlorine dioxide should not be considered as a substance with a carcinogenic potential since it is not implicated in the first step of the carcinogenesis.

Table 7.7/1: Results of the Initiation/Promotion assay

Treatment	Promotion (TPA)	No. of animals with tumour, %	Total tumours	Tumours/animal
Nondisinfected water	Yes	5/13 (16)	5	0.16
	No	0/16 (0)	0	0.00
Negative control (2% Emulphor)	Yes	3/35 (0)	3	0.09
	No	0/37 (0)	0	0.00
Positive control (Urethane 500 mg/kg)	Yes	13/20 (65)	18	0.90
Water disinfected with Chlorine dioxide	Yes	4/34 (12)	5	0.15
	No	0/14 (0)	0	0.00

 

Conclusions:

Chlorine dioxide did not initiate tumors in the mice.

Executive summary:

In 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 experimental weeks.

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.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

No data

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: No guideline or GLP compliance specified but the study is well conducted. No details on the animals conditions and the study is performed with water disinfected with chlorine dioxide.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

The rat liver foci assay is a short-term bioassay which determine the ability of a substance to initiate γ-glutamyltranspeptidase (GGT) positive foci, an indicator of preneoplastic liver changes. This enzyme found in many tissues, the most notable one being the liver, is involved in the transfer in the transfer of amino-acids across the cellular membrane and in leukotrien metabolism. It is involved in glutathion metabolism by transferring the glutamyl moiety to variety of acceptor molecules.
Rats were hepatectomised on day 0 (2/3 partial hepatectomy), and treated 24 hours later by oral administration of the test and control materials (positive and negative). 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. All animals were sacrificed at day 70. Frozen liver sections were prepared for the histochemical detection and quantification of GGT-positive foci.

GLP compliance:

not specified

Species:

rat

Strain:

not specified

Sex:

not specified

Details on test animals or test system and environmental conditions:

no data

Route of administration:

oral: unspecified

Vehicle:

not specified

Details on exposure:

No data

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No data

Duration of treatment / exposure:

56 days

Frequency of treatment:

No data

Post exposure period:

14 days: all animals were sacrificed at day 70.

Remarks:

Doses / Concentrations:
no data
Basis:

No. of animals per sex per dose:

10 rats per group

Control animals:

yes, concurrent vehicle

Details on study design:

No data

Positive control:

Positive control: 50 mg/kg bw diethylnitrosamine (DENA)

Observations and examinations performed and frequency:

No data

Sacrifice and pathology:

Histopathology: frozen liver sections were prepared for the histochemical detection and quantitation of GGT foci.

Other examinations:

No data

Statistics:

No data

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

no effects observed

Details on results:

Histopathology: Chlorine dioxide did not initiate an incidence of GGT foci above that of the vehicle control group. The positive control diethylnitrosamine induced a high incidence of GGT foci, which indicated that the test was functioning properly (see table 7.7/1)

Relevance of carcinogenic effects / potential:

Chlorine dioxide was not considered as an initiator.Therefore, chlorine dioxide should not be considered as carcinogenic substance since it is not implicated in the first step of the carcinogenesis.

Table 7.7/1: Results of Carcinogenicity study

 

Sample	Number of animals	Mean ± SD no. of GGT-foci/cm^3
Nondisinfected water	9	21.0 ± 21.0
Negative control (2% Emulphor)	7	0.00
Positive control (DENA 50 mg/kg)	7	383 ± 97
Water disinfected with Chlorine dioxide	7	0.00

Conclusions:

Chlorine dioxide did not initiate an incidence of GGT foci in the rats.

Executive summary:

In a 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.

Concurrent 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) foci/cm³.

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 carcinogenic process.

Reference 3

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

No data

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: No guideline or GLP compliance specified but the study is well conducted. No details on the animals conditions and the study is performed with water disinfected with chlorine dioxide.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Chlorine dioxide was administered to male and female mice orally three times a week for 8 weeks. 16 weeks after the last administration, the lung was examined for the presence of Adenoma.

GLP compliance:

not specified

Species:

mouse

Strain:

Strain A

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: 6 week old
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum): no data
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
no data

IN-LIFE DATES: From: To: no data

Route of administration:

oral: unspecified

Vehicle:

other: water sample in 2% Emulphor

Details on exposure:

No data

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No data

Duration of treatment / exposure:

3 times a week for 8 weeks.

Frequency of treatment:

3 times a week.

Post exposure period:

16 weeks.

Remarks:

Doses / Concentrations:
Total volume applied = 0.25 mL, the sample are 2000- or 4000-X concentrate
Basis:

No. of animals per sex per dose:

20 animals per dose per sex.

Control animals:

yes, concurrent vehicle

Details on study design:

No data

Positive control:

Positive control: 10 mg urethane in a single dose by gavage.

Observations and examinations performed and frequency:

No data

Sacrifice and pathology:

GROSS PATHOLOGY: Yes: After lung perfusion, the adenomas were counted independently by 2 technicians
HISTOPATHOLOGY: Yes : histological confirmation was performed on 10% of the positive specimens.

Other examinations:

no data

Statistics:

No data

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

no effects observed

Details on results:

The body weight changes and the mortality data within the exposure groups and controls gave further indication that no-treatment-related effect was evident during the study.
See details for the lung adenoma results in Table 7.7/1.

Relevance of carcinogenic effects / potential:

Chlorine dioxide was not considered as an initiator.Therefore, chlorine dioxide is not considered as carcinogenic substance as it is not implicated in the first step of the carcinogenesis.

Table 7.7/1: Results of Carcinogenicity study

 

Sample	Female				Male
	2000 X concentrate		4000 X concentrate		2000 X concentrate		4000 X concentrate
	Animals with tumor	Tumors per animal	Animals with tumor	Tumors per animal	Animals with tumor	Tumors per animal	Animals with tumor	Tumors per animal
Nondisinfected water	5/20	0.30	5/19	0.32	1/20	0.05	2/29	0.11
Chlorine dioxide treated water	0/20	0.00	2/17	0.12	3/20	0.15	4/16	0.31
Negative control	1/20	0.05	-	-	1/19	0.05	-	-
Vehicle control (2% Emulphor)	1/20	0.05	-	-	2/15	0.13	-	-
Positive control (10 mg Urethane)	19/19	11.47	-	-	20/20	11.55	-	-

 

Conclusions:

Chlorine dioxide did not induce lung adenoma in the mice.

Executive summary:

In a 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.

Concurrent 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 with tumors.

Under the test conditions, lung adenoma was not observed in the mice dosed by chlorine dioxide via drinking water.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Harmonised classification:

The classification entered in the Annex VI to the CLP Regulation for Chlorine dioxide is not harmonised for the carcinogenicity category.

 

Self-classification:

No self-classification is proposed.

Additional information

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.