Registration Dossier

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Gene mutation (Bacterial reverse mutation assay / Ames test): negative with and without activation in S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2 (similar to OECD TG 471) (Shin Etsu, 1994).
Cytogenicity in mammalian cells: negative in Chinese hamster lung fibroblasts (similar to OECD TG 473) (Shin Etsu, 1995).
Mutagenicity in mammalian cells: negative in L5178Y mouse lymphoma cells (similar to OECD TG 476) (Litton Bionetics, 1978).

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1994-03-24 to 1994-04-11
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The restrictions were that duplicate plates were used, not triplicate, and 2-amino anthracene was the only control with metabolic activation. An authorised translation was available to the reviewer.
Qualifier:
according to
Guideline:
JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
yes
Remarks:
only duplicate plates; 2-AA only control +MA
Principles of method if other than guideline:
E coli Reverse mutation assay
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay
Target gene:
histidine operon (Salmonella strains); tryptophan operon (E. coli)
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2
Metabolic activation:
with and without
Metabolic activation system:
phenobarbital and 5,6-benzoflavone induced rat liver S9
Test concentrations with justification for top dose:
50 to 10000 µg/plate (range-finding);
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: acetone (dehydrated)
- Justification for choice of solvent/vehicle: insoluble in water
Untreated negative controls:
yes
Remarks:
sterility control
Negative solvent / vehicle controls:
yes
Remarks:
acetone
True negative controls:
no
Positive controls:
yes
Positive control substance:
furylfuramide
Remarks:
AF-2: TA98, TA 100 and E. coli WP2 uvrA without metabolic activation: 0.1 µg/plate (TA 98); 0.01 µg/plate (TA 100 and E. coli)
Untreated negative controls:
yes
Remarks:
sterility control
Negative solvent / vehicle controls:
yes
Remarks:
acetone
True negative controls:
no
Positive controls:
yes
Positive control substance:
sodium azide
Remarks:
NaN3: TA 1535 without metabolic activation: 0.5 µg/plate
Untreated negative controls:
yes
Remarks:
sterility control
Negative solvent / vehicle controls:
yes
Remarks:
acetone
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-methoxy-6-chloro-9(3-(2-chloroethyl)-aminopropylamino) acridine 1µg/plate
Remarks:
ICR-191: TA 1537 without metabolic activation
Untreated negative controls:
yes
Remarks:
sterility control
Negative solvent / vehicle controls:
yes
Remarks:
acetone
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-aminoanthracene: µg/plate: 0.5 (TA 98), 1 (TA 100), 2 (TA1535 and 1537) and 1 (E.coli)
Remarks:
2AA: all strains with metabolic activation
Details on test system and experimental conditions:
METHOD OF APPLICATION: preincubation

DURATION
- Preincubation period: 30 minutes
- Exposure duration: 48 hours

SELECTION AGENT (mutation assays): minimal agar

NUMBER OF REPLICATIONS: duplicate (triplicate for solvent controls); range-finding and main experiments evaluated.

DETERMINATION OF CYTOTOXICITY
- Method: other: condition of bacterial lawn; reduction in number of revertants

OTHER: ACTIVATION: S9 mix included glucose-6-phosphate, NADP and NADPH as cofactors, and 10% S9. 1.5 ml S9 mix was added to 0.3 ml of bacteria and 0.15 ml test substance -concentration of S9 was therefore approximately 7.5% during pre-incubation.
Evaluation criteria:
The test substance was judged positive if the number of revertants was more than twice the negative control, and the response was dose-dependent and reproducible.
Key result
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid

Table 1a Dose range finding test revertants per plate (mean of 2 plates)

Concentration µg/plate

TA 100

TA 1535

E. coli WP2 uvrA

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

0*

135

141

no

15

15

no

42

48

no

50

123

129

no

11

16

no

43

46

no

100

121

127

no

15

19

no

43

50

no

200

132

125

no

10

16

no

47

56

no

500

127

121

no

14

16

no

44

51

no

1000

118

117

no

13

19

no

47

53

no

2000

123

127

no

13

19

no

46

50

no

5000

129

108

no

9

19

no

39

49

no

10000

123

123

no

13

20

no

52

53

no

Positive control

539

1026

-

420

306

-

508

457

-

* Solvent control with acetone, mean of three plates

Table 1b Dose range finding test revertants per plate (mean of 2 plates)

Concentration µg/plate

TA 98

TA 1537

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

0*

27

31

no

11

19

no

50

26

29

no

8

18

no

100

28

31

no

8

16

no

200

27

33

no

10

19

no

500

33

27

no

6

19

no

1000

29

31

no

10

17

no

2000

24

32

no

11

13

no

5000

31

33

no

11

20

no

10000

32

32

no

9

12

no

Positive control

621

301

-

1581

203

-

* Solvent control with acetone, mean of three plates

Table 2a Main test revertants per plate (mean of 2 plates)

Concentration µg/plate

TA 100

TA 1535

E. coli WP2 uvrA

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

0*

128

133

no

16

17

no

46

52

no

313

122

128

no

14

11

no

50

46

no

625

129

129

no

13

12

no

43

48

no

1250

140

125

no

16

15

no

42

48

no

2500

124

121

no

11

13

no

38

49

no

5000

137

127

no

13

14

no

41

51

no

10000

144

133

no

13

16

no

40

50

no

Positive control

645

1042

-

445

273

-

547

492

-

* Solvent control with acetone, mean of three plates

Table 2b Main test revertants per plate (mean of 2 plates)

Concentration µg/plate

TA 98

TA 1537

-MA

+MA

Cytotoxic

-MA

+MA

Cytotoxic

0*

25

35

no

11

17

no

313

24

33

no

10

13

no

625

24

32

no

10

15

no

1250

26

31

no

12

14

no

2500

30

34

no

10

15

no

5000

22

40

no

10

10

no

10000

29

40

no

13

14

no

Positive control

627

318

-

1303

233

-

* Solvent control with acetone, mean of three plates

Conclusions:
Hexamethyldisiloxane has been tested according to a Japanese guideline that is similar to OECD 471 and under GLP, using the pre-incubation method. No evidence of test-substance induced increase in the number of revertants was observed in Salmonella typhimurium strains TA1535, TA1537, TA98, TA100 or E. coli WP2 uvrA, with or without metabolic activation, up a concentration exceeding current limit concentrations in either the dose finding test or the main assay. Appropriate solvent, positive and sterility controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test substance.
Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Remarks:
A certified translation from the original Japanese was reviewed.
Qualifier:
according to
Guideline:
other: Japan notification on partial revision of testing methods relating to new chemical substances nos 700, 1039 and 1014
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Species / strain / cell type:
mammalian cell line, other: CHL cells clone 11
Metabolic activation:
with and without
Metabolic activation system:
Phenobarbital, 5,6 benzoflavone induced rat liver S9
Test concentrations with justification for top dose:
31.25 to 125 µg/ml (without), 100 to 400 µg/ml (with metabolic activation)
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: 0.5% methylcellulose aqueous solution was used to prepare suspensions of the test substance. Suspensions were used within 2 hours of preparation.
- Justification for choice of solvent: none given in report
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
mitomycin C
Remarks:
without activation
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
Remarks:
with activation
Details on test system and experimental conditions:
METHOD OF APPLICATION: in suspension, added to medium

DURATION
- Exposure duration: 6 hours with activation, 24 and 28 hours without
- Expression time (cells in growth medium): 24 or 48 hours
- Fixation time (start of exposure up to fixation or harvest of cells): 24 or 48 hours

SPINDLE INHIBITOR (cytogenetic assays): colcemid added 2 hours before end of incubation period
STAIN (for cytogenetic assays): Giesma

NUMBER OF REPLICATIONS: duplicate cultures for each dose

NUMBER OF CELLS EVALUATED: 200

DETERMINATION OF CYTOTOXICITY
- Method: other: cell growth inhibition and cell division inhibition


OTHER EXAMINATIONS:
- Determination of polyploidy: yes
- Determination of endoreplication: yes
- Other: chromatid and chromosome structural aberrations (gap, break, exchange etc) were recorded. A gap was defined as a clear discontinuity, wider than one chromatid but narrower than two, accompanied by minimal misalignment of the chromatid.


Evaluation criteria:
A dose related, reproducible increase in the incidence of cells with any aberration including gaps was evaluated as positive if the increase was 10% or more. An increase of 5% or more was evaluated as suspect positive, and an incidence of lower than 5% was evaluated as negative.
Key result
Species / strain:
Chinese hamster lung fibroblasts (V79)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
100 µl/ml (without activation); 300 µg/ml (with activation)
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid

No treatment related increase in the percentage of cells with aberrations was observed with or without activation. No treatment-related polyploidy was observed.

Table 2: Results of chromosome analysis - without activation (% from total count from 2 cultures, 200 cells counted)

Treatment

Exposure time (h)

Concentration (µg/ml)

% polyploid cells

% cells with aberrations inc gaps

% cells with aberrations not inc gaps

Judgement

Solvent*

24

0

0

1

0.5

-

48

0

0

2

0.5

-

Test substance

24

31.25

0

0

0

-

62.5

0

1

1

-

125

1

1.5

1.5

-

48

31.25

0

0

0

-

62.5

0

1

1

-

125

0

1.5

1.5

-

Positive control

24

0.05

0

51.5

50.0

+++

48

0.05

67.0

65.0

+++

*0.5% methylcellulose

 

Table 3: Results of chromosome analysis - with activation, 6 h exposure (% from total count from 2 cultures, 200 cells counted)

Treatment

S9 mix

Concentration (µg/ml)

% polyploid cells

% cells with aberrations inc gaps

% cells with aberrations not inc gaps

Judgement

Solvent*

-

0

0.5

0

0

-

+

0

0.5

1

0.5

-

Test substance

_

100

0.5

2

1

-

200*

Toxic

-

400*

Toxic

-

+

100

1

0.5

0.5

-

200*

1

1

1

-

400*

0

2.5

1.5

-

Positive control

-

10

0.5

0.5

0.5

+++

+

10

0

28.5

28.5

+++

* precipitate

**0.5% methylcellulose

Conclusions:
Hexamethyldisiloxane has been tested under GLP in a valid Japanese guideline study according to a protocol that is similar to OECD TG 473. The test substance did not induce any chromosome aberrations with or without metabolic activation. There were no marked differences between replicate flasks. Expected results were obtained from vehicle and positive controls. It is concluded that the test substance is non-clastogenic (does not induce chromosome aberrations) in Chinese hamster lung cells under the conditions of the test.
Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The restrictions were that the test concentrations were not duplicated.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
Deviations:
yes
Remarks:
no duplicates
GLP compliance:
no
Type of assay:
mammalian cell gene mutation assay
Species / strain / cell type:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Metabolic activation system:
mouse liver S9
Test concentrations with justification for top dose:
0.0125, 0.025, 0.05, 0,1, 0.2 µl/ml
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: ethanol
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
ethylmethanesulphonate
Remarks:
without activation
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
N-dimethylnitrosamine
Remarks:
with activation
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium


DURATION
- Exposure duration: 4 hours
- Expression time (cells in growth medium): 3 days
- Selection time (if incubation with a selection agent): 10 days

SELECTION AGENT (mutation assays): BUdR

NUMBER OF REPLICATIONS: no replicates

DETERMINATION OF CYTOTOXICITY
- Method: other: loss of growth potential
Evaluation criteria:
A substance is considered mutagenic if there is a dose response relationship over 3 dose levels; minimum increase at high level of dose response is at least times greater than the solvent control value; solvent control data are within normal range of spontaneous background mutation rates.
Statistics:
No statistical analysis was carried out.
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
at 0.2 µl/ml, equivalent to approximately 200 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
Preliminary cytotoxicity testing indicated toxicity at > 0.2 µl/ml
Several scattered increases were thought by the authors to be the result of spurious fluctuations and cytotoxicity.

Table 1 Summary of mouse lymphoma mutagenicity results

Test substance concentration µl/ml   Activation   Relative growth %    Mutant frequency x 10E-06
 Solvent control  -MA  100  23.7
 Negative control  -MA  87.7  17.2
 Positive control  -MA  20.3  515.5
 0.0125  -MA   86.8   18.5
 0.025  -MA  73.1  15.8
 0.05  -MA  92.3  22.3
 0.1  -MA  62.0  9.5
 0.2  -MA  29.5  28.1
 Solvent control  +MA  100  29.9
 Negative control  +MA  94.9  23.1
 Positive control  +MA  25.1  196.0
 0.0125  +MA  90.4  42.1
 0.025  +MA  68.4  26.3
 0.05  +MA  72.5  40.3
 0.1  +MA  90.4  21.1
 0.2  +MA  0.1  50.7
Conclusions:
Hexamethyldisiloxane has been tested for mutagenicity in L5178Y cells in a valid and reliable study according to a protocol that is similar to OECD TG 476. The test substance did not cause a biologically significant increase in the mutation frequency; solvent and positive controls gave expected results. It is concluded that the test substance is not mutagenic under the conditions of the test.
Endpoint conclusion
Endpoint conclusion:
no study available

Genetic toxicity in vivo

Description of key information

Mammalian Bone Marrow Chromosome Aberration Test in rat (ip study) (similar to OECD TG 475): Negative (Dow Corning Corporation, 1982).

Link to relevant study records
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1980-11-26 to 1981-09-28
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
It was not compliant with GLP.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)
Deviations:
yes
Remarks:
only male animals used. Number of cells counted for determination of mitotic index not indicated - probably ca. 100, should be 1000
Principles of method if other than guideline:
The test was performed according to the Rodent Bone Marrow Cytogenetic Assay as recommended by the Ad Hoc Committee on Chromosome Methodologies in Mutagen Testing (Toxicology and Applied Pharm 22: 269-275, 1972) with modifications per the EPA Gene-Tox Program Cytogenetics Committee (12/3 to 12/5, 1980, Washington D.C.).
GLP compliance:
not specified
Type of assay:
chromosome aberration assay
Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS

- Age at study initiation: 14 - 16 weeks

- Weight at study initiation: 250 - 280 g for range finding. 290 - 430 g for cytogenetic study

- Housing: 6 per cage

- Diet (e.g. ad libitum): Charles River Agway

ENVIRONMENTAL CONDITIONS

- Temperature (°C): 68 ± 3 F

- Humidity (%): approx 50
Route of administration:
intraperitoneal
Vehicle:
- Vehicle(s)/solvent(s) used: paraffin oil

- Lot/batch no. (if required): A7M02

- Purity: Laboratory Grade
Duration of treatment / exposure:
single treatment
Frequency of treatment:
Single IP injection
Post exposure period:
6, 24 and 48 hours
Dose / conc.:
255 mg/kg bw/day (nominal)
Dose / conc.:
515 mg/kg bw/day (nominal)
Dose / conc.:
1 030 mg/kg bw/day (nominal)
No. of animals per sex per dose:
5 males/dose
Control animals:
yes, concurrent vehicle
Positive control(s):
cyclophosphamide, positive control agent, was included in the 24-hour group.  

- Route of administration: IP Injection

- Doses / concentrations: 22 mg/kg bw
Tissues and cell types examined:
Bone marrow from femur
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION: Based on two range finding studies conducted to determine the maximum dose the animals could tolerate.


Range finding studies: Range finding study 1: Animals Injected intraperitoneally with 1676, 504, 168 and 50 mg/kg and observed once a day for 7 days for signs of toxicity. Range finding study 2: 10 animals injected with 3911, 1825, 521, 183 and 52 mg/kg. In main study animals were sacrificed at 6, 24 and 48 hours


DETAILS OF SLIDE PREPARATION: Approximately 4 slides were prepared for each animal.  The chromosomes were prepared by standard methods and Giemsa stained.


TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields):
6h group: Stock solution of 321 mg/ml; volumes injected were 1.0, 0.5 and 0.25 ml, resulting in the following doses calculated from body weight: 1030 mg/kg +/- 3.2%; 515 mg/kg +/- 5.6%; 255 mg/kg +/- 1.2%

24 hour group: animals were injected with 1.0 or 0.5 ml of 321 mg/ml stock solution, or 1.0 ml of 91 mg/ml stock solution, resulting in the following doses calculated from body weight: 1030 mg/kg +/- 0.8%; 515 mg/kg +/- 5.6%; 255 mg/kg +/- 3.1%

48 hour group: animals were injected with 1.0 or 0.45 ml of 426 mg/ml stock solution, or 1 ml of 102 mg/ml stock solution. This resulted in the following doses calculated from body weight: 1030 mg/kg +/- 3.1%; 515 mg/kg +/- 9.3%; 255 mg/kg +/- 2.4%

METHOD OF ANALYSIS: metaphase cells analysed by projecting the negatives with a darkroom enlarger onto a white counter

OTHER:
Evaluation criteria:
In general, a minimum of 100 metaphase cells from each animal were scored for incidence of chromosomal aberrations.
Statistics:
Statistical methods: Chi2 test for comparison of expected and observed distribution of the number of breaks; Wilcoxon test was used as a nonparametric test.
Key result
Sex:
male
Genotoxicity:
negative
Remarks:
on mitotic index
Toxicity:
no effects
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
RESULTS OF RANGE-FINDING STUDY

- Dose range: Exp 1: 1676, 504, 168, 50 mg/kg. Exp 2: 3911, 1825, 521, 183, 52 mg/kg

- Clinical signs of toxicity in test animals: No deaths observed in initial study. In second study 3 of 10 animals dosed with 3911 mg/kg died, while all the other animals survived till terminal sacrifice.

- Harvest times: 7 days exp 1, 14 days exp 2.

- High dose with and without activation: 1676 exp 1, 3911 exp 2

RESULTS OF DEFINITIVE STUDY

See table 1

Negative controls: frequencies of breaks were 0.54%, 2.49% and 1.47% at sacrifice at 6, 24 and 48 hours respectively.

Table 1:Results of chromosome analysis in rat bone marrow cells: test substance (total number of aberrations observed)

 

Low dose (255 mg/kg bw)

Mid dose (515 mg/kg bw)

High dose (1030 mg/kg bw)

Sampling time (h)

6

24

48

6

24

48

6

24

48

Number of cells evaluated

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

Toxicity,specify effects

 

 

 

 

 

 

 

 

 

Chromosome aberrations

Gaps

6

11

3

3

6

25

 2

 12

 14

Breaks

 5

 2

 9

 10

 15

 6

 5

 6

 7

Other aberrations

 0

 0

 0

 0

 0

 0

 0

 0

Mitotic index (% range)

 2 – 5

2 - 5

1 - 4

 2 - 4

 2 - 5

 4 - 7

 1 - 6

 3 - 5

 2 - 5

Polyploidy

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

Endo reduplication

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

 N.R = Not Reported

Table 2 Results of chromosome analysis in rat bone marrow cells: control substances (total number of aberrations observed)

 

Vehicle control

Positive control

Sampling time (h)

6

24

48

48

Number of cells evaluated

 500 approx

 450 approx

 500 approx

 250 approx

Chromosome aberrations

Gaps

6

19

15

ND

 

Breaks

3

12

8

145

 

Other aberrations

0

0

0

4 quad, 6 tri, 5 del

Mitotic index (% range)

 

2-7

1-4

3-4

2-4

 N.R = Not Reported

quad = quadriradial tri = triradial del = deletion

Conclusions:
Hexamethyldisiloxane has been tested for the induction of chromosome aberrations in rat bone marrow cells in a valid study conducted according to a protocol that is similar to OECD 475. There was no evidence of induction of chromosomal damage in the bone marrow cells of rats following intraperitoneal injection. The test substance is considered to be non-clastogenic (negative for the induction of chromosome aberrations) in rat bone marrow cells under the conditions of the test.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Information is available from reliable studies for all the required in vitro endpoints. Where there was more than one result for an endpoint the most reliable study available was chosen as key study. Where there was more than one reliable study, the most recent study was selected. The results of all the studies were in agreement.

Bacterial mutagenicity

Hexamethyldisiloxane has been tested according to a Japanese guideline that is similar to OECD 471 and in compliance with GLP, using the pre-incubation method (Shin Etsu, 1994). The study is considered to be reliability 2 as duplicate not triplicate plates were used. No evidence of test-substance induced increase in the number of revertants was observed in Salmonella typhimurium strains TA1535, TA1537, TA98, TA100 or E.coli WP2 uvrA, with or without metabolic activation, up to a concentration exceeding current limit concentrations, in either the dose finding test or the main assay. Appropriate solvent, positive and sterility controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test substance. The key study is supported by a number of older, less reliable studies all of which reported negative results.

In vitro cytogenicity

Hexamethyldisiloxane has been tested under GLP in a valid Japanese guideline study according to a protocol that is similar to OECD TG 473 (Shin Etsu, 1995). The test substance did not induce any chromosome aberrations with or without metabolic activation. There were no marked differences between replicate flasks. Expected results were obtained from vehicle and positive controls. It is concluded that the test substance is non-clastogenic (does not induce chromosome aberrations) in Chinese hamster lung cells under the conditions of the test.

Mutagenicity to mammalian cells

Hexamethyldisiloxane has been tested for mutagenicity in L5178Y cells in reliability 2 study conducted according to a protocol that is similar to OECD TG 476 (Litton Bionetics, 1978). The test substance did not cause a biologically significant increase in the mutation frequency; solvent and positive controls gave expected results. It is concluded that the test substance is not mutagenic under the conditions of the test.

In addition, the test substance did not induce sister chromatid exchanges in mammalian cells, and an in vitro unscheduled DNA synthesis assay on mouse lymphoma L5178Y cells and DNA damage and repair assays using Saccharomyces cerevisiae and Escherichia coli W3110/polA+ P3478/polA- cells also gave negative results (Litton Bionetics, 1978).

In vivo

The conclusion reached from the in vitro results is confirmed by the negative result obtained when the substance was tested in vivo in a rat bone marrow chromosome aberration assay conducted according to a protocol that is similar to OECD 475 using intraperitoneal administration. The test substance was considered to be non-clastogenic (negative for the induction of chromosome aberrations) in rat bone marrow cells under the conditions of the test (Dow Corning Corporation, 1982). In addition, hexamethyldisiloxane does not include structural alerts for genetic toxicity (Benigni et. al., 2008). It is concluded that the available data does not indicate a potential for germ cell mutagenicity.

Benigni et. al. (2008).The Benigni/Bossa rule base for mutagenicity and carcinogenicity JR Scientific report EUR 23241 EN


Justification for classification or non-classification

Based on the available in vitro and in vivo genotoxicity data, hexamethyldisiloxane is not classified for mutagenicity according to Regulation (EC) No 1272/2008.