1,1,5,5,5-hexamethyl-3,3-bis[(trimethylsilyl)oxy]trisiloxane

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

No in vitro genetic toxicity studies are currently available for the registered substance. Studies have been commissioned and the dossier will be updated when the results are available. As an interim approach, the following key in vitro studies were read-across from the structural analogue 1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane] (CAS 17928-28-8).

Gene mutation (Bacterial reverse mutation assay / Ames test): negative result with and without metabolic activation in Salmonella typhimurium strains TA98, TA100, TA1535 and TA1537 and Escherichia coli WP2 conducted to an equivalent protocol to OECD Test Guideline 471 and not in compliance with GLP (Sarwar, 2001a, reliability 2).

Cytogenicity in mammalian cells: negative with and without metabolic activation in Chinese hamster CHL/IU cells conducted to an equivalent protocol to OECD Test Guideline 473

and not in compliance with GLP (Sarwar, 2001b, reliability 2).  

Mutagenicity in mammalian cells: negative with and without metabolic activation in L5178Y mouse lymphoma cells conducted to OECD Test Guideline 490 and in compliance with GLP (Charles River Laboratories, 2018, reliability 1).

In vitro bacterial mutagenicity (OECD Test Guideline 471) and mammalian chromosomal aberration (OECD Test Guideline 473) studies are planned for the registered substance but currently delayed.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2001

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

The report reviewed was a certified translation of the Japanese original, translated report dated 2001-07-11, indicating that the study was completed on this date. The study was not conducted in compliance with GLP.

Qualifier:

according to guideline

Guideline:

JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals

Version / remarks:

Ministry of Health and Welfare Ordinance No 1604: November 1, 1999 was followed as reference.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

yes

Remarks:

duplicate not triplicate plates

GLP compliance:

no

Type of assay:

bacterial reverse mutation assay

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Species / strain / cell type:

E. coli WP2 uvr A

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital and 5,6-benzoflavone activated rat liver S9

Test concentrations with justification for top dose:

156.3, 312.5, 625, 1250, 2500 and 5000 µg/plate

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: Acetone
- Justification for choice of solvent/vehicle: According to the sponsor, the test substance was insoluble in water and DMSO, whereas soluble and stable in acetone.

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 2-(2-Furyl)-3-(5-nitro-2-furyl) AF-2

Remarks:

TA98 (0.1 µg/plate), TA 100 and WP2uvrA (0.01 µg/plate) without metabolic activation

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

Remarks:

TA 1535 without metabolic activation: 0.5 µg/plate

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 2-aminoanthracene - 2-AA

Remarks:

TA98 - 0.5 µg/plate, TA100 - 1.0 µg/plate, TA1535 and TA1537 - 2.0 µg/plate, WP2uvrA - 10.0 µg/plate with metabolic activation

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

9-aminoacridine

Remarks:

TA 1537 without metabolic activation: 80.0 µg/plate

Details on test system and experimental conditions:

METHOD OF APPLICATION: preincubation

ACTIVATION: S9 mix contained glucose-6-phosphate, NADPH and NADH as co-factors, 0.5 ml of S9 mix containing 10% S9 was added to 2 ml top agar, 0.05 ml of test solution and 0.1 ml tester strain, giving a final concentration of approximately 2% S9.

DURATION
- Preincubation period: Not stated in translated study report
- Exposure duration: 48 hr at 37ºC

SELECTION AGENT (mutation assays): histidine deficient agar

NUMBER OF REPLICATIONS: duplicate plates, test repeated

DETERMINATION OF CYTOTOXICITY
- Method: other: condition of background lawn

Evaluation criteria:

The test substance was judged positive when the number of revertant colonies in the test substance treated plate increased dose dependently and became 2-fold compared to that of the negative control.

Statistics:

The statistical analysis was not done for the judgement.

Key result

Species / strain:

S. typhimurium TA 1535

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:

not applicable

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 1537

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:

not applicable

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 98

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:

not applicable

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 100

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:

not applicable

Positive controls validity:

valid

Key result

Species / strain:

E. coli WP2 uvr A

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:

not applicable

Positive controls validity:

valid

Reverse mutation - dose determination test - pre-incubation method (mean of two plates)

Concentration µg/plate	Mean number of revertants/plate
	TA 100		TA 1535		WP2uvrA		TA 98		TA 1537
	-S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9
Solvent control	131	127	10	11	27	30	23	27	10	15
5	124	139	10	8	23	29	22	36	9	15
10	122	121	11	11	27	26	21	32	11	14
50	110	111	17	14	30	29	19	34	10	16
100	117	121	10	11	30	34	17	38	9	15
500	130	126	11	17	27	35	19	31	10	15
1000	116	115	12	9	23	40	16	42	10	17
5000	116	119	13	13	33	31	19	33	12	17
Positive control	523	779	473	223	166	792	468	495	514	202

Pre-incubation test - revertants per plate (mean of two plates)

Concentration µg/plate	Mean number of revertants/plate
	TA 100		TA 1535		WP2uvrA		TA 98		TA 1537
	-S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9
Solvent control	142	147	10	12	30	31	20	29	6	11
156.3	133	165	11	9	33	33	17	27	6	12
312.5	153	147	8	10	35	37	23	25	7	12
625	127	136	8	9	35	35	26	28	8	13
1250	141	166	13	13	33	34	20	35	6	13
2500	145	152	9	13	31	33	21	40	9	10
5000	137	155	12	8	29	36	19	38	7	14
Positive control	551	949	563	209	226	1019	519	502	496	236

Conclusions:

1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for mutagenicity to bacteria, in a study which was conducted according to a Japanese guideline similar to OECD TG 471, not in compliance with GLP. No evidence of a test substance related increase in the number of revertants was observed with or without metabolic activation in the initial or the repeat experiment, both of which used the pre-incubation method. Appropriate 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.

Reference 2

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2001

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Qualifier:

according to guideline

Guideline:

other: Japanese ministry of health and welfare ordinance No. 1604: November 1, 1999

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

GLP compliance:

no

Type of assay:

in vitro mammalian chromosome aberration test

Species / strain / cell type:

other: Chinese hamster lung cells (CHL/IU, fibroblast cell line)

Details on mammalian cell type (if applicable):

- Type and identity of media: Eagle's minimum essential medium
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital and 5,6-benzoflavone activated rat liver S9

Test concentrations with justification for top dose:

777, 1554 and 3107 µg/ml

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: 1% CMC-Na (carboxymethyl cellulose sodium salt)
- Justification for choice of solvent/vehicle: According to the sponsor, the test substance was insoluble and stable in water and DMSO. So, 1% CMC-Na was selected as solvent and used in the test,

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

mitomycin C

Remarks:

without metabolic activation: 0.001 mg/ml

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

benzo(a)pyrene

Remarks:

with metabolic activation : 0.02 mg/ml

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium

ACTIVATION: S9 mix contained NADP and glucose-6-phosphate as co-factors, 0.3 ml of S9 fraction and pure water in each ml of mixture. Concentration of S9 in cultures not stated in translated report.

DURATION
- Preincubation period:
- Exposure duration: 6 hrs with and without S9, 24 and 48 hrs without S9
- Expression time (cells in growth medium): 18 hrs with and without S9, 24 and 48 hrs without S9


SPINDLE INHIBITOR (cytogenetic assays): Colcemid
STAIN (for cytogenetic assays): 1.5% Giemsa solution

NUMBER OF REPLICATIONS: 2 per dose level

NUMBER OF CELLS EVALUATED: 200 per dose level

DETERMINATION OF CYTOTOXICITY
- Method: cell growth inhibition test

OTHER EXAMINATIONS:
- Determination of polyploidy: yes
- Determination of endoreplication: not examined

Evaluation criteria:

The test substance was judged positive if the incidence of chromosomal aberrations increased dose dependently as compared with those of the concurrent negative control or a reproducible increase in the incidence of chromosomal aberrations at one or more concentrations and the others were judged negative.

Statistics:

No statistical analysis was followed for analysis

Key result

Species / strain:

other: Chinese hamster lung cells (CHL/IU, a fibroblast cell line)

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:

not applicable

Positive controls validity:

valid

Chromosomal aberration test results - all treatment times

Treatment time (h)	+ or – MA	Concentration (mg/ml)	Number of observed cells	Mean % of cells showing structural chromosomal aberrations
				Chromosomal damage %	Chromosome gap %	Cell growth index %
6-18*	-	Solvent control	200	1.0	0.5	100
6-18	-	0.777	200	1.0	0.0	100
6-18	-	1.554	200	0.0	0.0	93
6-18	-	3.107	200	0.5	0.0	86
6-18	-	Positive control	200	16.5	1.5	-
6-18	+	Solvent control	200	0.5	0.5	100
6-18	+	0.777	200	0.5	0.0	102
6-18	+	1.554	200	0.0	0.0	94
6-18	+	3.107	200	0.0	0.0	89
6-18	+	Positive control	200	47.0	4.5	-
24	-	Solvent control	200	0.5	0.5	100
24	-	0.777	200	0.0	0.0	97
24	-	1.554	200	0.5	0.0	99
24	-	3.107	200	0.5	0.0	99
24	-	Positive control	200	45.0	3.5	-
48	-	Solvent control	200	0.5	1.0	100
48	-	0.777	200	0.5	0.0	99
48	-	1.554	200	0.5	0.5	98
48	-	3.107	200	0.0	0.5	99
48	-	Positive control	200	55.5	4.5	-

*6 -18 indicates 6 h treatment followed by 18 h incubation

Conclusions:

1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for cytogenicity with mammalian cells, in a study which was conducted according to a Japanese guideline similar to OECD 473, not compliant with GLP. No evidence of a test substance related increase in chromosomal aberrations was observed with or without metabolic activation, in Chinese hamster CHL/IU cells. Appropriate controls were included and gave expected results. It is concluded that the test substance is negative for cytogenicity to mammalian cells under the conditions of the test.

Reference 3

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-01-29 to 2018-03-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 490 (In Vitro Mammalian Cell Gene Mutation Tests Using the Thymidine Kinase Gene)

Version / remarks:

2005

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

in vitro mammalian cell gene mutation tests using the thymidine kinase gene

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature
- Stability under test conditions: stable
- Solubility and stability of the test substance in the solvent/vehicle: Acetone - soluble
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: The test substance was stable in the vehicle, acetone.

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: The test item was dissolved in acetone to give the test concentrations.
- Preliminary purification step (if any): No correction was made for the purity/composition of the test item.
- Final dilution of a dissolved solid, stock liquid or gel: n/a
- Final preparation of a solid: n/a

Species / strain / cell type:

mouse lymphoma L5178Y cells

Details on mammalian cell type (if applicable):

CELLS USED
- Type and source of cells: L5178Y mouse lymphona cells
- Suitability of cells: sensitive indicators of mutagenic activity.

For cell lines:
- Absence of Mycoplasma contamination: yes
- Methods for maintenance in cell culture: in cell medium
- Periodically checked for karyotype stability: not specified
- Periodically ‘cleansed’ of spontaneous mutants: yes

MEDIA USED
- Type and composition of media, CO2 concentration, humidity level, temperature, if applicable: RPMI 1640 HEPES buffered medium (Dutch modification) containing penicillin/streptomycin (50 U/mL and 50 μg/mL, respectively), 1 mM sodium pyruvate and 2 mM L-glutamin. Growth medium contained of basic medium supplemented with 10% (v/v) heat-inactivated horse serum (=R10 medium). All incubations were carried out in a humid atmosphere (80 - 100%, actual range 70 - 97%) containing 5.0 ± 0.5% CO2 in air in the dark at 37.0 ± 1.0°C (actual range 35.7 - 37.5°C).

Additional strain / cell type characteristics:

not applicable

Metabolic activation:

with and without

Metabolic activation system:

Type and composition of metabolic activation system:
- source of S9 : Trinova Biochem GmbH, Giessen, Germany
- method of preparation of S9 mix: phenobarbital (80 mg/kg body weight) and ß-naphthoflavone (100 mg/kg body weight) induced rat liver
- concentration or volume of S9 mix and S9 in the final culture medium: S9 mix concentration was 4% (v/v). S9-mix was prepared immediately before use and kept refrigerated. S9-mix components contained per mL physiological saline: 1.63 mg MgCl2.6H2O; 2.46 mg KCl; 1.7 mg glucose-6-phosphate; 3.4 mg NADP; 4 μmol HEPES. The above solution was filter (0.22 μm)-sterilized. To 0.5 mL S9-mix components 0.5 mL S9-fraction was added (50% (v/v) S9-fraction) to complete the S9-mix.
- quality controls of S9 (e.g., enzymatic activity, sterility, metabolic capability)

Test concentrations with justification for top dose:

3-hour mutation assay with and without metabolic activation: 0.24, 0.49, 0.98, 1.95, 3.9, 7.8, 15.6 and 31.3 μg/mL
24-hour mutation assay without metabolic activation: 0.24, 0.49, 0.98, 1.95, 3.9, 7.8, 15.6 and 31.3 μg/mL
Since the test item was not toxic but difficult to dissolve in aqueous solutions, the highest concentration was determined by the solubility in the culture medium. The highest test item concentrations showed a slight precipitate in the exposure medium.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: acetone

- Justification for choice of solvent/vehicle: The test substance is insoluble in water and DMSO whereas soluble and stable in acetone.

- Justification for percentage of solvent in the final culture medium: 0.25% (v/v)

Untreated negative controls:

not specified

Negative solvent / vehicle controls:

yes

Remarks:

acetone

True negative controls:

not specified

Positive controls:

yes

Positive control substance:

cyclophosphamide

Remarks:

with metabolic activation

Untreated negative controls:

not specified

Negative solvent / vehicle controls:

yes

Remarks:

acetone

True negative controls:

not specified

Positive controls:

yes

Positive control substance:

methylmethanesulfonate

Remarks:

without metabolic activation

Details on test system and experimental conditions:

NUMBER OF REPLICATIONS:
- Number of cultures per concentration (single, duplicate, triplicate) : Solvent and positive control groups were cultured in duplicate. Single cultures for test groups were used.
- Number of independent experiments : two experiments: In the first experiment, cell cultures were exposed for 3 hours to the test item in exposure medium (R5-medium) in the absence and presence of S9-mix. In the second experiment, cell cultures were exposed to the test item in exposure medium (R10-medium) for 24 hours in the absence of S9-mix.

METHOD OF TREATMENT/ EXPOSURE:
- Cell density at seeding (if applicable): 8 x 10⁶ cells (10⁶ cells/mL for 3 hour treatment) or 6 x 10⁶ cells (1.25 x 10⁵ cells/mL for 24 hour treatment) were used.
- Test substance added in medium

TREATMENT AND HARVEST SCHEDULE:
- Preincubation period, if applicable: not applicable
- Exposure duration/duration of treatment: 3 hours or 24 hours
- Harvest time after the end of treatment (sampling/recovery times): not applicable

FOR GENE MUTATION:
- Expression time (cells in growth medium between treatment and selection): For expression of the mutant phenotype, the remaining cells were cultured for 2 days after the treatment period. During this culture period at least 4 x 10⁶ cells (where possible) were subcultured every day in order to maintain log phase growth. Two days after the end of the treatment with the test item the cells were plated for determination of the cloning efficiency (CEday2) and the mutation frequency (MF).
- Selection time (if incubation with a selective agent): 11 or 12 days
- Fixation time (start of exposure up to fixation or harvest of cells): n/a
- Method used: Microwell plates
- Selective agent: 5 µg/mL of Triflourothymidine (TFT). All groups except from the positive control group contained TFT and following incubation, the plates for the TFT-selection were stained for 2 hours, by adding 0.5 mg/mL MTT to each well.
- Number of cells seeded and method to enumerate numbers of viable and mutants cells: For determination of the mutation frequency, a total number of 9.6 x 105 cells per concentration were plated in five 96-well microtiter plates, each well containing 2000 cells in selective medium (TFT-selection), with the exception of the positive control groups where a total number of 9.6 x 105 cells/concentration were plated in ten 96-well microtiter plates, each well containing 1000 cells in selective medium (TFT-selection). The microtiter plates for CEday2 and MF were incubated for 11 or 12 days. Following the incubation period, the plates for the TFT-selection were stained for 2 hours, by adding 0.5 mg/mL MTT to each well. The plates for the CE day2 and MF were scored with the naked eye or with the microscope.
- Criteria for small (slow growing) and large (fast growing) colonies: The small colonies are morphologically dense colonies with a sharp contour and with a diameter less than a quarter of a well. A well containing more than one small colony was classified as one small colony. The large colonies are morphologically less dense colonies with a hazy contour and with a diameter larger than a quarter of a well. A well containing more than one large colony is classified as one large colony. A well containing one small and one large colony was classified as one large colony.

Evaluation criteria:

The result was considered positive when:
- The absolute cloning efficiency of the solvent controls (CEday2) is between 65 and 120% in order to have an acceptable number of surviving cells analyzed for expression of the TK mutation.
- The spontaneous mutation frequency in the solvent control is ≥ 50 per 10⁶ survivors and ≤ 170 per 10⁶ survivors.
- The suspension growth (SG) over the 2-day expression period for the solvent controls should be between 8 and 32 for the 3 hour treatment, and between 32 and 180 for the 24 hour treatment.
- The positive control should demonstrate an absolute increase in the total mutation frequency i.e. an increase above the spontaneous background MF (an induced MF) of at least 300 x 10⁻⁶. At least 40% of the IMF should be reflected in the small colony MF. And/or, the positive control has an increase in the small colony MF of at least 150 x 10⁻⁶ above that seen in the concurrent solvent control (a small colony IMF of 150 x 10⁻⁶).

Statistics:

Not stated

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

not determined

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

True negative controls validity:

not specified

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS
- Precipitation and time of the determination: The test item did not precipitate directly in the exposure medium at a concentration of 2000 μg/mL. However, moderate precipitation was observed in the exposure medium after 24 hours. An additional solubility experiment was performed where the test item precipitated in the exposure medium at concentrations of 31.3 μg/mL and above. The test item was tested beyond the limit of the solubility to obtain adequate cytotoxicity data, the concentration used as the highest test item concentration for the dose-range finding test was 62.5 μg/mL.

RANGE-FINDING/SCREENING STUDIES
In the dose-range finding test, L5178Y mouse lymphoma cells were treated with a test item concentration range of 1.95 to 62.5 µg/mL in the absence of S9-mix with 3 and 24 hour treatment periods and in the presence of S9-mix with a 3 hour treatment period.
Both in the absence and presence of S9-mix, no toxicity in the relative suspension growth was observed up to and including the highest test item concentration of 62.5 μg/mL compared to the suspension growth of the solvent control. The test item precipitated in the culture medium at the dose levels of 31.3 and 62.5 μg/mL.
No toxicity in the relative suspension growth was observed up to and including the highest
test item concentration of 62.5 μg/mL compared to the suspension growth of the solvent
control. The test item precipitated in the culture medium at the dose levels of 31.3 and
62.5 μg/mL.

STUDY RESULTS
- Concurrent vehicle negative and positive control data : Positive and negative controls were considered to be valid.

For all test methods and criteria for data analysis and interpretation:
- Concentration-response relationship where possible : No biologically relevant increase in the mutation frequency at the TK locus was observed after
3 and 24 hour treatment with the test item neither in the absence nor presence of S9-mix.
- Statistical analysis: there was no statistically significant increase in mutant colonies
- Any other criteria: There was no statistically significant increase in mutation frequency at any of the test concentrations.

Gene mutation tests in mammalian cells:
- Results from cytotoxicity measurements: No toxicity was observed and all dose levels were evaluated in the absence and presence of
S9-mix in both experiments.
o Relative total growth (RTG) was comparable to that of the negative control

- Genotoxicity results:
o When using the thymidine kinase gene on L5178Y cells: The
numbers of small and large colonies in the test item treated cultures were comparable to the numbers of small and large colonies of the solvent controls. No biologically relevant increase in the mutation frequency at the TK locus was observed after 3 and 24 hour treatment with the test item neither in the absence nor presence of S9-mix.No toxicity was observed and all dose levels were evaluated in the absence and presence of
S9-mix in both experiments.


HISTORICAL CONTROL DATA (with ranges, means and standard deviation, and 95% control limits for the distribution as well as the number of data)
- Positive historical control data: Positive control chemicals, methyl methanesulfonate and cyclophosphamide, both produced
significant increases in the mutation frequency. In addition, the mutation frequency found in the positive control cultures was within the 95% control limits of the distribution of the
historical positive control database
- Negative (solvent/vehicle) historical control data:The mutation frequency found in the solvent control cultures was within the acceptability criteria of this assay and within the 95% control limits of the distribution of the historical
negative control database

Table 1 - Historical Control Data of the Spontaneous Mutation Frequencies per 10⁶survivors

of the Solvent Controls for the Mouse Lymphoma Assay

	- S9-mix	- S9-mix	+ S9-mix
	3 hour treatment	24 hour treatment	3 hour treatment
Mean	96	92	96
SD	29	30	29
n	268	248	285
Upper control limit (95% control limits)	160	152	160
Lower control limit (95% control limits)	32	31	32

SD = Standard deviation

n = Number of observations

Distribution historical negative control data from experiments performed between November 2014 and November 2017. 

Table 2 - Historical Control Data of the Mutation Frequencies  per 10⁶survivors

of the Positive Controls for the Mouse Lymphoma Assay

	- S9-mix	- S9-mix	+ S9-mix
	3 hour treatment	24 hour treatment	3 hour treatment
Mean	808	684	1669
SD	239	206	843
n	136	124	146
Upper control limit (95% control limits)	1465	1222	4196
Lower control limit (95% control limits)	152	146	-859

SD = Standard deviation

n = Number of observations

Distribution historical positive control data from experiments performed between November 2014 and November 2017. 

Table 3a - Cytotoxic and Mutagenic Response of 1,1,1,3,5,5,5-Heptamethyl 3[(trimethylsilyl)oxy]trisiloxane in the Mouse Lymphoma L5178Y Test System– Without metabolic activation 3 h treatment

Dose (µg/ml)	RSG (%)	CE day2 (%)	RCE (%)	RTG (%)	Mutation   Total	Frequency survivors Small	per 10^6   Large
SC1	100	99	100	100	108	61	41
SC2	100	101	100	100	134	55	71
0.24	112	88	87	98	116	34	76
0.49	102	108	108	110	125	56	61
0.98	114	95	95	108	120	64	49
1.95	103	116	116	120	127	63	55
3.9	107	86	86	92	149	98	43
7.8	98	102	102	100	138	88	41
15.6	97	101	101	98	114	65	43
31.3	98	108	108	106	123	57	57
MMS	60	50	50	30	1186	670	354

 

Table 3b - Cytotoxic and Mutagenic Response of 1,1,1,3,5,5,5-Heptamethyl 3[(trimethylsilyl)oxy]trisiloxane in the Mouse Lymphoma L5178Y Test System– With metabolic activation 3 h treatment

Dose (µg/ml)	RSG (%)	CE day2 (%)	RCE (%)	RTG (%)	Mutation   Total	Frequency survivors Small	per 10^6   Large
SC1	100	84	100	100	136	85	44
SC2	100	91	100	100	93	61	28
0.24	86	107	122	105	92	49	39
0.49	102	101	115	117	136	92	36
0.98	100	91	104	104	90	70	17
1.95	103	110	125	129	95	54	35
3.9	92	97	110	102	103	73	27
7.8	97	101	115	112	130	65	57
15.6	88	101	115	101	112	74	32
31.3	88	98	112	99	90	55	32
MMS	46	45	52	24	2126	1036	616

Note: all calculations were made without rounding off RSG = Relative Suspension Growth; CE = Cloning Efficiency; RCE = Relative Cloning Efficiency; RTG = Relative Total Growth; SC = Solvent control = Acetone; MMS = Methylmethanesulfonate; CP = Cyclophosphamide (1) = the test item precipitated in the exposure medium

Table 4 - Cytotoxic and Mutagenic Response of 1,1,1,3,5,5,5-Heptamethyl-3[(trimethylsilyl)oxy]trisiloxane in the Mouse Lymphoma L5178Y Test System – without metabolic activation – 24 h treatment

Dose (µg/ml)	RSG (%)	CE day2 (%)	RCE (%)	RTG (%)	Mutation   Total	Frequency survivors Small	per 10^6   Large
SC1	100	86	100	100	123	66	50
SC2	100	90	100	100	131	66	57
0.24	111	101	114	127	109	52	51
0.49	118	85	96	113	97	47	46
0.98	123	99	113	139	107	48	53
1.95	143	95	108	155	98	46	48
3.9	130	98	111	145	77	34	40
7.8	119	99	113	135	77	28	46
15.6	130	83	94	121	78	42	34
31.3	116	75	85	98	97	43	51
MMS	107	77	87	93	843	458	258

Note: all calculations were made without rounding off RSG = Relative Suspension Growth; CE = Cloning Efficiency; RCE = Relative Cloning Efficiency; RTG = Relative Total Growth; SC = Solvent control = Acetone; MMS = Methylmethanesulfonate (1) = the test item precipitated in the exposure mediu

Conclusions:

1,1,1,3,5,5,5-Heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for mutagenicity in mouse lymphoma L5178Y cells according to OECD Test Guideline 490 and in compliance with GLP. No test-substance induced increase in the number of mutations was observed when tested with and without metabolic activation. Appropriate solvent and positive controls were included and gave the expected results. It is concluded that the test substance is negative for mutagenicity to mammalian cells under the conditions of the study.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

There are no genotoxicity data available for the registered substance. However, reliable data are available for a structural analogue, 1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane (CAS 17928-28-8).

1,1,1,3,5,5,5 -Heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for mutagenicity to bacteria, in a study which was conducted according to a Japanese guideline similar to OECD TG 471, not in compliance with GLP (Sarwar, 2001a, reliability 2). No evidence of a test substance related increase in the number of revertants was observed with or without metabolic activation in the initial or the repeat experiment, both of which used the pre-incubation method, in Salmonella typhimurium strains TA 98, TA 100, TA 1535 and TA 1537, and E.coli WP2 uvrA. Appropriate positive and solvent 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.

1,1,1,3,5,5,5-Heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for cytogenicity with mammalian cells, in a study which was conducted according to a Japanese guideline similar to OECD TG 473, not compliant with GLP (Sarwar, 2001b, reliability 2). No evidence of a test substance related increase in chromosomal aberrations was observed with or without metabolic activation in CHL/IU cells, tested to cytotoxic concentrations. Appropriate positive and solvent controls were included and gave expected results. It is concluded that the test substance is negative for cytogenicity to mammalian cells under the conditions of the test.

1,1,1,3,5,5,5-Heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane has been tested for mutagenicity in mouse lymphoma L5178Y cells according to OECD TG 490, and in compliance with GLP (Charles River, 2019, reliability 1). No test-substance induced increase in the number of mutations was observed when tested with and without metabolic activation. Appropriate solvent and positive controls were included and gave the expected results. It is concluded that the test substance is negative for mutagenicity to mammalian cells under the conditions of the study.

Justification for classification or non-classification

Based on the available read-across in vitro genotoxicity data, 1,1,1,5,5,5-hexamethyl-3,3-bis[(trimethylsilyl)oxy]trisiloxane is not classified for mutagenicity according to Regulation (EC) No 1272/2008.