Dodecamethylcyclohexasiloxane

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Dodecamethylcyclohexasiloxane

EC Number:

208-762-8

EC Name:

Dodecamethylcyclohexasiloxane

Cas Number:

540-97-6

Molecular formula:

C12H36O6Si6

IUPAC Name:

dodecamethylcyclohexasiloxane

Test material form:

other: liquid

Method

Target gene:

histidine (s. typhimurium) or tryptophan (E. coli) operon

Species / strain

Species / strain / cell type:

bacteria, other: Salmonella typhimurium (TA1535, TA1537, TA100 and TA98) and Escherichia coli (WP2uvrA

Metabolic activation:

with and without

Metabolic activation system:

Aroclor induced rat liver S9.

Test concentrations with justification for top dose:

10, 33, 100, 333, and 1000 µg/plate

Vehicle / solvent:

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

Controls

Controls 1

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 activation

Controls 2

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 activation

Controls 3

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: daunomycin

Remarks:

TA 98 without activation

Controls 4

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

methylmethanesulfonate

Remarks:

TA 100 without activation

Controls 5

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

Remarks:

E coli WP2 uvrA without activation

Controls 6

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 2-aminoanthracene

Remarks:

All strains with activation

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation)

DURATION
- Exposure duration: 48 hours
- Expression time (cells in growth medium): 48 hours
- Fixation time (start of exposure up to fixation or harvest of cells): 48 hours

NUMBER OF REPLICATIONS: Triplicate plates, in each of two independent experiments

DETERMINATION OF CYTOTOXICITY
- Method: mitotic index; cloning efficiency; relative total growth; other: reduction in number of revertants and condition of bacterial lawn.

OTHER: Range finding study was conducted as part of first experiment - 8 concentrations of TA 100 and E coli WP2uvrA were tested in triplicate

ACTIVATION: Aroclor induced rat liver S9. S9 mix included co-factors: NADP and glucose-6-phosphate; sodium phosphate buffer and magnesium chloride and potassium chloride. S9 mix included S9 at 5% v/v for experiment I and 10% v/v for experiment II). 0.5 ml S9 mix was added to the top agar (total volume 2.7 ml) giving a final concentration of S9 of approximately 1% in experiment I and approximately 2% in experiment II.

Evaluation criteria:

A reproducible, dose-related increase by at least two fold in the number of revertants relative to the control was considered positive.

Results and discussion

Test results

Key result

Species / strain:

bacteria, other: Salmonella typhimurium (TA1535, TA1537, TA100 and TA98) and Escherichia coli (WP2uvrA)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Remarks:

Tested to precipitating concentrations in experiment II and in some strains in experiment I.

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS

- Precipitation: occurred at concentrations of > 1000 µg/plate

RANGE-FINDING/SCREENING STUDIES: no toxicity observed

COMPARISON WITH HISTORICAL CONTROL DATA: Results of controls were within the ranges of historical controls

Any other information on results incl. tables

The test substance precipitated on the plates at 1000 µg/plate.  The bacterial background lawn was not reduced at all concentrations tested and no decrease in the number of revertants was observed. The test substance did not induce a
dose-related increase in the number of revertant (His+) colonies in each of the four tester strains (TA1535, TA1537,
TA98 and TA100) and in the number of revertant (Trp+) colonies in the tester strain WP2uvrA both in the absence
and presence of S9-metabolic activation.  These results were confirmed in an independently repeated experiment.

Table 1a Experiment II Number of revertants per plate (mean of 3 plates)

Strain	TA 1535			TA 1537			TA 98
Concentration µg/plate	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity
Positive control	283	354	-	244	372	-	124	895	-
Solvent control	19	16	-	6	10	-	13	16	-
10	15	16	no	8	8	no	15	12	no
33	16	19	no	5	6	no	13	14	no
100	16	19	no	9	7	no	12	14	no
333	17	16	no	7	7	no	12	16	no
1000*	18	22	no	6	5	no	12	14	no

* Precipitate

Table 1b Experiment I Number of revertants per plate (mean of 3 plates)

Concentration µg/plate	TA 100			E coli WP2uvrA
	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity
Positive control	964	1754	-	323	91	-
Solvent control	97	94	-	11	7	-
3	115	111	no	8	7	no
10	120	92	no	8	9	no
33	110	114	no	7	9	no
100	102	106	no	8	5	no
333	88	118	no	6	6	no
1000*	108	126	no	4	8	no
3330*	94	101	no	8	7	no
5000*	92	124	no	8	12	no

* Precipitate

Table 2a Experiment II Number of revertants per plate (mean of 3 plates)

Concentration µg/plate	TA 1535			TA 1537			TA 98
	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity
Positive control	152	277	-	575	247	-	132	924	-
Solvent control	5	10	-	4	4	-	15	21	-
10	11	12	no	3	7	no	14	25	no
33	11	11	no	4	8	no	16	22	no
100	11	12	no	3	4	no	15	26	no
333	10	9	no	4	7	no	16	23	no
1000*	11	9	no	5	6	no	15	28	no

* Precipitate

Table 2b Experiment II Number of revertants per plate (mean of 3 plates)

Concentration µg/plate	TA 100			E coli WP2uvrA
	- S9	+ S9	Cytotoxicity	- S9	+ S9	Cytotoxicity
Positive control	965	1722	-	386	152	-
Solvent control	84	95	-	7	9	-
10	93	109	no	9	10	no
33	85	97	no	9	14	no
100	83	106	no	8	8	no
333	83	109	no	10	12	no
1000*	73	101	no	6	8	no

* Precipitate

Applicant's summary and conclusion

Conclusions:

Dodecamethylcyclohexasiloxane has been tested in a reliable study conducted in accordance with OECD Test Guideline 471 and in compliance with GLP. No evidence of test substance induced increase in the number of revertants was observed when the substance was tested in the presence and absence of metabolic activation in Salmonella typhimurium strains TA1535, TA1537, TA100 and TA98 and Escherichia coli WP2uvrA, in either the initial or the independent repeat experiment. Appropriate solvent and positive controls were included and gave expected responses. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test.