Reaction mass of decamethyltetrasiloxane; dodecamethylpentasiloxane; hexamethyldisiloxane; octamethyltrisiloxane

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1994-03-24 to 1994-04-11

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1994

Report date:

1994

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals

Test guideline 2

Qualifier:

equivalent or similar to guideline

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

Test material

Test material information

Constituent 1

Reference substance name:

Hexamethyldisiloxane

EC Number:

203-492-7

EC Name:

Hexamethyldisiloxane

Cas Number:

107-46-0

Molecular formula:

C6H18OSi2

IUPAC Name:

Hexamethyldisiloxane

Method

Target gene:

histidine operon (Salmonella strains); tryptophan operon (E. coli)

Species / strain

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

Controls

Controls 1

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)

Controls 2

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

Controls 3

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

Controls 4

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.

Results and discussion

Test results

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

Any other information on results incl. tables

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

Applicant's summary and conclusion

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.