Octamethylcyclotetrasiloxane

Endpoint summary

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 all strains tested (OECD TG 471) (BRRC, 1993a).
Cytogenicity in mammalian cells: negative in cultured human lymphocytes (similar to OECD TG 473) (BRRC, 1993b).
Mutagenicity in mammalian cells: negative in L5178Y mouse lymphoma cells (similar to OECD TG 476) (Isquith, 1988a).

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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The range of strains used does not comply with current guidelines

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

1983

Qualifier:

according to guideline

Guideline:

other: EPA Fed Reg 50, 51, 51 (1987)

Principles of method if other than guideline:

preincubation method

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Species / strain / cell type:

S. typhimurium, other: TA98, TA100, TA1535, TA1537, TA1538

Metabolic activation:

with and without

Metabolic activation system:

Aroclor 1254-induced rat liver S9 

Test concentrations with justification for top dose:

0.0003 - 5.0 mg/plate (10 concentrations, cytotoxicity test); 0.1-5.0 mg/plate (5 concentrations, mutagenicity test)

Vehicle / solvent:

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

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 4-nitro-phenylenediamine

Remarks:

TA 98 and TA 1538 without 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 activation

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

Remarks:

TA 100 and TA 1535 without activation

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); preincubation;

DURATION
- Preincubation period: 20 minutes
- Exposure duration: 48-72 hours
- Expression time (cells in growth medium): 48-72 hours


NUMBER OF REPLICATIONS: triplicate


DETERMINATION OF CYTOTOXICITY
- Method: other: growth of background lawn, number of revertants

METABOLIC ACTIVATION
S9 homogenate from Aroclor 1254-induced rats was obtained from Microbiological associates, Bethesda, Maryland, and checked for activity with 7,12-dimethylbenzanthracene. S9 mix included 8 mM MgCl2, 33 mM KCl, 5 mM glucose-6-phophate, 4 mM NADP. 100 mM sodium phosphate pH 7.4, and S9. Amount of S9 was based on activity with 7,12-dimethylbenzanthracene.

Evaluation criteria:

A dose-related increase in the mean reversion frequency compared to solvent control in at least one strain was considered positive if at least one dose produced at least twice the reversion frequency of the solvent control

Statistics:

Mean an standard deviation of replicate plates

Key result

Species / strain:

other: Salmonella typhimurium TA98, TA100, TA1535, TA1537, TA1538

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

Concurrent sterility testing indicated that the test substance, the S9 mix, and all solvent and control agents were sterile.

Table 1a: Experiment 1 Plate incorporation Number of revertants per plate (mean of 3 plates)

Conc. (µl/ml)	TA 98			TA 100			TA 1535
	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)
0*	18	27	No	108	112	No	15	18	No
100	20	34	No	105	131	No	17	20	No
300	17	30	No	127	109	No	16	15	No
1000	29	27	No	123	116	No	18	18	No
3000	24	27	No	117	109	No	16	18	No
5000	20	31	No	125	112	No	18	16	No
Positive control	431	1216	-	933	1780	-	1033	15	-

*solvent control with ethanol

 

 

Table 1b : Experiment 1 Plate incorporation Number of revertants per plate

Conc. (µl/ml)	TA 1537			TA 1538
	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)
0*	13	6	No	9	17	No
100	9	12	No	8	16	No
300	9	7	No	12	24	No
1000	8	10	No	9	17	No
3000	7	9	No	6	20	No
5000	10	7	No	7	13	No
Positive control	118	169	-	924	1259	-

*solvent control with ethanol

 

Table 2a: Experiment 2 Plate incorporation Number of revertants per plate (mean of 3 plates)

Conc. (µl/ml)	TA 98			TA 100			TA 1535
	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)
0*	21	31	No	126	117	No	12	15	No
100	21	23	No	119	111	No	11	14	No
300	22	32	No	110	122	No	16	19	No
1000	19	21	No	105	91	No	15	14	No
3000	22	22	No	123	97	No	9	11	No
5000	13	26	No	107	102	No	12	14	No
Positive control	680	1038	-	942	2249	-	942	153	-

*solvent control with ethanol

 

 

Table 2b : Experiment 2 Plate incorporation Number of revertants per plate

Conc. (µl/ml)	TA 1537			TA 1538
	- MA	+ MA	Cytotoxic (yes/no)	- MA	+ MA	Cytotoxic (yes/no)
0*	7	9	No	7	16	No
100	8	6	No	5	14	No
300	7	5	No	9	12	No
1000	9	6	No	9	16	No
3000	8	6	No	9	13	No
5000	8	8	No	8	16	No
Positive control	282	337	-	715	1364	-

*solvent control with ethanol

Conclusions:

Octamethylcyclotetrasiloxane has been tested under GLP according to OECD 471 (1983). No increase in the number of reversions was observed. The test substance is considered to be negative for mutagenicity in 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:

1992-04-15 to 1992-04-16

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: EPA health effects testing Guideline 50 (188) 40 CFR part 798

Qualifier:

equivalent or similar to guideline

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:

Chinese hamster Ovary (CHO)

Details on mammalian cell type (if applicable):

- Type and identity of media: Ham's modified F12 medium (hypoxanthine free) supplemented with 10% v/v bovine serum albumen
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes

Metabolic activation:

with and without

Metabolic activation system:

Aroclor 1254-induced rat liver S9

Test concentrations with justification for top dose:

0.0003 - 0.01 mg/ml, (without activation) 0.003 - 0.03 mg/ml (with activation)

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: ethanol
- Justification for choice of solvent/vehicle: none given in study report

Untreated negative controls:

yes

Remarks:

untreated

Negative solvent / vehicle controls:

yes

Remarks:

ethanol

True negative controls:

no

Positive controls:

yes

Positive control substance:

triethylenemelamine

Remarks:

without activation: TEM 1.5 µg/ml

Positive control substance:

cyclophosphamide

Remarks:

with activation: CP 20 µg/ml

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium

DURATION
- Preincubation period:
- Exposure duration: 4 hours
- Expression time (cells in growth medium): 10 hours (without S9, with S9 at most doses), 24 hours (with S9, 0.03 mg/ml dose only)
- Selection time (if incubation with a selection agent):
- Fixation time (start of exposure up to fixation or harvest of cells):

SPINDLE INHIBITOR (cytogenetic assays): Colchicine 0.5 mg/ml
STAIN (for cytogenetic assays): Giesma

NUMBER OF REPLICATIONS: Duplicate cultures

NUMBER OF CELLS EVALUATED: 100 cells per culture

DETERMINATION OF CYTOTOXICITY
- Method: mitotic index; relative survival rates

OTHER: Cell cycle delay determined to optimise cell sampling times

METABOLIC ACTIVATION
S9 homogenate from Aroclor 1254-induced rats was obtained from Microbiological associates, Bethesda, Maryland, and checked for activity with 7,12-dimethylbenzanthracene. S9 mix included 10 mM MgCl2, 30 mM KCl, 10 mM CaCl2, 5 mM glucose-6-phophate, 4 mM NADP. 100 mM sodium phosphate pH 7.4, and S9. Amount of S9 was based on activity with 7,12-dimethylbenzanthracene. The concentration of S9 in the final cultures was not stated but was sufficient to induce mutagenicity in the positive control (cyclophosphamide).

Statistics:

Pearson Chi squared test

Key result

Species / strain:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

0.01 mg/ml without activation, 0.003 mg/ml with activation

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RANGE-FINDING/SCREENING STUDIES: A range-finding study determined that relative survival rates were decreased by almost 50% at a concentration of0.003 mg/ml in the absence of activation.


COMPARISON WITH HISTORICAL CONTROL DATA: not included


ADDITIONAL INFORMATION ON CYTOTOXICITY: In the range-finding study, a significant cell cycle delay was observed in the presence of activation at a dose of 0.03 mg/ml

There were no qualitative differences or significant quantitative differences between the types and frequencies of aberrations observed in the D4 -treated and solvent control cultures.

Without activation:

	mean percentage aberrant cells
D4-treated cultures:	1.0 -3.0%
solvent control:	1.50%
positive (TEM) control:	39.0%

With activation:

	mean percentage aberrant cells
D4-treated cultures:	1.5-2.5%
solvent control:	3.00%
positive (CP) control:	19.00%

             

Conclusions:

Octamethylcyclotetrasiloxane has been tested in a reliable study according to EPA health effects guideline for in vitro chromosome aberration under GLP. Appropriate replicates and controls were used in the study. The study was not repeated with a longer exposure time. No increase in the number of cells with aberrations was observed. It is concluded that octamethylcyclotetrasiloxane is negative for cytogenicity 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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)

Deviations:

not specified

Principles of method if other than guideline:

mouse lymphoma gene mutation assay (modification of Clive & Spector (1975)

GLP compliance:

not specified

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:

0.0032 - 0.05 µl/ml. equivalent to 3.2-50 µg/ml

Vehicle / solvent:

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

- Justification for choice of solvent/vehicle: none given in report

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:

other: dimethylnitrosomine

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 CELLS EVALUATED: 9 x 10E+06

DETERMINATION OF CYTOTOXICITY

- Method: relative total growth

Evaluation criteria:

A positive result is indicated by a dose-dependent, reproducible HRMF (highest relative mutation frequency) of 2.5 or greater.

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

at 50 µg/ml

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Compound	S-9	Dose range		Min TRG*	Max Response**			Dose related Response***
		Low	High		Dose	TRG	HRMF
Octamethylcyclotetrasiloxane	-	0.0032	0.05	7	0.05	7	1.4	b
	+	0.0032	0.05	61	0.025	107	1	b

TRG = total relative growth

HRMF = highest relative mutation frequency

*TRG is the product of relative suspension growth and relative clonal efficiency expressed as a percentage. The number provides an indication of cell survival relative to the control systems (100 %) over both expression and   selection periods; i.e. early and late toxicity at the doses indicated. This value indicates the minimum TRG achieved during all trials at some level of exposure.

**Maximum response dose indicates the concentration at which the maximum response occurred relative to the solvent controls; TRG the total relative growth at which this maximum response occurred; HRMF, the number in this column indicates the magnitude of the response of treated controls compared to the solvent controls expressed as a ratio of their mutation frequencies. The ratio represents the highest observed response that occurred at the dose and TRG indicated in the other columns.

***The letters refer to the basic shape of the dose-related response curve: a, mutation frequency increased with dose for at least the two highest doses; b, a saw-tooth pattern – the initial response may be high or low; c, the response at the central doses is higher than at either the low or high dose.

Conclusions:

Octamethylcyclotetrasiloxane has been tested in mouse lymphoma L5178Y cells in a valid study that was similar to OECD 476, but not in compliance with GLP. The test did not cause a statistically significant increase in mutation, and is therefore non-mutagenic in L5178Y mouse-lymphoma cells.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Micronucleus assay inhalation study in rat: Negative (similar to OECD TG 474) (BRRC, 1994b).
Rodent dominant lethal oral study in rat: Negative (OECD TG 426 - similar to OECD 478) (Dow Corning Corporation, 1982).

Link to relevant study records

Reference

Reference 1

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration

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 after exposure by inhalation for 6h per day for 5 days, sampling was carried out at 6 and 24 hours only; only 500 cells were scored to determine mitotic index.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)

Deviations:

yes

Remarks:

inhalation study, sampling times differ from recommended times

Principles of method if other than guideline:

Handbook of in vivo toxicity testing Arnold et al Academic press, New York NY.

GLP compliance:

yes

Type of assay:

micronucleus assay

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague Dawley
- Age at study initiation: 5 weeks
- Weight at study initiation: 213-242 g (males); 135-163 g (females)
- Assigned to test groups randomly: yes
- Fasting period before study: no
- Housing: individually in stainless steel wire mesh cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-22
- Humidity (%): 40-70 %
- Air changes (per hr): no information
- Photoperiod (hrs dark / hrs light): 12 hours

IN-LIFE DATES: From: 10 August 1993 To: 2 October 1993

Route of administration:

inhalation

Vehicle:

Vehicle: air

Details on exposure:

TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Wahmann inhalation chambers 101 x 101 x 60 cm, rectangular with pyramidal top and bottom; volume 900 l
- Source and rate of air: no information
- Method of conditioning air: filtered
- System of generating vapour: liquid D4 from a piston pump into heated glass evaporation chamber
- Temperature, humidity, pressure in air chamber:
- Air flow rate: approx 200 l/minute
- Air change rate: 13-14 air changes per hour
- Treatment of exhaust air: no information

TEST ATMOSPHERE
- Brief description of analytical method used: concentration in exposure chamber was monitored by flame ionization gas chromatography
- Samples taken from breathing zone: no information

Duration of treatment / exposure:

6 h/d

Frequency of treatment:

Once per day for 5 days

Post exposure period:

24 hours

Remarks:

Doses / Concentrations:
0, 720 ppm (actual mean)
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control(s):

- Positive control substance: cyclophosphamide monohydrate
- Justification for choice of positive control(s): none given
- Route of administration: ip injection
- Doses / concentrations: 30 mg.kg bw

Tissues and cell types examined:

Bone marrow

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION: maximum achievable concentration of vapour.

TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields): Animals were treated with Colchicine (4 mg/kg ip) 2-3 hours before sacrifice.

DETAILS OF SLIDE PREPARATION: Bone marrow cells were incubated for 20-30 minutes in hypotonic solution and then fixed with 3:1 methanol:acetic acid. Drops were air dried onto slides which were stained with Giesma. Additional slides were prepared as needed to ensure sufficient numbers of mitotic cells were available for analysis.

METHOD OF ANALYSIS: 5 animals per sex per treatment group per sampling time were selected for evaluation. Where possible, 100 cells per animal were scored for incidence and type of chromosome aberration.

OTHER: 500 cells per animal were scored to determine mitotic index.

Evaluation criteria:

A response is positive if there is a statistically significant exposure related increase in incidence of chromosomal aberrations.

Statistics:

Mann and Whitney's U-test.

Sex:

male/female

Genotoxicity:

negative

Toxicity:

no effects

Remarks:

in bone marrow

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

Positive control test substance cyclophosphamide induced markedly increased incidence of chromosomal aberrations in males and females.

There was a slight reduction in weight gain (males) or in body weight (females). There was no significant of dose-related increase in the incidence of chromosomal aberrations in rats exposed to D4 vapour. Table 1 Induction of chromosomal aberrations in rat bone marrow

Dose	0	700 ppm (6 hour)	700 ppm (24 hour)	Positive control
Number of animals	5	5	5	6
Cells counted	500	500	500	586
Total number of aberrant cells	2	5	6	99
Percentage aberrant cells	0.4	1.0	1.2	16.9

Conclusions:

Octamethylcyclotetrasiloxane has been tested under GLP in a valid study which was conducted according to a protocol that is similar to OECD 475 and in compliance with GLP. There was no statistically significant increase in chromosome aberrations in rat bone marrow cells as a result of exposure to the test substance. It is concluded that Octamethylcyclotetrasiloxane is negative for clastogenicity (induction of chromosome aberrations) in rats under the conditions of the test.

Reference 2

Endpoint:

in vivo mammalian germ cell study: cytogenicity / chromosome aberration

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 are that animals were dosed over an eight week period. It was not compliant with GLP.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 478 (Genetic Toxicology: Rodent Dominant Lethal Test)

Deviations:

yes

Remarks:

repeat exposure

Qualifier:

according to guideline

Guideline:

other: OECD 426 1981

GLP compliance:

yes

Type of assay:

rodent dominant lethal assay

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Spartan Research, Haslett, Michigan USA
- Age at study initiation: males 10-12 weeks, females younger
- Weight at study initiation:
- Assigned to test groups randomly: yes
- Fasting period before study:
- Housing: individually in wire-bottomed stainless steel cages
- Diet: libitum
- Water: ad libitum
- Acclimation period:7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 45-55
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: not available

Route of administration:

oral: gavage

Vehicle:

No information

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: no information- possibly undiluted test substance

Dosing: By gavage

Duration of treatment / exposure:

8 weeks

Frequency of treatment:

Males dosed daily at 5 days per week for eight weeks.

Post exposure period:

2 weeks mating (2 virgin females per week). Females removed if impregnated (judged by vaginal plug and microscopic determination of presence of sperm). Females sacrificed at 14 days after mid-week of mating.

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Remarks:

by gavage of gas chromatographically analysed test substance

Dose / conc.:

500 mg/kg bw/day (actual dose received)

Remarks:

by gavage of gas chromatographically analysed test substance

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

Remarks:

by gavage of gas chromatographically analysed test substance

No. of animals per sex per dose:

15 males per dose level, 2 females (untreated) per male

Control animals:

yes, concurrent vehicle

Positive control(s):

- Positive control substance: triethylenemelamine
- Justification for choice of positive control(s): a known clastogen was used as the positive control
- Route of administration: oral by gavage
- Doses / concentrations: 0.05 mg/kg bw/day

Tissues and cell types examined:

Rat bone marrow

Details of tissue and slide preparation:

Females were sacrificed and ovaries and uteri examined. The number of corpora lutea and living and dead implantations were counted for each pregnant female.

Evaluation criteria:

Statistically significant induction of dominant lethals.

Statistics:

Fischer's exact probability test (fertility index); t-test (total number of implantations, litter size and corpora lutea/pregnant female) Wilcoxson test (modified by Haseman and Hoel) (preimplantation loss and dead versus total implants per pregnant female). Comparison's were made on a per litter and a per put basis.

Sex:

male/female

Genotoxicity:

negative

Toxicity:

no effects

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

No effects on body weight, mortality, clinical signs
positive control test substance Triethylenemelamine induced clear dominant lethal syndrome
RESULTS OF RANGE-FINDING STUDY
- Other: a preliminary acute toxicity study failed to reach a maximum tolerated dosage volume, so MTD was assumed to be 1000 mg/kg bw/day

RESULTS OF DEFINITIVE STUDY
- Appropriateness of dose levels and route: The dose levels and route are judged to be appropriate. The dominant lethal assay was extended to increase the sensitivity of response to the administration of the test substance.
- Statistical evaluation: no statistically significant difference between negative control and test animals was observed.

Table 1 Effect of test substance on genetic parameters (average of 2 mating weeks)

		Negative control	100 mg/kg	500 mg/kg	1000 mg/kg	Positive control
Fertility Index	Pregnant females/mated females	0.45	0.44	0.36	0.38	0.22
Proportion of females with	1 or more dead implants %	48.2	39.1	45.0	47.6	76.9
	2 or more dead implant %	19.1	13.0	10.0	7.4	69.2
Generation of deciduomata - pups %		4.8	3.9	4.0	4.9	33.8
Corpora lutea distribution (mean)		15	15	15	14	14
Total implants		14	15	14	13	11
Litter size		13	14	13	13	7
Preimplantation loss %		6.2	3.7	5.2	3.7	24.5

 

Conclusions:

Octamethylcyclotetrasiloxane has been tested in rats using oral gavage administration in a Rodent Dominant Lethal assay. No statistically significant changes were observed in any reproductive parameter. Animals dosed with the positive control did express a dominant lethal syndrome. It is concluded that the test substance is negative for the induction of chromosome damage in germ cells.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Information is available from reliable studies for all the required in vitro endpoints from study reports on D4. 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 negative except in vitro cytogenicity study in L5178Y cells, where an ambiguous result was reported. This study was not chosen at the key study for this endpoint as it is an older study that was not well reported, and did not give a clear result.

Bacterial mutagenicity data are available from three reverse mutagenicity studies (BRRC, 1993a; Bayer AG, 1985b; Isquith, 1988a). None of these studies included a strain capable of detecting cross-linking or oxidising mutagens, as required by the current OECD guideline. In view of the lack of genetic toxicity demonstrated in studies on mammalian cells and in two different in vivo assays, and the absence of structural features that indicate that such mutagenicity is likely, testing in an appropriate 5^thstrain is not considered necessary. In addition, many of the organosilicon substances have been tested in an appropriate 5th strain, and the only organosilicon substance which has given a positive result in a bacterial strain capable of detecting cross-linking or oxidising mutagens contains an epoxy- side-chain (which is a structural feature associated with cross-linking mutagenicity), and this substance was positive in Salmonella typhimurium strains TA 100, TA 1535 as well as in E.coli WP2 uvrA. It is therefore considered that for all the organosilicon substances, whether or not the structure includes structural alerts for genetic toxicity (Benigni et al, 2008), genetic toxicity would be detected in Salmonella typhimurium strains TA 98, TA 100, TA 1535 or 1537.

D4 has been tested in a reliable study according to EPA health effects guideline for in vitro chromosome aberration in compliance with GLP, using Chinese hamster ovary cells (BRRC, 1993b). Appropriate replicates and solvent and positive controls were used in the study. The study was not repeated with a longer exposure time. No increase in the number of cells with aberrations was observed. It is concluded that D4 is negative for cytogenicity under the conditions of the test. The result of a chromosome aberration study using L5178Y cells is in agreement with this study; the increase in aberrations that was observed at overtly cytotoxic concentrations in the older study are not considered by the reviewer to be biologically relevant (Litton Bionetics, 1978).

D4 has been tested in mouse lymphoma L5178Y cells in a valid study that was similar to OECD 476, but not in compliance with GLP (Isquith, 1988a).The test did not cause a statistically significant increase in mutation, therefore it is considered that the test substance is non-mutagenic in L5178Y mouse-lymphoma cells.

Further indication of lack of genetic toxicity is available from a range of non-standard in vitro studies, including: gene mutation in Rat2Lambda lac I fibroblasts (Felix et al., 1998); DNA damage and repair in bacterial and yeast cells, and sister chromatid exchange in mammalian cells(Litton Bionetics, 1978).

Data are available for D4 from two in vivo studies. The results support the overall conclusion from the in vitro studies for lack of genetic toxicity.

D4 has been tested under GLP in a valid study which was conducted according to a protocol that is similar to OECD 475 and in compliance with GLP (BRRC, 1994b). There was no statistically significant increase in chromosome aberrations in rat bone marrow cells as a result of exposure to the test substance. It is concluded that D4 is negative for clastogenicity (induction of chromosome aberrations) in rats under the conditions of the test.

D4 has been tested in rats using oral gavage administration in a Rodent Dominant Lethal assay (Dow Corning Corporation, 1982). No statistically significant changes were observed in any reproductive parameter. Animals dosed with the positive control did express a dominant lethal syndrome. It is concluded that the test substance is negative for the induction of chromosome damage in germ cells.

References

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

The available information for the substance indicates that when tested in vitro, octamethylcyclotetrasiloxane (CAS number 556 -67 -2) does not induce mutations in bacterial or mammalian cells, nor chromosome aberrations in mammalian cells. In addition, negative results were obtained in a number of non-standard assays, including gene mutation in yeast, Sister chromatid exchange and DNA damage in mammalian cells. The conclusion reached from the in vitro results is confirmed by the negative results obtained when the substance was tested in vivo in an inhalation mouse micronucleus assay. In addition, the substance showed no signs of inducing chromosome damage in germ cells in a rodent dominant lethal assay (oral administration).

Based on the available data D4 does not require classification for genetic toxicity according to Regulation (EC) 1272/2008.