Hexadecyltrimethoxysilane

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Gene mutation (Bacterial reverse mutation assay / Ames test, OECD TG 471):
S. typhimurium TA 1535, TA 1537, TA 98, TA 100, and TA 102: negative with and without metabolic activation
S. typhimurium TA 1535, TA 1537, TA 98, TA 100, and E. coli WP2 uvrA: negative with and without metabolic activation

Mammalian cytogenicity (CHO chromosome aberration assay, OECD TG 473): negative with and without metabolic activation
Mammalian Mutagenicity (Mouse Lymphoma Assay, OECD TG 476, RA from CAS 5894-60-0): negative with and without metabolic activation

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2002-04-15 to 2002-07-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EC 92/69/EEC L383 A: part B Determination of Toxicity-Mutagenicity

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: ICH S2A Specific Aspects of Regulatory Genotoxicity Tests for Pharmaceuticals

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: ICH S2B: A Standard Battery for Genotoxicity Testing of Pharmaceuticals

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Target gene:

his operon

Species / strain / cell type:

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

Species / strain / cell type:

S. typhimurium TA 102

Metabolic activation:

with and without

Metabolic activation system:

cofactor supplemented post-mitochondrial fraction (S9 mix), prepared from the livers of rats treated with Aroclor 1254

Test concentrations with justification for top dose:

Pre-test: 0.316, 1, 3.16, 10, 31.6, 100, 316, 1000, 3160, 5000 µg/plate
Main test: 100, 316, 1000, 3160, 5000 µg/plate

Vehicle / solvent:

- Vehicle/solvent used: acetone
- Justification for choice of solvent/vehicle: Solubility properties and relative non-toxicity to bacteria

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

9-aminoacridine

2-nitrofluorene

sodium azide

cyclophosphamide

methylmethanesulfonate

other: 2-anthracene amide

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation); preincubation

DURATION
- Preincubation period: 60 minutes
- Exposure duration: 48 hours

NUMBER OF REPLICATIONS: triplicates in two independent experiments

DETERMINATION OF CYTOTOXICITY
- Method: growth of background lawn

OTHER:
Controls:
with S9: 2-anthracene amide (2-ATA - TA 1537, TA 98 and TA 102, 2 µg/plate in DMSO; cyclophosphamide (CS - TA 100 and TA1535, 1500 µg/plate in aqua ad iniectabilia)
without S9: sodium azide (NaN3 - TA 1535 and TA 100, 10 µg/plate in water); 9-aminoacridine (9-AA - TA 1537, 100 µg/plate in ethanol); 2-nitrofluorene (2-NF; TA 98, 10 µg/plate in DMSO), methyl methane sulfonate (MMS – TA 102, 1300 µg/plate in DMSO)

Evaluation criteria:

A result is considered positive if the number of revertants is significantly increased compared to the solvent control to at least 2-fold of the solvent control for TA 98, TA 100 and TA 102 and 3-fold of the solvent control for TA 1535 and TA 1537 in both experiments. In addition, a significant concentration related effect is observed in positive results, and positive results have to be reproducible and the histidine independence of revertants confirmed.

Positive results have to be reproducible and the histidine independence of the revertants has to be confirmed by streaking on histidine-free agar
plates.

Cytotoxicity is defined as a reduction in the number of colonies by >50% compared with the solvent control and/or a sparse background lawn.

Statistics:

MANN and WHITNEY and Spearman’s rank.

Species / strain:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

TA 1537 (at 5000 µg/plate, +S9, only in plate incorporation test)

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS

- Precipitation: Non-interfering substance precipitate was noted at 5000 µg/plate in all test strains

COMPARISON WITH HISTORICAL CONTROL DATA: Results were within range of historical control data

Table 2: Dose range-finding study number of revertants per plate (2 plates)

	TA100
Conc. (µg/plate)	Plate 1	Plate 2	Cytotoxic (yes/no)
0*	114	137	No
0.316	110	126	No
1	123	134	No
3.16	137	150	No
10	129	159	No
31.6	134	119	No
100	133	137	No
316	119	125	No
1000	141	129	No
3160	114	121	No
5000	132	119	No

*solvent control with acetone

Table 3: Experiment 1 (plate incorporation): number of revertants per plate (mean of 3 plates)

	TA98			TA100			TA102
Conc. (µg/plate)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+  MA	Cytotoxic (yes/no)
0*	30.3	31	No	128.3	144.3	No	269	287.7	No
100	38	27.7	No	122.7	137.7	No	265.7	289.3	No
316	28	27.3	No	122.3	137.3	No	251.3	282.3	No
1000	30.3	28.3	No	123.3	119.7	No	246	271	No
3160	31	30	No	127	136	No	257.7	285	No
5000	35.3	25.3	No	119.7	152	No	291	282	No
Positive control	1200.7	1211.3	No	1226.7	1259.7	No	1107.7	1277.7	No

*solvent control with acetone

Table 3: Experiment 1 (plate incorporation): number of revertants per plate (mean of 3 plates)

	TA1535			TA1537
Conc. (µg/plate)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)
0*	13.3	12.3	No	7	9.7	No
100	12.7	11.7	No	8.7	8.7	No
316	14.7	14.3	No	9.3	6.3	No
1000	12	12.7	No	10.3	6.7	No
3160	11	12.7	No	10.7	6	No
5000	12	14	No	9.3	0	Yes
Positive control	364	350	No	392.7	358	No

*solvent control with acetone

Table 4: Experiment 2 (preincubation): number of revertants per plate (mean of 3 plates)

	TA98			TA100			TA102
Conc. (µg/plate)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)
0*	51	34.3	No	127.3	164	No	278.7	290.3	No
100	51	37	No	127	152.7	No	167	278	No
316	46.7	36.3	No	120	146.7	No	278.7	298.7	No
1000	56.3	49.7	No	140.7	153.7	No	288.7	287	No
3160	52	43.7	No	132	158	No	297.7	286	No
5000	48.3	43	No	132	175.7	No	289.7	266.7	No
Positive control	910	906	No	1179.7	1226.7	No	1231.7	1220.3	No

*solvent control with acetone

Table 4: Experiment 2 (preincubation): number of revertants per plate (mean of 3 plates)

	TA1535			TA1537
Conc. (µg/plate)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)
0*	13	11.7	No	6	6	No
100	11	13.3	No	5	9	No
316	12.3	16.7	No	4.3	8	No
1000	13	16.3	No	5.3	7	No
3160	11	16.3	No	4	5	No
5000	12.3	14	No	4	6	No
Positive control	524.7	556.3	No	486.7	508.7	No

*solvent control with acetone

Conclusions:

Interpretation of results:
negative

No mutagenic effect was observed for the test substance tested up to the limit dose in any of the test strains in two independent
experiments without and with metabolic activation.

Reference 2

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

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

(adopted 1997)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministerium für Arbeit, Gesundheit und Soziales des Landes Nordrhein-Westfalen, Düsseldorf, Germany

Type of assay:

bacterial reverse mutation assay

Target gene:

his operon

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:

cofactor supplemented post-mitochondrial fraction (S9 mix), prepared from the livers of rats treated with Aroclor 1254

Test concentrations with justification for top dose:

Experiment I+II
- 62, 185, 556, 1667, 5000 µg/plate (with and without metabolic activation)
Experiment III:
- 1000, 2000, 3000, 4000, 5000 µg/plate (with and without metabolic activation)

Vehicle / solvent:

- Vehicle/solvent used: acetone

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: -S9: NaN3: 2 µg/plate (TA 100, TA 1535); 9-AA: 50 µg/plate (TA 1537); 2-NF: 4 µg/plate (TA 98); 4-NQO: 1 µg/plate (E.coli WP2 uvrA); +S9: 2-AA: 7 µg/plate (TA 1535, TA 1537), 2 µg/plate (TA 100), 10 µg/plate (E.coli WP2 uvrA); BaP: 30 µg/plate (TA 98)

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation)

DURATION
- Exposure duration: 48 h

NUMBER OF REPLICATIONS: triplicates in 3 independent experiments (test substance); six plates per experiment for the solvent control

DETERMINATION OF CYTOTOXICITY
- Method: growth of background lawn

Evaluation criteria:

A test substance producing no biologically relevant positive response in any one of the bacterial strains tested is considered to be non-mutagenic in this system. A biologically relevant response is described as follows: If the number of revertants is at least twice the spontaneous reversion rate for TA 1535, TA 98, TA 100 or WP2 uvrA (or three times for TA 1537) and/or if there is a concentration related increasing number of revertants over the range tested.

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: no cytotoxicity, but tested up to limit concentration; precipitates from 1000 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: no cytotoxicity, but tested up to limit concentration; precipitates from 1000 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: no cytotoxicity, but tested up to limit concentration; precipitates from 1000 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: no cytotoxicity, but tested up to limit concentration; precipitates from 1000 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: no cytotoxicity, but tested up to limit concentration; precipitates from 1000 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS
- Precipitation: from 1000 µg/plate and higher

COMPARISON WITH HISTORICAL CONTROL DATA: Historical control data were given in the study report. The results of the solvent control cultures lied within the range of the historical control data.

OTHER:
- Revertant counts higher than 1000 were counted and calculated as 1000.
- Study plan amendment: Due to invalid positive and solvent controls for the strains Salmonella typhimurium TA 100 and Escherichia coli WP2 uvrA parts of the first experiment had to be repeated (=second experiment).

Table 1: Mean values of experiment 1 and 2.

With or without S9-Mix	Test substance concentration (µg/plate)	Mean number of revertant colonies per plate (average of 3 plates ± Standard deviation)
		TA 1535	TA 1537	TA 98	TA 100	WP2 uvrA
–	0	9±3	4±3	20±4	207±34	17±6
–	62	7±3	3±1	23±6	202±30	16±3
–	185	10±2	3±3	24±3	219±26	19±4
–	556	6±3	8±3	20±1	222±39	15±5
–	1667, P	11±3	3±3	25±6	187±5	13±3
–	5000, P	9±5	5±3	27±3	200±9	12±2
Positive controls, –S9	Name	NaN3	9-AA	2-NF	NaN3	4-NQO
	Concentrations (µg/plate)	2	50	4	2	1
	Revertants per plate	677±107	328±45	363±64	1000±0	491±100
+	0	13±4	6±3	28±3	130±20	23±3
+	62	12±1	4±1	34±2	142±11	21±4
+	185	14±2	4±2	21±4	109±10	20±5
+	556	8±2	4±2	23±6	107±7	21±2
+	1667, P	12±2	4±3	28±6	129±12	19±4
+	5000, P	8±5	5±1	25±9	125±13	23±2
Positive controls, +S9	Name	2-AA	2-AA	B[a]P	2-AA	2-AA
	Concentrations (µg/plate)	7	7	30	2	10
	Revertants per plate	531±45	595±58	1000±0	1000±0	206±23

P: precipitation observed

 

Table 2: Results of experiment 3.

With or without S9-Mix	Test substance concentration (µg/plate)	Mean number of revertant colonies per plate (average of 3 plates ± Standard deviation)
		TA 1535	TA 1537	TA 98	TA 100	WP2 uvrA
–	0	9±2	4±1	21±4	105±12	20±6
–	1000, P	9±3	4±3	28±4	140±26	17±6
–	2000, P	13±5	1±1	22±4	134±33	28±11
–	3000, P	10±3	5±2	23±2	129±5	22±8
–	4000, P	10±4	2±2	19±1	137±21	25±1
–	5000, P	10±2	3±2	23±4	117±12	20±7
Positive controls, –S9	Name	NaN3	9-AA	2-NF	NaN3	4-NQO
	Concentrations (µg/plate)	2	50	4	2	1
	Revertants per plate	704±73	147±13	400±71	1000±0	613±41
+	0	9±2	4±1	21±4	105±12	20±6
+	1000, P	9±3	4±3	28±4	140±26	17±6
+	2000, P	13±5	1±1	22±4	134±33	28±11
+	3000, P	10±3	5±2	23±2	129±5	22±8
+	4000, P	10±4	2±2	19±1	137±21	25±1
+	5000, P	10±2	3±2	23±4	117±12	20±7
Positive controls, +S9	Name	2-AA	2-AA	B[a]P	2-AA	2-AA
	Concentrations (µg/plate)	7	7	30	2	10
	Revertants per plate	491±44	584±97	805±78	1000±0	274±103

 P: precipitation observed

Conclusions:

Interpretation of results:
negative

In a study according to OECD 471 and in compliance with GLP no mutagenic effect was observed for the test substance tested up to the limit concentration in any of the test strains in three independent experiments with and without metabolic activation.

Reference 3

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

02 Sep 2004 to 03 Dec 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

Version / remarks:

(adopted 1997)

Deviations:

no

GLP compliance:

yes

Type of assay:

in vitro mammalian chromosome aberration test

Target gene:

Not applicable

Species / strain / cell type:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Metabolic activation system:

phenobarbital and beta-naphthoflavone induced rat liver S9

Test concentrations with justification for top dose:

Experiment I+II:
- 10.2, 20.3, 40.6, 81.3, 163, 325, 650, 1300 µg/ml (with and without metabolic activation)

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: ethanol
- Justification for choice of solvent/vehicle: Solubility properties and relative non-toxicity to cells

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: -S9: mitomycin: 0.3 µg/ml (3 h treatment), 0.1 µg/ml (20 h treatment); +S9: cyclophosphamide: 15 µg/ml (3 h treatment)

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium

DURATION
- Preincubation period:
- Exposure duration: 3 h and 20 h
- Fixation time (start of exposure up to fixation or harvest of cells): 20 h

SPINDLE INHIBITOR (cytogenetic assays): colcemid (0.2 µg/ml; added 3 hours before harvest)
STAIN (for cytogenetic assays): Giemsa (3%)

NUMBER OF REPLICATIONS: 2 independent experiment

NUMBER OF CELLS EVALUATED: 100 cells from each culture were evaluated for chromosome abberations.

DETERMINATION OF CYTOTOXICITY
- Method: relative cell count

Evaluation criteria:

The test item is considered to have clastogenic properties if there is a statistically significant increase in the incidence of cells bearing aberrations at any dose level over the concurrent control. The increase must exceed historical control values. The increases must be reproduced in both cultures.

Statistics:

Where necessary, the frequency of cells with aberrations excluding gaps, and the frequency of polyploid cells was compared with the concurrent vehicle control using Fischer's Exact test.

Species / strain:

Chinese hamster Ovary (CHO)

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 examined

Positive controls validity:

valid

Additional information on results:

COMPARISON WITH HISTORICAL CONTROL DATA: Results were within range of historical control data

Table 2: Results of chromosome analysis Experiment 1, 3h treatment without activation (total count from 2 cultures)

		Untreated ***	Solvent* Control***	Positive Control**	Low dose***	Mid dose***	High dose***
Cytotoxicity		no	no	no	no	no	no
		Mean
Chromatid aberrations	gaps	0	0	3	0	0	1
	deletions	0	0	25	0	0	0
	interchanges	0	0	49	0	0	0
Chromosome aberrations	gaps	NR	NR	NR	NR	NR	NR
	deletions	0	0	3	0	0	0
	interchanges	0	0	0	0	0	0
Mitotic index		NR	NR	NR	NR	NR	NR
Polyploidy		0	0	0	0	0	0
Endo reduplication		0	0	0	0	0	0

 *Solvent control with ethanol

** Per 150 cells

*** Per 200 cells

NR not reported

Table 3: Results of chromosome analysis Experiment 1, 3h treatment with activation (total count from 2 cultures)

		Untreated ***	Solvent* Control***	Positive Control**	Low dose***	Mid dose***	High dose***
Cytotoxicity		no	no	no	no	no	no
		Mean
Chromatid aberrations	gaps	0	0	3	0	0	1
	deletions	0	0	25	1	0	22
	interchanges	0	0	49	0	0	40
Chromosome aberrations	gaps	NR	NR	NR	NR	NR	NR
	deletions	0	0	3	0	0	5
	interchanges	0	0	0	0	0	0
Mitotic index		NR	NR	NR	NR	NR	NR
Polyploidy		0	0	0	0	0	0
Endo reduplication		2	0	0	0	0	0

 *Solvent control with ethanol

** Per 150 cells

*** Per 200 cells

NR not reported

Table 4: Results of chromosome analysis Experiment 2, 20h treatment without activation (total count from 2 cultures)

		Untreated ***	Solvent* Control***	Positive Control**	Low dose***	Mid dose***	High dose***
Cytotoxicity		no	no	no	no	no	no
		Mean
Chromatid aberrations	gaps	0	0	0	0	0	1
	deletions	1	1	7	1	1	0
	interchanges	4	0	52	0	1	0
Chromosome aberrations	gaps	NR	NR	NR	NR	NR	NR
	deletions	0	0	9	2	3	0
	interchanges	0	0	0	0	0	0
Mitotic index		NR	NR	NR	NR	NR	NR
Polyploidy		0	0	0	0	0	0
Endo reduplication		0	0	0	0	0	0

 *Solvent control with ethanol

** Per 150 cells

*** Per 200 cells

NR not reported

Conclusions:

Interpretation of results:
negative

The substance was tested to OECD 473 (1997) under GLP. The test material did not induce any statistically significant, dose-related increases in the frequency of cells with chromosomal aberrations either in the presence or absence of metabolic activation or after various exposure times. The test material was therefore considered to be non-clastogenic to CHO cells in vitro under the conditions of the test.

Reference 4

Endpoint:

in vitro gene mutation study in mammalian cells

Remarks:

Type of genotoxicity: gene mutation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Conclusions:

Interpretation of results:
negative with and without metabolic activation

Executive summary:

The structural analogue trichloro(hexadecyl)silane (CAS 5894-60-0) was assessed for its potential to induce mutations at the mouse lymphoma thymidine kinase locus using the cell line L5178Y. It is concluded that the structural analogue is negative for mutagenicity to mammalian cells under the conditions of the test. As explained in the justification for type of information, a similar outcome is considered for the target substance as well.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

In vivo testing is not required as no ambiguous or positive results for genetic toxicity were found in the in vitro studies.

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In the key Ames test according to OECD TG 471 and in compliance with GLP, Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and E. coli strain WP2 uvrA were treated with up to 5000 µg/plate hexadecyl(trimethoxy)silane in the presence and absence of a metabolic activation system in a plate incorporation assay. No increase of the number of revertants was observed in any strain and in any experiment. Precipitation was observed beginning with 1000 µg/plate and no cytotoxic effects were noted (Evonik, 2011).

In an Ames test according to OECD TG 471 and in compliance with GLP, Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and TA 102 were treated with up to 5000 µg/plate hexadecyl(trimethoxy)silane in the presence and absence of a metabolic activation system in a preincubation and a plate incorporation assay. No increase of the number of revertants was observed in any strain and in any test. Precipitation was observed at 5000 µg/plate and cytotoxic effects were observed in strain TA 1537 at 5000 µg/plate in the plate incorporation assay, only (LPT, 2002d).

The results of both studies are in agreement and give evidence that the test substance is non-mutagenic in the bacterial reverse mutation assay under the applied test conditions.

 

In the chromosome aberration assay, according to OECD TG 473 and in compliance with GLP, Chinese Hamster Ovary Cells were treated with up to 1300 µg/mL hexadecyl(trimethoxy)silane in the presence and absence of metabolic activation (RTC, 2005). The cells were treated for 3 h (with and without metabolic activation) and for 20 h (without metabolic activation). After 20 h the cells were fixed and stained with Giemsa after previous exposure to colcemid. The test material did not induce any statistically significant, dose-related increases in the frequency of cells with chromosomal aberrations either in the presence or absence of metabolic activation or after various exposure times. The test material was therefore considered to be non-clastogenic to CHO cells in vitro under the conditions of the test.

 

No data is available for in vitro mammalian mutagenicity for the registered substance. However, an OECD TG 490 study with hexadecyl(trimethoxy)silane is on-going, but the results will not be available for this current dossier update. Therefore, as an interim measure, the hazard assessment was performed based on available data from the structural analogue trichloro(hexadecyl)silane (CAS 5894-60-0). In accordance with Regulation (EC) No. 1907/2006 Annex XI, 1.5 “Grouping of substances and read across” and in accordance with the Read across assessment framework (RAAF, ECHA 2017) read across from analogue substances has been applied to support the human health hazard assessment of hexadecyl(trimethoxy)silane (CAS 16415-12-6). Further details are provided in the analogue justification attached to the respective target entry.

In the key in vitro mammalian mutagenicity study (BSL, 2012), the structural analogue substance trichloro(hexadecyl)silane (CAS 5894-60-0) was assessed for its potential to induce mutations at the mouse lymphoma thymidine kinase locus using the cell line L5178Y. The study was conducted according to OECD TG 476 and in compliance with GLP. No biologically relevant increase of mutants was found after treatment with the test item (with and without metabolic activation). The Global Evaluation Factor (GEF; defined as the mean of the negative/vehicle mutant frequency plus one standard deviation; data gathered from ten laboratories) was not exceeded by the induced mutant frequency at any concentration. Concentrations with RTG values below 10% were not considered for evaluation of mutagenicity. No dose-response relationship was observed. Colony sizing showed no clastogenic effects induced by the test item under the experimental conditions (with and without metabolic activation). Appropriate solvent and positive controls were included in the test and gave the expected results. It was therefore concluded that the test substance is not mutagenic to mammalian cells under the conditions of the test.

Justification for classification or non-classification

The available data on genetic toxicity of the test substance do not meet the criteria for classification according to Regulation (EC) No. 1272/2008, and are therefore conclusive but not sufficient for classification.