Boron carbide

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Due to its physico-chemical characteristics boron carbide is considered not to show genetic toxicity which is underlined by the negative results of the "Ames Test" and the micronucleus study with human cells.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in mammalian cells

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Reference 2

Endpoint:

in vitro cytogenicity / micronucleus study

Type of information:

experimental study

Adequacy of study:

key study

Study period:

December 2009 - Septembert 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 487 (In vitro Mammalian Cell Micronucleus Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

in vitro mammalian cell micronucleus test

Species / strain / cell type:

mammalian cell line, other: human lymphocytes

Details on mammalian cell type (if applicable):

- Cell type:

Human peripheral blood lymphocytes from healthy and non-smoking donors with no known recent exposure to genotoxic chemicals and radiation. For this study (in each experiment) blood was collected only from a single donor to reduce inter-individual variability.

- Type and identity of media:

Complete Culture Medium: RPMI 1640 medium supplemented with:
15% foetal bovine serum (FBS)
100U/100 µg/mL penicillin/streptomycin solution
2 mM L-glutamine
2.4 µg/ml phytohaemagglutinin (PHA)

Treatment Medium (short-time exposure):
Complete culture medium without FBS.

After Treatment Medium / Treatment Medium (long-time exposure): Complete culture medium with FBS (15%) and cytochalasin B (6 µg/ml)

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with and without

Metabolic activation system:

liver microsome preparations (S9 mix)

Test concentrations with justification for top dose:

The test item was extracted in cell culture medium at a weight/volume ratio of 0.2 g/mL for 72h (±2h) at 37°C (± 1°C) according to ISO 10993-3, 2003 and ISO 10993-12, 2007. The extract was centrifuged at room temperature for 5 minutes at 1000 g and processed by sterile filtration (manufacturer: Whatman, batch: 8255139, material: cellulose acetate, pore size: 0.2 µm).

Duplicate cultures were treated at each concentration. The following concentrations were used in the main experiments:

Experiment I: with metabolic activation: 10, 20, 40, 60, 80, 100% Extract
Experiment I: without metabolic activation: 10, 20, 40, 60,80, 100% Extract.
Experiment II: without metabolic activation: 10, 20, 40, 60, 80, 100% Extract

The following concentrations were selected for the microscopic analyses:
Experiment I with short exposure (4 h): with metabolic activation: 60, 80, 100% Extract
Experiment I with short exposure (4 h): without metabolic activation: 60, 80, 100% Extract
Experiment II with extended exposure (44h): without metabolic activation: 10, 20, 40 and 60% Extract

Untreated negative controls:

yes

Remarks:

Negative controls (cell culture medium) are treated in the same way as all dose groups.

Positive controls:

yes

Remarks:

Clastogenic control substance

Positive control substance:

ethylmethanesulphonate

Remarks:

Dissolved in RPMI (Roswell Park Memorial Institute medium). Final concentration: 600 µg/mL

Positive controls:

yes

Remarks:

Clastogenic control substance

Positive control substance:

cyclophosphamide

Remarks:

Dissolved in RPMI (Roswell Park Memorial Institute medium). Final concentration: 7.5 µg/mL.

Positive controls:

yes

Remarks:

Aneugenic control substance

Positive control substance:

other: Colcemide

Remarks:

Dissolved in RPMI (Roswell Park Memorial Institute medium). Final concentration: 0.08 - 0.8 µg/mL

Details on test system and experimental conditions:

Cells:
Human peripheral blood lymphocytes from healthy and non-smoking donors with no known recent exposure to genotoxic chemicals and radiation are used to examine the ability of chemicals to induce cytogenetic damage. Blood samples were drawn by venous puncture and collected in heparinized tubes. Before use the blood was stored under sterile conditions at 4°C for a maximum of 4 h. Whole blood samples treated with an anti-coagulant (e. g. heparin) are pre-cultured in the presence of mitogen (phyto-haematogglutinin, PHA).

Mammalian Microsomal Fraction S9 Homogenate:
The S9 liver microsomal fraction was prepared at BSL BIOSERVICE GmbH. Male Wistar rats were induced with phenobarbital (80 mg/kg bw) and ß-naphthoflavone (100 mg/kg bw) for three consecutive days by oral route. A stock of the supernatant containing the microsomes was frozen in aliquots of 2 and 4.5 mL and stored at -75°C. The protein concentration in the S9 preparation was 33 mg/mL.

Evaluation criteria:

There are several criteria for determining a positive result:
- a concentration-related increase or reproducible increase in the number of cells containing micronuclei
- a biologically relevant increase in the number of cells containing micronuclei for at least one of the dose groups, which is higher than the laboratory negative
control range.

A test item is considered to be negative if there is no biologically relevant increase in the percentages of cells with micronuclei above concurrent control levels, at any dose group.

Cytotoxicity:
As an assessment of the cytotoxicity, a cytokinesis block proliferation index (CBPI) was determined from 500 cells. At least three analysable concentrations of the test item extract with no more than half log spacing between the concentrations should be tested. If toxicity is found, the highest concentration evaluated should induce approximately 60% toxicity. If possible, the concentration tested should exhibit substantial toxicity, intermediate toxicity and/or no toxicity.
Assessment of cytotoxicity and/or cytostasis should be quantified from Cytokinesis-Block Proliferation Index (CBPI) in both treated and control cultures.

Statistics:

Statistical methods may be used as an aid in evaluating the test results. Statistical significance should not be the only determination of a positive response. No statistics performed as no effect occured.

Species / strain:

lymphocytes: human

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

other: In experiment II without metabolic activation at an extract concentration of 60% a relative CBPI of 45% was noted.

Vehicle controls validity:

not applicable

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Toxicity
In experiment I without and with metabolic activation no decrease of the relative cytokinesis block proliferation index (CBPI) below 70% was noted.
In experiment II without metabolic activation no decrease of the relative CBPI below 70% was noted up to an extract concentration of 40%. At an extract concentration of 60% a relative CBPI of 45% was noted.

Clastogenicity / Aneugenicity
In experiment I without metabolic activation the micronucleated cell frequencies of the negative control (0.80%) were within the range of the historical control data of the negative control (0.4% - 2.3%). The numbers of micronucleated cells found after treatment with the test item were within the historical control data range of the negative control. The mean values noted were 0.70% (60%), 0.85% (80%) and 0.80% (100%). The number of micronucleated cells found in the groups treated with the test item did not show a biologically relevant increase compared to the corresponding negative control.

In experiment I with metabolic activation the micronucleated cell frequency of the negative control (0.80%) was within the historical control data of the negative control (0.6% - 2.1%). The numbers of micronucleated cells found after treatment with the test item were within the historical control data range of the negative control. The mean values of micronucleated cell frequencies found after treatment with the test item noted were 0.65% (60%), 0.85% (80%) and 0.65% (100%). The number of micronucleated cells found in the groups treated with the test item did not show a biologically relevant increase compared to the corresponding negative control.

In experiment II without metabolic activation the micronucleated cell frequency of the negative control (0.75%) was within the historical control data of the negative control (0.4% - 2.3%,). The numbers of micronucleated cells found after treatment with the test item were within the historical control data range of the negative control. The mean values noted were 1.25% (10%), 1.20% (20%) ,0.65% (40%) and 1.0% (60%). The number of micronucleated cells found in the groups treated with the test item did not show a biologically relevant increase compared to the corresponding negative control.

EMS (600 µg/ml-) and CPA (7.5 µg/mL) were used as clastogenic controls and colcemid as aneugenic control (0.08 and 0.8 µg/ml). They induced distinct and biologically relevant increases of micronucleus frequency. This demonstrates the validity of the assay.

Conclusions:

In conclusion, it can be stated that during the study described and under the experimental conditions reported, the test item boron carbide B4C did not induce structural and/or numerical chromosomal damage in human lymphocytes. Therefore, boron carbide B4C is considered to be non-mutagenic with respect to clastogenicity and/or aneugenicity in the in vitro Mammalian Cell Micronucleus Test.

Executive summary:

In order to investigate an extract of boron carbide for a possible potential to induce micronuclei in human lymphocytes in vitro a Micronucleus assay was carried out. The test item was extracted in cell culture medium at a weight/volume ratio of 0.2 g/mL. The extract was centrifuged and processed by sterile filtration. The test item extract was diluted in cell culture medium prior to treatment.

In experiment I with and without metabolic activation 100% Extract was selected as highest dose group for the microscopic analysis of micronuclei. In experiment II without metabolic activation 60% Extract was selected as highest dose group for the microscopic analysis of micronuclei. No precipitate of the test item was noted in all dose groups evaluated in experiment I and II. In experiment I without and with metabolic activation no decrease of the relative CBPI below 70% was noted. In experiment II without metabolic activation no decrease of the relative CBPI below 70% was noted up to an extract concentration of 40%. At an extract concentration of 60% a relative CBPI of 45% was noted. In the main experiment I with and without metabolic activation no biologically relevant increase of the micronucleus frequency was noted after treatment with an extract of the test item. In the main experiment II without metabolic activation no biologically relevant increase of the micronucleus frequency was noted after treatment with an extract of the test item. In conclusion, it can be stated that during the study described and under the experimental conditions reported, the test item boron carbide B4C did not induce structural and/or numerical chromosomal damage in human lymphocytes. Therefore, boron carbide B4C is considered to be non-mutagenic with respect to clastogenicity and/or aneugenicity in the in vitro Mammalian Cell Micronucleus Test. Ethylmethanesulfonate and Cyclophosphamide were used as clastogenic controls. Colcemide was used as aneugenic control. All induced distinct and biologically relevant increases of micronucleus frequency. This demonstrates the validity of the assay.

Reference 3

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18.02.2010 - 22.03.2010

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:

EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.5100 - Bacterial Reverse Mutation Test (August 1998)

GLP compliance:

yes (incl. QA statement)

Remarks:

GLP according to Chemikaliengesetz and Directive 2004/9/EC

Type of assay:

bacterial reverse mutation assay

Target gene:

his

Species / strain / cell type:

other: S. typhimurium TA 98, TA 100, TA 1535, TA 1537, TA 102

Details on mammalian cell type (if applicable):

Not applicable

Additional strain / cell type characteristics:

other: TA 98: his D 3052; rfa-; uvrB-; R-factor: frame shift mutations TA 1OO: his G 46;rfa-; uvrB-; R-factor: base-pair substitutions TA 1535: his G 46;rfa'; uvrB-: base-pair substitutions TA 1537: his C 3076; rfa-; uvrB-; frame shift mutations TA I02: his G 42

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital and ß-Naphthoflavone induced rat liver S9

Test concentrations with justification for top dose:

10, 20, 40, 60, 80, 100%
The l00% extract concentration corresponds to a weight/volume-ratio of 0.2 g/ml 0.9% NaCl resp. DMSO
Using 100µl per plate corresponds to 2, 4, 8, 12, 16, 20mg/plate

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: [Water/ DMSO, 0.9% NaCl]
- Justification for choice of solvent/vehicle: polar and non-polar solvent stable in contact with test substance

Untreated negative controls:

yes

Remarks:

Vehicle controls, consisting of vehicle alone, as well as untreated controls were treated in the same way as the treatment groups., results see table 1 and table 2

Negative solvent / vehicle controls:

yes

Remarks:

results see table 1 and table 2

True negative controls:

no

Positive controls:

yes

Remarks:

results see table 1 and table 2

Positive control substance:

other: Sodium azide, 4-nitro-o-phenylene-diamine,Methyl methane sulfonate,2-aminoanthracene.

Details on test system and experimental conditions:

The test item was extracted in a polar extraction medium (0.9% NaCl Lot No.: 200110) and in a non-polar extraction medium (DMSO Lot No.: 80000119) for 72 (±2) h at 37 (±1)°C at a weight/volume ratio of 0.2g/ml. After extraction the polar and non-polar extracts were centrifuged at room temperature for 5 minutes at 1000 g. The polar extract was further processed by sterile filtration (primary filter: manufacturer: Roth, batch R75N27660, material: cellulose nitrate and cellulose acetate, pore size: 0.45 µm; main filter: manufacturer: Whatman, batch: 8479109, material: cellulose acetate, pore size: 0.2 µm).

Five strains of S. typhimurium with the following characteristics were used:
TA 98:
his D 3052; rfa-; uvrB-; R-factor: frame shift mutations
TA 100:
his G 46;rfa-; uvrB-; R-factor: base-pair substitutions
TA 1535:
his G 46;rfa'; uvrB-: base-pair substitutions
TA 1537:
his C 3076; rfa-; uvrB-; frame shift mutations
TA 102:
his G 428 (pAQl); rfa-; R-factor: base-pair substitutions

Samples of each tester strain were grown by culturing for 12h at 38.5 °C in nutrient broth to the late exponential or early stationary phase of growth.
The nutrient medium consists per litre:
8 g Nutrient Broth
5 g NaCl
A solution of ampicillin (125 µL, 10 mg/ml) (TA 98, TA 100 and rA 102) was added in order to retain the phenotypic characteristics of the strain.

Vogel-Bonner-salts contain per litre:
10 g MgSO4 x7 H2O
100 g Citric acid
175 g NaNH4HPO4x4H2O
500 g K2HPO4
Sterilisation was performed at 121°C in an autoclave.

Vogel-Bonner Medium E agar plates contain per litre:
15 g Agar Agar
20 mL Vogel-Bonner salts
50 mL Glucose-solvent (40%)
Sterilisation was performed at 121°C in an autoclave.

The overlay agar contains per litre:
7.0 g Agar Agar
6.0 g NaCl
10.5 mg L-histidine x HCI x H2O
12.2 mg Biotin
Sterilisation was performed at 121°C in an autoclave.

The 59 liver microsomal fraction was prepared at BSL BIOSERVICE GmbH. Male Wistar rats were induced with Phenobarbital (80 mglkg bw) and ß-Naphthoflavone (100 mg/kg bw) for three consecutive days by oral route.
The following quality control determinations are performed:
a) Biological activity in the Salmonella typhimurium assay
b) Sterility Test
A stock of the supernatant containing the microsomes was frozen in ampoules of 2 and 4.5 mL and stored at <=-75 °C. The protein concentration in the S9 preparation (Lot: 091009) was 33 mg/ml. The 59 mix preparation was performed according to Ames.

The following materials were mixed in a test tube and incubated for 60 min. at 37 °C (pre-incubation method):
100 µL Test extract at each dose level, extract vehicle control, negative control or reference mutagen solution (positive control),
500 µL S9 mix (for testing with metabolic activation) or S9 mix substitution buffer (for testing without metabolic activation),
100 µL Bacteria suspension (cf. Preparation of Bacteria, preculture of the strain),
After the incubation period (60 min), the overlay agar (2000 µL) was added and poured onto the surface of a minimal agar plate.
For each strain and dose level, including the controls, three plates were used.
After solidification the plates were inverted and incubated at 37 °C for at least 48 h in the dark.

Evaluation criteria:

Criteria of Validity
A test is considered acceptable if for each strain:
- the bacteria demonstrate their typical responses to ampicillin (TA 98, TA 100, TA 102)
- the control plates without S9 mix are within the following ranges (mean values of the spontaneous reversion frequency are within the historical control data range):
without S9
TA 98: 18 - 46
TA 100: 77 - 163
TA 1535: 5 -29
T.A1537: 5-30
TA 102: 164 - 390
with S9
TA 98: 18-57
TA 100: 78 - 165
TA 1535: 5- 27
TA 1537: 5 -36
TA 102: 163 - 472
-corresponding background growth on negative control, extract vehicle control and test plates is observed.
- the positive controls show a distinct enhancement of revertant rates over the control plate.

Evaluation of Mutagenicity
The Mutation Factor is calculated by dividing the mean value of the revertant counts through the mean values of the extract vehicle control.
A test item is considered as mutagenic if:
- a clear and dose-related increase in the number of revertants occurs
and/or
- a biologically relevant positive response for at least one of the dose groups occurs
in at least one tester strain with or without metabolic activation.
A biologically relevant increase is described as follows:
- if in tester strains TA 100 and rA 102 the number of reversions is at least twice as high
- if in tester strains TA 98, TA 1535 and TA 1537 the number of reversions is at least three times higher
than the reversion rate of the extract vehicle control.
According to OECD guidelines, the biological relevance of the results is the criterion for the interpretation of results, a statistical evaluation of the
results is not regarded as necessary.
A test item producing neither a dose related increase in the number of revertants nor a reproducible biologically relevant positive response at any of the dose groups is considered to be non-mutagenic in this system.

Statistics:

The revertant counts are calculated as mean value of three plates

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

see table 1 and table 2

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Remarks:

Cytotoxicity can be detected by a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately < 0.5 in relation to the extract vehicle control.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

see table 1 and table 2

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Remarks:

Cytotoxicity can be detected by a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately < 0.5 in relation to the extract vehicle control.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

see table 1 and table 2

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Remarks:

Cytotoxicity can be detected by a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately < 0.5 in relation to the extract vehicle control.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

see table 1 and table 2

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Remarks:

Cytotoxicity can be detected by a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately < 0.5 in relation to the extract vehicle control.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 102

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

see table 1 and table 2

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Remarks:

Cytotoxicity can be detected by a clearing or rather diminution of the background lawn or a reduction in the number of revertants down to a mutation factor of approximately < 0.5 in relation to the extract vehicle control.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Table 1: Number of revertants per plate using 0.9%NaCl as solvent (mean of 3 plates)

 

		TA 98			TA 100			TA 1535			TA 1537			TA 102
	Concentration per plate	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)
NegativeControl	Aquadest.	25	29	no	114	120	no	6	6	no	8	7	no	295	222	no
	0.9%NaCL	19	29	no	121	125	no	7	7	no	8	8	no	245	239	no
Substanceextract	Test item 10%	17	36	no	117	124	no	17	11	no	9	11	no	269	245	no
	Test item 20%	18	27	no	136	124	no	6	8	no	7	8	no	283	256	no
	Test item 40%	20	26	no	121	116	no	5	7	no	9	7	no	295	243	no
	Test item 60%	15	30	no	118	116	no	10	11	no	7	8	no	259	245	no
	Test item 80%	19	28	no	123	98	no	15	9	no	8	6	no	279	242	no
	Test item 100%	20	26	no	121	117	no	14	8	no	7	10	no	269	235	no
PositiveControl	4-NOPD 10µg (40µg TA1537)	527	-	yes	-	-	-	-	-	-	113	-	yes	-	-	-
	NaN3     10µg	-	-	-	792	-	yes	1256	-	yes	-	-	-	-	-	-
	MMS       1µl	-	-	-	-	-	-	-	-	-	-	-	-	979	-	yes
	2-AA    2.5µg (10µg TA102)	-	1474	yes	-	1514	yes	-	79	yes	-	91	yes		722	yes

 

Table 2: Number of revertants per plate using DMSO as solvent (mean of 3 plates)

		TA 98			TA 100			TA 1535			TA 1537			TA 102
	Concentration perplate	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)	— MA	+ MA	Cytotoxic (yes/no)
NegativeControl	Aquadest.	20	26	no	115	110	no	8	6	no	9	12	no	265	264	no
	DMSO	23	31	no	98	90	no	6	7	no	9	5	no	234	161	no
Substanceextract	Test item 10%	25	27	no	109	96	no	12	7	no	8	12	no	209	139	no
	Test item 20%	23	24	no	110	93	no	8	7	no	7	6	no	231	165	no
	Test item 40%	24	31	no	92	92	no	7	4	no	4	5	no	199	114	no
	Test item 60%	21	27	no	100	89	no	6	10	no	10	5	no	238	129	no
	Test item 80%	25	24	no	96	76	no	10	8	no	10	11	no	241	92	no
	Test item 100%	23	26	no	114	89	no	9	7	no	7	5	no	200	132	no
PositiveControl	4-NOPD 10µg (40µg TA1537)	440	-	yes	-	-	-	-	-	-	113	-	yes	-	-	-
	NaN3     10µg	-	-	-	961	-	yes	1147	-	yes	-	-	-	-	-	-
	MMS       1µl	-	-	-	-	-	-	-	-	-	-	-	-	980	-	yes
	2-AA    2.5µg (10µg TA102)	-	2790	yes	-	1675	yes	-	76	yes	-	156	yes		655	yes

 

Conclusions:

In conclusion, it can be stated that during the described mutagenicity test and under the experimental conditions reported, the test item extracts did not cause gene mutations by base pair changes or frameshifts in the genome of the tester strains used. Therefore, extracts (polar and non-polar) of boron carbide are considered to be non-mutagenic in this bacterial reverse mutation assay.

Executive summary:

In order to investigate the potential of extracts (polar and non-polar) of boron carbide (B4C) for its ability to induce gene mutations the pre-incubation test was performed with the Salmonella typhimurium strains TA98, TA 100, TA 1535, TA 1537 and TA 102. The test item extracts were tested at several concentrations. The assays were conducted with and without metabolic activation. The concentrations, including the controls, were tested in triplicate. The following concentrations of the test item extracts were prepared and used in the experiment: 10, 20, 40, 60, 80 and 100%. The l00% extract concentration corresponds to a weight/volume-ratio of 0.2 g/ml 0.9% NaCl resp. DMSO. No toxic effects of the test item extracts were noted in any of the five tester strains used up to the highest extract concentrations evaluated (with and without metabolic activation) in experiment I and II. No biologically relevant increases in revertant colony numbers of any of the five tester strains were observed following treatment with boron carbide at any concentration level, neither in the presence nor absence of metabolic activation in experiment I and II. The reference mutagens induced a distinct increase of revertant colonies indicating the validity of the experiments.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Boron carbide, a covalent non-metallic carbide, is an inorganic solid with a high chemical inertness. It does not noticeably react with chlorine or oxygen below 1,000 °C, it is completely inert against hydrogen fluoride and hot nitric acid and is practically insoluble in water (see section 4.8 of the IUCLID dossier) and organic solvents. Due to its inherent physical-chemical properties boron carbide does not cross biological membranes and therefore is not bioavailable and not systemically available, which is underlined by the results of all toxicological and ecotoxicological studies. The absence of bioavailability and mutagenic potential of boron carbide has been demonstrated by the negative results of a pre-incubation test (Ames Test) performed with several Salmonella typhimurium strains and an in vitro micronucleus assay with human cells. Against this background and due to its physico-chemical characteristics boron carbide is considered not to show genetic toxicity.

Justification for classification or non-classification

Boron carbide is considered not to show genetic toxicity, therefore, classification according to the criteria set out in Annex I of Regulation (EC) 1272/2008 (CLP criteria) is not warranted.