Boron carbide

Acute Toxicity: inhalation

Administrative data

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1993

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well reported study not following available guidelines. Test material not identical to registration substance.

Data source

Reference

Reference Type:

publication

Title:

Pulmonary Response, in vivo, to Silicon Carbide Whiskers

Author:

Gerald L. Vaughan, Sharon A. Trently and Ronald B. Wilson

Year:

1993

Bibliographic source:

Environmental Research 63, 191-201 (1993)

Materials and methods

Test guideline

Qualifier:

no guideline available

Principles of method if other than guideline:

Fischer rats were exposed to boron carbide whiskers (BCW) administered by intratracheal instillation.

GLP compliance:

not specified

Test type:

other: Intratracheal instillation of whiskers

Test material

Test material information

1

Reference substance name:

Boron carbide

EC Number:

235-111-5

EC Name:

Boron carbide

Cas Number:

12069-32-8

Molecular formula:

CB4

IUPAC Name:

2,3,4,5-tetraboratetracyclo[2.1.0.0¹,³.0²,⁵]pentane

Details on test material:

- Name of test material (as cited in study report): Boron carbide whiskers (BCW)
- Substance type: Inorganic
- Physical state: Solid, whiskers
- Source: American Matrix, Inc. (Knoxville, TN)
- Particle size: Dimensional characteristics of each material were estimated from scanning electron micrographs with 2.68-µm latex beads (Dow, Midland, Ml) included for size comparison. Diameter (geometric mean): 6.1 µM, Length (geometric mean): 80.9.

Test animals

Species:

rat

Strain:

other: Fischer F344N/TacfBR

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic, Germantown, NY.
- Age at study initiation: 9 weeks.
- Housing: Animals were maintained under veterinary supervision in a facility approved by the American Association for Laboratory Animal Care.

Administration / exposure

Route of administration:

other: intratracheal

Vehicle:

other: phosphate-buffered saline (PBS)

Details on inhalation exposure:

Stocks of test materials were weighed, autoclaved, and suspended by sonication at 1 mg/ml in the appropriate sterile solution. For intratracheal instillation, phosphate-buffered saline (PBS) (grams per litre: NaCl, 8.0; KCl, 0.20; KH2PO4, 0.20; NaHPO4x7H2O, 2.16; pH 7.4) was used as a suspending agent.
Animals were anesthetized by intramuscular injection of a mixture of 12.0 mg ketamine (Bristol Labs, Syracuse, NY) and 0.8 mg acepromazine (Ayerst Labs, New York) in a volume of 0.2 ml. Since deeply anesthetized animals often did not survive the procedure, they were permitted to begin recovery from anesthesia prior to instillation of test materials. For instillation, animals were restrained supine on an inclined surface with intense external illumination provided to the neck region. A 16-gauge, 5.25-in. angiocatheter (Deseret Medical Inc., Sandy, UT) was inserted into the trachea, From a rodent ventilation graph (Harvard Equipment Inc., Boston, MA), a minute respiratory volume (MRV) was estimated for each animal and test materials in suspension were diluted to 1.0 mg/100 ml MRV for a low dose and 5.0 mg/100 ml MRV for a high dose. Using a mechanical pipette, appropriate doses of fibres were removed from a stirred suspension and introduced as the animal inhaled followed by two 5.0-ml air injections. Control animals received equivalent volumes of PBS. Animals recovered in a warm environment before being returned to cages.

Analytical verification of test atmosphere concentrations:

not specified

Remarks on duration:

One itratracheal instillation

Concentrations:

1.0 mg/100 ml minute respiratory volume and 5.0 mg/100 ml minute respiratory volume

No. of animals per sex per dose:

25

Control animals:

yes

Details on study design:

- Duration of observation period following administration: 18 months
- Frequency of observations and weighing: Body weight and general health were monitored biweekly during the first 2 months and monthly thereafter
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, histopathology after 18 months, bronchopulmonary leavage 1,7, or 28 days postinstillation

Results and discussion

Effect levels

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Mortality:

No significant effects observed.

Clinical signs:

other: No significant effects observed.

Body weight:

No significant effects observed.

Gross pathology:

No significant effects observed.

Any other information on results incl. tables

Table 1: Histopathologic Analysis

	Boron Carbide Whiskers
	High Dose (20)	Low Dose (24)
Lung
Cranulomas	n.d.	n.d.
Hyperplasia	n.d.	n.d.
Fibrosis	n.d.	n.d.
Giant cells	n.d.	n.d.
Macrophages (f)	n.d.	n.d.
Macrophages (p)	n.d.	n.d.
Neutrophils	n.d.	n.d.
Pneumonia	n.d.	n.d.
Mucinosis	n.d.	n.d.
Atelectasis	n.d.	n.d.
Trachea
Metaplasia	n.d.	n.d.
Macrophages (f)	n.d.	n.d.
Macrophages (p)	n.d.	n.d.
Lymphoid	n.d.	n.d.
lnfiltration	n.d.	n.d.
Neutrophils	n.d.	n.d.
Siderophage	n.d.	n.d.
Mucinosis	n.d.	n.d.
Lymph nodes
Macrophages (f)	n.d.	n.d.
Spleen
Splenomegaly	n.d.	n.d.
Kidney
Monocytes	n.d.	n.d.
Lymphoid	n.d.	n.d.
Infiltration	n.d.	n.d.
Liver
Lymphocytes	n.d.	n.d.
Bile duct	n.d.	n.d.
Hyperplasia	n.d.	n.d.

Treatment groups received low doses (LD: 1 mg/100 ml MRV) and high doses (HD : 5 mg/100 ml MRV).

Controls received volume equivalents of PBS.

Frequencies tested by x² at P< 0.10. f, fibers.

Values in parentheses represent N.

N.d. means none detected.

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

Boron carbide is not systemically available and not acute toxic when instilled intratracheal to rats. Boron carbide whiskers are harmless compared to other mineral whiskers like asbestos or SiC with respect to prolonged inflammatory response and histopathological changes of lung and trachea.

Executive summary:

Fischer rats were exposed to silicon carbide whiskers (SiCW), boron carbide whiskers (BCW), silicon carbide platelets (SiCP), or crocidolite asbestos separately administered by intratracheal instillation. No initial response to whisker/fibre installation was observed for boron carbide whiskers. Usually in this study response to whiskers included elevated neutrophil and macrophage titers. Macrophage levels usually (not for boron carbide whiskers) remained high over the first month in populations recovered from lavage fluids and were noted in histological preparations of pulmonary tissues taken from treated animals l8 months after exposure. These findings are indicative of a prolonged inflammatory response. In such responses the incomplete phagocytosis of particles often resulting in macrophage death, is believed to initiate some of the cellular events leading to fibrogenesis and neoplasia. Furthermore, boron carbide whisker treatments produced no significant histopathological changes (see table 1). These results underline that boron carbide is not systemically available and not acute toxic when instilled intratracheal to rats. Boron carbide whiskers are harmless compared to other mineral whiskers like asbestos or SiC.