Silicon boride oxide

Endpoint summary

Description of key information

28d inhalation toxicity study: NOAEC systemic 250 mg/m3
28d inhalation toxicity study: NOAEC local 10 mg/m3

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

February - June 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study according to OECD TG and GLP

Qualifier:

according to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River
- Age at study initiation: about 8 weeks
- Housing: Groups up to 5
- Diet (e.g. ad libitum): mouse/rat laboratory diet “GLP”, 10 mm pellets (Provimi Kliba SA, Kaiseraugst, Basel Switzerland) ad libitum
- Water (e.g. ad libitum): and tap water ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24°C
- Humidity (%): 30 - 70%
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose/head only

Vehicle:

other: conditioned air

Remarks on MMAD:

MMAD / GSD: MMAD was below 1 um (0.5-0.9um) for all air samples analyzed.

Details on inhalation exposure:

The test substance was used unchanged.
For each concentration the dust aerosol was generated with the dust generator and compressed air inside a mixing stage mixed with conditioned
dilution air and passed into the inhalation system.
The control group was exposed to conditioned air.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentrations of the inhalation atmospheres in test groups 1 - 3 were analyzed by gravimetric measurement. Daily means were calculated based on three measured samples per concentration and exposure. From the daily mean values of each concentration, mean concentrations and standard deviations for the entire study were derived. In these groups, the constancy of concentrations in the inhalation systems were continuously monitored using scattered light photometers. The control atmosphere was not sampled.

Duration of treatment / exposure:

6 hours

Frequency of treatment:

each workday over 4 weeks (20 exposures)

Remarks:

Doses / Concentrations:
10, 50, 250 mg/m3
Basis:
other: target concentration

Remarks:

Doses / Concentrations:
10.5, 53.7, 243.5 mg/m3
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

other: yes, conditioned air

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: The clinical condition of the test animals was recorded once during the pre-exposure period and on post-exposure observation day and at least 3 times (before, during and after exposure) on exposure days. During exposure only a group wise examination was possible.

BODY WEIGHT: Yes
- Time schedule for examinations: The body weight of the animals was determined before the exposure period on study days -5 and -2, at the start of the exposure period on study day 0 and on study day 2. Afterward body weights were determined twice a week, as well as on the day before gross necropsy. As a rule, the animals were weighed at the same time of the day.

FOOD CONSUMPTION:
- Food consumption was determined weekly and calculated as mean food consumption in grams per animal and day.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: upon necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: all
- The following parameters were checked: Leukocyte count, Erythrocyte count, Hemoglobin, Hematocrit, Mean corpuscular volume, Mean corpuscular hemoglobin, Mean corpuscular hemoglobin concentration, Platelet count, Differential blood count, Reticulocytes

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: upon necropsy
- Animals fasted: Yes
- How many animals: all
- The following parameters were checked: ALT, AST, ALP, GGT, Sodium, Potassium, Chloride, Inorganic Phosphate, Calcium, Urea, Creatinine, Glucose, Total bilirubin, Total protein, Albumin, Globulins,Triglycerides, Cholesterol, Bile acids

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

At the end of the study in males of test group 10 mg/m3 absolute and relative large unstained cell counts were higher compared to controls, but this change followed no dose-dependency. Therefore, it was regarded as incidental and not treatment-related.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Details on results:

No mortalities or clinical signs were observed during the course of the stucy. No effects were observed on body weight and weight gain and food consumption. At the end of the study in males of test group 10 mg/m3 absolute and relative large unstained cell counts were higher compared to controls, but this change followed no dose-dependency. Therefore, it was regarded as incidental and not treatment-related. No changes were observed in clinical chemistry examinations.
The absolute and relative lung weight were increased in a dose-dependent manner (see table below); this effect was considered treatment-related. The absolute and relative spleen weights of females in the low dose group was reduced, however in the absence of dose-dependency and histological correlates, this finding was considered incidental and not treatment-related.
In histopathological examinations, treatment-related findings were observed in the lungs (see table below), mediastinal and tracheobronchial lymph nodes and in the nasal cavity at level I and III. The incidence and grading of these findings is given in the following tables. In the lungs, a multifocal inflammation was observed in all males and females of middle and high dose groups. The inflammation was localized in the lumen of the alveolar ducts and adjacent alveoli and was characterized by a predominant accumulation of macrophages (histiocytosis) and a less prominent and more irregular presence of neutrophilic granulocytes. In addition, the walls of the alveolar ducts appeared more or less thickened due to a minimal epithelial hypertrophy/hyperplasia. The affected alveolar ducts were regarded as part of the inflammatory process. Furthermore, the terminal bronchioles of all males and females of test groups 2 (50 mg/m3) and 3 (250 mg/m3) showed epithelial hypertrophy/hyperplasia, characterized by an increase in the size and number of epithelial cells.
The draining mediastinal and tracheobronchial lymph nodes of almost all males and females in test group 3 (250 mg/m³) and only 1 of 5 males of test
group 2 (50 mg/m³) were secondarily affected with multifocal macrophage aggregates.
In the nasal cavity in test group 3 (250 mg/m³), minimal hypertrophy/hyperplasia of the respiratory epithelium was found at level III affecting 3 out of 5 males and 4 out of 5 females, and minimal squamous metaplasia at level I, affected 2 out of 5 males. These changes were regarded as treatment-related.

Dose descriptor:

NOAEC

Remarks:

(local effects)

Effect level:

10 mg/m³ air

Based on:

test mat.

Sex:

male/female

Dose descriptor:

NOAEC

Remarks:

(systemic effects)

Effect level:

250 mg/m³ air

Based on:

test mat.

Sex:

male/female

Critical effects observed:

not specified

Lung weights compared to controls

Lungs	male animals			female animals
Test group	1	2	3	1	2	3
(mg/m^3)	(10)	(50)	(250)	(10)	(50)	(250)
absolute	106%	116%	133%**	106%	119%*	141%**
relative	107%	113%	137%**	105%	115%	133%**

Histological findings

Lungs	Male animals				Female animals
Test group	0	1	2	3	0	1	2	3
(mg/m^3)	(0)	(10)	(50)	(250)	(0)	(10)	(50)	(250)
animals examined	5	5	5	5	5	5	5	5
Inflammation, multifocal	0	0	5	5	0	0	5	5
·        Grade 1			4				5
·        Grade 2			1	2				2
·        Grade 3				3				3
Hypertrophy/hyperplasia, terminal bronchiole	0	0	5	5	0	0	5	5
·        Grade 1			5				5
·        Grade 2				5				5

Microscopic findings in the nasal cavity

Lungs	Male animals				Female animals
Test group	0	1	2	3	0	1	2	3
(mg/m^3)	(0)	(10)	(50)	(250)	(0)	(10)	(50)	(250)
Animals examined	5	5	5	5	5	5	5	5
Level I
Metaplasia, squamous	0	0	0	2
·        Grade 1				2
Level III
Hypertrophy/hyperplasia, respiratory epithelium	0	0	0	3	0	0	0	4
·        Grade 1				3				4

Conclusions:

The NOAEC for local toxicity at the respiratory tract was 10 mg/m³ for male and female rats based on histological findings in nasal cavity, lung, mediastinal and tracheobronchial lymph nodes.
The NOAEC for general, systemic toxicity was 250 mg/m³ for the male and females rats.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

250 mg/m³

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP and guideline study with detailed report

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

February - June 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study according to OECD TG and GLP

Qualifier:

according to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River
- Age at study initiation: about 8 weeks
- Housing: Groups up to 5
- Diet (e.g. ad libitum): mouse/rat laboratory diet “GLP”, 10 mm pellets (Provimi Kliba SA, Kaiseraugst, Basel Switzerland) ad libitum
- Water (e.g. ad libitum): and tap water ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24°C
- Humidity (%): 30 - 70%
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose/head only

Vehicle:

other: conditioned air

Remarks on MMAD:

MMAD / GSD: MMAD was below 1 um (0.5-0.9um) for all air samples analyzed.

Details on inhalation exposure:

The test substance was used unchanged.
For each concentration the dust aerosol was generated with the dust generator and compressed air inside a mixing stage mixed with conditioned
dilution air and passed into the inhalation system.
The control group was exposed to conditioned air.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentrations of the inhalation atmospheres in test groups 1 - 3 were analyzed by gravimetric measurement. Daily means were calculated based on three measured samples per concentration and exposure. From the daily mean values of each concentration, mean concentrations and standard deviations for the entire study were derived. In these groups, the constancy of concentrations in the inhalation systems were continuously monitored using scattered light photometers. The control atmosphere was not sampled.

Duration of treatment / exposure:

6 hours

Frequency of treatment:

each workday over 4 weeks (20 exposures)

Remarks:

Doses / Concentrations:
10, 50, 250 mg/m3
Basis:
other: target concentration

Remarks:

Doses / Concentrations:
10.5, 53.7, 243.5 mg/m3
Basis:
analytical conc.

No. of animals per sex per dose:

5

Control animals:

other: yes, conditioned air

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: The clinical condition of the test animals was recorded once during the pre-exposure period and on post-exposure observation day and at least 3 times (before, during and after exposure) on exposure days. During exposure only a group wise examination was possible.

BODY WEIGHT: Yes
- Time schedule for examinations: The body weight of the animals was determined before the exposure period on study days -5 and -2, at the start of the exposure period on study day 0 and on study day 2. Afterward body weights were determined twice a week, as well as on the day before gross necropsy. As a rule, the animals were weighed at the same time of the day.

FOOD CONSUMPTION:
- Food consumption was determined weekly and calculated as mean food consumption in grams per animal and day.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: upon necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: all
- The following parameters were checked: Leukocyte count, Erythrocyte count, Hemoglobin, Hematocrit, Mean corpuscular volume, Mean corpuscular hemoglobin, Mean corpuscular hemoglobin concentration, Platelet count, Differential blood count, Reticulocytes

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: upon necropsy
- Animals fasted: Yes
- How many animals: all
- The following parameters were checked: ALT, AST, ALP, GGT, Sodium, Potassium, Chloride, Inorganic Phosphate, Calcium, Urea, Creatinine, Glucose, Total bilirubin, Total protein, Albumin, Globulins,Triglycerides, Cholesterol, Bile acids

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

At the end of the study in males of test group 10 mg/m3 absolute and relative large unstained cell counts were higher compared to controls, but this change followed no dose-dependency. Therefore, it was regarded as incidental and not treatment-related.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Details on results:

No mortalities or clinical signs were observed during the course of the stucy. No effects were observed on body weight and weight gain and food consumption. At the end of the study in males of test group 10 mg/m3 absolute and relative large unstained cell counts were higher compared to controls, but this change followed no dose-dependency. Therefore, it was regarded as incidental and not treatment-related. No changes were observed in clinical chemistry examinations.
The absolute and relative lung weight were increased in a dose-dependent manner (see table below); this effect was considered treatment-related. The absolute and relative spleen weights of females in the low dose group was reduced, however in the absence of dose-dependency and histological correlates, this finding was considered incidental and not treatment-related.
In histopathological examinations, treatment-related findings were observed in the lungs (see table below), mediastinal and tracheobronchial lymph nodes and in the nasal cavity at level I and III. The incidence and grading of these findings is given in the following tables. In the lungs, a multifocal inflammation was observed in all males and females of middle and high dose groups. The inflammation was localized in the lumen of the alveolar ducts and adjacent alveoli and was characterized by a predominant accumulation of macrophages (histiocytosis) and a less prominent and more irregular presence of neutrophilic granulocytes. In addition, the walls of the alveolar ducts appeared more or less thickened due to a minimal epithelial hypertrophy/hyperplasia. The affected alveolar ducts were regarded as part of the inflammatory process. Furthermore, the terminal bronchioles of all males and females of test groups 2 (50 mg/m3) and 3 (250 mg/m3) showed epithelial hypertrophy/hyperplasia, characterized by an increase in the size and number of epithelial cells.
The draining mediastinal and tracheobronchial lymph nodes of almost all males and females in test group 3 (250 mg/m³) and only 1 of 5 males of test
group 2 (50 mg/m³) were secondarily affected with multifocal macrophage aggregates.
In the nasal cavity in test group 3 (250 mg/m³), minimal hypertrophy/hyperplasia of the respiratory epithelium was found at level III affecting 3 out of 5 males and 4 out of 5 females, and minimal squamous metaplasia at level I, affected 2 out of 5 males. These changes were regarded as treatment-related.

Dose descriptor:

NOAEC

Remarks:

(local effects)

Effect level:

10 mg/m³ air

Based on:

test mat.

Sex:

male/female

Dose descriptor:

NOAEC

Remarks:

(systemic effects)

Effect level:

250 mg/m³ air

Based on:

test mat.

Sex:

male/female

Critical effects observed:

not specified

Lung weights compared to controls

Lungs	male animals			female animals
Test group	1	2	3	1	2	3
(mg/m^3)	(10)	(50)	(250)	(10)	(50)	(250)
absolute	106%	116%	133%**	106%	119%*	141%**
relative	107%	113%	137%**	105%	115%	133%**

Histological findings

Lungs	Male animals				Female animals
Test group	0	1	2	3	0	1	2	3
(mg/m^3)	(0)	(10)	(50)	(250)	(0)	(10)	(50)	(250)
animals examined	5	5	5	5	5	5	5	5
Inflammation, multifocal	0	0	5	5	0	0	5	5
·        Grade 1			4				5
·        Grade 2			1	2				2
·        Grade 3				3				3
Hypertrophy/hyperplasia, terminal bronchiole	0	0	5	5	0	0	5	5
·        Grade 1			5				5
·        Grade 2				5				5

Microscopic findings in the nasal cavity

Lungs	Male animals				Female animals
Test group	0	1	2	3	0	1	2	3
(mg/m^3)	(0)	(10)	(50)	(250)	(0)	(10)	(50)	(250)
Animals examined	5	5	5	5	5	5	5	5
Level I
Metaplasia, squamous	0	0	0	2
·        Grade 1				2
Level III
Hypertrophy/hyperplasia, respiratory epithelium	0	0	0	3	0	0	0	4
·        Grade 1				3				4

Conclusions:

The NOAEC for local toxicity at the respiratory tract was 10 mg/m³ for male and female rats based on histological findings in nasal cavity, lung, mediastinal and tracheobronchial lymph nodes.
The NOAEC for general, systemic toxicity was 250 mg/m³ for the male and females rats.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

10 mg/m³

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP and guideline study with detailed report

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The inhalation exposure of rats to silicon boride oxide for 28 days caused no substance related findings regarding clinical signs, body weight, clinical pathology parameters in blood. Histopathological examinations revealed morphological changes in nasal cavity, lung and lung-associated lymph nodes, which were considered adverse and substance-related. Based on these findings, the following NOAECs were derived:

The NOAEC for general, systemic toxicity was 250 mg/m³ for the male and females rats (highest concentration tested).

The NOAEC for local toxicity at the respiratory tract was 10 mg/m³ for male and female rats based on histological findings in nasal cavity, lung, mediastinal and tracheobronchial lymph nodes.

The observed local effects can be attributed to a lung overload with poorly soluble particles. Thereby, the lung clearance mechanisms are exceeded and excessive particle burden facilitates the recruitement of inflammatory cells to the sites of particle deposition, leading to inflammation and epithelial hyperplasia. Rats are more sensitive to lung overload than other species, including mice, hamsters, and monkeys (Ref. 1). In particular, monkeys do not show the inflammatory response observed in rats after exposure to poorly soluble particles (Ref. 2). Epidemiological studies in human populations exposed to high concentrations of poorly soluble particles (i.e., workers exposed to titanium dioxide or carbon black) have thus far not found evidence for lung overload (Ref. 2). Further, alveolar and/or bronchiolar epithelial hyperplasia is typically associated with the occurence of lung overload in rodents, but is not observed in humans in response to exposure to poorly soluble particles (Ref. 3). According to the ECHA guidance on the application of CLP criteria (Version 5.4, June 2015), "The relevance of lung overload in animals to humans is currently not clear and is subject to continued scientific debate."

References:

1 - Nikula K.J., 2000. Inhalation Toxicology 12:97 -119.

2 - Olin S.S. 2000. Inhalation Toxicology 12:1 -17.

3 - Green F.H.Y., 2000. Inhalation Toxicology 12:59 -95.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Guideline and GLP conformant study

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
Guideline and GLP conformant study

Justification for classification or non-classification

Based on the data available, silicon boride oxide does lead to local effects at concentrations of greater than 10 mg/m³, which are consistent with lung overload. The relevance of this condition to human health is currently subject to debate (see Discussion section). Effects that are not considered relevant for humans should not be used to support classification. Therefore, classification for specific target organ toxicity (STOT) repeated exposure (inhalation) does not apply to silicon boride oxide and non-classification is warranted.