Silicon tetrachloride

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2014

Report date:

2014

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 001

Cas Number:

112926-00-8

Test material form:

solid - liquid: suspension

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Orient Bio, Korea
- Age at study initiation: 6 weeks old at purchase
- Weight at study initiation: 187.9-205.3 grams for males and 143.3-167.1 grams for females
- Fasting period before study: No
- Housing: Two animals per cage were housed in stainless steel wire cages
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 8 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.5-23.3°C
- Humidity (%): 42.0-51.4 %
- Air changes (per hr): 10-15 per hour
- Photoperiod (hrs dark / hrs light): 12 hours dark / 12 hours light

IN-LIFE DATES: No data

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other: Distilled water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: Colloidal silica NPs with 20 nm and 100 nm diameters were diluted in distilled water and each of the tested doses were formulated by dilution of the highest dose with distilled water. Working samples of each dose formulation were prepared daily during the study. The formulated test particles were homogenised by vortexing just prior to administration.

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

90 days

Frequency of treatment:

Daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

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

Remarks:

20 nm synthetic amorphous silica particles

Doses / concentrations 2

Dose / conc.:

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

Remarks:

20 nm synthetic amorphous silica particles

Doses / concentrations 3

Dose / conc.:

2 000 mg/kg bw/day (actual dose received)

Remarks:

20 nm synthetic amorphous silica particles

Doses / concentrations 4

Dose / conc.:

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

Remarks:

100 nm synthetic amorphous silica particles

Doses / concentrations 5

Dose / conc.:

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

Remarks:

100 nm synthetic amorphous silica particles

Doses / concentrations 6

Dose / conc.:

2 000 mg/kg bw/day (actual dose received)

Remarks:

100 nm synthetic amorphous silica particles

No. of animals per sex per dose:

Control and 2000 mg/kg bw/day: 15 (includes 5 animals for the recovery group);
500 and 1000 mg/kg bw/day: 10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: A 14-day dose range-finding study was conducted where 5 male and 5 female rats were randomly distributed to each dose groups so the final mean body weight was approximately equal. The highest dose was selected to 2000 mg/kg bw/day, middle dose to 1000 mg/kg bw/day and the low dose to 500 mg/kg bw/day. A negative control group was included where the animals received distilled water. Clinical signs and body weight were monitored throughout the study whereas gross pathology was examined on the scheduled necropsy day. No toxicity was observed at the highest dose tested, therefore, the main study used the same highest dose of 2000 mg/kg bw/day.
- Post-exposure recovery period in satellite groups: Control and highest dose group had 5 extra animals each, which were observed for a recovery period of two weeks following the 90-day treatment period.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed once daily after treatment for well-being, mortality and clinical signs of toxicity (no further detail).

DETAILED CLINICAL OBSERVATIONS: It is not clear how detailed the observations were as it was not described in the publication.

BODY WEIGHT: Yes
- Time schedule for examinations: Prior to the administration of the test substance and thereafter, once a week.

FOOD CONSUMPTION: Yes
g food per rat was calculated.

FOOD EFFICIENCY: No

WATER CONSUMPTION: Yes
- Time schedule for examinations: Daily, calculated by difference between supplied amounts and remaining amounts measured the next day.

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Last week of 90-day treatment period
- Dose groups that were examined: Control and highest dose groups

HAEMATOLOGY: Yes
- Time schedule for collection of blood: The night before scheduled necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in table 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: The night before scheduled necropsy
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in table 1 were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: For five animals per group of each sex during the last week of the 90-day treatment period. Total urine volume was calculated from the urine collected over a 24-h period.
- Metabolism cages used for collection of urine: Yes, for five animals from the control and highest dose group over a 3-h sampling period.
- Animals fasted: No data
- Parameters checked in Table 1 were examined.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see Table 2), on moribund or dead animals, and on all animals at the end of the 90-day exposure period.
HISTOPATHOLOGY: Yes (see Table 2), tissues from the control and highest dose group were examined histopathologically.

Statistics:

Body weight values, feed and water consumption data, haematological data, blood biochemistry data, and organ weight values were analysed for homogeneity of variance using Levene’s test. One-way analysis of variance was performed to evaluate the significance of differences. If the variance was homogeneous and a significant difference was identified, Scheffe’s multiple comparison test was performed as a post hoc test. If the variance was not homogeneous, the data were analysed using Dunnett’s T3 test. Analysis of data from the recovery groups was performed using the Student’s t-test. All analyses were performed using Statistical Package for the Social Sciences version 19.0 software (SPSS Inc, Chicago, IL, USA).

Results and discussion

Results of examinations

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Irrespective of particle size, no treatment-related clinical signs occurred during the experimental period for rats of either sex. A few occurrences of salivation, loss of fur and wound scratching were observed in the 2000 mg/kg bw/day group for 20 nm silica. However, due to the sporadic nature and no dose-dependency, the study authors concluded that these observations were not related to treatment.

Mortality:

no mortality observed

Description (incidence):

No mortality occurred in any dose groups.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Regardless of SiO2 particle size, there were no statistically significant differences in body weight between treated rats and their respective control groups for either males or females.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

There were sporadic increases in food consumption for 20 nm silica and sporadic increases in food consumption for 100 nm silica. However, these differences were not considered as treatment-related.

Food efficiency:

not examined

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

effects observed, non-treatment-related

Description (incidence and severity):

There were sporadic decreases in water consumption for 20 nm and 100 nm silica, however, these were not considered to be treatment-related.

Ophthalmological findings:

not specified

Description (incidence and severity):

The results were not reported although ophthalmoscopic examination was performed.

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

In the high dose recovery group for 20 nm silica, a statistically significant increase in lymphocyte counts was observed compared to the control recovery group. There were no findings for the groups treated with 100 nm silica and therefore, the findings were not considered as treatment-related.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

No differences between treated and control animals were observed for 20 nm silica. For females of the high dose recovery group treated with 100 nm silica, aspartate aminotransferase and creatine kinase concentrations were statistically significantly decreased compared with the controls.

Urinalysis findings:

no effects observed

Description (incidence and severity):

There were no statistically significant differences in urinalysis parameters in any treated group compared with the respective control groups for either 20 nm or 100 nm silica.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

Relative liver weight was statistically significantly decreased whereas the absolute and relative lung weights were statistically significantly increased in males of the 2000 mg/kg bw/day dose group exposed to 20 nm silica compared to the control group. A statistically significantly increase in absolute weights of kidney, lung and submandibular glands and a statistically significant increase in the relative weights of kidneys and lungs were observed in the male 2000 mg/kg bw/day recovery group exposed to 100 nm silica. Females in the high dose recovery group had statistically significantly decreased absolute and relative ovary weights. The study authors concluded that due to the sporadic nature of the organ weight findings, the observations were not treatment related. No further details are available.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Pale yellowish discoloration on the posterior surface of the left lateral lobe of the liver was observed in one male animal from the 20 nm silica 500 mg/kg bw/day group. With regard to 100 nm silica, a small-sized right testis and epididymis were observed in one male from the 500 mg/kg group. A light yellow discoloration of the left lateral lobe of the liver (about 1 mm diameter), and a light yellow-coloured cyst with adjacent fat near the right kidney were also observed in another male in the 1000 mg/kg group. In addition, a small-sized left ovary was observed in one female from the 2000 mg/kg recovery group. However, no dose-dependency occurred and the effects were not considered to be related to treatment.

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

Granulomatous inflammation was observed in one male rat from the 1000 mg/kg bw/day group and two from the 2000 mg/kg bw/day group treated with 20 nm silica. Chronic bronchioalveolar inflammation was observed in one male rat from the 2000 mg/kg bw/day group treated with 20 nm silica. There were no adverse findings from the groups treated with 100nm silica. These lesions were observed in four cases in total and were minimal to mild in severity.

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Effect levels

Key result

Dose descriptor:

NOAEL

Effect level:

>= 2 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse observed effects were observed

Target system / organ toxicity

Critical effects observed:

no

Any other information on results incl. tables

Table 1 - Organ weights and organ weight to body weight ratios of male rats in the 90-day gavage study (main group) of 20 nm SiO2 nanoparticles*

	0 (vehicle control)	500 mg/kg bw/day	1000 mg/kg bw/day	2000 mg/kg bw/day
Number of animals	10	10	10	10
Male
Necropsy body weight	565.9±43.4	553.7±45.1	529.1±48.4	526.6±48.9
Liver
Absolute (g)	14.70±1.90	13.65±1.26	13.11±1.94	12.59±1.71
Relative (%)	2.59±0.18	2.47±0.14	2.47±0.16	2.38±0.11^a

*Organ (absolute) weights and body weights are given in grams: organ weight to body (relative) weights are given as mg organ weight/g body weight (mean ± standard deviation); ^aP<0.05 significantly different from control, by Scheffe’s test.

Table 2 - Organ weights and organ weight to body weight ratios for the recovery group in the 90-day gavage study of SiO2 nanoparticles*

	0 (vehicle control)	2000 mg/kg bw/day
Number of animals	5	5
SiO2 (20 nm)
Male
Necropsy body weight	569.8±38.4	545.9±35.0
Lung
Absolute (g)	1.61±0.07	1.81±0.12^a
Relative (%)	0.28±0.02	0.33±0.02^a
SiO2 (100 nm)
Male
Necropsy body weight	577.4±60.5	603.3±22.0
Kidney
Absolute (g)	3.27±0.21	3.69±0.21^a
Relative (%)	0.57±0.03	0.61±0.02^a
Lung
Absolute (g)	1.62±0.09	1.93±0.08^a
Relative (%)	0.28±0.02	0.32±0.02^a
Submaxillary gland
Absolute (g)	0.78±0.04	0.96±0.12^a
Relative (%)	0.14±0.01	0.16±0.02
Female
Necropsy body weight	303.9±47.8	304.9±16.9
Ovary
Absolute	0.094±0.009	0.066±0.022^a
Relative	0.0314±0.0040	0.0217±0.0069^a

*Organ (absolute) weights and body weights are given in grams: organ weight to body (relative) weights are given as mg organ weights/g body weight (mean ± standard deviation); ^aP<0.05, significantly different from control by Scheffe’s test.

Applicant's summary and conclusion

Conclusions:

In a 90-day oral repeated dose toxicity study, conducted according to OECD Test Guideline 408 and in compliance with GLP, the NOAEL for 20 nm and 100 nm colloidal silica particles were concluded to be ≥2000 mg/kg bw/day in Sprague-Dawley rats based on no adverse effects observed.