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Toxicological information

Repeated dose toxicity: oral

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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:
OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents)
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid - liquid: suspension

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals 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 g for males and 143.3-167.1 g 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
- Humidity (%): 42.0-51.4
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

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 / concentrationsopen allclose all
Dose / conc.:
500 mg/kg bw/day (actual dose received)
Remarks:
20 nm particles
Dose / conc.:
1 000 mg/kg bw/day (actual dose received)
Remarks:
20 nm particles
Dose / conc.:
2 000 mg/kg bw/day (actual dose received)
Remarks:
20 nm 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: Doses were based on the results from a 14-day repeated dose toxicity study (details in Kim et al., 2014) in which no significant adverse effects were observed at doses of 1000 and 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 they were not described in the publication.

BODY WEIGHT: Yes
- Time schedule for examinations: Once per week.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: yes, but g food per rat calculated.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: 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: 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: 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, hematological 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:
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):
no effects observed
Ophthalmological findings:
not specified
Description (incidence and severity):
Examination conducted but results not discussed.
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
no effects observed
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
not examined
Details on results:
CLINICAL SIGNS AND MORTALITY: Irrespective of particle size, there were no animal deaths and no treatment-related clinical signs during the experimental period for rats of either sex. There were a few occurrences of salivation, loss of fur and wound scratching in the 2000 mg/kg bw/day group for 20 nm silica. However, due to the sporadic nature there was no dose-dependency, so the study authors concluded that these observations were not related to treatment.

BODY WEIGHT AND WEIGHT GAIN: 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: There were sporadic increases in food consumption for 20 nm silica and sporadic increases in food consumption for 100 nm silica. Therefore the authors concluded that these differences were not treatment-related.

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

OPHTHALMOSCOPIC EXAMINATION: The results of the ophthalmic examination were not reported.

HAEMATOLOGY: In the high dose recovery group for 20 nm silica there were statistically significant increases in lymphocyte counts compared with the control recovery group. There were no findings for the groups treated with 100 nm silica.

CLINICAL CHEMISTRY: 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: 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.

ORGAN WEIGHTS: For 20 nm silica relative liver weight was statistically significantly decreased in males of the highest dose group compared with the control group. Absolute and relative lung weights were statistically significantly increased in males of the high dose recovery group compared with the controls. For 100 nm silica there was a statistically significantly increase in absolute weights of kidney, lung and submandibular glands in the male high dose recovery group. In the same group relative weights of kidneys and lungs were statistically significantly increased. Females in the high dose recovery group had statistically significantly decreased absolute and relative ovary weights. These data are summarised in Table 3 and 4. No other details are available. The study authors concluded that due to the sporadic nature of the organ weight findings they were not due to treatment.

GROSS PATHOLOGY: 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 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, there was no dose-dependency, so the study authors concluded that they were not related to treatment.

HISTOPATHOLOGY: 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.

Effect levels

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: There were no observed adverse effects following repeated oral exposure to two different sizes of colloidal silica particles (20 and 100 nm).

Target system / organ toxicity

Critical effects observed:
no

Any other information on results incl. tables

Table 3 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±0.11a

*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 4 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±0.12a

  Relative (%)  

0.28±0.02

0.33±0.02a

 
  SiO2 (100 nm)    
 Male    
 Necropsy body weight  

577.4±60.5

 

603.3±22.0

 Kidney    
  Absolute (g)  

3.27±0.21

 

3.69±0.21a

Relative (%)   

0.57±0.03

 

0.61±0.02a

 Lung    
  Absolute (g)  

1.62±0.09

1.93±0.08a

 
  Relative (%)  

0.28±0.02

0.32±0.02a

 
 Submaxillary gland    
  Absolute (g)  

0.78±0.04

0.96±0.12a

 
  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±0.022a

  Relative  

0.0314±0.0040

0.0217±0.0069a

 

*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:
Based on a 90-day oral repeated dose toxicity study conducted to OECD test guideline 408 and to GLP, the NOAEL for 20nm and 100nm colloidal silica particles is ≥2000 mg/kg bw/day in Sprague-Dawley rats.