Silicon tetrachloride

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

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:

2015

Report date:

2015

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

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: particulate/powder

Remarks:

powder

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Germany GmbH
- Age at study initiation: 12-15 weeks
- Weight at study initiation: 195.3- 271g
- Fasting period before study: Not relevant
- Housing: Individually in Macrolon type III cages, with a bedding of dust-free wood shavings and wooden gnawing blocks as environmental enrichment.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2°C
- Humidity (%): 30-70%
- Air changes (per hr): approximately 15 changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: No data

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other: highly deionised water containing 10% foetal bovine serum

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Dosing formulations of synthetic amorphous silica were pre-pared with highly deionized water containing 10% foetal bovine serum in order to avoid agglomeration.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The formulations were analysed by scanning electron microscopy after shock freezing and in situ analytical ultracentrifugation.

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1-2 untreated females with 1 untreated male
- Length of cohabitation: Not stated but mating occurred between 15:30 and 7.30 on the day after cohousing started.
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy

Duration of treatment / exposure:

Gestation day 6-19

Frequency of treatment:

One dose per day

Duration of test:

Approximately 21 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

100 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

300 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

1 000 mg/kg bw/day

No. of animals per sex per dose:

25 females per dose

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Highest dose was chosen as the limit dose according to the test guideline.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: described as 'regular'

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: described as 'regular'

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes (described as 'regular')

WATER CONSUMPTION: No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: uterus and ovaries

Ovaries and uterine content:

The ovaries and uterine content were examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes, but no data on number examined

Statistics:

The data for food consumption, maternal, litter weight and body weight change, carcass and gravid uterus weight, number of corpora lutea and implantations, number of resorptions, number of live foetuses, percent pre- and post- implantation loss, percent live foetuses per litter, number of pups per litter, post- implantation loss, and mean placental weights were analysed by the two-sided Dunnett’s test for the hypothesis of equal means. The female mortality, number of pregnant females, and number of litters with foetal proportions. Proportions of foetuses per litter with findings were analysed by pairwise comparison of each dose group with the control group by a one-sided Wilcoxon test for the hypothesis of equal medians.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

no effects observed

Description (incidence and severity):

No treatment-related clinical signs occurred throughout the study.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

No treatment-related mortality occurred throughout the study.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No difference in the body weight or body weight gain occurred throughout the study.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

No difference in the food consumption occurred throughout the study.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

The average carcass weight was not affected by the treatment throughout the study.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No treatment-related findings were observed at necropsy.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Maternal developmental toxicity

Number of abortions:

not specified

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

A slightly higher pre-implantation loss occurred in the groups treated with SAS when compared to the control group. However, this was not considered as treatment-related as treatment started after implantation. No other differences occurred throughout the study.

Total litter losses by resorption:

not specified

Early or late resorptions:

not examined

Dead fetuses:

no effects observed

Changes in pregnancy duration:

not examined

Changes in number of pregnant:

effects observed, non-treatment-related

Description (incidence and severity):

Three rats of the control group, four rats of the low dose group and two animals of the high dose group were not pregnant. Since there was no dose-relationship occurring, the findings were not considered as treatment-related.

Other effects:

effects observed, non-treatment-related

Description (incidence and severity):

The mean number of corpora lutea was not affected.
The blood coagulum around the placenta or fused placenta were observed for 1-2 littermates of the control, the mid and the high dose group. This was considered as spontaneous and therefore, not considered as treatment-related.

Some isolated cartilage findings without impact on the respective bony structures occurred in all groups including the controls. The observed cartilage findings were related to the skull and the sternum. Although, the incidence of notched manubrium was statistically significantly higher in the high-dose group which was within the historical control range. Therefore, these changes were not considered as treatment-related.

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Remarks:

Maternal

Effect level:

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

Based on:

test mat.

Basis for effect level:

other: No adverse effects observed in maternal animals.

Maternal abnormalities

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Description (incidence and severity):

The mean foetal weights did not show any biologically relevant differences between the test substance-treated groups and the control.

Reduction in number of live offspring:

not specified

Changes in sex ratio:

no effects observed

Description (incidence and severity):

No differences in the sex distribution occurred throughout the study.

Changes in litter size and weights:

not specified

Changes in postnatal survival:

not examined

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

One foetus in the low and one in the high dose group had multiple malformations. Mandibular micrognathia mirrored the severely malformed skull bones found during skeletal examination in one foetus. The changes were considered to be related to each other. The cleft palate observed in the other foetus is present in the historical control data at a comparable incidence. Both findings were considered to be spontaneous in nature and without a relation to dosing. The total incidence of external malformations in treated animals did not differ significantly from that of the control group.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Skeletal malformations were noted in single foetuses at dose levels of 0, 100 and 1000 mg/kg bw/day which affected individual foetuses. However, there were no statistically significant differences between the test groups and not a dose-response relationship. Additionally, the overall incidences of skeletal malformations were comparable to those found in the historical control data.
Skeletal variations of different bone structures were observed with or without effects on corresponding cartilage. The observed skeletal variations were related to several parts of foetal skeletons and appeared without a relation to dosing. The overall incidences of skeletal variations were comparable to the historic control data. There were no dosing-related statistical significance and the incidences were within historical control ranges and consequently, not considered as treatment-related.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

In the control group, one soft tissue malformation, supernumerary unilateral liver lobes were observed in the control group. Three soft tissue variations i.e. short innominate, enlarged atrial chamber of the heart and uni- or bilateral dilation of renal pelvis were detected. However, no dose response occurred. The observable differences between the groups reflect the usual fluctuation for this parameter and were clearly withing the range of the historical control data.

Other effects:

no effects observed

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: There were no adverse effects on developmental parameters.

Fetal abnormalities

Abnormalities:

no effects observed

Overall developmental toxicity

Developmental effects observed:

no

Any other information on results incl. tables

Table 1- Summary of reproductive and developmental results

Dose (mg/kg bw/d)		0 (vehicle control)	100	300	1000
Females mated	N	25	25	25	25
Pregnant	N	22	21	25	23
Conception rate	%	88	84	100	92
Aborted	N	0	0	0	0
Premature births	N	0	0	0	0
Dams with viable foetuses	N	22	21	25	23
Dams with total litter loss	N	0	0	0	0
Female mortality	N	0	0	0	0
Pregnant at terminal sacrifice	N	22	21	25	23
	%	88	84	100	92
Corpora lutea^D	mean ± SD	14.2 ± 2.4	13.9 ± 2.08	14.0 ± 1.99	14.7 ± 2.03
Implantation sites^D	mean ± SD	13.5 ± 2.56	12.5 ± 2.8	12.8 ± 1.62	13.4 ± 2.27
Pre-implantation loss (%)^D	mean ± SD	4.9 ± 7.31	9.4 ± 17.69	7.7 ± 11.81	8.4 ± 12.31
Post-implantation loss (%)^D	mean ± SD	8.3 ± 9.96	5.2 ± 5.22	9.9 ± 16.2	6.0 ± 3.56
Early resorptions (%)^D		7.6 ± 9.27	5.2 ± 5.22	9.9 ± 16.2	5.6 ± 3.75
Late resorptions (%)^D		0.7 ± 2.26	0	0	0.3 ± 1.49
Dead foetuses		0	0	0	0
Dams with viable foetuses	N	22	21	25	23
Live foetuses^D	mean ± SD	12.4 ± 2.59	11.8 ± 2.71	11.5 ± 2.47	12.7 ± 2.23
Live foetuses (% implantation)^D	mean ± SD	91.7 ± 9.96	94.8 ± 5.22	90.1 ± 16.2	94.0 ± 3.56
Males^D	mean ± SD	5.9 ± 1.7	5.5 ± 1.91	6.5 ± 1.85	5.7 ± 1.79
Males (%)^D	mean ± SD	43.7 ± 10.64	46.5 ± 18.79	50.9 ± 14.23	43.2 ± 13.09
Females^D	mean ± SD	6.5 ± 1.95	6.3 ± 2.76	5.0 ± 2.34	6.9 ± 2.21
Females (%)^D	mean ± SD	48.0 ± 11.17	48.3 ± 18.55	39.2 ± 15.98	50.9 ± 11.85
Sex ratio (% males)		47.4	46.8	56.3	45.4
Placental weights^D	mean ± SD	0.47 ± 0.040	0.47 ± 0.042	0.46 ± 0.038	0.47 ± 0.038
	N	22	21	25	23
Of male foetuses^D	mean ± SD	0.49 ± 0.038	0.48 ± 0.036	0.47 ± 0.043	0.48 ± 0.037
	N	22	21	25	23
Of female foetuses^D	mean ± SD	0.46 ± 0.042	0.46 ± 0.052	0.46 ± 0.044	0.46 ± 0.041
	N	22	20	25	23
Foetal weights^D	mean SD	3.4 ± 0.26	3.4 ± 0.15	3.4 ± 0.24	3.4 ± 0.14
	N	22	21	25	23
Males^D	mean SD	3.5 ± 0.27	3.4 ± 0.18	3.5 ± 0.24	3.5 ± 0.14
	N	22	21	25	23
Females^D	mean SD	3.3 ± 0.25	3.3 ± 0.17	3.4 ± 0.28	3.3 ± 0.15
	N	22	20	25	23

*p<0.05; **p<0.01 (D, two-sided Dunnett's test)

Table 2 - Summary of foetal malformations

Dose (mg/kg bw/d)		0 (vehicle control)	100	300	1000
Litters evaluated	N	22	21	25	23
Foetuses evaluated	N	272	248	288	291
Total Malformations
Foetal incidence	N	3	1	0	1
	%	1.1	0.4	0.0	0.3
Litter incidence^F	N	2	1	0	1
	%	9.1	4.8	0.0	4.3
Affected foetuses per litter^W	mean% ± SD	1.3 ± 4.07	0.4 ± 1.98	0.0 ± 0.00	0.3 ± 1.60

*<0.05; **p<0.01 (F, one-sided Fisher's exact test; W, one-sided Wilcoxon)

Applicant's summary and conclusion

Conclusions:

In a developmental toxicity study, conducted according to OECD Test Guideline 414 and in compliance with GLP, the NOAEL for general systemic and developmental toxicity was concluded to be ≥1000 mg/kg bw/day based on no adverse effects observed.