Tetraethyl orthosilicate

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2002/09/27 - 2005/04/29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Tetraethyl orthosilicate

EC Number:

201-083-8

EC Name:

Tetraethyl orthosilicate

Cas Number:

78-10-4

Molecular formula:

C8H20O4Si

IUPAC Name:

tetraethyl orthosilicate

Test material form:

liquid

Test animals

Species:

rat

Strain:

Sprague-Dawley

Remarks:

Crl CD (SD) IGS BR

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, France.
- Age at study initiation: Males: 8 weeks, females: 10 weeks, for principal, toxicity, and complementary
groups
- Weight at study initiation: Males: 283-339 g, females: 213-285 g, for principal, toxicity, and
complementary groups
- Fasting period before study: None
- Housing: Individually in suspended wire-mesh cages. From day 14 post-coitum, females housed
individually in polycarbonate cages
- Diet (e.g. ad libitum): A04 C pelleted maintenance diet, ab libitum
- Water (e.g. ad libitum): Tap water, ab libitum
- Acclimation period: 9 days for principal and toxicity groups, 11 days for complementary

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ±2
- Humidity (%): 50 ±20
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 2002/03/09 - 2002/11/21 for principal and toxicity groups. From: 2004/03/23 -
2004/04/30 for complementary groups.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

Details on exposure
PREPARATION OF DOSING SOLUTIONS: Doses selected based on a 7-day range-finding study. The test substance was mixed with the required quantity of vehicle at concentrations of 3.33, 16.66 and 33.33 mg/mL. The dosage forms were performed as follows: the required quantity of test substance was weighed into an appropriate container; 75% of the final volume of the vehicle was added and the preparation was homogenised with a magnetic stirrer. Sufficient vehicle was thereafter added to make the solutions up to the required volume. The vehicle for the control group was measured first, followed by preparation of the low and intermediate, then the high dose forms to avoid contamination. Solutions were kept for up to 9 days.

VEHICLE
- Justification for use and choice of vehicle (if other than water): Not specified
- Concentration in vehicle: 3.33, 16.66 and 33.33 mg/mL
- Amount of vehicle (if gavage): Various depending on concentration
- Lot/batch no. (if required): 81K2204 and 062K0006
- Purity: Not specified.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Verification of dosing solutions:
- Principal and toxicity groups: Concentration from one sample (1 mL) from each control and test item dosage forms prepared for use in weeks 1, 2, 3, 4, 5, 6, 7 and 8 was determined
- Complementary group: Concentration of samples taken from each control and test item dosage forms prepared for the complementary groups in weeks 1 and 4 was determined.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: Overnight
- Proof of pregnancy: Vaginal plug / sperm in vaginal smear referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: Each female was placed with the same male until mating occurred or 14 days elapsed
- After successful mating each pregnant female was caged (how): From day 14 post-coitum, females housed individually in polycarbonate cages

Duration of treatment / exposure:

28 days up to 53 days:
- Principal males: Pre-mating period (15 days), during the mating and post-mating periods until
final sacrifice for the males (at least 4 weeks in total)
- Principle (maternal) females: Pre-mating (15 days) and mating period, during pregnancy and
lactation, until day 4 post-partum inclusive (or until sacrifice for un-mated females) for the females
- Toxicity females: Same as principal males
- Complementary animals: Same as principal males

Frequency of treatment:

daily

Duration of test:

28 days up to 53 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

10 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

50 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

100 mg/kg bw/day

No. of animals per sex per dose:

10M, 10F

Control animals:

yes, concurrent vehicle

Details on study design:

- Rationale for animal assignment (if not random): Random

Examinations

Maternal examinations:

Examinations in parental animals and/or toxicity females:
- Clinical signs: All animals were examined for mortality and clinical signs twice a day.
- Neurobehavioral: In all males of the principal group and in all females of the toxicity groups, landing footsplay, forelimb grip strength, and rectal temperature were measured before the first day of treatment and shortly before terminal sacrifice. In all males and females of the complementary groups, touch response, pupil reflex, visual stimulus, auditory startle reflex, tail pinch response, landing footsplay, forelimb grip strength, rectal temperature, righting reflex were assessed before the first day of treatment and shortly before terminal sacrifice.
- Motor activity: Measured in all males in the principal group, all females in the toxicity group, and all animals in complementary group, before the first day of treatment and shortly before terminal sacrifice, over 10 minutes for principal / toxicity groups, 60 minutes for complementary.
- Body weight: The body weight of each male in the principal, each female in the toxicity and each animal in the complementary groups, was recorded on treatment day 1, then once a week until sacrifice. The body weight of each female from the principal groups was recorded treatment day 1, then once a week until mated (or until sacrifice) and on days 0, 7, 14 and 20 post-coitum and days 1 and 4 post-partum.
- Food consumption: The quantity of food consumed by each animal of all groups was recorded once a week, over a 7-day period (except during the mating period) until sacrifice. The quantity of food consumed by each female of the principal group was recorded once a week during the pre-mating period and then on days 0-7, 7-14, 14-20 post-coitum and days 1-4 post-partum.
- Parturition: From day 20 post-coitum, the females were observed at least three times per day (twice a day during weekends and public holidays). Females were allowed to litter normally and rear their progeny until day 4 post-partum. Any sign of a difficult or prolonged parturition was recorded. The day of completed parturition was designated day 1 post-partum. The length of gestation was calculated.
- Blood samples: Collected from all males of the principal groups and from all females of the toxicity groups at the end of the treatment period, with hematology and biochemistry analysis.

Ovaries and uterine content:

The ovaries were weighed and subjected to gross and microscopic exam after termination. The uterine content was examined.

Uterine examinations included:
- Gravid uterus weight: Not specified
- Number of corpora lutea: Not for maternal animals, but recorded for 2 non-pregnant / non-mated females
- Number of implantations: Yes
- Number of early resorptions: Not specified
- Number of late resorptions: Yes

Fetal examinations:

PARAMETERS EXAMINED
Pup and litter weight was recorded on days 1 and 4 post-partum. During lactation, pups were observed daily for clinical signs or abnormal behavior. The total litter size and numbers of pups of each sex were recorded as soon as possible after birth. The litters were observed daily, with number of live, dead and cannibalized pups and of any runts noted.

GROSS EXAMINATION
Any gross malformations in pups were noted. No further examination performed.
- Soft tissue examinations: No
- Skeletal examinations: No
- Head examinations: No

Statistics:

These statistical methods were used to assess the results: Kolmogorov-Lilliefors, Bartlett, Fisher, Dunn, Mann-Whitney / Wilcoxon, Student, Dunnett, one-way analysis of variances, Fischer exact probability (proportions). The specific method(s) applied varied by endpoint, number of groups, nature of the data.

Indices:

Live birth index: No. live born pups / No. of pups delivered x 100
Viability index (on day 4 post-partum): No. surviving pups on day 4 post-partum / No. live born pups x 100

Historical control data:

Discussed in context of male / female hematology and blood biochemistry, and for number of pups per litter

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Details on results:

See 7.5.184 for maternal related findings, primary result was slight treatment-related degenerative/necrotic nephropathy in 3/10 toxicity females at 100 mg/kg bw/day.

Maternal developmental toxicity

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

No significant changes in the number of implantation sites in the control and the treated groups. Slightly lower number of implantation sites at 100 mg/kg bw/day, not considered treatment related, see litter size below.

Dead fetuses:

no effects observed

Description (incidence and severity):

No stillborn pups.

Details on maternal toxic effects:

No substance-related effects on the maternal animals. However, the finding of slight degenerative/necrotic nephropathy in 3/10 toxicity group females at 100 mg/kg bw/day is considered relevant to the parent females.

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Fetal body weight changes:

no effects observed

Description (incidence and severity):

All groups were similar.

Reduction in number of live offspring:

effects observed, non-treatment-related

Description (incidence and severity):

No stillborn pups. Number of liveborn pups was similar in the 10 and 50 mg/kg/day groups when compared to the controls, while it was slightly lower at 100 mg/kg/day. This lower value was the contribution of one female in this group with five implantation sites and a low litter size of three liveborn fetuses. Finding considered to be incidental.

Changes in sex ratio:

no effects observed

Description (incidence and severity):

Similar in the control and the treated groups, and close to a theoretical value of 50%.

Changes in litter size and weights:

effects observed, non-treatment-related

Description (incidence and severity):

Slightly low mean number of pups delivered per litter at 100 mg/kg bw/day was linked to the slightly lower number of implantation sites and mainly due to one female. Not considered treatment related since the change was slight, not statistically significant and within the range of historical control data.

Changes in postnatal survival:

no effects observed

Description (incidence and severity):

Post-natal mortality was similar between groups.

External malformations:

no effects observed

Description (incidence and severity):

No gross external treatment-related abnormalities.

Skeletal malformations:

not examined

Visceral malformations:

not examined

Other effects:

no effects observed

Description (incidence and severity):

No notable clinical signs in the pups.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

>= 100 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

no effects observed

Overall developmental toxicity

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

In study conducted according to OECD Test Guideline 422 and in compliance with GLP (reliability score 1), the NOAEL for developmental effects in offspring from rats treated with tetraethyl orthosilicate was at least 100 mg/kg bw/d, the highest dose tested. The NOAEL for the dams was 50 mg/kg bw/day based on renal tubular nephropathy at 100 mg/kg bw/day in toxicity group females. The developmental toxicity finding contributes to the overall weight of evidence for this endpoint.