Disodium hexafluorosilicate

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The test parameters evaluated in this study do not totally comply with a specific test guideline, but are well documented and scientifically acceptable. The study was conducted accordiing to Good Laboratory Practice regulations.

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2001

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The developmental effects of continous exposure to 0, 25, 100, 175 or 250 ppm sodium fluoride in drinking water over three generations of rats were evaluated.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Sodium fluoride

EC Number:

231-667-8

EC Name:

Sodium fluoride

Cas Number:

7681-49-4

IUPAC Name:

sodium fluoride

Details on test material:

- Name of test material (as cited in study report): sodium fluoride (NaF); CAS No. 7681-49-4
- Physical state: solid
- Analytical purity: as pure as the standard reference sample purchased from the U.S. Pharmacopeia, Rockvile, MD
- Impurities (identity and concentrations): no trace element impurities were detected
- Lot/batch No.: 109F0102

Test animals

Species:

rat

Strain:

other: Caesarean-derived (CD CRL:CD-BR)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Willmington, MA, USA
- Weight at time of receipt: 51-75 g for males and females
- Weight at study initiation: (P) Males: 100.5 - 100.9 g; Females: 93.9 -94.8 g
- Housing during exposure period: Single animals were housed in stainless-steel cages suspended in stainless-steel racks. Pregnant females were housed in polycarbonate tubs with Sani-Chips (P.J. Murphy Forest Products Corp., Montville, NJ)
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 1 week


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.7 - 22.8
- Humidity (%): 35-67
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: To:

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

- Animals were exposed to sodium fluoride in drinking water at concentrations of 0, 25, 100, 175 or 250 ppm.
- Drinking water used in the study was obtained by filtering house-distilled water through a Hydro Pico pure water system.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Sodium fluoride concentrations for both the control and treated groups were determined at the FDA by potentiometric titration of the fluoride ion with a fluoride ion electrode by using an EA 940 pH/ISE meter with appropriate electrodes and filling solutions for fluoride analysis. Sodium fluoride concentrations were determined each time dosing solutions were prepared for any treatment group, including the control.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: no longer than 1 week; females that failed to mate after 1 week were remated to a different male within the same group
- Proof of pregnancy: presence of sperm in vaginal lavage referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: yes - Each female was allowed up to 3 weeks for mating.
- After successful mating each pregnant female was caged in a polycarbonate tub with Sani-Chips

Duration of treatment / exposure:

P and F1 generation male and female rats were dosed for 10 weeks prior to mating, and females were dosed throughout gestation.

Frequency of treatment:

continuous, 7 days per week

Duration of test:

Effects of sodium fluoride in drinking water on developmental toxicity was measured during the parental (P) generation and two filial (F1 and F2) genereations.

Doses / concentrations

Remarks:

Doses / Concentrations:

Basis:
nominal in water
0, 25, 100 or 250 ppm

No. of animals per sex per dose:

The P generation contained 48 male and 48 female rats per group that were dosed for a 10 week period before mating. Eight mated P females per group were selected for caesarean sections on gestation day 20 to assess development effects of sodium fluoride on F1 generation litters. The remaining P generation female rats were allowed to litter and wean their F1 pups. On postnatal day 21, 36 F1 male and 36 F1 female pups were randomly selected to continue being dosed for a 10 week period before being allowed to mate and provide F2 generation litters. At gestation day 20, the mated F1 females were observed for the last time, euthanized, and caesarean sections were performed on the F2 generation litters to assess development effects of sodium fluoride.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The 25, 100 and 175 ppm sodium fluoride doses were based on results of the National Toxicology Program (NTP 1990) chronic 2-year toxicology and carcinogenicity study in rats and mice. The 250 ppm sodium fluoride dose was based on results of a developmental study in rats conducted in the current study's laboratory in which rats tolerated this dose without adverse effects (Collins et al. 1995).

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily


BODY WEIGHT: Yes
- Time schedule for examinations: Initial body weight on gestation day 0 and at termination on gestation day 20


WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: Initial measurement on gestation day 0 and at termination on gestation day 20


POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 20
- Organs examined: no data

Ovaries and uterine content:

The ovaries and uterine content was 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:

F1 Fetuses
- External examinations: Yes: all per litter
- Soft tissue examinations: No data
- Skeletal examinations: No data
- Head examinations: No data

F2 Fetuses
- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: all per litter
- Skeletal examinations: Yes: all per litter
- Head examinations: Yes: all per litter

Statistics:

For feed consumption, number of corpora lutea, implants, total alive, male and female alive, an analysis of variance (ANOVA) was performed. If the ANOVA indicated a significant effect, then a least significant difference (LSD) test was run to compare the control with each treated group. For implantation efficiency and early, late and total (early + late) resorptions, the data were first transformed using a Freeman-Tukey arcsine transformation followed by an ANOVA. If the ANOVA indicated a significant effect, then a LSD test was performed. For body weight gain and gravid uterine weight, an analysis of covariance (ANCOVA) was performed. If the ANCOVA showed a significant effect, a LSD test was run to compare the control with each treated group. For fetal weight and crown-rump measurements, a nested ANOVA followed by a LSD test was performed on the groups if the nested ANOVA showed a significant effect. For the incidences of clinical signs in male and female rats, and specific soft-tissue, sternebral, and skeletal variations in fetuses, a Fisher's exact test was used to compare treated groups to the control group. The same test was used to compare the control with each treated group for the number of litters with at least one, at least two, and at least three soft-tissue, sternebral and skeletal variations. For the average number of fetuses per litter with at least one, at least two, and at least three soft-tissue, sternebral or skeletal variations, the data were first transformed by a Freeman-Tukey arcsine transformation. The transformed data were then analyzed using an ANOVA followed by a LSD test. For the average number of ossified vertebrae in fetuses, a nested ANOVA was performed on the data. If the nested ANOVA results were significant, a LSD test was performed to compare the control with each treated group.

Historical control data:

Developmental effects of sodium fluoride on rats from an earlier study by Collins et al., 1995 are referred to in the current study.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:no effects

Effect levels (maternal animals)

1

Dose descriptor:

NOEC

Effect level:

ca. 175 ppm (nominal)

Basis for effect level:

other: developmental toxicity

2

Dose descriptor:

LOEC

Effect level:

ca. 250 ppm (nominal)

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
Clinical Findings & Morphological Development: Clinical findings were unremarkable during gestation of P and F1 females. Morphological development of F1 and F2 fetuses was similar in all groups.
Maternal and Reproductive Findings: Reproduction of either P or F1 dams was not affected by the sodium fluoride doses. In P and F1 dams, the mean number of corpora lutea, mean number of implants, implantation efficiency, mean number of viable fetuses, and average percentage of early and late deaths per litter showed no dose-related differences. The number of P and F1 females with one and with two early plus late deaths (combined) was similar in all groups. Sex distribution of F1 and F2 fetuses showed no dose-related response. No F1 litters were totally resorbed. Three F2 litters were totally resorbed, one litter each in the 0, 25 and 175 ppm groups. Fetal body weight and crown-rump length of F1 and F2 fetuses were not affected. A single statistically significant decrease in crown-rump length of F2 females at 175 ppm was considered random. Very few runts were observed among the F1 and F2 litters, and the incidence of runts was not dose-related.
Fetal Skeletal Development Analysis: The number of F2 fetuses with incompletely ossified, non-ossified, bipartite, or malformed sternebrae was similar in control and treated groups. The number of litters containing fetuses with malaligned sternebrae was greater in all treated groups than in the control group, but the increases were not dose-related. One fetus with fused sternebrae in the control group was considered random. When the incidence of sternebral variations in fetuses and the number of fetuses with at least one, at least two, and at least three variations per litter were analyzed, no dose-related increases were seen. The significant increase in the percentage of litters with at least one variation at 175 ppm was considered random due to lack of dose relationship. As an additional measure of ossification deficiency, data on the individual sternebrae that were bipartite or showed reduced or lack of ossification were combined and analyzed; no dose-related effects were seen. The following single occurrences were considered random: one fetus with 15 ribs (0 ppm), one fetus per group with reduced ossification of the ischium (0, 25, 175 ppm), one fetus with reduced ossification of the scapula (100 ppm), and one fetus per group with reduced ossification of the humerus (175 ppm). Sodium fluoride did not affect the ossification of caudal vertebrae. Decreased ossifcation of the hyoid bone was observed at 175 and 250 ppm, and the ossifiction at 250 ppm was statistically significant. When the incidence of skeletal variations was analyzed by fetus and by litter, no dose-rrelated significant differences were observed. Vertebral ossification, also considered a measure of fetal ossification, showed no dose-related effects.
Fetal Visceral Development Analysis: No dose-related changes were noted in the development of fetal soft tissues. The significant increases in the incidence of moderate hydroureter at 25 ppm and 100 ppm, and the incidence of moderate enlargement of the ureter at the kidney at 25 ppm were considered random because of the lack of dose relationship. When the incidence of soft-tissue variations was analyzed by fetus and by litter, no dose-related changes were noted in any treated group. The following single occurrences were considered random: one fetus with moderate edema (25 ppm), one fetus with ectopic kidney (25 ppm), one fetus with enlarged kidney (100 ppm), and one fetus with four vessels off the aortic arch (100 ppm).

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

A concentration of 175 ppm sodium fluoride in drinking water of a parental (P) and two filial generations (F1 and F2) of rats did not produce developmental effects and is considered a no-observed effect concentration for developmental toxicity. A concentration of 250 ppm sodium fluoride in drinking water of a parental (P) and two filial generations (F1 and F2) of rats caused statistically significant decreased ossification of the hyoid bone in F2 fetuses and is considered an effect concentration for developmental toxicity.