Fluorine

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

Studies on developmental toxicity are not available for fluorine. Under physiological conditions, fluorine will react instantly and violently under formation of hydrogen fluoride. Hydrogen fluoride will reach its possible targets only as (partly organically bound) fluoride and therefore studies with other inorganic fluoride, such as NaF, will provide insight in fluoride developmental toxicity and will also be applicable to fluorine.

Cross-reference

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Published study, similar to guidelines.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

The animals were Caesarean-derived, viral anitbody-free (CD-CRL:CD-BR, VAF+) rats obtained from Charles River Laboratories, MA, USA. On arrival the males weighed 351-375g, and the females weighed 175-200g. During the study, rats were housed in stainless steel cages suspended in stainless steel racks. Light was provided on a 12 hour light/dark cycle (light 07.30-19.30hr). The temperature was 17.8-25.6oC (64-78oF). Humidity ranged from 15-73%; the lowest humidity value (15%) was recorded once during the first week of the study. During the remainder of the study the range of low humidity values was 24-42%. During mating rats were housed in groups of 2 females and 1 male. Female rats were fed low-fluoride NIH-07 diet (7.95ppm fluoride). The diet was identical to that used in the NTP (1990) study obtained from Ziegler Bros. Inc., PA, USA.

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

Weight/volume NaF solutions were prepared in Aqua Cool Ultra Pure water (Ionics, Inc., MA, USA). Test solutions were presented to rats as drinking water available ad libitum. Only female rats were exposed to NaF drinking water (males were used as sires only).

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No information available

Details on mating procedure:

Rats were cohabited from approximately 16.30hr on each mating day, until the following morning. The ratio of females to males was 2:1. On each morning after cohabitation, the females were removed from the mating cages and individually smeared for the presence of sperm in the vaginal lavage. The females that were confirmed as having mated were presumed pregnant and proceeded onto the study.

Duration of treatment / exposure:

20 days (from gestation days 0-20).

Frequency of treatment:

Daily

Duration of test:

From mating until gestation day 20.

No. of animals per sex per dose:

The numbers of females in each dose group (in ascending dose order): 35, 35, 35, 36, 37 and 37.

Control animals:

yes, concurrent vehicle

Details on study design:

Doses were selected on the basis of doses used in the NTP carcinogenicity study (1990), with an additional lower and higher dose to increase the range. Once mating was confirmed, female rats were assigned to treatment groups by stratified random procedure.

Maternal examinations:

Fluid consumption was measured every 3 days, feed consumption was measured on gestation days 7, 14 and 20. Body weights were recorded at 3 day intervals during gestation and on day 20 prior to sacrifice. Behavioural signs and clinical toxicity were recorded. The numbers of corpora lutea were counted and recorded.

Ovaries and uterine content:

Caesarean sections were performed on gestation day 20. Each uterus was examined in situ for the presence and position of resorption sites, implantation sites, and live or dead foetuses. Deciduomas were called early deaths, and implantation sites with placentas and with complete but non-viable foetuses that were of subnormal size, that showed retarded development, or that were in a macerated condition, were classed as late deaths.

Fetal examinations:

Each viable foetus was weighed, sexed, measured for crown-rump length, and examined under magnification for the presence of external abnormalities. Viable foetuses were alternately evaluated for skeletal abnormalities using Alzarin Red S stain or for soft tissue abnormalities following serial sections.

Statistics:

ANOVA and two-tailed LSD test.

Indices:

Average percentage early + late deaths/litter

Historical control data:

No information

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
There was no dose-related behavioural changes or clinical signs. Water consumption was significantly reduced at 175 and 200 pm, and feed consumption was significantly reduced at 250 ppm, body weights reflected feed consumption trends; significant decreases in body weight gain were seen in 250 ppm females on days 0-3 and 6-9, and overall on days 0-20. The mean number of implants per litter was significantly reduced in the 250 ppm was significantly decreased, however findings correspond with a lower number of corpora lutea in this group.

Dose descriptor:

NOAEL

Effect level:

175 ppm (nominal)

Basis for effect level:

other: maternal toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
A significant increase was seen in the average number of foetuses with 3 or more skeletal variations in the 250 ppm group, and the numbers of litters with foetuses with 3 or more skeletal variations was also increased in this group but not significantly so.

Dose descriptor:

NOAEL

Effect level:

250 ppm (nominal)

Basis for effect level:

other: teratogenicity

Abnormalities:

not specified

Developmental effects observed:

no

Water consumption by females was lower at dose levels of 175 and 200 ppm. This resulted in a lower than expected NaF consumption. Pregnancy rate was over 90% in all groups. A significantly lower number of corpora lutea was seen in the dams of the 250 ppm group. Implantation efficiency (% corpora lutea that implanted) was more than 90% in all groups except the 25 ppm group, although the small decrease was not significant. The occurrence of in utero deaths was similar in the control and treated groups. The mean number of male foetuses per litter was significantly decreased in the 175 ppm group compared to the control, but was not dose related therefore considered to be random.

Foetal growth was not affected by NaF, even in the high dose groups with dams exhibiting reduced food and water consumption. Male control foetuses weighed 4.0 g, and crown-rump length was 4.1cm; male foetuses from treated groups weighed 3.9 -4.1 g and crown-rump length was 4.0 -4.1 cm. Female control foetuses weighed 3.8 g and crown-rump length was 4.0 cm; female foetuses from treated groups weighed 3.7 -3.8 g and crown-rump length was 3.9 -4.0 cm.

Conclusions:

No evidence of developmental toxicity was seen in this study.

Executive summary:

The developmental toxicity of sodium fluoride was determined in rats. Mated females were exposed to sodium fluoride in the drinking water at concentrations of 0, 25, 100, 175 and 250 ppm on gestation days 0 -20. Caesarean sections were performed on gestation day 20 and foetuses were examined. Sodium fluoride was not teratogenic at any dose tested. There was no effect on the development of specific bones including sternebrae. Foetal growth was not affected by sodium fluoride, even in dams exhibiting significantly decreased food and water consumption (250 ppm; decreased feed and water consumption, 175 ppm decreased water consumption). A significant increase was seen in the average number of foetuses with three or more skeletal variations in the 250 ppm group, however the number of affected litters was not significantly increased. There was no dose related effect on sodium fluoride on the incidence of soft tissue variations.

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

Fluorine

EC Number:

231-954-8

EC Name:

Fluorine

Cas Number:

7782-41-4

Molecular formula:

F2

IUPAC Name:

fluorine

Test material form:

gas

Details on test material:

No further information.

Results and discussion

Results: maternal animals

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

175 ppm (nominal)

Basis for effect level:

other: maternal toxicity

Remarks on result:

other:

Results (fetuses)

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

250 ppm (nominal)

Basis for effect level:

other: teratogenicity

Overall developmental toxicity

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

A NOAEL of 11.1 mg Fluoride/kg b.w./d for maternal toxicity and developmental effects was derived from a developmental toxicity study with NaF (Collins et al., 1995).