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Administrative data

carcinogenicity: oral
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
tudy was performed in accordance with acceptable procedures and under the conditions of GLP. This study is considered to be comparable to a guideline study. The reliability has been restricted to reliability 2 on the basis that the study was conducted on an analogous substance (NaF). NaF is considered to be analogous to disodium fluorophosphate in terms of toxicological profile for the following reasons; - A combined 28-day reprotoxicity screening toxicity study (OECD 422) performed on disodium fluorophosphate confirmed the leading health effects to be consistent with the effects reported for exposure to inorganic fluorides (fluorosis). In particular severe effects were noted in the mucosal lining of the stomach and are consistent with exposure to fluoride. - Results of studies on NaF are considered to present a worst case for exposure as NaF contains approximate 47% F compared to 13% F in disodium fluorophosphate. - The phosphate content of sodium fluorophosphate is not considered to present a hazard in terms of systemic toxicity. Phosphate is an essential element; a maximum tolerable daily intake value (MTDI) for phosphates is reported to be 70 mg/kg bw/day. This value greatly exceeds the limit value placed on an inorganic fluoride (OEL = 2.5 mg/kg bw/day F) and as such is not considered to be relevant for risk assessment.

Data source

Referenceopen allclose all

Reference Type:
study report
Report date:
Reference Type:
Results and conclusions of the national toxicology program's rodent carcinogenicity studies with sodium fluoride
Bucher JR, Hejtmancik MR, Toft JD, Persing RL, Eustis SL & Haseman JK
Bibliographic source:
Int. J. Cancer: 48, 733-737

Materials and methods

Test guideline
no guideline followed
Principles of method if other than guideline:
The toxicity and carcinogenicity of sodium fluoride was investigated following administration of sodium fluoride in the drinking water for 2 years.
Groups of 100 rats of each sex received 0 or 175 ppm NaF and groups of 70 rats of each sex received 25 or 100 ppm of sodium fluoride in deionised drinking water ad libitum for up to 103 weeks. Interim sacrifices occurred at 27 and 66 weeks.
GLP compliance:

Test material

Constituent 1
Chemical structure
Reference substance name:
Sodium fluoride
EC Number:
EC Name:
Sodium fluoride
Cas Number:
Molecular formula:
sodium fluoride
Constituent 2
Reference substance name:
Details on test material:
- Name of test material (as cited in study report): sodium fluoride
- Physical state: white crystalline powder
- Analytical purity: > 99%
- Impurities (identity and concentrations): hydrogen (<0.05%); water (< 0.002%); chlorine (<180 ppm); all other impurities detected at < 57 ppm
- Lot/batch No.: A022085
- Stability under test conditions: No degradation of the sodium fluoride in deionized water was detected throughout the study
- Storage condition of test material: Stored at 25 °C (room temperature) in sealed polypropylene containers protected from light.

Test animals

Fischer 344
Details on test animals or test system and environmental conditions:
- Source: National Cancer Institute's Frederick Cancer Research Facility, Frederick, MD, USA
- Age at study initiation: 6 weeks
- Weight at study initiation: mean range from 133 to 136 g for males and mean range from 104 to 105 g for females
- Fasting period before study: none
- Housing: 5/cage
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 12-13 days

- Temperature (°C): 19.4-26.1
- Humidity (%): 22-76
- Air changes (per hr): 10/hour
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: drinking water
Details on exposure:

Dose formulations were prepared weekly throughout the study by mixing appropriate quantities of NaF with deionised water to obtain the required concentrations. Stability of the solutions was analysed and 25 ppm NaF solutions were found to be stable for up to 3 weeks under simulated animal dosing conditions when stored at room temperature in sealed polyproylene containers protected from light.
Periodic analysis of the dose formulation was performed weekly on all formulations for the first 6 months and then every 8 weeks for the duration of the study.

- Rate of preparation of diet (frequency): Formulated semisynthetic low fluoride diet, Biomix #1409 (Bioserv, Frenchtown, NJ); one control group of male rats was fed NNIH-07 Rat and Mouse Ration pellets (Zeigler Bros., Gardners, PA).

- Concentration in vehicle: 0, 25, 100, 175 ppm sodium fluoride in deionised water.
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Periodic dose formulation analyses utilizing a potentiometric method with a fluoride ion electrode were conducted weekly on all dose formulations during approximately the first 6 months of the 2-year study and then every 8 weeks for the duration of the study. These analyses indicated that all dose formulations were within plus or minus 10% of target concentrations throughout the study. Results of periodic referee analyses by Midwest Research Laboratory agreed with these results. Analyses of deionized water for pH and fluoride concentration were all within acceptable limits of pH equal or greater than 5 (except on four occasions) and fluoride concentration equal or less than 0.1 ppm.
Duration of treatment / exposure:
Up to 103 weeks
Frequency of treatment:
Continuous - 7 days/week (ad libitum)

Doses / concentrations
Doses / Concentrations:
0, 25, 100, 175 pm
nominal in water
No. of animals per sex per dose:
100 rats per sex per 0 ppm and 175 ppm; 70 rats per sex per 25 ppm and 100 ppm (10 rats per sex per dose level sacrificed at 27 weeks; 10 rats per sex per dose level sacrificed at 66 weeks; 80 rats per sex per 0 and 175 ppm and 50 rats per sex per 25 and 100 ppm sacrificed at 105 weeks)
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: Doses selected for this 2 year carcinogenicity study were based on results of a 6 month toxicity study in rats and a subsequent first -year toxicity study in rats. In the 6 month study, 300 ppm sodium fluoride in drinking water produced notable lower weight gains in male and female rats and the occurrence of what were considered potentially life-threatening lesions in the stomach of rats. In the first 2-year toxicity study, sodium fluoride concentrations of 0, 10, 30 and 100 ppm in the drinking water of rats were evaluated with the results indicating that the animals could tolerate higher concentrations. Thus, drinking water concentrations of 0, 25, 100 and 175 ppm sodium fluoride were selected for the current 2-year carcinogenicity study.
- Rationale for selecting satellite groups: For the purpose of assessing early toxicological effects, ten rats per sex per dose were sacrificed at 27 and 66 weeks to assess haematology, clinical chemistry, urinalysis, urine concentrating ability, and fluoride concentrations in serum, urine and bone. Additionally, organ weights for brain, right and left kidneys, and liver were recorded at these two sacrifice intervals. The incidence of neoplasms and non-neoplastic lesions for animals sacrificed at 27 and 66 weeks were also recorded.
- Post-exposure recovery period in satellite groups: None
Positive control:
Not applicable


Observations and examinations performed and frequency:
- Time schedule: twice per day

- Time schedule: Once per week for the first 13 weeks and once per month thereafter

- Time schedule for examinations: Weighed initially, weekly through week 13, and monthly thereafter

- 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: Yes

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: Every 4 weeks, consumption was recorded for a 1-week period


- Time schedule for collection of blood: 27, 66 and 105 weeks
- Anaesthetic used for blood collection: Yes (mixture of carbon dioxide and oxygen)
- Animals fasted: no data
- How many animals: 10 rats per sex per dose level
- Parameters examined: red blood cell count, haemoglobin, haematocrit, white blood cell count with differential, platelet count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, reticulocyte count, and erythrocyte morphology

- Time schedule for collection of blood: 27, 66 and 105 weeks
- Animals fasted: No data
- How many animals: 10 rats per sex per dose level
- Parameters examined: serum calcium concentration, inorganic phosphorus concentration, and alkaline phosphatase activity

- Time schedule for collection of urine: 27, 66 and 105 weeks
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters examined: colour and appearance, volume to nearest 100 µL, specific gravity, urine sediment, protein, glucose, calcium, and inorganic phosphorus


- Fluoride concentration in bone, serum and urine was measured at 27, 66 and 105 weeks.
Sacrifice and pathology:

GROSS PATHOLOGY: Yes - A necropsy was performed on all animals including those found dead. Lateral and dorsal-ventral view radiographs were taken of all animals at necropsy. During necropsy of animals sacrificed at 27, 66 and 105 weeks, all organs and tissues were examined for grossly visible lesions. Organ weights were measured and recorded for liver, right and left kidney, and brain. Tooth abnormalities (attrition, deformity, discoloration, malocclusion, mottling) were also examined.

HISTOPATHOLOGY: Yes - Histopathological examinations included adrenals, bone (femur, humerus, mandible, maxilla, tibia, and vertebra), bone marrow, brain (frontal cortex and basal ganglia, parietal cortex and thalamus, cerebellum and pons), clitoral gland, epididymis, oesophagus, eyes (when grossly abnormal), heart, kidney, large intestines (cecum, colon, rectum), liver, lung with bronchi, lymph nodes (mandibular, mesenteric), mammary glands, nasal cavity and turbinates, ovaries, pancreas, parathyroid, pharynx (when grossly abnormal), pituitary, preputial gland, prostate, salivary gland, sciatic nerve (when neurologic signs were present), seminal vesicles, skeletal muscle (thigh), skin, small intestines (duodenum, ileum, jejunum), spinal cord (when neurologic signs were present), spleen, stomach (including forestomach and glandular stomach), teeth, testes, thymus, thyroid, trachea, urinary bladder, and uterus.
Survival Analyses: Probability of survival was estimated by the product-limit procedure of Kaplan and Meier. Statistical analysis for possible dose-related effects on survival used Cox's method for testing two groups for equality and Tarone's life table test for dose-related trends.
Analysis of Tumour Incidence: The primary statistical method used was a logistic regression analysis, which assumed that the diagnosed tumours were discovered as the result of death from an unrelated cause and, thus, did not affect the risk of death. In this approach, tumour prevalence was modelled as a logistic function of chemical exposure and time. Both linear and quadratic terms in time were incorporated initially, and the quadratic term was eliminated if it did not significantly enhance the fit of the model. The dosed and control groups were compared on the basis of the likelihood score test for the regression coefficient of dose. This method of adjusting for intercurrent mortality is the prevalence analysis of Dinse and Lagakos. When tumours are incidental, this comparison of the time-specific tumour prevalence also provides a comparison of the time-specific tumour incidences. In addition to logistic regression, alternative methods included the life table test of Tox and Tarone which was appropriate for rapidly lethal tumours and the Fisher exact test and the Cochran-Armitage trend test procedures based on the overall proportion of tumour-bearing animals.
Analysis of Continuous Variables: For all end points, dosed groups were compared with the control group using the nonparametric multiple comparison test of Dunn or Shirley. Jonckheere's test was used to assess the significance of the dose response trends and to determine whether Dunn's or Shirley's test was more appropriate for pairwise comparisons.

Results and discussion

Results of examinations

Clinical signs:
effects observed, treatment-related
mortality observed, treatment-related
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
no effects observed
Water consumption and compound intake (if drinking water study):
no effects observed
Ophthalmological findings:
effects observed, treatment-related
Haematological findings:
no effects observed
Clinical biochemistry findings:
effects observed, treatment-related
Urinalysis findings:
effects observed, treatment-related
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
effects observed, treatment-related
Details on results:
CLINICAL SIGNS AND MORTALITY: While numerous clinical signs were recorded during the study, most occurred with such low frequency or with such similarity across dosed and control groups that they were not considered related to treatment. The exceptions were abnormalities in the teeth of rats dosed with 100 and 175 ppm sodium fluoride. There was a dose-related increase in tooth mottling and whitish discoloration typical of dental fluorosis (these alterations to the incisors were more frequent in males than females).

BODY WEIGHT AND WEIGHT GAIN: No significant, chemically-related, differences in body weights were observed.

FOOD EFFICIENCY: Administration of sodium fluoride in drinking water at the concentrations used in this study had no effect on feed consumption.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Average daily water consumption for control and treated groups ranged from 19.8 to 21.2 g for males and 13.1 to 13.6 g for females. Administration of sodium fluoride in drinking water at the concentrations used in this study had no effect on water consumption. When averaged over the 2-year study, the daily amounts of sodium fluoride ingested were 1.3 mg/kg for low-dose males, 5.2 mg/kg for mid-dose males, 8.6 mg/kg for high-dose males, 1.3 mg/kg for low-dose females, 5.5 mg/kg for mid-dose females, and 9.5 mg/kg for high-dose females.

OPHTHALMOSCOPIC EXAMINATION: Although there were ocular effects observed in the cornea, lens, and anterior chamber of some rats in this study, none were considered related to treatment.

HAEMATOLOGY: There were no biologically significant differences in haematological indices (red blood cell count, haemoglobin, haematocrit, white blood cell count with differential, platelet count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, reticulocyte count, and erythrocyte morphology.

CLINICAL CHEMISTRY: There were no biologically significant differences in serum concentrations of phosphorus or calcium, or alkaline phosphatase activity, among dosed and control male or female rats at the 27-week or 66-week interim evaluations. Serum fluoride concentrations were increased over control values in females dosed with 100 and 175 ppm sodium fluoride in drinking water at 27 weeks and in all exposed males and females at 66 weeks. These increases ranged as high as almost threefold over control values in high-dosed rats.

URINALYSIS: There were no biologically significant effects related to sodium fluoride administration with the possible exception of a small increase in calcium excretion in high-dose female rats at 27 and 66 weeks. A dose-related increase was observed in the fluoride concentration of urine from male and female rats at both the 27 and 66 week interim evaluations.
ORGAN WEIGHTS: There were no changes in organ weights that appeared related to sodium fluoride administration.
GROSS PATHOLOGY: The teeth of rats were visibly affected by exposure to sodium fluoride. Primarily in males, dose-related increased incidences of whitish discoloration and deformity leading to malocclusion were observed. Approximately 50% of high-dose male rats showed attrition of the lower incisors at the end of the study.

HISTOPATHOLOGY (NON-NEOPLASTIC): Non-neoplastic lesions of bone occurred in control and exposed male and/or female rats included fibrous ostiodysrophy and osteosclerosis. Fibrous osteodystrophy was always associated with advanced nephropathy, principally in male rats, and was considered to be due to renal secondary hyperparathyroidism. Osteosclerosis is a spontaneous bone disease of unknown cause that occurs in aging F344/N rats, primarily females. The incidences of osteosclerosis was increased in female rats receiving 175 ppm sodium fluoride relative to untreated controls (6/80 control; 18/81 high-dose, P = 0.04). The incidence of uterine stromal polyps was higher in controls (12/80) than in the low-dose (4/50), mid-dose (6/50), or high-dose (2/81) female rats. It was uncertain whether the decreased incidence was related to sodium fluoride administration. In the teeth of male and female rats treated with 100 or 175 ppm sodium fluoride there was evidence of dentine dysplasia and ameloblast degeneration.

HISTOPATHOLOGY (NEOPLASTIC): Osteosarcomas of the bone were observed in 1 male rat receiving 100 ppm sodium fluoride and in 3 male rats receiving 175 ppm sodium fluoride. Of the three male rats receiving 175 ppm sodium fluoride, two had osteosarcomas involving vertebrae, and the third had an intramedullary neoplasm in the proximal portion of the humerus. None occurred in control or low-dose males or in any of the female sodium fluoride dosed groups. Squamous cell papilloma or carcinoma arising from the epithelium of the oral mucosa occurred in several dosed and control rats. The incidence of papilloma or carcinoma combined was marginally increased in male and female rats receiving 175 ppm sodium fluoride, but it was not significantly greater than that of the controls. Squamous cell neoplasms of the oral mucosa were observed but the incidences in the treated groups were not significantly greater than in concurrent controls and were within the range of historical controls. There was a marginal numerical increase in follicular cell neoplasms in thyroid gland of male rats receiving 175 ppm sodium fluoride, the incidence was not significantly greater than that in controls and it was within the ranges of historical untreated controls. The incidence of squamous cell neoplasms of the skin (keratoacanthoma, trichoepithelioma, or squamous cell papilloma combined) in high-dose female rats was not significantly greater than that of controls and was not considered related to sodium fluoride administration.

HISTORICAL CONTROL DATA: Historical incidences of osteosarcomas, oral cavity tumours, and thyroid gland follicular cell neoplasms in untreated F344/N rats from previous the testing laboratory and from previous NTP studies were presented and compared to the same types of lesions that were found in this study.
OTHER FINDINGS: For all treatment groups, dose-related fluoride concentrations in bone were significantly increased over control values for all evaluation periods. Fluoride content of bone also increased as a function of age.

No significant sodium fluoride-related effects on survival were observed throughout this study.

Relevance of carcinogenic effects / potential:
There was inclonclusive evidence of a possible association between sodium fluoride and an increase in osteosarcomas in males rats dosed with NaF at 100 and 175 ppm.

Effect levels

open allclose all
Dose descriptor:
Effect level:
ca. 25 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: see 'Remark'
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Dose descriptor:
Effect level:
ca. 175 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: There was no evidence of carcinogenic activity of sodium fluoride in female rats at a concentration of 175 ppm.
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Applicant's summary and conclusion

There was equivocal evidence* of carcinogenic activity of sodium fluoride in this 2-year drinking water study based on the occurrence of a small number of osteosarcomas in male rats dosed at concentrations of 100 and 175 ppm. The findings are weakly supportive of an association between sodium fluoride administration in drinking water, but are considered inconclusive (see below for explanation of the term ‘equivocal evidence’). No evidence of carcinogenic activity was found in male rats receiving 25 ppm sodium fluoride in drinking water or in female rats receiving up to 175 ppm sodium fluoride in drinking water. It should be noted that a concurrent 2-year toxicology and carcinogenicity study of sodium fluoride in drinking water using male and female B6C3F1 mice did not find evidence of carcinogenic activity at concentrations up to 175 ppm.

*Equivocal evidence of carcinogenic activity is demonstrated by studies that are interpreted as showing a marginal increase of neoplasms that may be chemically related.