Magnesium fluoride

Endpoint summary

Description of key information

Oral:

The oral NOAEL (mice, male, subchronic) 2690 mg/kg bw/day (2.5 % solution) (magnesium chloride)

The oral NOAEL (mice, female, subchronic) 3260 mg/kg bw/day (2.5 % solution) (magnesium chloride)

The oral NOAEL (rat, females, chronic) 175 mg/kg bw/day (sodium fluoride)

The oral NOAEL (rat, male, chronic) 175 mg/kg bw/day (sodium fluoride)

 

Inhalation:

No relevant studies available

 

Dermal:

No relevant studies available

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: oral

Remarks:

Combined repeated dose toxicity and carcinogenicity studies

Type of information:

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

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Read-across justification is provided in Appendix 3 of the CSR.
The available toxicological data on the target and source substances is outlined in the data matrix (Table 8).
The toxicological properties of the target substance are related to the magnesium cations (Mg2+) and fluoride anions (F-). Thus, data on other magnesium salts (mainly magnesium chloride) and inorganic fluorides (mainly sodium fluoride) are justified in the human health hazard assessment.
Humans take in between 250 and 350 mg/day of magnesium and need at least 200 mg, but the body deals very effectively with this element, taking it form food when it can, and recycling what we already have when it cannot. There is no evidence that magnesium produces systemic poisoning although persistent over-indulgence in taking magnesium supplements and medicines can lead to muscle weakness, lethargy and confusion.
Chloride is relatively not toxic to human health but does pose organoleptic issues. Accordingly, EPA has set the potable limit for chloride in drinking water at 250 mg/L.

Experimental data obtained with the magnesium chloride indicate that it has low oral toxicity after repeated exposure. The available data does not show any test item related adverse effects on the highest doses (> 2000 mg/kg bw/day) tested. Sodium fluoride administration did not cause test item related adverse effects in rats dosed up to 175ppm for 2 years. Only exceptions were abnormalities in the teeth of rats in the two highest dose groups (100 and 175 ppm sodium fluoride).

Sodium is a compound of many foodstuffs, for instance of common salt. It is necessary for humans to maintain the balance of the physical fluids system. Sodium is also required for nerve and muscle functioning. Thus, there is no evidence that sodium produces systemic poisoning at reasonably possible exposures.

Fluoride has both positive and negative effects on human health, but there is a narrow range between intakes that are associated with these effects. Exposure to all sources of fluoride, including drinking-water and foodstuffs, is important There is little information to characterize the dose–response relationships for the different adverse effects. In particular, there are few data on total exposure, particularly with respect to intake and fluoride absorption. The most serious effect is the skeletal accumulation of fluoride from long-term excessive exposure to fluoride and its effect on non-neoplastic bone disease — specifically, skeletal fluorosis and bone fractures. There is clear evidence from India and China that skeletal fluorosis and an increased risk of bone fractures occur at total intakes of 14 mg fluoride/day and evidence suggestive of an increased risk of bone effects at total intakes above about 6 mg fluoride/day.
The data of repeated dose toxicity and reproduction toxicity are proposed to be used for read-across according to the information requirements of Annex VIII.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Toxicity and carcinogenicity was evaluated after administering fluoride in drinking water of rats for two years.

GLP compliance:

yes

Specific details on test material used for the study:

Test was conducted on a read-across substance, sodium fluoride (CAS 7681-49-4; EC 231-667-8)

Species:

rat

Strain:

Fischer 344

Sex:

male/female

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
Housing: 5/cage; Polycarbonate (Lab Products, Rochelle Pa& NJ)
Bedding: Beta-Chip hardwood chips (Northeastern Products, Warrensburg, NY); changed twice/week
Diet: NIH47 Rat and Mouse Pellets Low Fluoride (Zegler Brothers, Gardncrs, PA); available ad libitum
Water: Deionized water; tap water (City of Columbus, OH) deionized at study laboratory with equipment from Peck Water Systems (North Canton, OH); supplied in glass bottles with rubber stoppers and stainless steel sipper tubes (Lab Products, Maywood NJ) that were changed twice weekly; available ad libitum
Acclimation period: 12 days

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

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

Concentrations of sodium fluoride in deionized drinking water were 0, 25, 100 or 175 ppm, which is equivalent to 0, 11, 45 or 79 ppm fluoride, respectively.

Analytical verification of doses or concentrations:

yes

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 were in agreement 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 per week) ad libitum

Remarks:

Concentrations: 0, 25, 100, 175 ppm

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 sacrificiced at 105 weeks)

Control animals:

yes, concurrent vehicle

Details on study design:

Sodium fluoride was administered to rats via drinking water in concentrations of 0, 25, 100 and 125 ppm for a period of 2-years. The doses used were selected on the basis of a prior 6-month study, where male and female rats given 300 ppm sodium fluoride in drinking water showed notably lower weight gains and the occurrence of what were considered potentially life-threatening lesions in the stomach. Based on these results, the concentrations selected for the first 2-year sodium fluoride studies in rats were 0, 10, 30, and 100 ppm. However, when the study was completed it was determined that the animals could tolerate higher concentrations of sodium fluoride. Thus, drinking water concentrations selected for 2-year study reported here were 0, 25, 100 and 175 ppm.

In order to assess early toxicological effects, interim sacrifices of ten animals of each sex per dose groups were performed at week 27 and week 66 of the study. The same clinical examinations and pathology were performed on the satellite animals as for the animals completing the full study period (elaborated in next section).

In addition, additional groups of 50 animals of each sex was included to provide paired (age-matched) controls. These animals received deionized drinking water. If one or more animals from any group receiving sodium fluoride-supplemented water was found dead or killed in a moribund condition, one animal of the same sex was chosen at random from the paired control group and killed.

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: All animals were observed for morbidity and mortality twice per day
CLINICAL SIGNS: Once a week for the first 13 weeks and once a month thereafter
BODY WEIGHT: Once a week for the first 13 weeks and once a month thereafter
DIET AND WATER CONSUMPTION: Every 4 weeks consumption was measured for a 1-week period
BIOAVAILABILITY OF FLUORIDE CONTAINED IN THE DIET: Only on male rats at approximately 6, 12 and 18 months of study
URINANALYSIS: At 27 and 66 weeks, 10 animals per sex per dose group, analysis included measuring volume, specific gravity, protein, glucose, calcium, inorganic phosphorus and fluoride as well as microscopic examination of sediment
URINE CONCENTRATION: At 27 and 66 weeks, 10 animals per sex per dose group, analysis included measuring volume and specific gravity
HEMATOLOGY: At 27 and 66 weeks, 10 animals per sex per dose group, analysis included red blood cell count, hemoglobin, hematocrit, white blood cell count with differential, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, reticulocyte count, and erythrocyte morphology.
CLINICAL CHEMISTRY: At 27 and 66 weeks, 10 animals per sex per dose group, analysis included serum calcium concentration, inorganic phosphorus concentration, and alkaline phosphatase activity
FLUORIDE CONCENTRATION: At 27 and 66 weeks, 10 animals per sex per dose group, fluoride concentration was measured in bone serum and urine

Sacrifice and pathology:

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, all organs and tissues were examined for grossly visible lesions. For all interim sacrifices, weights were recorded for liver, right and left kidney, and brain.
HISTOPAHTOLOGY: the following organs and/or tissues were included in complete histopathological examinations: 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, esophagus, 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.
The tissues listed above were examined microscopically for all animals found dead or killed before scheduled sacrifice, on all control and highdose animals at the 27-week interim sacrifice, on all animals at the 66-week interim sacrifice, and on all animals at terminal (105 week) sacrifice.

Statistics:

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 TUMOR INCIDENCE: The primary statistical method used was a logistic regression analysis, which assumed that the diagnosed tumors were discovered as the result of death from an unrelated cause and, thus, did not affect the risk of death. In this approach, tumor prevalence was modeled 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 tumors are incidental, this comparison of the time-specific tumor prevalence also provides a comparison of the time-specifc tumor incidences. In addition to logistic regression, alternative methods included the life table test of Cox and Tarone which was appropriate for rapidly lethal tumors and the Fisher exact test and the Cochran-Armitage trend test, procedures based on the overall proportion of tumor-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 tes was more appropriate for pairwise comparisons.

Clinical signs:

effects observed, treatment-related

Mortality:

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 specified

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: 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 in the two highest dose groups (100 and 175 ppm sodium fluoride). Male rats had the most severe dental effects, with attrition and tooth deformity as a result of abnormal wear leading to malocclusion in 13% of the animals given the highest dose of sodium fluoride.
MORTALITY: No significant chemical-related effects on survival were observed.
BODY WEIGHT: No significant chemically related differences in body weights were observed in any dose group of either sex.
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 hematologic indices.
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 evaluaitons. Serum fluoride concentations were increased over control values in females receiving drinking water containing 100 and 175 ppm sodium fluoride 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: No biologically significant effects related to fluoride administration were observed with the possible exception of a small increase in calcium excretion in high-dose female rats at weeks 27 and 66. A dose-related increase was observed in the fluoride concentration of urine from male and female rats at both the 27-week and 66-week interim evaluation.
ORGAN WEIGHT: There were no changes in organ weights that appeared to be related to sodium fluoride administration.
GROSS PATHOLOGY: The teeth of rats in the groups receiving 100 and 175 ppm sodium fluoride were clearly affected by the subtance. Discolouration, deformity and malocclusion was observed, more severely on male rats.
HISTOPATHOLOGY (NON-NEOPLASTIC): Nonneoplastic 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 sponstaneous 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 teeth of rats of both sexes administered with 175 ppm sodium fluoride showed evidence of dentine dysplasia and ameloblast degeneration.
HISTOPATHOLOGY (NEOPLASTIC):Osteosarcomas 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 ralated to sodium fluoride administration.
HISTORICAL CONTROL DATA: Historical incidences of osteosarcomas, oral cavity tumors, 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 evaluaiton 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.

Dose descriptor:

NOAEL

Effect level:

ca. 175 ppm

Sex:

female

Basis for effect level:

other: There was no evidence of carcinogenic activity in female rats receiving sodium fluoride at concentrations of 25,100, or 175 ppm

Dose descriptor:

NOAEL

Effect level:

ca. 175 ppm

Sex:

male

Basis for effect level:

other: There was equivocal evidence of osteosarcomas in male rats at the two highest dose group, but the findings are considered to be inconclusive

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

100 ppm

System:

other: dental effects

Organ:

tooth

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

During the 2-year sodium fluoride in drinking water study, equivocal evidence of carcinogenic activity was found based on the occurence of a small number of osteosarcomas in male rats of the two highest dose groups. However, the findings are considered to be inconclusive. In female rats receiving up to 175 ppm sodium fluoride, no evidence of carcinogenic activity was found. It should be noted that in a parallel 2-year toxicology and carcinogenicity study of sodium fluoride in drinking water conducted on male and female B6C3F1 mice did not find evidence of carcinogenic activity at concentrations up to 175 ppm.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

175 mg/kg bw/day

Study duration:

chronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Data waiving:

exposure considerations

Justification for data waiving:

a short-term toxicity study does not need to be conducted because exposure of humans via inhalation in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment

Endpoint conclusion

Endpoint conclusion:

no study available

Quality of whole database:

Exposure considerations: A short-term toxicity study does not need to be conducted because exposure of humans via inhalation in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Data waiving:

exposure considerations

Justification for data waiving:

a short-term toxicity study does not need to be conducted because exposure of humans via inhalation in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Data waiving:

exposure considerations

Justification for data waiving:

a short-term toxicity study does not need to be conducted because exposure of humans via the dermal route in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment

Endpoint conclusion

Endpoint conclusion:

no study available

Quality of whole database:

Exposure considerations: A short-term toxicity study does not need to be conducted because exposure of humans via the dermal route in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment.

Repeated dose toxicity: dermal - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Data waiving:

exposure considerations

Justification for data waiving:

a short-term toxicity study does not need to be conducted because exposure of humans via the dermal route in production and/or use is not likely as based on the provided thorough and rigorous exposure assessment

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No specific repeated dose toxicity studies have been conducted for Magnesium fluoride. Weight of evidence approach is used to evaluate the toxicity of the target substance after repeated exposure. Two repeated dose oral (gavage or diet) toxicity studies are conducted for similar substances (magnesium chloride, sodium fluoride and magnesium sulphate), which are summarised below.

 

A 13-week subchronic oral toxicity study by Tanaka H. et al. 1993 on B6C3F1 mice receiving magnesium chloride in doses of 0.3, 0.6, 1.25, 2.5 or 5% in diet (equal to following intakes males: 0.61, 1.22, 2.69, 5.41, 11.40 g/kg bw/day; females: 0.77, 1.58, 3.26, 6.81, 13.83 g/kg bw/day), revealed no treatment related effects in terms of survival, clinical observation, haematology or clinical chemistry. However, the average body weights of both sexes receiving 5% magnesium chloride were lower than those of the controls throughout the study period, but no clinical chemistry or histopathological changes were documented. Thus, it was considered that the changes in the organ weights were simply related to the lower body weight. The NOAEL values for both sexes were 2.5 % magnesium chloride

 

Toxicology and carcinogenesis studies were conducted with F344/N rats of each sex by incorporating sodium fluoride into the drinking water in study lasting 2 years. The sodium fluoride concentrations selected for the 2-year studies in rats were 0, 25, 100 and 175 mg/kg bw/day). in drinking water. Mean body weights of dosed and control groups of rats were similair throughout the 2-year studies. Survival of rats and mice was not affected by sodium fluoride administration. Under the conditions of these 2-year dosed water studies, there was equivocal evidence of carcinogenic activity of sodium fluoride in male rats, based on the occurrence of a small number of osteosarcomas in dosed animals. Findings were uncertain showing marginal increase of neoplasms that may be related to substance administration. There were no evidence in carcinogenic activity in female rats receiving sodium fluoride

 

Justification for classification or non-classification

Based on the observations made after the repeated exposure to similair substances, magnesium chloride and sodium fluoride, there is no need to classify the target substance for repeated dose toxicity in accordance with the criteria of CLP Regulation 1272/2008.