Hexafluorosilicic acid

Carcinogenicity

Description of key information

No studies with HFS acid are available. High quality NTP studies and supporting studies in the rat and mouse are available for sodium fluoride as weight-of-evidence. In the rat NTP study, osteosarcomas were observed in males, however this was considered to be reminiscent of hyperplasia rather than true bone neoplasm, and in another combined chronic toxicity/carcinogenicity no increases in tumors were observed. In the mouse NTP study, no increases in tumors were observed; there was also and additional combined chronic toxicity/carcinogenicity, however this was considered invalid due to a retroviral infection. In conclusion, there was no evidence for carcinogenicity at dose levels that demonstrated fluoride related toxicity. Highest tested dose levels in drinking water were NOAELs for tumorigenicty, corresponding with ‘target’ NOAEL of at least 8 and 12 mg/kg bw/day in rats and mice, respectively. The lowest NOAEL of 8 mg/kg bw was selected as most conservative dose descriptor for carcinogenicity potential.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

See attached read-across justification

Reason / purpose for cross-reference:

read-across source

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:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Ophthalmological findings:

not examined

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:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY

There was no treatment-related mortality; survival was unaffected by treatment. Clinical signs were limited to the teeth of rats at 100 and 175 ppm (attrition, deformity, discoloration, mottling, malocclusion). Mottling of the teeth was apparent at 25 ppm.

BODY WEIGHT AND WEIGHT GAIN

Bodyweights and weight gain were unaffected by treatment with NaF.

FOOD CONSUMPTION

Food consumption was unaffected by treatment


WATER CONSUMPTION AND COMPOUND INTAKE

Water consumption was unaffected by treatment. The intake of sodium fluoride over the course of the study was estimated to be 1.3, 5.2 and 8.6 mg/kg bw/d in males; 1.3, 5.5 abd 9.5 mg/kg bw/d for females.


HAEMATOLOGY

Parameters were unaffected by treatment.

CLINICAL CHEMISTRY

Parameters were unaffected by treatment.

URINALYSIS

Parameters were unaffected by treatment, with the possible exception of a small increase in calcium concentration in 175 ppm females.


ORGAN WEIGHTS

Organ weights were unaffected by treatment.


HISTOPATHOLOGY: NON-NEOPLASTIC

The incidence of osteosclerosis was increased in females at 175 ppm. Aterations in the teeth (dentine dysplasia, odontoblast and ameloblast degeneration) were seen in the incisors and were more frequent in males than females.


HISTOPATHOLOGY: NEOPLASTIC

Osteocarcoma was seen in one male at 100 ppm (2%) and three males at 175 ppm (4%). Squamous cell tumours of the oral mucosa were seen in control and treated animals and were not considered to be related to treatment. A marginal increase in thyroid follicular cell neoplasms was not considered to be related to treatment. A decreased incidence of uterine stromal polyps was seen in females at 175 ppm.


HISTORICAL CONTROL DATA

Osteosarcoma was reported to occur with a mean incidence of 0.5% in untreated male rats in NTP studies and a maximum incidence of 6%. The incidences in treated males in this study are within the historical range.

OTHER FINDINGS

Plasma fluoride concentration, urine fluoride concentration and bone fluoride concentration were increased in all treated groups.

Relevance of carcinogenic effects / potential:

Based on the results of this study the NTP state that there was 'equivocal evidence of carcinogenic activity' of sodium fluoride in male F344/N rats based on the occurrence of a small number of osteosarcomas in dosed animals (equivocal evidence is a category for uncertain findings defined as studies that are interpreted as showing a marginal increase of neoplasms that may be related to chemical administration). There was no evidence of carcinogenic activity in female F344/N rats receiving sodium fluoride in their drinking water at 25, 100 or 175ppm.

Dose descriptor:

NOAEL

Remarks:

carcinogenicity

Effect level:

25 ppm (nominal)

Based on:

other: Sodium fluoride

Sex:

male

Basis for effect level:

other: Equivoval evidence of carcinogenicity was seen at 100 and 175 ppm

Dose descriptor:

NOAEL

Remarks:

carcinogenicity

Effect level:

175 ppm (nominal)

Based on:

other: Sodium fluoride

Sex:

female

Basis for effect level:

other: No evidence of carcinogenicity was seen at any dose level

Dose descriptor:

NOAEL

Remarks:

toxicity

Effect level:

< 25 ppm

Based on:

other: Sodium fluoride

Sex:

male/female

Basis for effect level:

other: Dental effects were apparent in all treated groups

Survival rates after 2 years were:

males - control 42/80; 25ppm 25/51; 100ppm 23/50; 175ppm 42/80

females - control 59/80; 25ppm 31/50; 100ppm 34/50; 175ppm 42/80.

The pairwise comparison of the incidence of osteosarcomas in the 175 ppm group versus that in the controls was not statistically significant, however osteosarcomas occurred with a statistically significant dose-response trend.

Bone osteosarcomas in male rats

Bone: Osteosarcoma	Control	25ppm	100ppm	175ppm
Overall rates^a	0/80 (0%)	0/51 (0%)	1/50 (2%)	3/80 (4%)^b
Adjusted rates^c	0.0%	0.0%	4.3%	5.3%
Terminal rates^d	0/42 (0%)	0/25 (0%)	1/23 (4%)	1/42 (2%)
First incidence (days)	-	-	729 (T)	388
Logisitic regression tests^e	P=0.027	-^f	P=0.380	P=0.099

(T) Terminal sacrifice

^aNumber of tumour bearing animals/number of animals necropsied.

^bOne extraskeletal osteosarcoma occurred in a high dose male rat.

^cKaplan-Meier estimated tumour incidence at the end of the study after adjustment for intercurrent mortality.

^dObserved incidence at terminal kill.

^eBeneath the control incidence are the P values associated with the trend test. Beneath the dosed group incidence are the P values corresponding to pairwise comparisons between the controls and that dosed group. The logistic regression tests regard these lesions as non fatal.

^fNo tumours in dosed group or control group; statistical test not performed.

Tooth abnormalities (gross observations) in rats

Observation^a	Control	25ppm	100ppm	175ppm
Male
Attrition^b	0 (0%)	0 (0%)	7 (30%)	22 (50%)
Deformity^c	1 (1%)	0 (0%)	12 (17%)	27 (27%)
Discolouration^c	1 (1%)	2 (3%)	15 (21%)	31 (31%)
Malocclusion^c	1 (1%)	1 (1%)	2 (3%)	13 (13%)
Mottling^b	2 (5%)	22 (85%)	22 (96%)	44 (100%)
Female
Attrition	0 (0%)	0 (0%)	1 (3%)	2 (4%)
Deformity	0 (0%)	0 (0%)	1 (1%)	8 (8%)
Discolouration	0 (0%)	2 (3%)	2 (3%)	8 (8%)
Malocclusion	1 (1%)	0 (0%)	0 (0%)	1 (1%)
Mottling	0 (0%)	8 (26%)	32 (94%)	53 (98%)

^aDiscolouration designates an overall effect, while mottling indicates variegated discolouration. The terms are not mutually exclusive.

^bThe incidences for this observation are for the lower incisors of animals observed at week 104 only (males n=43, 26, 23, 44; females n=59, 31, 34, 54).

^cThe incidences for this observation include interim and terminal sacrifice animals (males and females n = 100, 70, 70, 100).

Conclusions:

Based on the results of this study the NTP state that there was 'equivocal evidence of carcinogenic activity' of read-across substance sodium fluoride in male F344/N rats based on the occurrence of a small number of osteosarcomas in dosed animals (equivocal evidence is a category for uncertain findings defined as studies that are interpreted as showing a marginal increase of neoplasms that may be related to chemical administration). There was no evidence of carcinogenic activity in female F344/N rats receiving sodium fluoride in their drinking water at 25, 100 or 175ppm.

Executive summary:

The potential carcinogenic activity of read-across substance sodium fluoride was determined in a 2 year drinking water study using male and female F344/N rats. Rats were exposed to concentrations of 0, 25, 100 or 175ppm daily in their drinking water. Survival rates were not affected by sodium fluoride administration. The teeth of the rats showed a dose-dependent whitish discolouration, and males had an increased incidence of tooth deformities and attrition leading on occasion to malocclusion. Osteosclerosis of long bones was increased in female rats given 175ppm, no other significant nonneoplastic lesions appeared related to sodium fluoride administration. A small number of osteosarcomas were seen in male rats given 100 or 175ppm, none were seen in the control or 25ppm groups. Osteosarcomas occurred with a statistically significant dose-response trend, leading to the conclusion that a weak association may exist between

the occurrence of these neoplasms and the administration of sodium fluoride. Therefore, according to the NTP Explanations of Levels of Incidence, the NTP concluded that under the conditions of this study, there was 'equivocal evidence of carcinogenic activity' of sodium fluoride in male F344/N rats based on the occurrence of a small number of osteosarcomas in dosed animals. Equivocal evidence is a category for uncertain findings defined as studies that are interpreted as showing a marginal increase of neoplasms that may be related to chemical administration. There was no evidence of carcinogenic activity in female F344/N rats receiving sodium fluoride in their drinking water at 25, 100 or 175ppm.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

See attached read-across justification

Reason / purpose for cross-reference:

read-across source

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY

There was no treatment-related effect on survival or mortality. Clinical signs were limited to white teeth, which were first noted earliest in animals at the top dose level (Day 74), intermediate and low dose levels (Days 81-200) and controls (Day 508). Detailed dental investigation revealed attrition at 175 ppm; discoloration and mottling in all treated groups.

BODY WEIGHT AND WEIGHT GAIN

Bodyweights and weight gains were unaffected by treatment.

FOOD CONSUMPTION

Food consumption was unaffected by treatment.


WATER CONSUMPTION AND COMPOUND INTAKE

Water consumption was unaffected by treatment. The average intake of sodium fluoride was calculated to be 2.4, 9.6 and 16.7 mg/kg bw/d in males; 2.8, 11.3 and 18.8 mg/kg bw in females.


HAEMATOLOGY

There were no effects of treatment.

CLINICAL CHEMISTRY

There were no effects of treatment, with the exception of elevated serum alkaline phosphatase activity in females at 175 ppm.

ORGAN WEIGHTS

Organ weights were unaffected by treatment.


HISTOPATHOLOGY: NON-NEOPLASTIC

Dentine dysplasia was significnalty increased in male mice at 175 ppm.

HISTOPATHOLOGY: NEOPLASTIC

A marginal increase in the incidence of malignant lymphoma was not considered to be treatment-related. A slight numerical increase in hepatoblastoma was not considered to be biologically significant.

Relevance of carcinogenic effects / potential:

There was no evidence of carcinogenic activity of sodium fluoride in male or female mice receicing sodium fluoride at concentrations of 25, 100 or 175ppm in drinking water for 2 years.

Dose descriptor:

NOAEL

Remarks:

carcinogenicity

Effect level:

175 ppm (nominal)

Based on:

other: Sodium fluoride

Sex:

male/female

Basis for effect level:

other: There was no evidence of carcinogencity in this study.

Survival rates after 2 years were:

males - control 58/79; 25ppm 39/50; 100ppm 37/51; 175ppm 65/80

females - control 53/80; 25ppm 38/52; 100ppm 34/50; 175ppm 52/80.

Conclusions:

No evidence of carcinogenicity was seen under the conditions of this study with read-across substance sodium fluoride.

Executive summary:

The potential carcinogenic activity of read-across substance sodium fluoride was determined in a 2 year drinking water study using male and female B6C3F1 mice. Mice were exposed to concentrations of 0, 25, 100 or 175ppm daily in their drinking water. Survival rates were not affected by sodium fluoride administration. There was no evidence of carcinogenic activity in male or female B6C3F1 mice receiving sodium fluoride in their drinking water at 25, 100 or 175ppm for 2 years.

Reference 3

Endpoint:

carcinogenicity: oral

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

See attached read-across justification

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

A 30% reduction in weight gain was seen at the 25 mg/kg bw/day dose. Dental aberrations (ameloblast dysplasia and enamel hypoplasia) were dose relatedly increased in all groups. Dental fractures and malocclusions were enhanced at 10 and 25 mg/kg bw/day. Subperiosteal hyperostosis was observed in particular in the bones of the skulls of males and 10 mg/kg bw/day and above, this effect was less pronounced in the females. Relative and absolute stomach weight were significantly increased at 10 mg/kg bw/day and above. Mononuclear cell infiltration of the glandular epithelium was dose-relatedly increased from 4 mg/kg bw/day in the male and from 10 mg/kg bw/day in the females. Chronic inflammation and regeneration of the glandular mucosa occurred in the males at 10 mg/kg bw/day and above. In the females these effects were seen at 4 mg/kg bw/day and above and at 25 mg/kg bw/day, respectively. In 24 other tissues (including testes) no lesions were reported, but the EU RAR states that no quanititative data were provided. In some animals neoplastic bone lesions were seen (sarcoma, osteosarcoma, chordoma, chondroma) but these lesions were incidental and radnomly distributed across treatment groups. In the stomach of one controlm ale a papilloma was found. Other soft tissue neoplasms were not reported in detail but it was stated that there was no evidence that fluoride altered the incidence of prenoplastic and neoplastic lesions at sites of fluoride toxicity or at any other site in rats of either sex.

Relevance of carcinogenic effects / potential:

NaF is not thought to be carcinogenic to rats.

Dose descriptor:

NOEL

Remarks:

carcinogenicity

Effect level:

25 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: NaF was not carcinogenic to rats when tested up to 25 mg/kg bw/day

Dose descriptor:

LOEL

Remarks:

toxicity

Effect level:

10 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: Decreased body weight and morphological signs of fluoride toxicity were seen

No further information.

Conclusions:

Read-across substance NaF is not thought to be carcinogenic to rats.

Executive summary:

A combined toxicity/carcinogenicity study was conducted in male and female Sprague-Dawley rats with read-across substance sodium fluoride (NaF). Rats were fed 0, 4, 10 or 25 mg NaF/kg bw/day in a low fluoride diet for 2 years. Controls were fed a low fluoride diet or laboratory chow. A 30% reduction in body weight gain was seen in rats fed 25 mg/kg bw/day. Evidence of fluoride toxicity was seen in the teeth, bones and stomach, and the incidence and severity of these changes were related to the dose of NaF and the duration of exposure. The authors concluded that the incidence of preneoplastic and neoplastic lesions was not affected by NaF in either sex, and that read-across substance sodium fluoride is not carcinogenic to rats.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

8 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

high quality NTP studies

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

No classification is proposed. The EU RAR has reviewed all available data for HF and NaF and concludes that the data are sufficient to suggest that fluoride is not carcinogenic in animals.

Additional information

Justification for read-across from sodium fluoride

There are no carcinogenicity studies available for Hexafluorosilic acid. The effects of chronic Hexafluorosilic acid exposure will be dominated by local effects at the site of contact (irritation/corrosion), therefore performing studies with Hexafluorosilic acid cannot be supported for scientific reasons and also on animal welfare grounds. Once absorbed into the body Hexafluorosilic acid, will dissociate into its constituent ions and systemic toxicity will be due to fluoride. The analogous bevaviour of sodium fluoride (or any other water-soluble fluoride salts) means that read-across from NaF to target substance Hexafluorosilic acid is scientifically justified to be used as weight-of-evidence.

 

Studies in the rat

The potential carcinogenic activity of sodium fluoride was determined in a 2 year drinking water study using male and female F344/N rats. Rats were exposed to concentrations of 0, 25, 100 or 175 ppm daily in their drinking water (NTP, 1990). The NTP rat study showed evidence of an effect of sodium fluoride administration on the bones and teeth (teeth of the rats showed a dose-dependent whitish discolouration, and males had an increased incidence of tooth deformities and attrition leading on occasion to malocclusion), consistent with the findings of other studies. There was no effect on survival in this study; bodyweights, food and water consumption, haematological and clinical chemistry parameters and organ weights were unaffected by treatment. Serum, urine and bone fluoride concentrations were increased in all treated groups; the urine calcium concentration was also marginally higher in females at the highest dose level. Osteosclerosis was seen in females at the highest dose level. The incidence of osteosarcoma was increased in males at the intermediate dose level of 100 ppm (2%) and the high dose level of 175 ppm (4%) but was within the historical range (0 -6%; mean 0.5%). No increased in tumors was seen in female rats up to 175 ppm. The NTP concluded that the study provides 'equivocal evidence' for carcinogenicity in male rats. Taking into account the IARC (1987) and EU RAR (2001) conclusions below, the dose of 175 ppm can be considered as NOAEL.

Taking into account a daily water requirement of 20-30 mL/rat (Derelanko, The Toxicologist’s Pocket Handbook, Informa, 2008), the NOAEL of 175 ppm (175 mg/L) corresponds with 3.5- 5.25 mg/rat. Assuming a mean body weight of 250 g/rat, the NOAEL would be 14-21 mg/kg bw. Application of a conversion factor from source to target substance (see read-across justification) leads to ‘target’ NOAEL of at least 14 mg/kg bw x 0.57 = 8 mg/kg bw

An additional carcinogenicity study with sodium fluoride in the rat is available (Maurer et al, 1990). The study was a combined toxicity/carcinogenicity study in male and female Sprague-Dawley rats fed 0, 4, 10 or 25 mg/kg bw/day in a low fluoride diet for 2 years. Controls were fed a low fluoride diet or laboratory chow. A 30% reduction in body weight gain was seen in rats fed 25 mg/kg bw/day. Evidence of fluoride toxicity was seen in the teeth, bones and stomach, and the incidence and severity of these changes were related to the dose of NaF and the duration of exposure. The authors concluded that the incidence of preneoplastic and neoplastic lesions was not affected by NaF in either sex, and that sodium fluoride is not carcinogenic to rats. No evidence of carcinogenicity was seen in this study, at dose levels sufficient to cause toxicity.

 

Studies in the mouse

The potential carcinogenic activity of sodium fluoride was determined in a 2 year drinking water study using male and female B6C3F1 mice (NTP, 1990). Mice were exposed to concentrations of 0, 25, 100 or 175 ppm daily in their drinking water. The NTP mouse study showed evidence of an effect of sodium fluoride administration on the teeth, consistent with the findings of other studies. There was no effect on survival in this study; bodyweights, food and water consumption, haematological parameters and organ weights were unaffected by treatment. Clinical chemistry revealed elevated ALP activity in females at the highest dose level. Microscopic findings were limited to dentine dysplasia in male mice at 175 ppm. There was no evidence of carcinogenicity in either sex.

Taking into account a daily water requirement of 3-7 mL/rat (Derelanko, The Toxicologist’s Pocket Handbook, Informa, 2008), a highest dose of 175 ppm (175 mg/L) corresponds with 0.525- 1.225 mg/mouse. Assuming a mean body weight of 25 g/mouse, the NOAEL would be 21-49 mg/kg bw. Application of a conversion factor from source to target substance (see read-across justification) leads to a NOAEL of at least 21 mg/kg bw x 0.57 = 12 mg/kg bw.

An additional carcinogenicity study with NaF is available (Maurer et al, 1993). This was a combined toxicity/carcinogenicity study in male and female mice exposed at nominal concentrations of 0, 4, 10 and 25 mg/kg bw/day in a low fluoride diet. Controls received unsupplemented low fluoride diet or laboratory chow. A high level of osteosarcomas was seen in all (control and treated) groups in this study, a finding which was attributed to infection with a retrovirus. No conclusion on the carcinogenicity of sodium fluoride can be drawn from this study.

 

Conclusion

Fluorides (inorganic, used in drinking-water) were not classifiable as to their carcinogenicity to humans (IARC, 1987). The osteosarcomas in rats dosed with sodium fluoride were in the rat NTP study was considered to be reminiscent of hyperplasia rather than true bone neoplasm. The available data is sufficient to suggest that fluoride is no a carcinogenic substance in animals. In humans, evidence for carcinogenicity of orally taken fluoride was inadequate: no reliable evidence of an association between consumption of fluoridated drinking water ad increased incidence of mortality due to cancer could be established (EU RAR, 2001).