Ammonium hydrogendifluoride

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No additional data are available.

Effect on fertility: via oral route

Dose descriptor:

NOAEL

10 mg/kg bw/day

Additional information

Fluoride studies

Under physiological conditions, AMBI will dissociate with the production of fluoride and ammonium ions. No studies of reproductive toxicity are available for AMBI, however read-across to other soluble fluorides, ammonia and soluble ammonium salts is appropriate

Fluorides: published studies

Araibi et al (1989) report adverse effects on the fertility of male rats administered sodium fluoride in the diet at concentrations of 100 and 200 ppm. Exposure resulted in a reduction in succesful matings and reduced litter size; findings were associated with a reduction in seminiferous tubule diameter and a thickened peritubular membrane. The numbers of tubules containing spermatozoa were decreased and serum testosterone levels were also reduced. Chinoy & Sequeira (1989) report alterations in the histoarchitecture of the testes in mice gavaged with sodium fluoride at dose levels of 10 and 20 mg/kg bw/d for 30 days. Findings were characterised by severe disorganisation and denudation of germinal epithelial cells of the seminiferous tubules, absence of sperm from the tubular lumen, reduced in epithelial cell height, nuclear pkynosis, denudation of cells and absence of sperm occurred in the cauda epididymis. The effects seen after 30 days administration were reversible. Chinoy et al (1992) report reduced fertility in male rats administered sodium fluoride by gavage at dose levels of 5 and 10 mg/kg bw for 30 days. Findings were accompanied by reduced sperm count and motility and various biochemical changes in the testes.

The results of these studies are consistent, however their value and reliability is significantly compromised by the absence of any information on the fluoride levels in diet and/or drinking water. The actual levels of fluoride exposure cannot be accurately assessed. It is also notable that the findings of these published investigative studies of non-standard design contrast with the total absence of reproductive toxicity at comparable dose levels in the FDA studies reported below.

Messer et al (1973) investigated the reproductive toxicity of sodium fluoride in a two-generation study in which female mice were administered the test material in the drinking water at dose levels of 0, 50, 100 or 200 ppm. A progressive decline in litter production was seen in the control group. All females administered 200 ppm fluoride died over the study period; only a small number of litters were produced at the 100 ppm. It is suggested that a level of 50 ppm sodium fluoride (equivalent to approximately 7.5 mg/kg bw.d fluoride) is required to maintain reproductive capacity in female mice. In a 3 -generation mouse study (Tao & Suttie, 1976), no effects of fluoride on reproduction were seen. The study is of limited value, however the authors suggest that the effects of fluoride seen in the study of Messeret al (1973) was due to the influence of fluoride on the absorption of iron from a low iron diet.

Fluorides: FDA studies

The effects of sodium fluoride administration on spermatogenesis in rats were investigated in a two-generation study (Sprando et al, 1997). In contrast to the previous studies, no effects were observed on reproductive organ weights, sperm parameters or biochemical parameters at dose levels of up to 250 ppm (drinking water). Additional deatiled investigations by the same authors did not reveal any effects on spermatogenesis in F1 males (Sprando et al, 1998). No effects on reproduction were seen at the highest dose level of 250 ppm in a guideline-comparable two-generation rat study (Collins et al, 2001). In a further FDA study designed primarily to assess the potential effects of fluoride on spermatogenesis (as indiceted in various published studies), Sprando et al (1996) demonstrated that injection of sodium fluoride into the rat testis was without effect on spermatogenesis.

In contrast to the other studies which report effects of fluoride on male fertility and spermatogenesis, no effects were observed in the FDA studies following extensive investigation. The two-generation FDA study is of standard design and is comprehensively reported, and it is notable in these studies that thr contribution of diet and drinking water to the total fluoride intake was assessed. The EU RAR for HF also considers the data available for the reproductive toxicity of NaF and concludes that the FDA studies are key, for reasons of design, reporting and control of fluoride levels. The EU RAR concludes that the NOAEL for reproductive toxicity is 250 ppm NaF, which corresponds to approximately 10 mg/kg bw/d fluoride. The absence of any apparent effects on the reproductive organs in chronic toxicity and carcinogenicity studies is also notable.

Ammonia/ammonium studies

A guideline-comparable two-generation study with ammonium perchlorate did not identify any effects on reproductive parameters at dose levels of up to and including 100 mg/kg bw/day. The study did identify effects on the parental thyroid associated with perchlorate exposure, however findings are not attributable to ammonium. The results of the study therefore confirm that exposure to ammonium is not associated with reproductive toxicity (York et al, 2001). There is no evidence that exposure to ammonium ions causes reproductive toxicity. Inhalation exposure to ammonia will result in an equilibrium in the blood (at physiologically relevant pH) between non-ionised ammonia (NH3) and ionised ammonium (NH4+) in a ratio of approximately 1:100. The same equilibrium will exist in animals orally exposed to ammonium salts, therefore read-across is appropriate. Human maternal blood contains measurable levels of ammonia as a consequence of protein catabolism; the blood in the hepatic portal circulation contains much higher levels of ammonia due to its generation from urea by the gastrointestinal flora. Ammonia is rapidly and effectively detoxified in the liver by the urea cycle and also via additional pathways, therefore will not accumulate and is unlikely to cause any reproductive effects.

Short description of key information:
No studies with AMBI are available. However a number of studies of various designs are available with the read-across substance NaF, including high quality studies performed by the US FDA. The results of these studies indicate that exposure to fluoride is the critical effect.

Effects on developmental toxicity

Description of key information

No studies with AMBI are available.  However a number of studies of various designs are available with the read-across substance NaF, including high quality studies performed by the US NTP and FDA.  No evidence of any developmental effects was seen in studies with ammonia or ammonium salts.  The physiological role of ammonia indicates that it is unlikely to be a developmental toxin at relevant exposure levels.  The results of these studies indicate that exposure to fluoride is the critical effect.

Effect on developmental toxicity: via oral route

Dose descriptor:

NOAEL

14 mg/kg bw/day

Additional information

Fluoride studies

Under physiological conditions, AMBI will dissociate with the production of fluoride and ammonium ions. No studies of developmental toxicity are available for AMBI, however read-across to other soluble fluorides, ammonia and soluble ammonium salts is appropriate.

In a rat developmental toxicity study (NTP, 1994; Heindel et al, 1996), maternal toxicity (transiently reduced bodyweight gain) was apparent at the highest dose level of 300 ppm sodium fluoride (in drinking water), equivalent to 13 mg/kg bw/d fluoride. No evidence of developmental toxicity was seen at this dose level. No clear evidence of developmental toxicity was seen in an FDA rat study (Collins et al, 1995) at dose levels of up to 250 ppm sodium fluoride in drinking water (equivalent to 12.3 mg/kg bw/d fluoride). Maternal toxicity in this study was limited to reduced food intake at the highest dose level. No evidence of developmental toxicity was seen in a rabbit study (NTP, 1993; Heindel et al, 1996) at dose levels of up to 400 ppm sodium fluoride (equivalent to 14 mg/kg bw/d fluoride from all sources).

Ammonia/ammoinum studies

No evidence of developmental toxicity was seen in a guideline-compliant rabbit study with ammonium perchlorate (York et al, 2001) at the highest dose level of 100 mg/kg bw/day. The influence of ammonium ions on foetal development was investigated in mice in a non-standard study involving in vitro exposure prior to transplantation into dams (Lane & Gardner, 1994). Examination on gestational day 15 showed an apparent relationship between the duration of exposure and the incidence of exencephaly. Embryos that were cultured with various concentrations of ammonium ion before being transferred to recipient dams showed increased incidence of exencephaly and a decreased percentage of implantation sites with increased ammonium concentration. It is unclear how embryos might be exposed to ammonia or ammonium in vivo or if in vivo exposure would affect foetal development and implantation in a way similar to that described in this study.

No evidence of foetal toxicity was seen in a study in pigs (Diekman et al, 1993) exposed to maternally toxic concentrations of ammonia by inhalation. Although the design of the study is somewhat limited, it can be concluded that the relatively low concentrations of ammonia required to induce local irritant effects are very unlikely to cause systemic toxicity or any developmental toxicity.

Conclusion

There is no evidence that exposure to ammonium ions causes specific developmental toxicity in vivo. Inhalation exposure to ammonia will result in an equilibrium in the blood (at physiologically relevant pH) between non-ionised ammonia (NH3) and ionised ammonium (NH4+) in a ratio of approximately 1:100. The same equilibrium will exist in animals orally exposed to ammonium salts, therefore read-across is appropriate. Human maternal blood contains measurable levels of ammonia as a consequence of protein catabolism; levels of ammonia in foetal blood are slightly higher. The blood in the hepatic portal circulation contains much higher levels of ammonia due to its generation from urea by the gastrointestinal flora. Ammonia is rapidly and effectively detoxified in the liver by the urea cycle and also via additional pathways, therefore will not accumulate and is unlikely to cause any devlopmental toxic effects at relevant exposure levels.

Justification for classification or non-classification

Reliable studies do not indicate any developmental toxicity or reproductive toxicity of fluoride. No classification is therefore proposed.