Norflurane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via inhalation route

Dose descriptor:

NOAEC

208 000 mg/m³

Additional information

In a dominant lethal assay, CD1 male mice were exposed to up to 50000 ppm HFC 134a for 5 days. After the last exposure, each male was housed with 2 virgin females for 4 consecutive nights. Further matings with new females were conducted at weekly intervals for a total of 8 times. The study indicated that HFC 134a did not affect male fertility or cause mutagenic effects through sperm (Hodge et al 1979).

1,1,1,2 -tetrafluoroethane (HFC 134a) was administered to AHA rats by snout only inhalation to assess the effects on reproduction and development. In the fertility element of the study, rats were exposed to atmospheres of 2500, 10 000 or 50 000 ppm HFC 134a for 1 hour /day throughout gametogenesis, mating, pregnancy and lactation.

The only treatment related effect was a slight reduction in body weight gain of the treated parental generation at 50 000 ppm (208000 mg/m3).

There were no adverse effects of HFC 134a on the fertility and reproductive performance of treated animals or on the development, maturation or reproductive performance of up to two successive generations. (Alexander et al 1996).

In a 2 -generation reproductive toxicity study in the rat, performed on the structural analogue 1,1,1,3,3 -pentafluoropropane (HFC 245fa), no adverse effects on fertility were observed at 2000 ppm.

1,1,1,2 -tetrafluoroethane (HFC 134a) has been in worldwide human use for all age groups as the primary propellant in asthma MDI inhalers for over 26 years with no adverse reproductive effects reported.

Short description of key information:
HFC 134a showed no adverse effects on fertility in a dominant lethal study in mice, and showed no adverse effects on fertility in a multi-generational reproductive toxicity study in the rat.

Effects on developmental toxicity

Description of key information

HFC 134a was not teratogenic in rats and rabbits. Only non-specific effects on foetal maturation (delayed ossification of the foetus) in the rat were observed following exposure to 50000ppm HFC-134a (208000 mg/m3) and above.

Effect on developmental toxicity: via inhalation route

Dose descriptor:

NOAEC

166 400 mg/m³

Additional information

In the key teratology study groups of 25 rabbits were exposed to HFC 134a 6hr/day at levels of upto 40000ppm on days 7 -19 of gestation. No treatement related-developmental or teratogenic effects were seen (Wickramaratne 1989).

In an earlier study, pregnant Alpk/APfSD Wistar-derived rats (29 - 30/group) were exposed (6 h/d) to 0, 1,000, 10,000 and 50,000 ppm (0, 4,170, 41,700, 208,000mg/m3) HFC-134a from day 6 to 15 of gestation. The exposure to HFC-134a produced abnormal clinical signs but did not affect the maternal body weights. Mean foetal weights were slightly but significantly lower in the offspring of rats exposed to 50,000 ppm. Embryonic and foetal survival were unaffected by the treatment. There was no evidence for teratogenicity but skeletal ossification was slightly retarded in the top dose (50,000 ppm). It was concluded that HFC-134a was neither teratogenic nor embryotoxic at levels up to 50,000 ppm, but at this highest level HFC-134a might be slightly foetotoxic (Hodge 1980 et al).

However, in another study using similar exposure conditions to Hodge et al 1980, groups of rats were exposed to upto 300000 ppm HFC 134a 6hr/day of days 6 -15 of gestation. Oxygen was added to maintain oxygen levels near 20%. No teratogenic effects were observed although there was some decrease of maternal body weight gain and retarded foetal development in the form of delayed ossification. The minimum maternal effect exposure level was demonstrated to be 100,000 ppm, and the minimum embryo/foetal effect exposure level was demonstrated to be 300,000 ppm (Lu 1981).

In a multigenerational study in the rat at exposure levels of upto 50000ppm HFC 134a, no treatment related effects were observed on reproductive perfomance, maturation or development of the offspring were reported (Alexander et al 1996).

Update October 2011

Following a further review of the data, the Registrant has concluded that HFC134a causes no significant developmental effects at any exposure concentration that has been studied. A NOAEC of 40,000 ppm (166,400 mg/m3) HFC134a can be derived for developmental endpoints, based on the highest concentration utilised in a study in the rabbit. This conclusion is drawn from the results of three informative studies, each judged to be Reliability 1.

1)     Pregnant rabbits were exposed for 6 hours/day from day 7 to day 19 of gestation to concentrations of HFC134a up to 40,000 ppm. Exposure to concentrations of 10,000 and 40,000 ppm HFC134a was associated with slight maternal toxicity manifest as reduced body weight gain and food consumption. There was no evidence for maternal toxicity at the exposure level of 2,500 ppm. No evidence of either embryo-toxicity or foeto-toxicity was observed at any concentration studied. The NOAEC of HFC134a for both embryo-toxicity and foeto-toxicity in the rabbit was 40,000 ppm (Wickramaratne, 1989).

2)     Pregnant rats were exposed for 6 hours/day from day 6 to day 15 of gestation to concentrations of HFC134a of 30,000, 100,000 or 300,000 ppm. There were signs of toxicity (response to sound either reduced or absent; reduced weight gain) in the dams exposed to 100,000 ppm HFC134a and above. There was evidence of reduced foetal weight and of delayed ossification in the offspring of rats exposed to 300,000 ppm, but not 100,000 ppm. The delayed ossification was considered by the authors to be a variant and not a malformation. The NOAEC of HFC134a for both embryo-toxicity and foeto-toxicity in the rat in this study was 100,000 ppm (Lu, 1981).

3)     Pregnant rats were exposed for 6 hours/day from day 6 to day 15 of gestation to concentrations of 1,000, 10,000 and 50,000 ppm HFC134a. Mean foetal weight of the offspring exposed to 50,000 ppm HFC134a was reduced when compared to controls but there was no decrease in mean litter weight. The effect on mean foetal weight was statistically significant. There was some evidence of delayed ossification in the offspring of rats exposed to 50,000 ppm. This effect was confined to decrements in ossification of cervical centra 1-2, the sternebrae, the calcaneum and the digits of both forelimbs and hindlimbs. The incidence of bipartite or misaligned sternebrae in this group was also increased. Reductions in ossification were also observed to a lesser extent in the offspring of rats exposed to 1,000 ppm but not to 10,000 ppm HFC134a. The authors of the report concluded that the test substance was neither teratogenic nor embryo-toxic at 50,000 ppm, but might be slightly foeto-toxic at this concentration in rats (Hodge et al, 1980).

The increased incidence of delayed ossification in the offspring of rats exposed to 50,000 ppm HFC134a was minimal and, when assessed on a litter basis, was only considered significant in the hind limb digits. Delayed ossification is a common variant and, when it occurs in conjunction with reduced foetal weight, is considered to be a transient effect. This pattern of response is not considered to be an adverse effect (Carney & Kimmel, 2007) and is of minimal relevance in the assessment of human risk. As a consequence, it is concluded that 50,000 ppm is a NOAEC for HFC134a for embryo-toxicity in the rat in this study, but that 10,000 ppm is a NOEC for slight foeto-toxicity that might have occurred in rats exposed to 50,000 ppm HFC134a.

Taking into account all of the available evidence, it is concluded that HFC134a causes no significant developmental effects at any exposure concentration that has been studied. A NOAEC of 40,000 ppm HFC134a can be derived for developmental endpoints, based on the highest concentration utilised in a study in the rabbit, which is acknowledged as being a sensitive species for the determination of developmental effects. It also takes into account the delayed ossification seen in rats exposed to 50,000 ppm HFC134a. Delayed ossification is a common variant and, when it occurs in conjunction with reduced foetal weight, is considered to be a transient effect. This pattern of response is not considered to be an adverse effect (Carney & Kimmel, 2007) and is of minimal relevance in the assessment of human risk.

References

Carney, EW and Kimmel, CA. “Interpretation of Skeletal Variations for Human Risk Assessment: Delayed Ossification and Wavy Ribs”. Birth Defects Research (Part B), 80, 473-496, 2007

Hodge, MCE, Kilmartin, M, Riley, RA, Weight, TM and Wilson, J. “Arcton 134a: teratogenicity study in the rat”. Report No: CTL/P/417, ICI Central Toxicology Laboratory, 1980.

Lu, M, “1,1,1,2-tetrafluoroethane (FC-134a): embryo-foetal toxicity and teratogenicity study by inhalation in the rat”. Haskell Laboratory Report Number 317-81. E.I. Du Pont de Nemours and Company, Newark, DE 19711, USA, 1981.

Wickramaratne, GA. “HFC 134a: teratogenicity inhalation study in the rabbit”. Report No: CTL/P/2504, ICI Central Toxicology Laboratory, 1989.

Justification for classification or non-classification

HFC 134a showed no adverse effects on fertility in a dominant lethal study in mice, and showed no adverse effects on fertility in a multi-generational reproductive toxicity study in the rat. In four developmental/teratology studies, HFC 134a was shown not to be teratogenic in rats and rabbits. Only non-specific effects on foetal maturation (delayed ossification of the foetus) in the rat were observed following exposure to 50000ppm HFC-134a (208000 mg/m3) and above.

A NOAEC of 40,000 ppm HFC134a (166,400 mg/m3) can be derived for developmental endpoints, based on the highest concentration utilised in a study in the rabbit.

Therefore it is considered that classification is not warranted as toxic for reproduction according to EU Directive 67/548/EEC and EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.