Dinitrogen oxide

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Some epidemiological and animal studies have demonstrated a significantly increased risk of reduced fertility and spontaneous abortion in occupationally exposed persons (MAK value documentation, 1993 & 2007).

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via inhalation route

Endpoint conclusion:

adverse effect observed

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Reproductive toxicity: oral and dermal route

Since nitrous oxide is a gas, the oral and dermal route is not relevant for the assessment of reproductive toxicity.

Reproductive toxicity: via inhalation

For the assessment of reproductive toxicity of nitrous oxide at the workplace fertility studies with 4-hour to 8-hour daily exposure were evaluated. The summary of the studies was derived from MAK value documentation (1993 and 2007).

Female fertility

The fertility of 12 female rats exposed to a nitrous oxide concentration of 500 ml/m³ (8 hours/day, 35 days) was reduced compared to that of control animals. The ovulation cycle was disturbed in all the exposed rats but returned to normal after the end of exposure. After mating, 6/12 of the exposed animals and 12/12 of the control animals produced young. Effects on litter size and birth weights were not detected. A disturbance in the luteinizing-hormone-releasing hormone system caused by nitrous oxide was thought to cause the reduction in fertility (Kugel et al. 1989).

Male fertility

After exposure of male rats (6 hours/day, 5 days/week, 4 weeks) to a nitrous oxide concentration of 5000 ml/m³, a reduction in size and morphological abnormalities were observed in the sperm (Vieira and Cleaton-Jones 1980). After mating, litter size, and weight and size of the young were reduced (Vieira et al. 1983a).

There are further studies available examining effects on testis, spermatogenesis and male fertility which are summarised by the MAK Commission (1993)  as follows:

At least 2 days exposure of male rats (8 to 24 hours/day, 5 to 7 weeks) to a nitrous oxide concentration of 200000 ml/m3 was required to cause an increase in the number and size of Leydig’s cells (Gremigni et al. 1978) and a reversible reduction in sperm, spermatocyte and spermatogonium counts (Kripke et al. 1976); intermittently exposed animals were affected to a lesser extent.

In contrast,  Holson et al. (1995)  studied effects of nitrous oxide (1000, 5000, 10 000 ppm; 0.1, 0.5, 1.0%) on male fertility by mating treated males with untreated females and examining uterine contents. There was no evidence for a substantial decline in fertility of exposed males, although there was a small dose-related trend for resorptions to increase and live births to decrease with increasing paternal exposure.

Based on the available data impairment of male and female fertility by nitrous oxide at concentrations slightly higher than expected at the workplace cannot be excluded (ACGIH, 2001)

References

- Gremigni D, Colosi G, Peduto VA (1978) Modificazioni del didimo di ratto dopo somministrazione di protossido di azoto. Arch Ital Anat Embriol 83: 153–162

General remark

1 mL/m³ (ppm) = 1.83 mg/m³

Effects on developmental toxicity

Description of key information

In concentrations used for anesthesia (≥ 700 000 mL/m³, equivalent to 1 260 000 mg/m³) nitrous oxide is embryotoxic and teratogenic in rats after a single exposure at the critical time point (GD 9 in rats) and also after continuous exposure (24h/d) covering GD 9 (MAK Evaluation German 1993 + 2007). This is, however, a non-chemical use at concentrations causing unconsciousness as the primary effect.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Developmental toxicity: oral and dermal route

Since nitrous oxide is a gas, the oral and dermal route is not relevant for the assessment of developmental toxicity.

Developmental toxicity: via inhalation

For the assessment of developmental toxicity of nitrous oxide at the workplace prenatal developmental toxicity studies with 4-hour to 8-hour daily exposure were evaluated. The summary of the studies was derived from MAK value documentation (2007).

No significant foetal effects were observed in prenatal developmental toxicity studies after exposure of rats to nitrous oxide concentrations of up to 1000 mL/m³ on days 1 to 19 or days 10 to 19 of gestation (Corbett et al. 1973; Vieira et al. 1983). A working group observed foetotoxic effects at 5000 mL/m³, but no increased incidence of malformations (Vieira et al. 1983). Concentrations of 10 000 mL/m³ also induced effects on litter size, birth weights and postnatal body weight gain and body length in a study with postnatal examination (Vieira et al. 1978). These effects could not be reproduced in another modern and valid developmental toxicity study with postnatal examination. No effects were observed on litter size, postnatal body weight gain or postnatal behaviour up to this concentration (Holson et al. 1995). A further prenatal developmental toxicity study revealed prenatal toxic effects only at concentrations of 100 000 mL/m³ and above, but not at 10 000 mL/m³ (Pope et al. 1978). Therefore, a NOAEC of 10 000 mL/m³ can be derived for prenatal and postnatal developmental toxicity from studies in rats using intermittent exposure relevant for assessing workplace exposure (Holson et al. 1995; Pope et al. 1978). If the MAK value of 100 mL/m³ is observed, prenatal toxicity is not expected to occur.

In concentrations used for anesthesia (≥ 700 000 mL/m³) nitrous oxide is embryotoxic and teratogenic in rats after a single exposure at the critical time point (GD 9 in rats) and also after continuous exposure (24h/d) covering GD 9 (MAK Evaluation German 1993 + 2007). This is, however, a non-chemical use at concentrations causing unconsciousness as the primary effect.

General remark

1 mL/m³ (ppm) = 1.83 mg/m³

Justification for classification or non-classification

Classification, Labelling, and Packaging Regulation (EC) No 1272/2008

The available test data does not trigger a classification for reproductive and developmental toxicity of nitrous oxide under Regulation (EC) No 1272/2008 as amended for fifteenth time in Regulation (EU) No 2020/1182 as evidence for adverse effects on fertility and developmental occur mainly at concentrations causing unconsciousness as the primary effect. Consequently exposure regime and concentrations used are not typical for occupational exposure and are therefore considered insufficient for classification.