Dinitrogen tetraoxide

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

 In accordance with Column 2 of section 8.7 of REACH Annex IX, the study does not need to be conducted because the substance is known to be a germ cell mutagen and appropriate risk management measures are implemented.

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

As the classification of dinitrogen tetraoxide as Mutagenic 1B., H340 is proposed in accordance with Regulation 1272/2008/EC, and appropriate risk mitigation measures are implemented, a performance of reproductive toxicity studies is not warranted in accordance with column 2 of Section 8.7 of REACH Annex IX. Available limited information on reproductive toxicity of the substance is summarized below.

Reproductive toxicity of the monomer of dinitrogen tetraoxide (N₂O₄), nitrogen dioxide (NO₂) has been discussed in detail in the reports of MAK (2005) and the Scientific Committee on Occupational Exposure Limits (SCOEL, 2014). Dinitrogen tetraoxide exists in equilibrium with nitrogen dioxide, with ca. 25% present in the form of NO₂ at 25 °C. At greater dilution, e.g. with air, the amount of NO₂ is greater. Therefore it would seem inevitable that toxicological studies performed with either of the two substances would share a common mechanism. Therefore read-across from NO₂ to N₂O₄ is considered to be justified.

 

Overall, available information on reproductive toxicity of NO₂ is limited. None of the individual studies fulfill the requirements of current guidelines. Most also have clear restrictions in methodological data and representation of data and are therefore of only of limited use for classification.

Twenty-one day exposure (7 hours/day, 5 days/week) of male rats to a single concentration of 1 ppm NO₂ did not result in changes in spermatogenesis, germ cell atrophy or Leydig cell abnormalities (Kripke and Sherwin 1984, study quoted in MAK 2005). Exposure of female rats to NO₂ concentration of 2.4 ppm for 12 hours/day for 3 months resulted in the increase in the length of estrous cycle (9.1 days vs. 5.3 days in controls). Histopathological examinations revealed a reduction in the number of functional primordial follicles in the ovaries and dystrophy of the glandular epithelium in the uterus, as well as changes in the adrenal gland, the thyroid gland and the pituitary gland. The length of estrous cycle returned back to normal after 3 months recovery period. No effects were seen at 0.13 ppm. Mating of the female rats exposed to 2.4 ppm for three months with untreated males had no effects on the number of females which became pregnant, but resulted in reduced litter size (5.1 vs. 8.0 in controls), as well as reduced weight of the newborn pups and the body weight gains in the first 12 days of life.

Effects on developmental toxicity

Description of key information

 In accordance with Column 2 of section 8.7 of REACH Annex IX, the study does not need to be conducted because the substance is known to be a germ cell mutagen and appropriate risk management measures are implemented.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

As the classification of dinitrogen tetraoxide as Mutagenic 1B., H340 is proposed in accordance with Regulation 1272/2008/EC, and appropriate risk mitigation measures are implemented, a performance of developmental toxicity studies is not warranted in accordance with column 2 of Section 8.7 of REACH Annex IX. Available limited information on developmental toxicity of the substance is summarized below.

Developmental toxicity of the monomer of dinitrogen tetraoxide (N₂O₄), nitrogen dioxide (NO₂) has been discussed in detail in the report of MAK (2005). Dinitrogen tetraoxide exists in equilibrium with nitrogen dioxide, with ca. 25% present in the form of NO₂ at 25 °C. At greater dilution, e.g. with air, the amount of NO₂is greater. Therefore it would seem inevitable that toxicological studies performed with either of the two substances would share a common mechanism. Therefore read-across from NO₂ to N₂O₄ is considered to be justified.

Overall, available information on developmental toxicity of NO₂ is limited. None of the individual studies fulfill the requirements of current guidelines and most also have clear restrictions in methodological data and representation of data and are therefore of only of limited use for classification.

Exposure of pregnant mice on days 7-18 and 8-18 of gestation to 22 and 45 ppm NO₂ caused hematomas, reduced body weights and increased mortality in the fetuses (Singh 1984, 1988, study quoted in MAK 2005). Furthermore, nitrogen dioxide exposure at both levels significantly increased the time required by the pups for the righting reflex on PND 1 and aerial righting scores on PND 12, but did not affect negative geotaxis and activity scores on PND 10 and 28. The studies reported no visible signs of maternal toxicity.

Exposure of pregnant rats for 6 hours/day during the whole gestation length (days 1-21) to 0.53 ppm NO₂ resulted in the signs of maternal toxicity, evidenced as lipid peroxidation in the lungs and placenta, smaller and darker placenta, and in the increased post-implantation losses, as well as reduced fetal weights, delayed ossification and hydrocephalus (Tabacova and Balabaeva 1986, 1988, original study available only as an abstract; study quoted in MAK 2005). Gofmekler et al., 1977 (study quoted in MAK 2005) reported increased incidence of developmental anomalies, intrauterine hemorrhaging, and fetal death in rats exposed throughout the whole gestation period to 0.034, 0.085 and 0.8 mg/m3. However, the original study (published in Russian) could not be recovered, and no further information on experimental details is available. The available abstract suggests that the animals were likely to be exposed 24 hours/day and that the observed effects at the lowest dose level were more severe than at the mid-dose. This makes the reliability of the study questionable. Furthermore, the studies of Tabacova and Balabaeva (1986, 1988) report comparable effects being observed only at 10 -fold higher concentration levels.

The study of Tabacova et al. (1985) investigated the effects of NO₂ exposure in utero on postnatal development of the pups by exposing pregnant rats during gestation days 1-21 for 6 hours/day, 7 days/week to NO₂ concentrations of 0.053, 0.53 and 5.3 ppm. The viability and weight gain of the pups were statistically significantly reduced at 5.3 ppm (PND 21), and their neuromotor development was impaired (startle reflex to acoustic stimulus, air righting, hindlimb support). A dose-dependent delay in eye opening and incisor eruption was observed from 0.53 ppm and above. Neuromotor development (righting, negative geotaxis) was impaired at 0.53 ppm. Lipid peroxidation in the liver was observed starting from this concentration and above. At 0.053 ppm and above changes were observed in the posture and gait in 9- and 14-day-old pups, which however were no longer visible after the weaning.

Toxicity to reproduction: other studies

Additional information

No further data is available.

Mode of Action Analysis / Human Relevance Framework

As classification of dinitrogen tetraoxide as Mutagenic 1B, H340 is proposed, and the appopriate risk mitigation measures are implemented, the performance of new reproductive and developmental toxicity studies with the substance is considered to be not warranted.

Overall, due to their limitations the currently available studies do not allow a definite conclusion on the reproductive and developmental toxicity of NO₂ and the relevance of the observed effects for humans.

Justification for classification or non-classification

As classification of dinitrogen tetraoxide as Mutagenic 1B, H340 is proposed, and the appopriate risk mitigation measures are implemented, the performance of new reproductive and developmental toxicity studies with the substance is considered to be not warranted. No classification for reproductive and developmental toxicity of dinitrogen tetraoxide is proposed based on the available data.