# Hydrogen inhalation: in vivo rat genotoxicity tests.
> 水素吸入の生体内遺伝毒性評価：ラットを用いたICHガイドライン準拠試験


## Abstract

This study evaluated the genotoxic potential of inhaled molecular hydrogen in male Wistar rats exposed to a 3.1% H2 gas mixture for 72 hours, following ICH S2(R1) guidelines. Three experimental groups were established: a negative control, a positive control administered methyl methanesulfonate, and an H2-exposed group. Alkaline comet assays, formamidopyrimidine DNA glycosylase (Fpg)-modified comet assays, and bone marrow micronucleus assays were conducted. Across all assessed tissues—blood, liver, lungs, and bronchoalveolar lavage fluid—no elevation in comet-tail DNA intensity or hedgehog frequency was detected. Additionally, no increase in Fpg-sensitive oxidative DNA lesions in lung tissue, no induction of micronuclei, and no alteration in the immature-to-total erythrocyte ratio were observed. The complete ICH S2(R1) test battery confirmed an absence of in vivo genotoxicity under these conditions.

### Mechanism

Exposure to 3.1% H2 gas for 72 hours did not elevate markers of oxidative DNA damage, chromosomal aberration, or micronucleus formation in multiple tissues, indicating no genotoxic mechanism was activated.

## Bibliographic

- **Authors**: Salomez-Ihl C, Tanguy S, Alcaraz JP, Davin C, Pascal-Moussellard V, Jabeur M, et al.
- **Journal**: Mutat Res Genet Toxicol Environ Mutagen
- **Year**: 2024
- **PMID**: [38432775](https://pubmed.ncbi.nlm.nih.gov/38432775/)
- **DOI**: [10.1016/j.mrgentox.2024.503736](https://doi.org/10.1016/j.mrgentox.2024.503736)
- **Study type**: animal study
- **Delivery route**: inhalation
- **Effect reported**: null
- **H2 concentration**: 3.1%

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 38432775. https://h2-papers.org/en/papers/38432775
> **Source**: PubMed PMID [38432775](https://pubmed.ncbi.nlm.nih.gov/38432775/)