Hydrogen sulphide

Endpoint summary

Description of key information

H2S is regarded as irritating to skin, eyes and moucous membranes (of the respiratory tract).

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Additional information

Skin irritation/ corrosion:

There is no specific study on the skin irritation/corrosion of H2S avaliable. Nevertheless it seems meaningful to evaluate the irritating potential of H₂S from the existing studies with inhalative exposure. The inhalative exposure was done in chambers with whole body exposure. No effects on the skin were observed up to lethal concentrations.

However the skin irritation potential can further be evaluated on the basis of an acute dermal toxicity study with NaHS which showed irritating potential.

At 20 °C H₂S dissolves in water up to 3.98 g/L. H₂S can stay present in water for several hours. Nevertheless because of its considerable vapour pressure H₂S will evaporate from the water into the breathing air. In aqueous environments, H₂S and e.g. the corresponding salt NaHS are immediately hydrolyzed in water and, as a function of pH, an equilibrium is established between S^2-, HS^-, and H₂S, with increasing H₂S formation at decreasing pH.

As there is no acute dermal toxicity study with H₂S available, the acute dermal toxicity study with 31 -32% NaHS can be taken to evaluate the acute dermal toxicity of H₂S. The lethal effects emerged within 2 hours after application. After 24 hours the skin at the application site showed mild reddening and eschar. Beside this local effect in all doses all dosed animals showed symptoms of unbalancing, lowest dosage: 100 mg/kg bw (= 19.6 mg H₂S/ kg). Under consideration that 10 mL/kg test solution were applied and a water solubility of 4 mg/mL a maximum possible dose of 40 mg/kg H₂S within this 10 mL can be calculated. Although the exposure in the study was unrealistically long with respect to the working situation the substance H₂S is classified as irritating to the skin.

Eye irritation:

There is no guideline study on the eye irritation/corrosion of H₂S avaliable. Nevertheless it is possible to evaluate the irritating potential of H₂S from the existing studies with inhalative exposure. Male Fischer 344 rats (number per group not stated) were exposed to 0, or 400 ppm hydrogen sulfide for 4 hours or 1500 ppm hydrogen sulfide for 4 minutes. Immediately after exposure, the eyes were washed with 0.4 ml of saline and the lavage fluid collected for exfoliative cytology. Exposure to hydrogen sulfide increased the number of exfoliated cells and the proportion of conjunctival to corneal epithelial cells recovered compared to controls. This can be seen as a consequnece of an irritation to the eye.

Respiratory irritation:

Studies with repeated (Dorman 2000) inhalative exposure revealed irritation of the mucous membranes in the nose after 6 hours exposure to concentrations of H₂S in the air of 30 ppm (42 mg/m³) and higher. Based on the respiratory lesions observed in the studies with inhalation exposure by Dorman et al. (2000) H2S is calssified as H335: May cause respiratory irritation, according to the CLP-criteria/R37: Irritating to the respiratory system, according to DSD.

Although there are no specific guideline studies availiable, the existing data allow an evaluation of the irritating / corrosive potential of H₂S. Further animal studies are not necessary.

Justification for selection of skin irritation / corrosion endpoint:
There is no specific study on the skin irritation/corrosion of H2S avaliable. Nevertheless it seems meaningful to evaluate the irritating potential of H2S from the existing studies with inhalative exposure. The inhalative exposure was done in chambers with whole body exposure. No effects on the skin were observed up to lethal concentrations.
However the skin irritation potential can further be evaluated on the basis of an acute dermal toxicity study with NaHS which showed irritating potential.
At 20 °C H2S dissolves in water up to 3.98 g/L. H2S can stay present in water for several hours. Nevertheless because of its considerable vapour pressure H2S will evaporate from the water into the breathing air. In aqueous environments, H2S and e.g. the corresponding salt NaHS are immediately hydrolyzed in water and, as a function of pH, an equilibrium is established between S2-, HS-, and H2S, with increasing H2S formation at decreasing pH.
As there is no acute dermal toxicity study with H2S available, the acute dermal toxicity study with 31 -32% NaHS can be taken to evaluate the acute dermal toxicity of H2S. The lethal effects emerged within 2 hours after application. After 24 hours the skin at the application site showed mild reddening and eschar. Beside this local effect in all doses all dosed animals showed symptoms of unbalancing, lowest dosage: 100 mg/kg bw (= 19.6 mg H2S/ kg). Under consideration that 10 mL/kg test solution were applied and a water solubility of 4 mg/mL a maximum possible dose of 40 mg/kg H2S within this 10 mL can be calculated. Although the exposure in the study was unrealistically long with respect to the working situation the substance H2S is classified as irritating to the skin.

Justification for selection of eye irritation endpoint:
There is no guideline study on the eye irritation/corrosion of H2S avaliable. Nevertheless it is possible to evaluate the irritating potential of H2S from the existing studies with inhalative exposure.
Male Fischer 344 rats (number per group not stated) were exposed to 0, or 400 ppm hydrogen sulfide for 4 hours or 1500 ppm hydrogen sulfide for 4 minutes. Immediately after exposure, the eyes were washed with 0.4 ml of saline and the lavage fluid collected for exfoliative cytology. Exposure to hydrogen sulfide increased the number of exfoliated cells and the proportion of conjunctival to corneal epithelial cells recovered compared to controls.
This can be seen as a consequnece of an irritation to the eye.

Effects on skin irritation/corrosion: slightly irritating

Effects on eye irritation: slightly irritating

Effects on respiratory irritation: irritating

Justification for classification or non-classification

Based on the evaluation of the available data hydrogen sulphide is regarded as irritating to skin, eyes and irritating to the moucous membranes (of the respiratory tract) after repeated exposure. The skin irritation potential is relevant for H₂S in aqueous solutions only.

In accordance with Regulation (EC) No 1272/2008 H₂S shall be classified as

- Category 2, skin irritant (H315: Causes skin irritation),

- Category 2 (irritating to eyes) (H319: Causes serious eye irritation),

- STOT Single Exp. 3 (H335: May cause respiratory irritation),

and as R38, R36, R37 respectively in accordance with directive 67/548/EEC.