Sodium hydrogensulphide

Endpoint summary

Additional information

General

A literature search and evaluation programme on animal and human genetic toxicity data of sodium sulfide and sodium hydrogensulfide has been conducted.All data sources were assessed by expert toxicologists for quality and reliability, as well as relevance for regulatory risk assessment under REACH. The results are attached to the technical dossier in atabular report (IUCLID section 13).

Read-across from Na₂S to NaHS:

Given that sodium sulfide and sodium hydrogensulfide dissociate in aqueous media, it can safely be assumed that under most physiologically relevant conditions ( i.e., neutral pH) sulfide and hydrogen sulfide anions are present at almost equimolar concentrations, thus facilitating unrestricted read-across between both species. Only under extreme conditions such as gastric juice (pH << 2), sulfides will be present predominantly in the form of the non-dissociated hydrogen sulfide. In turn,hydrogen sulfide (H₂S) may be formed from both soluble sulfides, according to the following equilibria:

                           Na₂S + H₂O   →  NaOH + NaHS (2Na⁺/ OH^-/ HS^-)

                           NaHS + H₂O  →  NaOH + H₂S (Na⁺/ OH^-/ H₂S)

Similarly, hydrogen sulfide dissociates in aqueous solution to form two dissociation states involving the hydrogen sulfide anion and the sulfide anion, according to the following equilibrium:

                           H₂S  ↔  H⁺  +  HS^-  ↔  2 H⁺  +  S^2-

In conclusion, under physiological conditions, inorganic sulfides or hydrogensulfides as well as H2S will dissociate to the respective species relevant to the pH of the physiological medium, irrespective the nature of the “sulfide”, which is why read-across between these substances and H₂S is considered to be feasible without any restrictions.

Results:

All three available studies, performed with sodium sulfide or sodium hydrogensulfide, yielded negative results concerning genetic toxicity

- in the reliable in-vitro HPRT test (Stone_2010) it is concluded that sodium sulfide, anhydrous did not induce mutation at thehprtlocus of mouse lymphoma cells when tested under the conditions employed in this study. Based on unlimited read-across the same result applies for sodium hydrogensulfide.

- in the reliable in-vitro Ames test (reverse gene mutation assay) reported by Gelbke_1989 it is concluded that sodium hydrogensulfide is not mutagenic under the experimental conditions.

- a reliable in-vivo micronucleus test (Gocke_1981) had a negative result for sodium sulfide: no significant exerted mutagenic action was observed. Based on unlimited read-across the same result applies for sodium hydrogensulfide.

The REACH requirements according to the endpoints in section 8.4, Annex VII-X in Regulation (EC) 1907/2006 are fulfilled. No further testing is required.

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Short description of key information:
In-vitro studies:
- The HPRT test (Covance_2010) performed with sodium sulfide (anhydrous) according to OECD guideline 476 was rated as RL=1 (reliable without restrictions) and used as a key study. The study had a negative result for induction of mutation at the hprt locus of mouse lymphoma cells. Read-across applies from sodium sulfide to sodium hydrogensulfide.
- The key study on in vitro gene mutation of sodium hydrogensulfide (bacterial reverse mutation assay; Gelbke_1989) was rated as reliable with restrictions and had a negative result for mutagenic properties.

In-vivo studies:
Chromosome aberration of sodium sulfide has been tested in-vivo in a micronucleus assay performed in mice similar to OECD guideline 474 (Gocke_1981). This study was rated as reliable with restrictions (RL=2) and is used as a key study. The study had a negative result. Read-across applies from sodium sulfide to sodium hydrogensulfide.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

All available reliable studies showed no genetic toxicity for sodium sulfide or sodium hydrogensulfide. Read-across between the two compounds is unrestricted. Thus, no classification is required for sodium hydrogensulfide.