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EC number: 215-686-9 | CAS number: 1344-08-7
The actual chamber concentrations (mean+/-SD) were 10.0+/-0.6, 30.1+/-0.8, and 79. 5+/-2.4 ppm for the target concentrations 10, 30, and 80 ppm, respectively. H2S was not detected in the control chamber (limit of detection was 0.6 ppm H2S in air). Overall mean daily chamber temperatures ranged from 22.0 to 23.5°C, and the relative humidity in the 1-m3 inhalation chambers ranged from 41 to 46%.
The authors suggested that H2S exposure is unlikely to result in significant reproductive toxicity or developmental neurotoxicity following exposures at concentrations relevant for most occupational exposures (i.e., ≤ 10 ppm).
Read across H2S to Na2S:
Valid toxicological data on toxicity to reproduction specifically for sodium sulfide from animal studies are not available. Therefore, because of the lack of appropriate experimental data, read-across from studies with H2S is proposed based on the following reasoning:
As discussed in the dossier section on toxicokinetics, unrestricted read-across between the substances sodium sulfide, sodium hydrogensulfide and dihydrogen sulfide is considered feasible, in view of the potential systemic toxicity being driven by the sulfide ion as the only relevant species released from any of the sulfide substances under physiological conditions. In this context, it is further considered to be very unlikely that the sodium ions add any toxicological concern.
The soluble compound sodium sulfide (Na2S) can safely be assumed to be present dissociated in water and relevant biological media (Beauchamp et al., 1984)1. From sodium sulfide, hydrogen sulfide (H2S) may be formed according to the following equilibria:
Na2S + H2O → NaOH + NaHS (2Na++ OH-+ HS-)
NaHS + H2O → NaOH + H2S (Na++ OH-+ H2S)
The toxic effects resulting from the sodium ion is negligible. Hydrogen sulfide dissociates in aqueous solution to form two dissociation states involving the hydrogen sulfide anion and the sulfide anion:
H2S ↔ H+ + HS- ↔ 2 H+ + S2-
The pKa values for the first and second dissociation steps of H2S are 7.04 and 11.96, respectively. Therefore, at physiological pH values, hydrogen sulfide in the non-dissociated form (H2S) and the hydrogen sulfide anion (HS-) will be present in almost equimolar proportion, whereas only very small amounts of the sulfide anion (S2-) will be present. 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.
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