Sodium hydrogensulphide

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

8 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

15

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

15

Dose descriptor:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

2 mg/m³

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

Additional information - workers

The derivation of DNELs for sodium hydrogensulfide is described in detail in the DNEL report attached to the technical dossier and summarised in the CSR. The report also includes the justification for not deriving DNELs for certain exposure patterns and the justification for assessment factors for those DNELs derived.

In brief, no DNEL was derived for any dermal exposure to sodium hydrogensulfide since the substance is classified as corrosive by considerations based on the pH value > 11.5. For workers a qualitative approach is required based on the corrosive potential of sodium hydrogensulfide.

 Assessment of oral exposure DNELs for workers is not required in accordance with ECHA guidance.

 A DNEL for acute exposure, systemic effects by inhalation was not derived, because there is no reason of concern for systemic toxicity with respect to acute inhalation, since high exposure levels which are not covered by the long-term DNEL are not expected.

 A long-term DNEL, systemic effects by inhalation for sodium hydrogensulfide was derived for workers, because there is a potential for exposure via the inhalation route at the workplace. The DNEL is based on the results of a repeated dose inhalation study with dihydrogen sulfide in which some minor effects on food consumption and body weight were observed, but exposure up to the highest does of 80 ppm H2S did not result in toxicologically relevant alterations in haematological indices, serum chemistry, or gross pathology. Therefore, the concentration of 80 ppm H₂S (111 mg/m³) is considered as NOAEC for systemic effects.

 Long-term DNEL, local effects by inhalation: From the repeated dose study on H2S inhalation, a NOAEC of 10 ppm H₂S for local effects was derived which is based on an increased incidence of olfactory neuronal loss (ONL) at 30 and 80 ppm of hydrogen sulfide. Due to the lack of experimental data specifically for sodium hydrogensulfide, read-across from data with H₂S was regarded as appropriate. Considering local effects in the respiratory tract related to inhalation exposure to sodium hydrogensulfide, two mechanisms of toxicity can be assumed: the first mechanism can be related to the local effects of HS^-present in the respiratory tract (ONL) following exposure to sulfides, and the second effects can be attributed to the very high pH resulting from the presence of OH^-ions. In order to cover both effects, DNELs were derived based on the NOAEC for local effects of H₂S, and in addition the DNEL for NaOH. As a precautionary principle, the lower value for sodium hydrogensulfide was selected as DNEL for local effects.

 Acute DNEL, local effects by inhalation: Sodium hydrogensulfide is classified as corrosive by default. Therefore, and in accordance to the ECHA guidance on information requirements and chemical safety assessment – chapter R.8: Characterisation of dose [concentration]-response for human health, May 2008 a DNEL for acute inhalation toxicity should be derived based on the toxicological profile of the substance concerned. This should be derived for a specified fraction of the daily exposure duration (usually 15 minutes for workers). SCOEL recommendations exist for H2SO4, HCL, H3PO4 and F2, all of which are classified either as R34 or R35 and without doubt have a higher corrosive potential compared to Na2S. The above mentioned documents all mention an 8-hour TWA as well as an STEL for 15 minutes. All STEL values are merely derived by applying a factor of 2 to the 8 hour TWA. Based on the toxicological observations as summarised in these SCOEL documents, a factor of 2 for the extrapolation from the long-term DNEL to an acute DNEL should be appropriate. Hence the DNEL for long-term inhalation, local effects for sodium hydrogensulfide will be used for deriving a DNEL for acute inhalation effect, worker for sodium hydrogensulfide by multiplying the long-term DNEL with a factor of 2. The long-term DNEL for local effects in workers exposed by inhalation for NaHS*0.93H2O (representing NaHS, max. 77 %) is 1.0 mg/m3, corresponding to a STEL (15 min) for workers of 2.0 mg/m3.

General Population - Hazard via inhalation route

Systemic effects

Acute/short term exposure

DNEL related information

Local effects

Acute/short term exposure

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

General Population - Hazard via oral route

Systemic effects

Acute/short term exposure

DNEL related information

Additional information - General Population

The derivation of DNELs for sodium hydrogensulfide is described in detail in the DNEL report attached to the technical dossier and summarised in the CSR. The report also includes the justification for not deriving DNELs for certain exposure patterns and the justification for assessment factors for those DNELs derived.

 In brief, exposure of the general population to sodium hydrogensulfide is of no concern for any route of exposure (oral, dermal, inhalation).Since sodium hydrogensulfide is instable and prone to oxidation in ambient air and used merely as intermediates and not in consumer products, there can neither be any quantitatively relevant emissions from industrial sites nor from use of sulfide-containing products. Therefore, for lack of consumer or indirect exposure, the derivation DNELs for the general population is not considered to be required.