Reaction mass of disodium sulphide and sodium carbonate and sodium hydrogensulphide

Endpoint summary

Description of key information

Acute oral toxicity: Acute oral toxicity of sodium hydrogensulphide is assessed from the key study (Kirsch, 1986), supported by the results from Kramer, Weigand, 1974. An LD50 value of 115 mg/kg could be derived for sodium hydrogensulphide (ca. 70 %) from the key study. The result indicates that the LD50 calculated for the most concentrated commercial form NaHS, 77 %, would be 105 mg/kg bw. An LD50 of 184 mg/kg bw was calculated from the supportive study for Sulfhydrat (sodium hydrogensulfide, ca. 30 %). The result indicate that the LD50 for NaHS, 77 %, would be 72 mg/kg bw. Two further oral studies were available for Sodium hydrogensulphide, however both were assessed as not reliable because of significant methodological deficiencies or deficiencies in the documentation. As NaHS is present in Scrubber Liquid at 24.4%, this would give an extrapolated LD50 for Scrubber Liquid of 227 mg/kg bw and as such a classification of “toxic if swallowed".
Acute inhalation toxicity: No reliable studies available for sodium hydrogen sulphide or sodium sulphide. For sodium carbonate there is one reliable acute inhalation toxicity study (Busch et al., 1983) which reported an LC50 of 2300 mg/cm3 (2 hour exposure) in male rats, an LC50 of 800 mg/cm3 (2 hour exposure) in male guinea pigs and an LC50 of 1200 mg/cm3 (2 hour exposure) in male mice.
Acute dermal toxicity: no reliable study available, since the Hollander & Weigand study (1974) is assessed as not reliable because the skin has been hurt during performance.  For sodium carbonate there is one reliable acute oral toxicity study (Study report 1978) which gave an LD50 value of >2000 mg/kg bw in rabbits.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Value:

mg/kg bw

Additional information

General

A literature search and evaluation programme on animal and human acute toxicity data of sodium hydrogensulphide, sodium sulphide and sodium carbonate 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.

Acute oral toxicity:

For sodium hydrogensulphide, two reliable acute oral toxicity studies (RL=2, Kirsch_1986 and Kramer; Weigand_1974) are available, which are broadly comparable to OECD Guideline 401. However, the Kirsch (1986) study was defined as the key study based on methodological quality criteria. Several not reliable, non-standard acute studies are available; these studies were performed in various species, non-relevant routes of exposure and using various exposure times. Two disregarded studies (Gamer_1988 and Zeller; Hoffmann_1968) were presented as they describe dosing by oral route, although they were rated as not reliable.

The result of the key study (Kirsch, 1986) indicates that the LD50 -oral for the most concentrated commercial form NaHS, 77 % would be 105 mg/kg bw. The result of the supportive study (Kramer & Weigand, 1974) indicates an LD50 -oral for NaHS, 77 % of 72 mg/kg bw.

Both reliable studies result in LD50 values for the most concentrated commercial form sodium hydrogensulphide (77 %) which would lead to a classification as toxic according to the criteria specified by Directive 67/548/EC, Regulation (EC) No 1272/2008 and subsequent regulations. Further, the two disregarded studies also result in LD50 values which would also lead to a classification as toxic if swallowed.

For sodium sulphide, two reliable acute oral toxicity studies (RL=1, Ullmann_1986 and Mason_1998) are available. However, the resulting LD50 values vary markedly (factor seven) between both studies:

Ullmann_1986: LD50 =254 mg/kg bw for Na2S (ca. 60 %) ->the LD50calculated for the most concentrated commercial form Na2S, 62 %,would be 246 mg/kg bw. Mason_1998: LD50 = 1122 mg/kg bw for Na2S (anhydrous) -->the LD50calculated for the most concentrated commercial form Na2S, 62 %,would be 1810 mg/kg bw. Despite yielding a “borderline” result, the Ullmann-study would formally lead to a classification as “toxic if swallowed” according to the criteria specified by Directive 67/548/EC, Regulation (EC) No 1272/2008 and subsequent regulations. In contrast, the Mason-study would merely lead to a classification as “harmful if swallowed” according to the criteria specified by Directive 67/548/EC, Regulation (EC) No 1272/2008 and subsequent regulations.

For clarification of this seeming discrepancy, read-across to sodium hydrogensulfide as an analogous substance is made: there, two reliable studies exist which however both yield an LD50 < 250 mg/kg bw, thus necessitating a classification as “toxic if swallowed“. Thus, by applying a weight-of-evidence approach, it is proposed to use the lower LD50 value of the commercial form (246 mg/kg for Na2S, 62 %) from the Ullmann (1986) study report for a more conservative classification of the substance.

For sodium carbonate there is one reliable acute oral toxicity study (Study report 1978) which gave an LD50 value of 2800 mg/kg bw in male/female rats.

As NaHS was the most toxic of the constituents of Scrubber Liquid, an extrapolation from the lowest LD50 (Kramer & Weigand, 1974) indicates an oral LD50 for NaHS (77 %) of 72 mg/kg bw. As NaHS is present in Scrubber Liquid at 24.4%, this would give an extrapolated LD50 for Scrubber Liquid of 227 mg/kg bw and as such a classification of “toxic if swallowed”.

 

Acute inhalation toxicity:

No reliable data is available for acute inhalation toxicity of NaHS. Although this is a potential route of exposure for workers, testing is not justified since the test substance is proposed for classification as “corrosive to skin”.

According to section 8.5.2, column 2, Annex VIII of regulation (EC) 1907/2006), the in-vivo acute toxicity study, inhalation does not need to be conducted if the test substance is classified as corrosive to skin. Based on the structural analogy to sodium sulfide (which is classified as corrosive to skin) and the alkaline pH value (pH 12.1; as saturated solution), sodium hydrogensulphide is proposed for the classification “corrosive to skin”. For sodium carbonate there is one reliable acute inhalation toxicity study (Busch et al., 1983) which reported an LC50 of 2300 mg/cm³(2 hour exposure) in male rats, an LC50 of 800 mg/cm³(2 hour exposure) in male guinea pigs and an LC50 of 1200 mg/cm³(2 hour exposure) in male mice.

 

Acute dermal toxicity:

The Hollander, Weigand_1974 study was assessed for relevance and reliability for risk assessment according to the criteria proposed by Klimisch et al. (1997), with the following conclusion: the study was rated as not reliable (RL=3) for use in EU risk assessment, because the skin of the animals was hurt by application of a corrosive substance and an intact skin area, which is the basis for the acute dermal toxicity testing, was no longer given.

Thus, no reliable and relevant data on acute dermal toxicity of sodium hydrogensulfide is available. Although this is a potential route of exposure for workers, testing is not justified for animal welfare grounds: sodium hydrogensulfide (ca. 72 %) has a pH value of 12.1 (as saturated solution) and is proposed for classification as corrosive to skin. In accordance with IUCLID section 8.5.3, column 2 of REACH Annex VIII, the in-vivo acute toxicity study, dermal does not need to be conducted if the test substance is classified as corrosive to skin. There was no reliable dermal toxicity data for sodium sulphide. For sodium carbonate there is one reliable acute oral toxicity study (Study report 1978) which gave an LD50 value of >2000 mg/kg bw in rabbits.

 

 

Justification for classification or non-classification

Acute toxicity, oral:

Both reliable studies for acute oral toxicity testing (Kirsch_1986 and Kramer; Weigand_1974) resulted in LD50 values (72 and 105 mg/kg bw) for the most concentrated commercial form sodium hydrogensulphide (77 %). As NaHS is present in Scrubber Liquid at 24.4%, this would give an extrapolated LD50 for Scrubber Liquid of 227 mg/kg bw which will lead to a classification as toxic if swallowed according to the criteria specified by Directive 67/548/EC, Regulation (EC) No 1272/2008 and subsequent regulations (T; R25 according to 67/548/EEC and toxic category III, H301 according to GHS). Thus, classification as "toxic if swallowed" is proposed for scrubber liquid.

Specific target organ toxicant (STOT) – single exposure: oral

The classification criteria according to regulation (EC) 1272/2008 as specific target organ toxicant (STOT) – single exposure, oral are not met. No additional classification required.

 

Acute toxicity, inhalation:

No classification is required for acute inhalation toxicity in the absence of an appropriate study. According to the data requirements as outlined in section 8.5, Annexes VII-VIII of Regulation (EC) 1907/2006, no new testing should be conducted as the substance has constituents which are skin corrosive and proposed for classification as skin corrosive Cat.1b (causes severe skin burns and eye damage) according to Regulation (EC) No 1272/200.

 

Acute toxicity, dermal:

Although the LD50 values from the dermal toxicity study performed with Sulfhydrat F150 theoretically triggers classification with harmful to toxic for sodium hydrogensulphide (77 %), this is not justified based on the study results, because of the corrosive nature of NaHS. The results of the acute toxicity, dermal study (d_Hollander, Weigand_1974) should be considered as questionable as the skin is hurt by application of a corrosive substance and an intact skin area, which is the basis for the acute dermal toxicity testing, is no longer given.

No classification is required for acute dermal toxicity in the absence of an appropriate study; the acute dermal toxicity of the constituent sodium hydrogensulfide is dominated by local corrosivity and irritancy and is therefore sufficiently addressed by the classification of the substance as corrosive to skin.