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Key value for chemical safety assessment

Effects on fertility

Additional information

Justification for read across

The derivation of the DNELs is based on read across to other sulfur based substances. Toxicological data specifically for Sodium sulfide (Na2(Sx)) 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:

                    

Unrestricted read-across between the substances Sodium sulfide (Na2(Sx)), 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.

 

Aqueous Na2Sx solutions are only stable at pH > 10. At lower pH values they are decomposed to H2S and S ([1, 2, 3, 4, 5])

 

The soluble compound Sodium sulfide (Na2(Sx)) can safely be assumed to be present dissociated in water and relevant biological media([6]). From Sodium sulfide (Na2(Sx)), hydrogen sulfide (H2S) may be formed according to the following equilibria:

Na2Sx+ H2O → NaOH + NaHSx(2 Na++ HSx-+ OH-)

NaHSx +H2O → (x-1)S + 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 hydrogen sulfides 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.

 

[1] E. Dachselt, „Thioplaste“, Deutscher Verlag für Grundstoffindustrie, Leipzig 1971, pp. 35

[2] M.B. Berenbaum, “Polysulfide Polymers” in N. G. Gaylord, ”Polyethers”, Interscience Publishers, 1962, 49-51

[3] D. Peschanski; G. Valensi, J. chim.Phys. 46(1949), pp. 602

[4] M. Menzel, Expert statement “Investigation of the reaction of sodium polysulfide solution with diluted hydrochlorioc acid”, AkzoNobel, Greiz (March 2010)

[5] Hagg-graph

[6]Beauchamp et al. (1984): A critical review of the literature on hydrogen sulfide toxicity; CRC Crit. Rev. Toxicol. 13, 25-97.

Results:

Due to expert judgment the fertility and developmental neurotoxicity screening study, similar to OECD guideline 421, reported by Dorman et al. (2000) with the test substance H2S together with the information from subchronic inhalation toxicity studies in Sprague-Dawley rats, Fisher rats and B6C3F1 mice reported by Morgan et al. (1983) and re-evaluated by Dorman in 2004 can be regarded as adequate to fulfil the REACH-requirements for the endpoint "Toxicity to reproduction".

In the reproduction screening assay, female Sprague-Dawley rats were exposed by inhalation (6h/d, 7d/wk) to concentrations up to 80 ppm H2S during the pre-mating (2 weeks) and mating (2 weeks) periods, during gestation (day 0-19) and post partum (5-18). Males were exposed for a total of 70 days starting 2 weeks before mating. The results did not indicate effects on reproductive performance. There were no effects of exposure on mating and fertility indices, post implantation loss and number of late resorptions or still births. The number of females with live pups, litter size, average length of gestation and the average number of implants per female were not different between exposed and control rats. Examination of testis did not indicate affects of sperm production or sperm morphology. Histopathological investigations did not reveal any changes in the reproductive organs of male and female animals.

In the subchronic toxicity studies (Morgan et al. (1983), re-evaluated by Dorman in 2004, see IUCLID section 7.5 Repeated dose toxicity), rats and mice were exposed by inhalation to similar concentrations of H2S (6h/d, 5d/wk) for 90 days. In these studies, gross pathology and organ weight analysis did not indicate exposure related effects on ovaries and testis, and no lesions were observed by histopathological examinations in non-respiratory tissues. Although details on histopathological evaluations of non-respiratory tissues are not presented in detail the re-evaluated study report (Dorman et al. 2004), the statement on the lack of any effects on non-respiratory tissues can be judged as reliable based on the overall high quality of the study. Major effects of inhalation exposure are local effects in the respiratory tract (olfactory neuronal loss) already occurring at a dose level of 30 ppm. The highest dose level of 80 ppm represents a NOAEC for systemic effects. The original study report from Morgan et al. 1983 is only available as an abstract.

Based on the available information, a NOAEC for reproduction of 80 ppm hydrogen sulfide (ca. 111 mg H2S/m3air at 25 °C) may be derived from the screening study for reproductive toxicity in rats. Based on the lack of any effects on reproductive performance and organs, the reproductive tract is not considered to represent a target organ of toxicity. Thus, further testing in a two-generation reproduction toxicity study according to OECD guideline 416 is not regarded to be required.

Performance of further reproductive toxicity studies is not considered to be required for the following reasons:

-The DNEL derived for local effects would be lower than for effects on reproduction and development, and thus the derived DNELlocalis regarded as protective enough for both endpoints.

-The available data indicating major effects resulting from local toxicity, and thus, from an animal welfare point of view, it appears to be not feasible to investigate reproductive toxicity in a dose range which would be sufficient high to cause reproductive effects, but would be acceptable for the animals, due to the irritating properties of the test compounds.

-It appears not appropriate to conduct animal studies, because of the alkaline pH in aquatic media (corrosive potential).

-In addition, there is sufficient information available (see below) from a fertility and developmental toxicity study in combination with a repeated dose toxicity study to rule out the reproductive system as target organ of toxicity.

NOEAC calculation for reproductive effects of sodium sulfide Na2(Sx (x=1.5 -5)) by read-across from H2S:

Worst-case for NOAEC calculation:

(i)            H2S = 34 g/mol = 111 mg/m3

(ii)           S2-= 32 g/mol -->104.5 mg/m3

(iii)          Na2 (Sx(1.5 -5)) = 94.1 -206.35 g/mol

(iv)         32 g/mol : 94.1 -206.35 g/mol = 34 -15.5 % (mass percentage S2 -in Na2(Sx(x=1.5 -5))

(v)          34 -15.5 % = 104.5 mg/m3 -->100 % Na2(Sx(x=1.5 -5)) = 307 -604 mg/m3

Accordingly, based on read-across from the NOAEC for reproductive effects (fertility) of H2S, a concentration of 307 mg/m3was derived as the worst case NOEAC for reproductive effects via inhalation to Na2(Sx(x=1.5 -5)).

Short description of key information:

No reliable data on toxicity to reproduction of sodium sulfide (Na2(Sx)) are available. Due to expert judgment the fertility and developmental neurotoxicity screening study, similar to OECD guideline 421, reported by Dorman et al. (2000) with the test substance H2S together with the information from subchronic inhalation toxicity studies in Sprague-Dawley rats, Fisher rats and B6C3F1 mice reported by Morgan et al. (1983) and re-evaluated by Dorman in 2004 can be regarded as adequate to fulfil the REACH-requirements for the endpoint "Toxicity to reproduction". Based on the available information, a NOAEC for reproduction of 80 ppm hydrogen sulfide (ca. 111 mg H2S/m3 air at 25 °C) may be derived from the screening study for reproductive toxicity in rats. Based on the lack of any effects on reproductive performance and organs, the reproductive tract is not considered to represent a target organ of toxicity. Thus, further testing in a two-generation reproduction toxicity study according to OECD guideline 416 is not regarded to be required

Effects on developmental toxicity

Description of key information

No reliable data on developmental toxicity and teratogeniciy of sodium sulfide (Na2(Sx)) are available.  Due to expert judgment the fertility and developmental neurotoxicity screening study, similar to OECD guideline 421, reported by Dorman et al. (2000) with the test substance H2S can be regarded as adequate to fulfil the REACH-requirements for the endpoint “Developmental toxicity / teratogenicity”.  Findings of further studies with pre- and postnatal exposure of rats and pups to H2S are not contradictory. No indications of a teratogenic potential of H2S were observed in these studies. Thus, a NOAEC of 80 ppm hydrogen sulfide (ca. 111 mg H2S/m3 air at 25 °C) may be derived from the screening study for developmental toxicity in rats and further testing in prenatal developmental toxicity studies according to OECD guideline 414 is not considered necessary.

Additional information

Justification for read across

The derivation of the DNELs is based on read across to other sulfur based substances. Toxicological data specifically for Sodium sulfide (Na2(Sx)) 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:

                    

Unrestricted read-across between the substances Sodium sulfide (Na2(Sx)), 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.

 

Aqueous Na2Sx solutions are only stable at pH > 10. At lower pH values they are decomposed to H2S and S ([1, 2, 3, 4, 5])

 

The soluble compound Sodium sulfide (Na2(Sx)) can safely be assumed to be present dissociated in water and relevant biological media([6]). From Sodium sulfide (Na2(Sx)), hydrogen sulfide (H2S) may be formed according to the following equilibria:

Na2Sx+ H2O → NaOH + NaHSx(2 Na++ HSx-+ OH-)

NaHSx +H2O → (x-1)S + 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 hydrogen sulfides 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.

 

[1] E. Dachselt, „Thioplaste“, Deutscher Verlag für Grundstoffindustrie, Leipzig 1971, pp. 35

[2] M.B. Berenbaum, “Polysulfide Polymers” in N. G. Gaylord, ”Polyethers”, Interscience Publishers, 1962, 49-51

[3] D. Peschanski; G. Valensi, J. chim.Phys. 46(1949), pp. 602

[4] M. Menzel, Expert statement “Investigation of the reaction of sodium polysulfide solution with diluted hydrochlorioc acid”, AkzoNobel, Greiz (March 2010)

[5] Hagg-graph

[6]Beauchamp et al.(1984): A critical review of the literature on hydrogen sulfide toxicity; CRC Crit. Rev. Toxicol. 13, 25-97.

 

Results:

Due to expert judgment the fertility and developmental neurotoxicity screening study, similar to OECD guideline 421, reported by Dorman et al. (2000) with the test substance H2S can be regarded as adequate to fulfil the REACH-requirements for the endpoint “Developmental toxicity / teratogenicity”.

In the reproduction screening assay, female Sprague-Dawley rats were exposed by inhalation (6h/d, 7d/wk) to concentrations up to 80 ppm H2S during the pre-mating (2 weeks) and mating (2 weeks) periods, during gestation (day 0-19) and post partum (5-18). Males were exposed for a total of 70 days starting 2 weeks before mating. The F1 offspring generation was examined extensively for occurrence of external defects post partum and for developmental landmarks (pinnae detachment, surface righting, incisor eruption, negative geotaxis, eyelid separation, vaginal patency, preputial separation) and developmental neurotoxicity (motor activity, passive avoidance, FOB, acoustic startle) during the postnatal period. Gross macroscopic examination and organ weight analysis were conducted on all F1 offspring upon necropsy on PND 63 +/- 3, and histopathological examinations of the brains of control and high dose animals was done. In addition, neuropathology was conducted in selected weanling rats and adult offspring. The results of this study did not indicate effects of treatment on the in-uteri and postnatal development of offspring from parents exposed continuously including the phase of organogenesis. Thus, a NOAEC of 80 ppm hydrogen sulfide (ca. 111 mg H2S/m3 air at 25 °C) may be derived from the screening study for developmental toxicity in rats.

In addition, findings of further supporting studies with pre- and postnatal exposure of rats and pups to H2S are not contradictory (Hayden, 1990; Skranjny, 1992). However, the relevance of the finding on neuronal transmitter levels (Skranjny, 1992) in the brain of offspring from rats exposed during gestation to 20 and 75 ppm H2S is on the development of offspring is questionable in light of the lack of any effects on behavioural neurotoxicity and developmental landmarks in the extended study reported by Dorman et al.( 2000). No indications of a teratogenic potential of H2S were observed in these studies. Thus, further testing in prenatal developmental toxicity studies according to OECD guideline 414 is not considered necessary.

 

Performance of further reproductive toxicity studies is not considered to be required for the following reasons:

-The DNEL derived for local effects would be lower than for effects on reproduction and development, and thus the derived DNELlocalis regarded as protective enough for both endpoints.

-The available data indicating major effects resulting from local toxicity, and thus, from an animal welfare point of view, it appears to be not feasible to investigate reproductive toxicity in a dose range which would be sufficient high to cause reproductive effects, but would be acceptable for the animals, due to the irritating properties of the test compounds.

-It appears not appropriate to conduct animal studies, because of the alkaline pH in aquatic media (corrosive potential).

-In addition, there is sufficient information available (see below) from a fertility and developmental toxicity study in combination with a repeated dose toxicity study to rule out the reproductive system as target organ of toxicity.

 

NOEAC calculation for reproductive effects of sodium sulfide by read-across from H2S:

Worst-case for NOAEC calculation:

(i)            H2S = 34 g/mol = 111 mg/m3

(ii)           S2-= 32 g/mol -->104.5 mg/m3

(iii)          Na2(Sx(1.5 -5)) = 94.1 -206.35 g/mol

(iv)         32 g/mol : 94.1 -206.35 g/mol = 34 -15.5 % (mass percentage S2 -in Na2(Sx(x=1.5 -5))

(v)          34 -15.5 % = 104.5 mg/m3-->100 % Na2(Sx(x=1.5 -5)) = 307 -604 mg/m3

Accordingly, based on read-across from the NOAEC for reproductive effects (fertility) of H2S, a concentration of 307 mg/m3was derived as the worst case NOEAC for reproductive effects via inhalation to Na2(Sx(x=1.5 -5)).

 

Human data:

No reliable data on sodium sulfide are available. However, there is some evidence from two retrospective studies on female workers in China and Finland that exposure to hydrogen sulfide may be associated with an increased rate of spontaneous abortion. Since the exposure to H2S and potential co-exposure to other chemicals was not determined in these studies, these studies are not rated as reliable.

Justification for classification or non-classification

All available reliable studies showed no toxicity to reproduction, developmental toxicity or teratogenicity of hydrogen sulfide. Based on the lack of any effects on reproductive performance and organs, the reproductive tract is not considered to represent a target organ of toxicity. No indications of a teratogenic potential of H2S were observed in these studies. Based on these data and on read-across from H2S to Na2S, classification is not proposed for sodium sulfide (Na(2Sx)).