Magnesium dihydrogen disulphite

Endpoint summary

Description of key information

Based on the described read-across methodology information from sodium sulfite (CAS 7757-83-7), sodium metabisulfite (CAS 7681 -57 -4) and potassium metabisulfite (CAS 16731 -55 -8) were used to determine acute toxicity values (oral, dermal and inhalative) for magnesium dihydrogensulfite.
Please see `discussion` below.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

Read-across concept for sulfites, hydrogensulfites, metabisulfites, dithionites and thiosulfates:

A comprehensive read-across concept has been developed for sulfites, hydrogensulfites and metabisulfites, based on the pH-dependant equilibrium in aqueous solutions which is summarised in the following equations:^[1],[2]

           SO₂+ H₂O <->`H₂SO₃´         H₂SO₃<->H⁺+ HSO₃^-<->2H⁺+SO₃^2-    2HSO₃^-<->H₂O +S₂O₅^2-

Since the nature of the cation (i.e., sodium, potassium, ammonium…) is not assumed to contribute substantially to differences in toxicity and solubility (all compounds are very soluble in water), only the chemical and biological properties of the anion are considered as relevant determinants. Based on the described equilibrium correlations, unrestricted read-across between the groups of sulfites, hydrogensulfites and metabisulfites is considered justified.

 

Additionally, it is known that sodium dithionite disproportionates in water to form sodium hydrogen sulfite and sodium thiosulfate (equation II)^2,[1], so that this substance can also be considered to be covered by the read-across concept described above. Since it can easily be anticipated that the substance is not stable enough under physiological conditions to fulfil the requirements of study guidelines, instead the products of decomposition have to be considered:

 

       2 S₂O₄^2-+ H₂O→2HSO₃^-+ S₂O₃^2-

 

Not fully covered by this read-across concept is the substance class of thiosulfates: although the thiosulfates are also well known to disproportionate in aqueous solution to form polythionic acids and SO₂(HSO₃^-), this requires somewhat different, more acidic conditions. Therefore, read-across to sulfites is primarily restricted to appropriate physiological conditions, i.e. oral administration where the gastric passage with the strongly acidic conditions in the stomach will facilitate the chemical disproportionation described above:

 

       HS₂O₃^-+ H₂S₂O₃→HS₃O₃- + SO₂+ H₂O

 

[1]Hollemann Wiberg, Lehrbuch der Anorganischen Chemie, 101.Auflage

[2]Handbook of Chemistry and Physics, Ed. Lide, DR, 88^thedition, CRC Press

Acute toxicity oral:

In total, four reliable animal studies on acute oral exposure for sulfite substances are available, conducted equivalent or similar to OECD guideline 401. One study (Grundler, 1981) indicates a LD50 value of >2610 mg/kg/bw (male and female rats) for the test item sodium sulfite (CAS 7757 -83 -7). One study performed with potassium metabisulfite (CAS 16731 -55 -8) as test item indicated a LD50 >2000 mg/kg/bw (no clinical symptoms were observed in the concentration rang 200 - 2000 mg/kg bw). Two animal study reports on acute oral exposure to sodium metabisulfite (CAS 7681 -57 -4) are available (Hofmann & Jung, 1987 and Zeller&Hofmann, 1974), conducted according to or equivalent/similar to OECD guideline 401. The study of Hofmann & Jung indicated a LD50 >1540 mg/kg/bw. whereas the study performed by Zeller & Hofmann indicated a LD50 value of >3200 mg/kg bw.

 

Acute dermal toxicity:

One study on acute dermal toxicity, performed according to OECD 402 for the test item sodium sulfite (CAS 7757 -83 -7) is available. LD50 value was determined to be greater than 2000 mg/kg/bw (limit test).No systemic clinical observations were observed during clinical examination. No local effects were observed.

 

Acute inhalation toxicity:

One study equivalent or similar to OECD 403 for sodium sulfite (CAS 7757 -83 -7) has been performed which indicated a LC50 >5.5 mg/l (limit test).During exposure nothing abnormal was detected. After exposure: substance-contaminated heads, and unstable, staggering gait. After one day nothing abnormal was detected.

Justification for classification or non-classification

Acute oral toxicity:

(for further information, please see `discussion`)

The references Grundler (1981) which indicates a LD50 value of > 2610 mg/kg bw (male and female rats), the references Hofmann & Jung (1987) which states a LD50 of 1540 mg /kg bw, and the reference Zeller & Hofmann (1974) where a LD50 of >3200 mg/kg bw was determined as well as the reference Zeller & Hofmann (1974) which indicates a LD50 > 2000 mg /kg bw, are considered as the key studies for acute oral toxicity and will be used for classification.

According to the criteria specified by Directive 67/548/EEC and subsequent regulations, the test item magnesium dihydrogensulfite is not classified as acute toxic via the oral route. According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item magnesium dihydrogensulfite is not classified as acute toxic via the oral route.

 

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

The classification criteria acc. to regulation (EC) 1272/2008 as specific target organ toxicant (STOT) – single exposure, oral are not met since no reversible or irreversible adverse health effects were observed immediately or delayed after exposure and no effects were observed at the guidance value, oral for a Category 1 classification of 300 mg/kg bw and at the guidance value, oral for a Category 2 classification of 2000 mg/kg bw. No classification required.

 

Acute dermal toxicity:

(for further information, please see `discussion`).

The reference Cords (2009) is considered as the key study for acute dermal toxicity which indicates a LD50 of > 2000 mg/kg bw and will be used for classification.

No systemic clinical signs were observed during clinical examination. No local effects were observed.

According to the criteria specified by Directive 67/548/EEC and subsequent regulations, the test item is not classified as acute toxic via the dermal route. According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is not classified as acute toxic via the dermal route.

Based on the read-across concept, classification for magnesium dihydrogensulfite as acute toxic via dermal route is not anticipated.

 

Acute inhalation toxicity:

(for further information, please see `discussion`)

The reference Klimisch (1982) that indicates a LC50 value of > 5.5 mg/l is considered as the key study for acute inhalation toxicity and will be used for classification.

According to the criteria specified by Directive 67/548/EEC and subsequent regulations, the test item is not classified as acute toxic via the inhalation route. According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is not classified as acute toxic via the inhalation route.

Based on the read-across concept, classification for magnesium dihydrogensulfite as acute toxic via inhalation route is not anticipated.

 

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

The classification criteria acc. to regulation (EC) 1272/2008 as specific target organ toxicant (STOT) – single exposure, inhalation dust/mist/fume are not met since no reversible or irreversible adverse health effects were observed immediately or delayed after exposure and no effects were observed at the guidance value, inhalation dust/mist/fume for a Category 1 classification of 1.0 mg/L/4h and at the guidance value, inhalation dust/mist/fume for a Category 2 classification of 5.0 mg/L/4h. Therefore, no classification is required. Finally, any category 3 classification should primarily be based on human data. However, such classification is also not warranted, since only unspecific observations in test animals (mainly rats) were observed at artificially high inhalation exposure levels which are without relevance to current workplace conditions. It can be safely assumed that standard occupational hygiene measures provide a sufficient level of worker protection.