Use of this information is subject to copyright laws and may require the permission of the owner of the information, as described in the ECHA Legal Notice.
EC number: 240-795-3 | CAS number: 16731-55-8
Read-across principle for sulfite-disulfite
In aqueous solutions, sulfite compounds are competely dissociated in into countercations ond the sulfite anion. At neutral pH, a mixture of approx. 50% sulfite (SO32-) and 50%bisulfite (HSO3-) is present. However, at concentrations above 1M, bisulfite anions will dimerise with the elimination of water to form metabisulfite (S2O52-). On the other hand, low concentration of metabisulfite bought into solution will dissolve and hydrolise to form bisulfite.
There is thus a (pH-dependent) equilibrium between different forms of S(IV), i.e., sulfite, bisulfite, metabisulfite and sulfur dioxide. In general, the predominant forms under physiological and environmental conditions are sulfite and bisulfite, irrespective of the initially applies form of S(IV).
Consequently, all ecotoxicity data that were generated using a (di)sulfite compound with low-toxic counter ions (e.g., potassium, sodium), can be pooled together and – when expressed as S(IV) or SO32-, used in a read-across approach for all (di-)sulfite compounds.
For the long-term assessment of these compounds, one has to take into account that sulfite is oxidized to sulfate either catalytically by air oxygen or by microbial action. Halflife in deionized water was determined to be 77h (Tsunogai, 971), and this period should be considered as a worst-case as the presence of cations like iron, copper or manganese in the environment significantly accellerates the oxidation rate (WHO, 1979). Zhang and Millero (1991) reported that the reaction is more than five times faster in seawater comparted to distilled water.
These processes are important when interpreting (long)term) toxicity data for sulfites: sulfite is rapidly oxydised to sulfate thereby consuming oxygen. Observed toxic effects may therefore be caused by either sulfite toxicity or lack of oxygen (or a combination of both).
Summary of acute toxicity data
Table below gives an overview of reliable toxicity data that were identified for sulfite/disulfite compounds.
Table: Overview of reliable acute toxicity data for sulfite/disulfite compounds.for hazard assessment purposes.
BASF AG, 1989
BASF AG, 1990
Reliable acute data were available for three trophic levels: fish, aquatic invertebrates, aquatic algae and microorganisms. The lowest effect value was a 72h EC50 of 36.8 mg SO32-/L.
Summary of chronic toxicity data
An overview of the key species-specific chronic toxicity data for sulfites/disulfite compounds is given below. All relevant effects data are expressed as mg SO32-/L.
Table3: Overview of most sensitive species-specific EC10/NOEC-values for sulfite ion the freshwater environment
Three long-term results (e.g. NOECs) from species representing three trophic levels (algae, invertebrates, fish) are available. The lowest value for chronic toxicity was and unbounded NOEC of 8.41 mg SO32-/L.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
Welcome to the ECHA website. This site is not fully supported in Internet Explorer 7 (and earlier versions). Please upgrade your Internet Explorer to a newer version.
Close Do not show this message again