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Environmental fate & pathways

Hydrolysis

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Description of key information

Hydrolysis studies  as function of the pH are not required.

Four peer reviewed articles on the chemical stability of polysulfides in aqueous solution are given.  

Key value for chemical safety assessment

Additional information

Polysulfides are considered readily biodegradable. Studies on the hydrolysis as function of the pH are therefore not required.

 

The dissociation (acidity) constants of polysulfides are not known accurately, but they are so low that polysulfides in aqueous solutions present in nature and wastewater treatment plants will practically always be deprotonated (Schwarzenbach and Fischer, 1960). At neutral and slightly alkaline conditions, S62 -, S52 -, and S42 - dominate (Kamyshny et al, 2004). These polysulfides are unstable especially under acidic conditions. Polysulfide dissolved in water disproportionate as for instance according to the following reaction; Sn2-+ H+--> Sn-1+ HS-.

Polysulfides are not stable under oxic conditions and rapidly decompose to thiosulfate and elemental sulfur (Steudel et al, 1996) The chemical oxidation of polysulfide has been studied at pH 7-12. The rates of polysulfide oxidation are high compared to the oxidation rates of sulfide (Kleinjan et al, 2005). The half-life of sulfide under oxic condions is considered to be in the order of a few hours to days.