Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Stability

Polysulfides in aqueous solutions will practically always be deprotonated. At neutral and slightly alkaline conditions, S62-, S52-, and S42- dominate. These polysulfides are unstable especially under acidic conditions because polysulfides dissolved in water disproportionate as for instance according to the following reaction; Sn2- + H+--> Sn-1+ HS-. The rates of polysulfide oxidation are high compared to the oxidation rates of sulfide. The half-life of sulfide under oxic condions is considered to be in the order of a few hours to days.

Biodegradation

A valid ready biodegradability test result for polysulfides is not available because this substance is inorganic. Nevertheless all aspects important for achieving a ready biodegradability test result i.e. 1) ultimate (complete) biodegradation, 2) high rates of degradation and 3) occurrence of competent microorganisms in unacclimated ecosystems are fulfilled. Ready biodegradability tests only detect growth-linked biodegradation. Microorganisms are capable of growth on polysulfides under aerobic conditions (formation of sulfate (completely oxidized)) and anaerobic conditions in the presence of a reducing agent (formation of hydrogen sulfide (completely reduced)). Maximum growth rates of > = 0.8h-1are sufficiently high to enable a ready biodegradability test result. Transformation of reduced sulfur compounds has been detected in soils, fresh water, marine ecosystems and biological wastewater treatment plants. These findings demonstrate the wide distribution of polysulfide transforming microorganisms. Polysulfides should therefore be classified as readily biodegradable.

 

 

Table Summary of degradation rate constants in various (eco)systems based on the ready biodegradability of polysulfides using TGD default values.

 

(Eco)system

Method

Result 

Comment

Surface water (fresh)

TGD default value

Half live 15 days

Classification: readily biodegradable

Surface water (fresh)

Growth rate of sulfide oxidixing miroorganisms

Half live

1 hour

Result of publication in peer reviewed journal

Aerobic sediment layer

TGD default value

Half live 30 days

Kpsed 1.7 l/kg default of non hydrophobic

Anaerobic bulk sediment

TGD default value

Half live 30 days

Kpsed 1.7 l/kg default of non hydrophobic

Marine water

TGD default value

Half live 50 days

Classification: readily biodegradable

Marine water sediment

TGD default value

Half live 100 days

Kpsed 1.7 l/kg default of non hydrophobic

Soils

TGD default value

Half live 30 days

Kpsoil 0.7 l/kg default of non hydrophobic

Degradation in sewage treatment plants

Determined with bioreactor

>99%

Results of publications in peer reviewed journal (Vaiopoulou et al, 2005)

Bioaccumulation

Na2Sx will disassociate and react almost instantly when entering the environment (see chapter 5) to SO4 and therefore is considered a harmless substance that does not have bioaccumulation potential.

Transport and distribution

Na2Sx will disassociate and react almost instantly when entering the environment (see chapter 5) to SO4 and therefore a harmless natural substance.