Reaction mass of disodium sulphide and sodium carbonate and sodium hydrogensulphide

Biodegradation in water: screening tests

Description of key information

According to column 2 of the REACH annexes on information requirements, no biodegradability tests should be conducted when the substance is inorganic. However, because of the importance of microorganism-mediated reactions in the natural sulphur cycle, this endpoint is not entirely irrelevant. When sulphide compounds such as Na2S and NaHS are released to the environment, the sulphur in the compounds will enter the natural sulphur cycle. In this cycle, sulphur transformations are mediated to an important extent by sulphur oxidising and reducing microorganisms. In aerobic environments, sulphur oxidising microorganisms will transform sulphides into - eventually - sulphates, whereas in anaerobic environments, sulphur reducing microorganisms will reduce oxidised sulphur compounds in the presence of reducing agents. Oxidation of reduced sulphur compounds has been detected in soils, freshwater and marine ecosystems, and biological waste water treatment plants. These findings demonstrate the wide distribution of sulphide transforming microorganisms. Half-lives for sulphide oxidation between 0.4 and 65 h have been reported, depending on the environment under consideration (Bagarinao, 1992). These half-lives represent half-lives based on combined abiotic and microorganism-mediated oxidation reactions.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater