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According to Column 2 of the REACH annexes on information requirements, no biodegradability tests should be conducted when the substance is inorganic. BaS is considered to be an inorganic substance; however, because of the importance of microorganism-mediated reactions in the natural sulfur cycle, this endpoint is not entirely irrelevant. When sulfide compounds such as BaS are released to the environment, the sulfur in the compounds will enter the natural sulfur cycle. In this cycle, sulfur transformations are mediated to an important extent by sulfur oxidizing and reducing microorganisms. In aerobic environments, sulfur oxidizing microorganisms will transform sulfides into - eventually - sulfates, whereas in anaerobic environments, sulfur reducing microorganisms will reduce oxidized sulfur compounds in the presence of reducing agents. Oxidation of reduced sulfur compounds has been detected in soils, freshwater and marine ecosystems, and biological waste water treatment plants. These findings demonstrate the wide distribution of sulfide transforming microorganisms. Half-lives for sulfide 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.

The guidance that is given in Column 2 of Annex VII if REACH legislation and Chapter R.7b (Endpoint Specific Guidance) of the ECHA REACH Guidance Document, (November 2012), is relevant for barium that is released from BaS, i.e. that the requirements for “Ready biodegradability” can be waived if the substance is inorganic.

Annex VIII states that "Further degradation testing shall be considered if the chemical safety assessment according to Annex I indicates the need to investigate further the degradation of the substance. The choice of the appropriate test(s) will depend on the results of the chemical safety assessment." Waiving of the need for data for this environmental endpoint may be considered if “The substance is highly insoluble in water), or if “The substance is readily biodegradable” (ECHA 2012, Chapter R.7b– Endpoint Specific Guidance).

However, for an inorganic substance like barium for which the chemical assessment is based on the elemental concentration (i.e., pooling all inorganic speciation forms together), biotic degradation in the environment is an irrelevant process: biotic processes may alter the speciation form of an element, but it will not eliminate the element from the environment by degradation or transformation processes. This elemental-based assessment (pooling all speciation forms together) can be considered as a worst-case assumption for the chemical assessment.