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Ecotoxicological information

Toxicity to soil microorganisms

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Description of key information

Reliable toxicity data for soil micro-organisms could not be identified for barium, sulfide or sulfate.

Key value for chemical safety assessment

Additional information

Toxic effects of released sulfide from BaS are not relevant for the hazard assessment of BaS in soils as sulfide is oxidized to sulfate, and thus the toxicity of sulfate should be assessed. Sulfate is essential to all living organisms, their intracellular and extracellular concentrations are actively regulated and thus, sulfates are of low toxicity to the environment, including soils (OECD SIDS for Na2SO4). Further, the solubility product constant of barium sulfate of 1.1×10–10 indicates that once sulfide released from BaS is oxidized to sulfate, barite (BaSO4) precipitates and is rendered less bioavailable and less toxic. Thus, the barium cation is the moiety of toxicological concern (if any), and the soil hazard assessment is based on barium.

Based on the low microbial toxicity of sulfate, i.e. a NOEC of 5.4 g/L for the presence of stalked ciliates in activated sludge, and barium, i.e., a NOEC of ≥622 mg Ba/Lon microbial respiration inhibition in a standard test with activated sludge, it appears that the potential for microbial toxicity og BaS is low. Thus, microbes in natural soils are not expected to be more sensitive to BaS than invertebrates.