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Long-term toxicity to fish

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The release of barium upon dissolution of BaS determines the chronic toxicity of BaS to fish under normal environmental conditions, and the unbounded NOEC of ≥ 1.55 mg BaS/L (dissolved) is considered in the CSA.
Toxicity data for sulfate were not identified; it should be noted that sulfide will rapidly oxidize to the less toxic sulfate under normal environmental conditions that are relevant for the aquatic environment. Sharma and Yuan (2010), for example, demonstrated that sulfide is oxidised to sulfate and other oxidised S-forms in less than one hour.

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Additional information

Reliable chronic toxicity data for fish are available for barium and sulfide but not for sulfate.

The lowest reliable chronic toxicity for fish with regard to sulfide was reported by Smith et al (1976a) for mortality of the juvenile bluegillLepomis macrochirus, yielding in an unbounded 826d-NOEC of 0.0046 mg H2S/L. Toxic effects of released sulfide from BaS are not relevant for the chronic hazard assessment of BaS as it is oxidized to sulfate, and thus the toxicity of sulfate should be assessed. In freshwater, however, sulfate appears to be of low toxicity to fish with acute LC/EC50 values far above 1000 mg/L. The solubility product constant of barium sulfate of 1.1×10–10 indicates that once sulfide released from BaS is oxidized to sulfate, and that barite (BaSO4) precipitates. Further, 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 (OECD SIDS for Na2SO4). Therefore, it may conservatively be assumed that the toxicological moiety of concern for the long-term toxicity of BaS to fish (if any) is barium and further that the contribution of sulfate to the overall toxicity of BaS may be neglected.

One reliable long-term toxicity study (Klimisch 1, GLP) withDanio reriowas conducted. No effects were abserved at the highest test concentration of nominal 100 mg barium dichloride dihydrate/L corresponding to the following unbounded NOEC values: 

a) The NOEC ≥ 49.7 mg BaS/L (≥ 40.3 mg Ba/L) based on total barium concentration.

(b) The NOEC ≥ 1.55 mg BaS/L (≥ 1.26 mg Ba/L) based on dissolved barium concentration.

Sulfate released from 1.55 mg BaS/L remains below typical baseline levels for sulfate in pristine surface waters. The median value for sulfate in the FOREGS dataset amounts to 16.1 mg/L (www.gtk.fi/publ/foregsatlas). Thus, the contribution of sulfate to the overall toxicity of BaS may be neglected.Based on findings for other taxonomic groups and exposure periods, it is concluded that the chronic toxicity of BaS under normal environmental conditions is determined by the release of barium and the unbounded NOEC of ≥ 1.55 mg BaS/L (dissolved) is considered in the CSA.