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Long-term toxicity to aquatic invertebrates

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Description of key information

The release of barium upon dissolution of BaS determines the chronic toxicity of BaS to invertebrates under normal environmental conditions, and the 21-d NOEC of 3.58 mg BaS/L is considered in the freshwater CSA.
A nominal 7d-NOEC of 10 mg Ba/L was reported for embryonal hatching of the marine invertebrate Cancer anthonyi (Macdonald et al, 1988) corresponding to the 7d-NOEC of 12.3 mg BaS/L, and this endpoint is considered in the marine CSA.
The first study by Biesinger and Christensen reported a 21d-EC16 of 5.8 mg Ba/L (nominal values), which can be used for the estimation of a NOEC-value of 2.9 mg Ba/L (i.e., EC16/2; ECHA-guidance). This value translates to an 21d-NOEC of 3.58 mg BaS/L.
The second data point was generated for the marine invertebrate Cancer anthonyi (Macdonald et al, 1988). Here, a nominal 7d-NOEC of 10 mg Ba/L was reported, and this for the endpoint embryonal hatching. This value translates to a 7d-NOEC of 12.3 mg BaS/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
3.6 mg/L

Marine water invertebrates

Marine water invertebrates
Effect concentration:
12.3 mg/L

Additional information

Reliable chronic toxicity data for freshwater/marine invertebrates are available for barium but not for sulfate. 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 invertebrates with acute LC/EC50 values far above 1000 mg/L. 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). 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. Therefore, it may conservatively be assumed that the toxicological moiety of concern for the long-term toxicity of BaS to invertebrates (if any) is barium and further that the contribution of sulfate to the overall toxicity of BaS may be neglected.

Biesinger and Christensen (1972) reported a nominal 21-EC16of 5.8 mg Ba/L for the water fleaDaphnia magna. Measured concentration levels were not reported. According to ECHA Guidance, a NOEC can be estimated by dividing a reliable ECXby 2 when X refers to an effect between 10 and 20%. The 21d-EC16of 5.8 mg Ba/L is compliant with this criterion. Thus, a NOEC of 2.9 mg Ba/L is derived for the reproduction ofDaphnia magnain freshwater corresponding to the 21d-NOEC of 3.58 mg BaS/L. Sulfate released from 3.58 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, that the contribution of sulfate to the overall toxicity of BaS may be neglected.

Macdonald et al (1988) reported a 7d-NOEC of 10 mg Ba/L for the marine speciesCancer anthonyi. The outcome of this study is considered relevant for assessing long-term risks (chronic exposure) as the study combines a sensitive life-stage and endpoint (hatching/development of 24h embryos) with an exposure period (7d) that is significantly longer than conventional acute exposure periods for invertebrates (48-96 hours).