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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Reliable acute toxicity data for invertebrates are available for sulfide, sulfate and barium. Barium and sulfide are released upon dissolution of BaS in the aqueous environment. Sulfide is rapidly oxidised under natural environmental conditions. Thus, only acute but not long-term effects due to sulfide exposure are expected. Further, the toxicity of sulfate was considered. However, sulfate is of low toxicity.
Breteler et al (1991) reported a 4h-EC50 (based on survival) for the marine diatom Skeletonema costatum, and the NOEC of 0.204 mg BaS/L is used as estimate for acute toxicity of BaS to primary producers.
The release of barium upon dissolution of BaS determines the chronic toxicity of BaS to primary producers under normal environmental conditions, and the 72h-NOEC of 1.42 mg BaS/L (dissolved) for growth rate inhibition of Pseudokirchneriella subcapitata is considered in the freshwater CSA.

Key value for chemical safety assessment

Additional information

Reliable toxicity data for algae are available for barium, sulfide and sulfate.

Breteler et al. (1991) and Admiraal and Peletier (1979) report reliable toxicity data of H2S for marine diatoms. The lowest NOEC amounting to 0.041 mg H2S/L was observed by Breteler et al. (1991) for the marine speciesSkeletonema costatum. The exposure period, however, was only 4 hours and the evaluated endpoint was survival. Both endpoint and parameter are not in accordance with standard protocols such as OECD 201 for testing algae growth inhibition. This information, however, supports other findings of H2S being acutely toxic. The reported NOEC of 0.041 mg H2S/L corresponds to the NOEC of 0.204 mg BaS/L.

Reliable toxicity data of sulfide could not be identified for the freshwater environment. 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. 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. As essential nutrient, sulfate is not very toxic to plants or algae (OECD SIDS for Na2SO4). The study of Patrick et al (1968) was identified in the OECD SIDS for Na2SO4(the most relevant substance for assessing the risks of sulfate) as key study with regard to the acute toxicity of sulfate to algae. This study reports a 120h-EC50of 1900 mg Na2SO4/L for the freshwater diatomNitzschia lineariscorresponding to the 120h-EC50of 2266 mgBaS/L.

Reliable acute and chronic toxicity data of barium (Klimisch 1, GLP) are available for the freshwater green algaPseudokirchneriella subcapitata. Effects on growth rate were not observed up to and including the highest (nominal) test concentration of 30.1 mg Ba/L. The dissolved and total fraction were measured. Dissolved levels were below total levels presumbably due to the formation poorly soluble barium sulfate. At the highest concentration, dissolved and total Ba concentration were 1.14 and 30.1 mg/L, respectively (geometric mean measured concentration). Therefore, based on total Ba-levels in solution, the ErC50and NOEC are >30.1 and ≥ 30.1 mg Ba/L, respectively. Read-across to barium sulfide results in an ErC50>37.1 mg/L and a NOEC of ≥ 37.1 mg/L. Further, based on dissolved barium concentrations, ErC50and NOEC amount to >1.15 and ≥1.15 mg Ba/L corresponding to an ErC50>1.42 mg BaS/L and a NOEC of ≥ 1.42 mg BaS/L, respectively.

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