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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 strontium. Strontium and sulfide are released upon dissolution of SrS 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.
One reliable acute/chronic toxicity data point (Klimisch 1, GLP) for an algal species -the green algae Pseudokirchneriella subcapitata - has been identified for strontium. Based on measured Sr-level in the water column, a 72h-ErC50 and 72h-NOEC of is reported by Tobor-Kaplon (2010), using Sr(NO3)2 as test substance.
The release of strontium upon dissolution of SrS determines the chronic toxicity of SrS to primary producers under normal environmental conditions, and the 72h-NOErC of 59.1 mg SrS/L for growth rate inhibition of Pseudokirchneriella subcapitata is considered in the freshwater CSA.

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Additional information

Reliable toxicity data for algae are available for strontium, 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 0.144 mg SrS/L.

Reliable toxicity data of sulfide could not be identified for the freshwater environment. Toxic effects of released sulfide from SrS are not relevant for the chronic hazard assessment of SrS 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 1601 mg SrS/L.

One reliable acute/chronic toxicity data point (Klimisch 1, GLP) for an algae species - the freshwater green algaPseudokirchneriella subcapitata- has been identified. No effect (growth rate) was noted at the highest (nominal) test concentration of 100 mg test material/L. Based on measured Sr-levels, these effects levels translates to 43.3 mg Sr/L or 59.1 mg strontium sulfide/L.

Therefore, based on measured Sr-levels in solution, the ErC50and NOEC are >59.1 and >=59.1 mg SrS/L, respectively.