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Short-term toxicity to aquatic invertebrates

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The 48 h acute toxicity to aquatic invertebrates (Daphnia magna) was investigated in a study according to GLP and OECD 202 under semi-static conditions. It was not possible to determine effect levels based on effective measured concentrations of tantalum pentachloride due to high variability depending on slightly changing pH. Therefore, only nominal effect loading rates are given. The 48-hour EL50 was 3086 mg/L.

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The 48 h acute toxicity of tantalum pentachloride to Daphnia magna Straus was studied under semi-static conditions. Daphnids were exposed to a control containing no test substance and tantalum pentachloride at nominal loading rates of 593, 889, 1333, 2000 and 3000 mg/L for 48 h. Immobilization was recorded daily. Due to highly variable Ta5+ concentrations in solution, effect concentrations were based on nominal loading rates. The 48-hour EL50 was 3086 mg/L. The 48-h NOELR based on immobilization was 2000 mg/L and the LOELR was 3000 mg/L. It was not possible to determine effect levels based on measured effective test substance concentrations. After pH adjustment the measured Ta5+ concentrations were low and showed high variability. Measured values of Ta5+ ranged from < LOQ to 8.36 µg/L before chemical digestion of samples and from < LOQ to 144 µg/L after chemical digestion of samples. Therefore, no concentration-response relationship could be established. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test concentrations. Observed immobilization effects may therefore rather predominantly refer to elevated NaCl concentrations, originated from neutralization, than released Ta5+ ions. Reported EC50 values for sodium chloride vary but may be as low as 874 mg/L (ECHA registry for sodium chloride). Due to a concentration of approximately 2.34 g/L NaCl, present at the highest loading rate of 3000 mg/L test substance, and the sensitivity of D.magna to salinity, any hypothetical Ta5+ related effects cannot be distinguished from NaCl induced inhibition in the conducted test.