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Long-term toxicity to aquatic invertebrates

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Under the conditions of this chronic daphnia toxicity study the observed endpoints related to reproduction for the effect of cesium hydroxide monohydrate were the following: 21d NOEC: 15.8 mg/L; 21d LOEC: 30.0 mg/L; 21d EC50: > 15.8 mg/L. All reported biological results are related to the nominal concentrations. 
Based on these data, the calculated 21d-NOEC for cesium hydroxide anhydrous was 14.1 mg/L, the 21d-EC50>14.1 mg/L and the LOEC>26.8 mg/L.

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Additional information

A semi-static Daphnia magna reproduction test was performed according to OECD Guideline 211 and EU Method C.20. At this method Daphnia magna, aged lower or equal 24 h at the beginning of the test, are exposed to a range of cesium hydroxide monohydrate under defined conditions over a period of 21 days. In the definitive test the nominal concentrations were as follows: 2.3, 4.4, 8.3, 15.8 and 30 mg/L. The performed parallel running analytical determinations confirmed that the test item concentrations remained within the range of ±20 % of the nominal and of the initial concentrations (varied between 93 and 109 per cent of the nominal concentration); therefore all of the results are based on the nominal test item concentrations. In the main test the mean number of offspring produced per animal was slightly lower (100.1, 106.5 and 109.1) in concentrations of 2.3, 4.4 and 8.3 mg/L and somewhat higher (124.2) at the concentrations of 15.8 mg/L. Due to the 100 % mortality in parent animals at the highest concentration of 30 mg/L, results of this concentration is excluded from data analysis. Correspondingly the 21-day NOEC related to reproduction was determined to be 15.8 mg/L and the LOEC as 30 mg/L. At the highest tested concentration of 30 mg/L the produced offspring were excluded from data analysis (because all of parent animals were died by the end of the experiment) and the mean number of offspring produced in the next lower concentration (15.8 mg/L) was higher than produced in the control (i.e. NOEC), therefore the obtained results were not sufficient for an exact EC50 value estimation. A Probit analysis was not performed from the available data. The 21-day EC50 for cesium hydroxide monohydrate was determined to be higher than 15.8 mg/L.

Based on these data, the calculated 21d-NOEC for cesium hydroxide anhydrous was 14.1 mg/L, the 21d-EC50 > 14.1 mg/L and the LOEC > 26.8 mg/L.