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Short-term toxicity to aquatic invertebrates

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Description of key information

The 48-h EC50 for cesium potassium fluoroaluminate in water fleas (Daphnia magna) was found to be 60 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
60 mg/L

Additional information

One reliable study is available and was selected as key study. The study was performed according to OECD 202 and under GLP conditions. As cesium potassium fluoroaluminate is not completely soluble in the test medium due to formation of precipitates with salts in the medium, solutions from a loading rate at 100 mg/L were prepared. Daphnids were exposed to nominal concentrations of 0, 6.25, 12.5, 25, 50 and 100% under static conditions for 48 hours. The test solutions were analytically verified by measuring the fluoride content. The biological endpoints of the test are based on the average of the measured concentrations being 5.6, 11, 22, 49 and 95 mg/l. No immobility was observed in the control glass beakers. Therefore the test can be considered as valid. The 48 -hour EC50 was equal to 60 mg/L with 95% confidence interval of 52 - 69 mg/L.

A previous study (Bouwman, 2004b) performed by NOTOX BV according to OECD 202 has been disregarded because of deficiencies in the analytical method. The quantification of the test substance is based on the analysis of cesium which is present at 5.64% w/w in the test substance. The measured concentrations of the test substance were actually calculated by the measured concentrations of Cesium. The test solutions used in the range-finding test and the final test originated from the ones prepared for the simultaneously performed acute fish toxicity test (NOTOX project 394706). Analyses of a sample taken from the undiluted filtrate at the start of the final daphnia test showed a cesium concentration of 505 µg/L (8.9 mg/L) while a cesium concentration of only 178 µg/L (3.1 mg/L) was measured in the same solution at the start of the final fish test. In addition, this concentration was much lower than the concentration found in the range-finding test in which a cesium concentration of 889 µg/L (15.8 mg/L) was measured in the undiluted filtrate that was prepared in the same way and at the same concentration. Overall, the concentrations of cesium in the test solutions are significantly lower than expected based on the percentage of cesium in the test substance. No explanation was given for this difference.

Since the analytical method used to quantify the test substance in the test solution is not considered sufficiently robust, the effect concentrations are disregarded for assessment. In addition, the test substance consists of four elements (Cs, K, Al and F) and the biological effects are expected to be mostly governed by the presence of fluoride and aluminium ions formed upon dissociation of the fluoroaluminate moieties. Therefore in order to reflect the toxicity of the test substance, it is not correct to express the results as the mean measured cesium concentrations.