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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The key study (Eisner, 2013) was an activated sludge respiration inhibition test performed with CeCl3 and yielding a 3-h EC50 and NOEC value of 436 and 91 mg Ce/L, respectively (corresponding to 767 and 160 mg CeCl3/L, respectively).

Key value for chemical safety assessment

EC50 for microorganisms:
436 mg/L
EC10 or NOEC for microorganisms:
91 mg/L

Additional information

Four studies were identified containing relevant information on the toxicity of cerium to aquatic microorganisms.

The key study (Eisner, 2013) was an activated sludge respiration inhibition study with CeCl3 yielding a 3-h NOEC and EC50 of 91 and 436 mg Ce/L, respectively (corresponding to 160 and 767 mg CeCl3/L, respectively)..

Dion (1990) investigated growth inhibition of Pseudomonas putida caused by cerium (added as Ce(NO3)3) and obtained a 16-h EC10 and EC50 value of 1.89 and 3.14 mg Ce/L. This study was considered reliable with restrictions (Klimisch 2). However, as the results of Pseudomonas putida growth inhibition tests should not be used for PNEC derivation unless no data on other relevant organisms or on activated sludge are available, the study was here considered as a supporting study. Indeed, when data are available on both isolated bacteria and whole bacterial populations, the latter is preferred as more representative of the whole functioning of the ecosystem.

In the third study (Tang et al., 1985), Tetrahymena pyriformis was exposed for up to 60 h to a concentration series of cerium added as CeCl3, yielding a NOEC of 60 mg Ce/L and a LOEC of 200 mg Ce/L, based on population growth. However, because no statistics were performed, NOEC and LOEC values needed to be visually determined from a figure. Therefore the study was not considered reliable. Nevertheless, the study supports the key study as the obtained NOEC was quite similar to that of the key study.

Finally, in the study of Bringmann and Kühn (1959), the effect of cerium (added as CeCl3) on the ciliate Microregma heterostoma was investigated by monitoring the uptake of bacteria by the ciliates (turbidity measurement). The 28-h LOEC was 8 mg Ce/L. This study was considered as supporting information and was not considered entirely reliable (Klimisch 3) because not all materials and methods are clearly reported, because only a LOEC is reported, and because no guideline was followed.