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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

72 h EL50 > 100 mg/L, EL10 =67 mg/L, NOELR = 25 mg/L, Scenedesmus subspicatus, OECD 201, EU Method C.3, RCC 2007 (read across cerium carbonate).

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
25 mg/L

Additional information

The influence of cerium carbonate (dicerium tricarbonate) on the growth of the green algal species Scenedesmus subspicatus was investigated in a 72 -hour static test conducted to GLP and in accordance with standardised guidelines EU C.3 (1992) and OECD 201 (2006).

During the study algal suspensions were exposed to the test material at a loading rate of 100 mg/L (corrected for water content) and to dilutions 1:2, 1:4, 1:8, 1:16, 1:32. A control was tested in parallel.

The algal cell densities were counted daily, and inhibition of algal growth was assessed. Inhibition of growth rate is summarized in the table below:

Based on the loading rates of the test material

(corrected from its water content):

Based on initially measured concentrations of

cerium carbonate in the test media 

72-h EL50 > 100 mg/L

72-h EL10 = 67 mg/L

72-h EL90 > 100 mg/L

72-h NOELR = 25 mg/L

72-h LOELR = 50 mg/L

72-h EL50 > 6.6 µg/L

72-h EL10 = 4.4 µg/L

72-h EL90 > 6.6 µg/L

72-h NOELR = 1.6 µg/L

72-h LOELR = 3.3 µg/L

The inhibition of algal growth was presumably caused by a secondary effect, the complexation of the essential algal nutrient phosphate by the test material. A statistically significant decrease of the phosphate concentration was determined at the loading rates of 50 and 100 mg/L. Thus the growth inhibition determined at these loading rates may have been caused by depletion of phosphate in the test medium.

No short-term toxicity data for aquatic plants are available for the registered substance, cerium oxalate. A valid study has been provided on the structural analogue, cerium carbonate. The similar toxicological profiles of cerium carbonate and cerium oxalate, along with the structural similarity, mean that this is considered to be an acceptable read-across.

The study was performed in line with a recognised OECD guideline and to GLP standard. It is assigned a score of 2 in line with the reliability scoring system of Klimisch (1997), based on the fact that a read across approach has been used.