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Toxicity to aquatic algae and cyanobacteria

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Description of key information

A study was performed with the water soluble Lanthanum trichloride hydrate.
Growth rate: EC50(72h) = 16 mg La/L and EC10(72h) = 1.3 mg La/L for Desmodesmus subspicatus (OECD 201).
Cell number: EC50(72h) = 13 mg La/L and EC10(72h) = 1.4 mg La/L for Desmodesmus subspicatus (OECD 201)
In contrast the closely related rare earth oxide Cerium dioxide that has a comparable low solubility no direct toxic effect was observed at the saturation concentration at a loading rate of 100 mg/L. Based on the low water solubility of Lanthanum oxide at the relevant pH of 6.29 to 6.85 of 69.6 micro-g/L no effects at saturation are expected.

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Additional information

A GLP -study according to OECD 201 on the toxicity to Desmodesmus subspicatus was performed with Lanthanum trichloride hydrate. The EC50 (growth rate) was determined as 16 mg La/L, the EC50 (cell number) as 13 mg La/L, based on the Lanthanum cation. The EC10 values for growth rate and cell number were 1.3 mg La/L and 1.4 mg La/L, respectively. Given the low water solubility of lanthanum oxide of 69.6 micro-g/L (at pH 6.29 to 6.85) it can reasonably be assumed that the Lanthanum oxide concentration at saturation in this test system would be below the NOEC of the lanthanum ion and Lanthanum oxide would no exert any toxicity to algae at the water solubility limit under the conditions of this test. This is also corroborated by a study with ceriumdioxide, a closely related substance of the lanthanide group with comparable low water solubility. With Cerium dioxide essentially no direct toxic effect was observed at the saturation concentration at a loading rate of 100 mg/L. A slight inhibition (EL10 of 91 mg/L based on loading concentration) was attributed to a secondary effect, the complexation of the essential algae nutrient, phosphate by the test item (complexation) as a significant decrease of phosphate was determined in the undiluted filtrate of the dispersion.

Toxicity data for marine species are not available.