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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

A standard respiration inhibition test according to OECD guideline 209 and GLP has been performed with the soluble Lanthanum trichloride hydrate and cerium dioxide. As the toxicity to microorganisms is likely mediated by the soluble  cation, the study with lanthanum trichloride  is used as a benchmark for  hardly water soluble lanthanum oxide, but the value for cerium dioxide is considered more representative due to its comparable solubility properties. Cerium dioxide was not toxic to sewage treatment plant microorganisms up to the maximum concentration of 1003.8 mg/L. 

Key value for chemical safety assessment

EC50 for microorganisms:
304 mg/L
EC10 or NOEC for microorganisms:
82 mg/L

Additional information

A standard respiration inhibition test according to OECD guideline 209 and GLP has been performed with the soluble Lanthanum trichloride hydrate (Muckle, 2009). As the toxicity to microorganisms is likely mediated by the lanthanum cation, this study is used as a benchmark for the hardly water soluble lanthanum oxide as well. The NOEC based on La3+ was 70 mgLa/L and the EC50 was 259 mg La/L, corresponding to 82 mg and 304 mg/L of La2O3. It should however be considered that the effect concentrations observed for the lanthanum ion are far above the water solubility of lanthanum oxide (69.6 micro-g/L (at pH 6.29 to 6.85))and it is therefore unlikely that lanthanum oxide will have any considerable toxicity to sewage treatment plant organisms. This is corroborated by a study with ceriumdioxide in which no significant inhibitory effect on the respiration rate of activated sludge after the incubation period of three hours at the limit test concentration of 1003.8 mg/L. Thus, the 3-hour NOEC of cerium dioxide to activated sludge microorganisms was > = 1003.8 mg/L. The 3-hour EC20, EC50 and EC80 were clearly higher than 1003.8 mg. It can therefore reasonably be assumed that lanthanum oxide will also have no significant inhibitory effects on sewage treatment plant organisms at a comparable loading rate.