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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Two reliable activated sludge respiration inhibition tests were used in a weight of evidence approach to cover the endpoint. The first study (Eisner, 2014) was performed using La(NO3)3 and yielded a NOEC, EC10 and EC50 of 171, 176 and 297 mg La/L, respectively (corresponding to a NOEC, EC10 and EC50 of 389, 400 and 676 mg lanthanum acetate/L, respectively). The other study (Muckle, 2009) was performed using LaCl3 and reported a NOEC and EC50 of 70.8 and 221 mg La/L, respectively. The latter values were selected as key values for this endpoint as they are the lowest. They correspond to 161 and 503 mg lanthanum triacetate/L.

Key value for chemical safety assessment

EC50 for microorganisms:
221 mg/L
EC10 or NOEC for microorganisms:
70.8 mg/L

Additional information

Four relevant studies have been identified for this endpoint. Two of them were performed on bacterial populations and the two other on isolated bacteria. When assessing toxicity to aquatic micro-organisms, consideration of bacterial populations is preferred as this better represents the functioning of the whole ecosystem. That the reason why the two activated sludge respiration inhibition tests were considered in a weight-of-evidence approach to cover the endpoint.

Two activated sludge respiration inhibition tests are available, one performed with LaCl3 (Muckle, 2009), and another performed with La(NO3)3 (Eisner, 2014). The test with LaCl3 yielded a NOEC, EC20 and EC50 of 70.8, 119 and 221 mg La/L, respectively, based on nominal lanthanum concentrations. The test with La(NO3)3 yielded a NOEC, EC20 and EC50 of 171, 211 and 297 mg La/L, respectively, also based on nominal lanthanum concentrations. Both studies are reliable and the results of both tests are consistent with each other. Therefore the two studies are used in a weight of evidence approach to cover the endpoint. The lowest NOEC and EC50 (70.8 and 221 mg La/L, respectively) were identified as key values, corresponding to 161 and 503 mg lanthanum triacetate/L respectively.

In the test of Bringmann and Kühn (1959) the effect of lanthanum (added as lanthanum acetate) on the feeding of the ciliate Microregma heterostoma was investigated by monitoring the uptake of bacteria by the ciliates (via turbidity measurement). The 28-h LOEC was 24 mg La/L. Lanthanum was not measured in this test. Results are therefore not considered entirely reliable as toxicity may have been underestimated. The study can however be considered as a supporting study.

In the study of Tang et al. (1985), Tetrahymena pyriformis was exposed for up to 60 h to a concentration series of lanthanum added as LaCl3, yielding a NOEC (visually observed from figure) of 50 mg La/L and a LOEC of 200 mg La/L, based on population growth. This study was not considered entirely reliable (Klimisch 3) because there was no analytical verification of test item concentrations and because no statistics were shown. The results of the study were however in accordance with the other test results.