Lanthanum trinitrate

Toxicity to microorganisms

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 (corresponding to a NOEC, EC10 and EC50 of 400, 412 and 695 mg La(NO3)3/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 165 and 517 mg La(NO3)3/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 microorganisms, consideration of bacterial populations is preferred as this better represents the functioning of the whole ecosystem. That is 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 thus 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 165 and 517 mg La(NO3)3/L, respectively.

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 no statistics were shown. The results of the study were however in accordance with the other test results.

The study of Bringmann and Kühn (1959) investigated the effect of lanthanum on the feeding of the ciliate Microregma heterostoma by exposing the organism to lanthanum acetate. In this study a 28-h LOEC was obtained of 24 mg La/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.