Lanthanum trinitrate

Endpoint summary

Additional information

Short-term toxicity

One reliable study was identified on the acute toxicity of lanthanum to fish (Hefner 2014a). This key study which was performed using La(NO3)3 was assigned a reliability score of 1. In this study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to lanthanum (added as La(NO3)3) for 96 h in a semi-static test. The 96-h LC50 was determined to be 0.42 mg La/L (corresponding to a 96-h LC50 of 1.01 mg La(NO3)3/L). Based on this result La(NO3)3 is considered to be toxic to fish.

Two reliable studies were identified on the acute toxicity of lanthanum to aquatic invertebrates, one in which La(NO3)3 was used (Hefner, 2014b), and another in which LaCl3 was used (Barry and Meehan, 2000). The first study (K1) was conducted with Daphnia magna and yielded a 48-h EC50 value of 3.0 mg La/L. The K2 study of Barry and Meehan (2000) exposed Daphnia carinata for 48 h to LaCl3 in three different test media with increasing water hardness. The 48-h EC50 values were 0.0432 mg La/L in tap water (hardness 22 mg CaCO3/L), 0.049 mg La/L in Daphnia medium (hardness 98 mg CaCO3/L) and 1.180 mg La/L in ASTM hard water (hardness 160 mg CaCO3/L). There is clearly a protective effect of water hardness, which may be due to competition for uptake of Ca2+ (and/or Mg2 +) and La3+ for uptake at the respective ion channels. The study with La(NO3)3 (Hefner, 2013b) was performed in a test medium with a water hardness of 250 mg CaCO3/L and therefore it is not surprising that the 48-h EC50 value was higher than the highest one obtained by Barry and Meehan (2000). Inter-species sensitivity differences may however also be responsible for the observed differences. Both studies are used in a weight of evidence approach to cover this endpoint. The lowest value of 0.0432 mg La/L from Barry and Meehan (2000) was not taken forward as it was obtained in a soft water (22 mg CaCO3/L), being representative for only a very small part of the European surface waters. Therefore the value of 0.049 mg La/L, which was tested at a water hardness of 98 mg CaCO3/L is being considered as the key value that will be taken forward for classification. For classification purposes, it is important to note that this key value corresponds to a 48-h EC50 of 0.1146 mg/L when expressed as La(NO3)3, meaning that lanthanum trinitrate is very toxic to aquatic invertebrates.

For algae, the key study was a study from Hefner (2014c) which was assigned a Klimisch score of 1. In this study, algal growth inhibition was studied in a 72-h static test according to OECD guideline 201 with the unicellular green alga Pseudokirchneriella subcapitata. The test substance was La(NO3)3. The growth-rate based 72-h EC50 and NOEC were determined to be 0.9 and 0.31 mg La/L, respectively (corresponding to 2.1 and 0.73 mg La(NO3)3/L respectively). Observations during the test indicated that the observed effects on algal growth were concurrent with phosphate depletion. Model calculations (Visual MINTEQ v3.0) indeed confirmed that whenever phosphate is in excess of lanthanum (i.e., at the lowest test concentrations), all lanthanum is precipitated from the test solution, whereas when lanthanum is in excess of phosphate (i.e., at the higher test concentrations), all phosphate is precipitated from the test solution. The latter results in phosphate deprivation effects in the algae. Therefore, the observed algal growth inhibition was due to an indirect effect rather than resulting from direct lanthanum toxicity. This problem cannot be resolved by adjusting the test set-up and therefore no further testing will be performed and the results of the algal growth inhibition studies will not be taken into account for classification purposes.

Two reliable studies were identified on the toxicity of lanthanum to microorganisms. These are activated sludge respiration inhibition tests, 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, 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. These values correspond to 165 and 517 mg La(NO3)3/L.

Long-term toxicity

Three reliable studies (Klimisch 2, reliable with restrictions) were identified for long-term toxicity to aquatic invertebrates and included in a weight of evidence approach to cover this endpoint. Lürling and Tolman (2010) exposed Daphnia magna to lanthanum, supplied as La(NO3)3, and observed adverse effects on reproduction at concentrations higher than 0.1 mg La/L (NOEC). In the study of Bogers (1995c), Daphnia magna neonates were exposed for 21 days to increasing lanthanum concentrations (supplied as LaCl3). Mortality seemed to be the most sensitive endpoint. The 21-d NOEC and EC50 were reported to be 0.1 and 0.552 mg La/L, respectively. Finally, in the study of Barry and Meehan (2000), Daphnia carinata neonates were exposed to a series of lanthanum concentrations (supplied as LaCl3) until their third brood was produced. The most sensitive endpoints seemed to be survival and age at maturity. A NOEC and LOEC of 0.03 and 0.039 mg La/L were obtained, respectively, for both endpoints. The NOEC of 0.03 mg La/L was selected as key value and will be taken forward to classification. For classification purposes, it is essential to note that this value corresponds to a NOEC of 0.07 mg/L, when expressed as La(NO3), meaning that lanthanum trinitrate is very toxic to aquatic invertebrates with long lasting effects.

Only one fish study was identified as containing relevant and reliable information on long-term toxicity to fish (Bogers, 1995a). In this study, carp (Cyprinus carpio) were exposed for 21 days to LaCl3, yielding a 21-d NOEC (based on mortality) of 0.26 mg La/L and a 21-d LC50 of > 5 mg La/L, based on geometric means of measured dissolved La concentrations. This study was however performed according to OECD guideline 204 (Fish, Prolonged toxicity test), which is insufficient to cover this endpoint in the absence of real long-term studies. The study lasted one week longer than recommended by the guideline (i.e., 21 instead of 14 days), however, since only mortality was studied as endpoint, the study can only be considered as a supporting study. Therefore, the NOEC cannot be taken into account for classification purposes.

Sensitivity

The acute tests with Daphnia and fish were performed at different water hardness levels. The LC50 for the fish study (0.39 mg La/L) was obtained in a test medium with a water hardness of 125 mg CaCO3/L. The EC50 values obtained for daphnids were 3.0 mg La/L for Daphnia magna at a water hardness of 250 mg CaCO3/L and 1.180, 0.049 and 0.0432 mg La/L for Daphnia carinata at water hardness levels of 160, 98 and 22 mg CaCO3/L, respectively. Based on this information, it is expected that for daphnids a lower EC50 would be obtained at a water hardness of 125 mg CaCO3/L than the LC50 obtained in the fish study at that water hardness level. Therefore, daphnids were considered the most sensitive group of organisms, acutely.