Niobium

Endpoint summary

Additional information

Acute aquatic toxicity data is available for one trophic level, including one key study with aquatic algae (OECD 201). Chronic aquatic toxicity data is available for two trophic levels, i.e. freshwater algae and invertebrates, respectively. Furthermore, a long-term test with fish (OECD 210) is ongoing CCH-D-2114517391-56-01/F). Reasons for the delay are summarized in the statements attached in IUCLID section 6.1.2 (‘Status of Fish early life stage toxicity Tests (OECD 210) with Niobium metal powder’ (Sept. 2022) and Status of Aquatic Toxicity Tests (OECD 201, 210 and 211) with Niobium metal powder (May 2022).

Freshwater algae were identified to show the highest long term sensitivity to niobium (CAS 7440-03-1) after exposure for 72 h to saturated niobium solutions (0.45 µm filtered after 96 h of stirring, pH 8.5), resulting in an ErC10 (72 h) of 16.1 mg/L (nominal, OECD 201). No adverse acute effects were observed (ErC50 72h) > 100 mg/L in the same test. Furthermore, niobium did not cause chronic effects to Daphnia magna in a chronic toxicity test according to OECD 211 resulting in unbounded 21 d NOEC values of ≥ 10 and (nominal).

No toxic effects to aquatic microorganisms were observed in an OECD 209 (NOEC ≥ 1000 mg/L).

Due to the particulate properties (sedimentation of particles, broad range in particle size distribution including particles sizes < 0.45 µm) of the test item it was not possible to achieve homogenous and reproducible test item concentrations and to reliably measure the real exposure concentration in the test medium. Therefore, effect concentrations in both tests were based on nominal instead of measured concentrations.

Dynamic light scattering measurements, revealed the presence of non-dissolved niobium in the test medium of the algae test, as well as in the aquatic invertebrate test. Furthermore, transformation dissolution data of different niobium materials indicate a low solubility in environmental media: Dissolved niobium concentrations after 28 d were found to be < 0.01 and < 0.4 µg/L at a loading rate of 1 and 10 mg/L (nominal), respectively. Although the measured initial niobium test medium concentrations in the algae test are not considered to represent reliably the real exposure concentrations in the test medium (4.90 – 102 µg/L), they give an indication that the algae toxicity test was performed at niobium water concentrations above the solubility limit of niobium. Non-dissolved niobium has the potential to exert physical effects on test organisms unrelated to the intrinsic toxicity of the test item. Therefore, it is concluded that the observed effects are linked to mechanical effects and not to the intrinsic toxic properties of the test item. Furthermore, the determined bounded ErC10 (72 h) value of 16.1 mg/L (nominal) of niobium (CAS 7440-03-1) is more than tenfold above the chronic hazard classification criteria defined in Regulation (EC) No 1272/2008. Thus the available acute and chronic ecotoxicity data show that, niobium (CAS 7440-03-1) is not acutely and chronically toxic to freshwater organisms.

 

This conclusion will be re-evaluated, based on the results of the already ongoing long-term test with fish (OECD 210, CCH-D-2114517391-56-01/F).

 

All key studies were conducted according to appropriate guidelines and GLP conditions.