Niobium carbide

Short-term toxicity to aquatic invertebrates

Description of key information

No data on the acute toxicity of NbC to aquatic invertebrates are available. Thus, information on NbCl5 is used in a read-across approach.

The 48 h EL50 (nominal) is 1498 mg/L (95 %CI: 1286–1723 mg/L).  

Due to methodological difficulties, it was not possible to calculate effect concentrations based on measured concentrations. Hence, values are reported based on the nominal loading rates.

Observed effects on daphnids were predominantly related to elevated NaCl concentrations, originated from neutralization of the test solutions, than related to release of Nb5+ ions.

Additional information

Available data from niobium pentachloride are appropriate to be used for the read-across approach. Due to lower water solubility for niobium carbide compared to niobium pentachloride the resulting toxicity is also expected to be lower. Hence, the read across to the substance niobium pentachloride is sufficiently protective. The 48-h acute toxicity of niobium pentachloride to Daphnia magna was studied under semi-static conditions (OECD 202). Daphnids were exposed to a control containing no test substance and niobium pentachloride at nominal loading rates of 889, 1333, 2000, 3000 and 4500 mg/L for 48 h. Immobilization was observed daily. Due to highly variable Nb5+ concentrations in solution, effect concentrations were based on nominal loading rates.The 48-hour EL50 was 1498 mg/L. The 48-h NOELR based on immobilization was 889 mg/L and the LOELR was 1333 mg/L. This study is classified as acceptable and satisfies the guideline requirements for an acute toxicity study with freshwater invertebrates. However, it was not possible to determine effect levels based on measured effective test substance concentrations.

Measured values ranged from 1.6 to 729 µg/L in the nominal loading rates of 889 to 4500 mg/L

After pH adjustment the measured Nb5+ concentrations were low and showed high variability. Therefore, no concentration-response relationship could be established. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test concentrations. Observed immobilization effects may therefore rather predominantly refer to elevated NaCl concentrations, originated from neutralization, than released Nb5+ ions.Reported EC50 values for sodium chloride vary but may be as low as 874 mg/L (ECHA registry for sodium chloride). Due to a concentration of approximately 4.68 g/L NaCl, present at the highest loading rate of 4500 mg/L test substance, and the sensitivity of D.magna to salinity, any hypothetical Nb5+ related effects cannot be distinguished from NaCl induced inhibition in the conducted test.