Niobium carbide

Short-term toxicity to fish

Description of key information

The 96-h LC50 of NbC was > 100 mg/L (nominal concentration), and the 96-h LC0 was ≥ 100 mg/L.

These data are further supported by results for NbCl5: a OECD 203 limit test applying a nominal loading rate of 100 mg/L, corresponding to a mean measured concentration of 11.88 µg/L  of the test substance, did not lead to mortality in fish within 96h. No further study was carried out.

Additional information

In a 96-h acute toxicity study according to OECD guideline 203, Zebra fish (Danio rerio) were exposed to niobium carbide (NbC) at nominal concentrations of 0 and 100 mg/L under semi-static conditions (limit test).

Five fish were used per test concentration. The solutions were prepared as follows: Proper weights of the test substance (100.02-100.09 g) were added into the jar filled with 10 L water. Before the fish were exposed, the test solutions were stirred. The test duration was 96 hours. At intervals of 24 hours the fish were transferred to different jars containing freshly prepared solutions. Dissolved oxygen and pH were measured at the beginning of the test and at 24-hour intervals during the 96-hour exposure period in both control and test vessels. The fish were observed for toxic signs and deaths.

During the 96-hours exposure period, neither mortality nor toxic symptoms were found in the control group or treatment group. The 96-h LC50 of NbC was > 100 mg/L (nominal concentration, highest tested concentration), and the 96-h LC0 was ≥ 100 mg/L.

These results are further supported by data on niobium pentachloride which are considered appropriate for read-across. Due to lower water solubility for niobium carbide compared to niobium pentachloride the potential toxicity is also expected to be lower. Hence read across to niobium pentachloride is sufficiently protective. In the course of a 96-h limit test according to OECD guideline 203 (July 1992) under GLP, Danio rerio was exposed to niobium pentachloride at nominal loading rates of 0 (control) and 100 mg/L under semi-static conditions. No mortality was observed. Therefore, no further testing was carried out. The analytically measured dissolved niobium concentration showed high variability and ranged from 101 to 2.2 µg/L. This was mainly due to the fact that small changes in pH caused significant changes in the soluble fraction of niobium. Additionally, niobium pentachloride precipitated after adjusting the pH. Furthermore, agglomeration reactions and effects of adsorption to vials and analytical instruments contributed to the variable measured dissolved niobium concentrations. Therefore, effect levels are given as nominal loading rates and mean measured concentrations of niobium. The chemical analysis revealed a geometric mean of 11.88 µg/L (measured) of the test substance in the test media. Hence, the 96-h LL50 (nominal) is > 100 mg/L, and the LC50 (geometric mean of measured concentrations) is > 11.88 µg/L.