Niobium pentachloride

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

no hazard identified

Marine water

Hazard assessment conclusion:

no hazard identified

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

no hazard identified

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Data describing the acute aquatic toxicity of niobium pentachloride to aquatic organisms are available for fish, invertebrates, algae and microorganisms.

In a study conducted according to OECD guideline 203 zebra fish (Danio rerio) were exposed to niobium pentachloride at nominal concentrations of 0 and 100 mg/L under semi-static conditions (limit test). No mortality could be observed. Due to methodological constraints, effect levels are provided as nominal loading rates. Hence, the 96-h LL₅₀(nominal) is > 100 mg/L.

An activated sludge respiration inhibition test with niobium pentachloride according to OECD 209 resulted in an EL50 > 1000 mg/L and an NOEL ≥ 1000 mg/L.

In a study in accordance with OECD guideline 202 the 48-h acute toxicity of niobium pentachloride to Daphnia magna was studied at nominal concentrations of up to 4500 mg/L. 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.

The toxicity of niobium pentachloride to cultures of Pseudokirchneriella subcapitata after 72-h (growth inhibition test) was investigated in accordance with OECD Guideline 201 at nominal concentrations of up to 2000 mg/L. Results based on growth rate after 72 h were as follows:

-         EL50 = 533 mg/L;

-         LOELR: ≤ 125 mg/L;

-         NOELR: < 125 mg/L.

Please note that in aquatic toxicity tests conducted with niobium pentachloride it was not possible to determine effect levels based on measured effective test substance concentrations. Addition of NbCl₅ to water leads to strong temperature rise and a strong shift in pH value (<1). Thus, pH values had to be adjusted in all tests by the addition of NaOH. 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 item varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test item concentrations. Observed effects in daphnia and algae at very high test substance concentrations may therefore rather predominantly refer to elevated sodium chloride (NaCl) concentrations, originated from neutralization, than released Nb5+ions.

Reported EC50 values in daphnia and inhibitory concentrations in algae for NaCl vary but may be as low as EC50 = 874 mg/L (ECHA registry for sodium chloride) and IC50 = 0.87-2.5 g/L (IC = inhibition of fluorescence; Santos et al., 2007, in Heisterkamp, 2015; Geis et al., 2000), respectively. Due to concentrations of approximately 4.68 g/L NaCl and 2.92 g/L NaCl present at the highest loading rate in OECD test 202 (daphnia; 4500 mg/L test substance) and OECD test 201 (algae; 2000 mg/L test substance), respectively, and the sensitivity of D. magna and the freshwater alga P. subcapitata to salinity, any hypothetical Nb⁵⁺ related effects cannot be distinguished from NaCl induced inhibition. However, effects can be rather attributed to NaCl than to the release of Nb⁵⁺ions.

Conclusion on classification

Niobium pentachloride hydrolyses immediately in contact with water, forming an extremely acid solution. Upon neutralisation bulk of the dissolved niobium precipitates as niobium hydroxide and only a few micrograms per litre remain in solution. Generally, no adverse effects attributable to dissolved niobium could be identified in aquatic toxicity tests, irrespective of the test species and trophic level. Although some immobility in Daphnia and growth inhibition in algae (yet no mortality in fish) was observed, there was no consistent concentration-response relationship; moreover, these adverse effects were indistinguishable from high salinity effects resulting from neutralisation. In conclusion, no adverse effects on aquatic organisms could be attributed to niobium at maximum water solubility of niobium pentachloride after neutralisation. Therefore, no hazard to aquatic organisms is identified. Niobium pentachloride hence does not require classification for environmental hazards.