Tantalum

Endpoint summary

Description of key information

Data describing the aquatic toxicity of Ta metal are not available. Due to the high water insolubility of the substance (0.043 µg/L according to OECD 29 (loading 1 mg/L after 28 days), toxicity to aquatic organisms is not expected.

This expectation is substantiated by data available for the read-across source TaCl₅ (for justification please refer to IUCLID section 13).

Additional information

Data describing the acute aquatic toxicity of TaCl₅ 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 TaCl₅ 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 TaCl₅ 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 TaCl₅ to Daphnia magna was studied under semi-static conditions at nominal concentrations of up to 3000 mg/L. The 48-hour EL50 was 3086 mg/L. The 48-h NOELR based on immobilization was 2000 mg/L and the LOELR was 3000 mg/L.

The toxicity of TaCl₅ 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: > 2000 mg/L;

-         LOELR: 500 mg/L;

-         NOELR: 250 mg/L.

Please note that in aquatic toxicity tests conducted with TaCl₅ it was not possible to determine effect levels based on measured effective test substance concentrations. Addition of TaCl₅ 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 Ta⁵⁺ 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 significant 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 Ta⁵⁺ 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 NaCl concentrations of approximately 2.92 g/L present at the highest loading rate of 2000 mg/L test substance in the OECD 201 test, and 2.34 g/L present at the highest loading rate of 3000 mg/L in the OECD 202 test, and the sensitivity of P. subcapitata and D.magna to salinity, any hypothetical Ta⁵⁺ related effects cannot be distinguished from NaCl induced growth inhibition/immobility in these tests. Therefore, effects can be rather attributed to NaCl than to the release of Ta⁵⁺ ions.

This information is used in a read-across approach in the assessment of the substance to be registered.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.