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Toxicity to aquatic algae and cyanobacteria

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In a 72 -h growth inhibition test, cultures of Pseudokirchneriella subcapitata (Strain No. 61.81 SAG) were exposed to tantalum pentachloride at nominal concentrations of 0 (control), 125, 250, 500, 1000 and 2000 mg/L under static conditions in accordance with the OECD Guideline 201 (March 2006) and under GLP. Results based on growth rate after 72 h were as follows: EL50: > 2000 mg/L; EL20: 464 mg/L (95 % C.l. 218 – 713 mg/L); EL10: 122 mg/L (95 % C.l. 19.0 – 247 mg/L); LOELR: 500 mg/L; NOELR: 250 mg/L. The values indicate effects at nominal loading rates. Due to methodological constraints, it was not possible to determine effect levels based on measured test item concentrations.

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In a 72 -h growth inhibition test, cultures of Pseudokirchneriella subcapitata (Strain No. 61.81 SAG) were exposed to tantalum pentachloride at nominal concentrations of 0 (control), 125, 250, 500, 1000 and 2000 mg/L under static conditions in accordance with the OECD Guideline 201 (March 2006) and under GLP. The % growth inhibition in the treated algal culture as compared to the control ranged from 10.0 % at a nominal concentration of 125 mg/L to 39.4 % at a nominal concentration of 2000 mg/L. Specific results based on growth rate after 72 h were as follows: EL50: > 2000 mg/L; EL20: 464 mg/L (95 % C.l. 218 – 713 mg/L); EL10: 122 mg/L (95 % C.l. 19.0 – 247 mg/L); LOELR: 500 mg/L; NOELR: 250 mg/L. The values indicate effects at nominal loading rates. Due to methodological constraints, it was not possible to determine effect levels based on measured test item concentrations. Measured concentrations were more than a factor of 1000 lower than in the respective nominal loading rates after pH adjustment. After pH adjustment the measured Ta5+ concentrations were low and showed high variability.

Measured concentrations were mostly below the limit of quantification (LOQ) in samples that were not chemically digested. Only at 0 h, measured concentrations were with 2.38 to 11.7 µg/L in the three highest loading rates above the LOQ. Samples taken at the end of the test (72 h) were analysed after being chemically digested to analyse the total (soluble plus insoluble) test item concentration. Here, values ranged from 2.97 to 14.4 µg/L, but no relation between measured concentration and the nominal loading rate could be observed. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. Therefore, no concentration-response relationship can be delineated.

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 growth inhibition effects may therefore rather predominantly refer to elevated NaCl concentrations, originated from neutralization, than released Ta5+ ions. Reported effects of sodium chloride concerning the freshwater alga P. subcapitata vary but inhibitory concentrations of 2.5 g/L, respectively 0.87 g/L have been determined (Geis et al., 2000 and Santos et al., 2007, in Heisterkamp, 2015). Due to a concentration of approximately 2.92 g/L NaCl, present at the highest loading rate of 2000 mg/L test substance, and the sensitivity of P. subcapitata to salinity, any hypothetical Ta5+ related effects cannot be distinguished from NaCl induced inhibition in the conducted test.This study is classified as acceptable and satisfies the guideline requirements for an algae growth inhibition toxicity study.