Dipraseodymium tricarbonate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The NOELR, the LOELR and EL50 values for the analogous test material Praseodymium III, IV oxide, based on the growth rate, were 22 mg/L, 48 mg/L and > 100 mg/L, respectively. It is important to note that a significant phosphate depletion was observed at the two highest tested concentrations (saturated solution: loading rate = 100 mg/L, dilution 1:2.1: loading rate = 48 mg/L), probably due to a complexation process with the test item. As a consequence, the reduction of growth here observed, and leading to the LOELR and NOELR above cited, was probably caused by an indirect effect of phosphate lack, rather than a toxic effect of praseodymium oxide. By analogy, it can be thus anticipated that dipraseodymium tricarbonate should not exert any toxicity to algae. 

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

22 mg/L

Additional information

The key study was conducted on the analogous material Praseodymium III, IV oxide in line with GLP and the standardised guidelines OECD 201 and EU Method C.3. It was assigned a reliability score of 2 in accordance with the criteria detailed by Klimisch (1997).

In a 72 hour toxicity study, cultures of the green algal species Scenedesmus subspicatus were exposed to the test material at the loading rates of 4.8, 10, 22, 48 and 100 mg/L under static conditions.

The NOELR, the LOELR and EL50 values based on the growth rate were 22 mg/L, 48 mg/L and > 100 mg/L, respectively.

Additional remark:

The analysis of the impact of the loading rate on the phosphate amount in the test media showed that the saturated solution had a statistically significant impact on the phosphate concentration in the test medium at all time points (except at 72 hours, where the loss of phosphate over time had a stronger impact on the phosphate concentration than the test item). The dilution 1:2.1 (loading rate of 48 mg/L) had a statistically significant impact on the phosphate concentration at 0 and 48 hours. At test start, this impact was significant even at the dilution1:10 (loading rate of 10 mg/L) and above. The depletion of phosphate in the test medium during the test might have been the reason for the inhibition of algal growth determined at these test concentrations. As a result, growth inhibition due to a secondary effect (i.e. the complexation of the essential algal nutrient phosphate by the test item) cannot be excluded.