Caesium iodide

Toxicity to aquatic algae and cyanobacteria

Description of key information

In the 72-h algal growth inhibition test on Pseudokirchneriella subcapitata with cesium iodide the observed endpoints based on the growth rate were the following: 72-h EC50 > 100 mg/L (635.75 mg/L); NOEC = 6.25 mg/L; LOEC = 12.5 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

635.75 mg/L

EC10 or NOEC for freshwater algae:

6.25 mg/L

Additional information

The purpose of this study was to determine the effect of the test item cesium iodide on the growth of a unicellular green algal species Pseudokirchneriella subcapitata (formerly: Selenastrum capricornutum). Exponentially growing cultures of Pseudokirchneriella subcapitata were exposed to various concentrations of the test item over several generations under defined conditions. The algal growth in relation to a control culture was determined over a fixed test period of 72 hours and thus, over several algal generations. The test method of application and the test species Pseudokirchneriella subcapitata are recommended by the test guidelines In the 72-h algal growth inhibition test on Pseudokirchneriella subcapitata with cesium iodide, the 72-h EC50 based on biomass was determined to be 47.94 mg/L, based on the growth rate higher than 100 mg/L (635.75 mg/L) and based on the yield the 72-h EC50 was 59.40 mg/L. The nominal test item concentrations were 3.125; 6.25; 12.5; 25; 50; and 100 mg test item/L. The test item concentration of the test solutions was measured by flame photometer method at the start and at the end of the test. At the start and at the end of the test the two highest (nominal) concentrations, 50 and 100 mg/L were above the quantification limit (the limit of quantification of the analytical method was 29 mg test item/L) of the analytical method, and these measured test item concentrations were 100-105 % of the nominal at the start and 95 -99 % of the nominal at the end of the test. The concentrations of 3.125;6.25; 12.5 and 25 mg/L were out of the measurable range.There is evidence that the concentrations of the tested substance (3.125-100 mg/L) were satisfactorily maintained within ± 20 % of the nominal concentrations throughout the test. The not analysed concentration levels were considered as being within the ± 20 % of the nominal range; therefore the analysis of the results was based on the nominal concentration values. All reported biological results are related to the nominal concentrations of the test item. The NOEC was determined to be 6.25 mg/L based on the growth rate and yield, while it was 3.125 mg/L based on biomass. The LOEC was calculated to be 12.5 mg/L based on the growth rate and yield, while it was 6.25 mg/L based on biomass (all calculations were based on nominal concentrations). Therefore, the overall NOEC was determined to be 3.125 mg/L, while the overall LOEC was calculated to be 6.25 mg test item/L.