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Long-term toxicity to fish

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Description of key information

In an early life stage toxicity study (FELS, OECD guideline 210) in Zebrafish (Danio rerio) with test item, no significant lethal or sub-lethal effects were observed.
The calculated endpoints (35 days LOEC and NOEC) obtained were > 43 mg test item/L and 43.0 mg test item/L respectively. Based on these data, the calculated NOEC (35 d) for cesium hydroxide anhydrous was 38.38 mg/L and the LOEC (35 d) was greater than 38.38 mg/L

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater fish:
43 mg/L

Additional information

The purpose of this study was to evaluate the chronic toxicity of the test item to early life stages (embryo, larvae and juveniles) of fish. For this purpose, eggs were exposed in a semi static test to aqueous test media containing the test item for 35 days at a range of concentrations under defined conditions. Lethal and sub-lethal effects were assessed (as much as possible) and compared with control values to determine the lowest observed effect concentration (LOEC) and hence the no observed effect concentration (NOEC).

The test was considered to be valid because assay acceptance criteria were fulfilled. The following nominal test concentrations were selected for the early life stage toxicity test according to the Sponsor’s request: 8.5 mg/L, 12.8 mg/L, 19.2 mg/L, 28.7 mg/L and 43.0 mg/L.

Test item concentrations were analyzed in the test solutions by flame photometry. Test item concentration in the test solutions was determined at 6 renewal periods. Mean measured concentrations were calculated for each treatment concentrations. The overall measured concentrations were within the range of ± 20 % of the mean measured values meeting the validity criteria. Since the mean measured concentrations of the Cesiumhydroxidmonohydrat 99,95 varied between 89 % and 120 % of the nominal concentration when determined at the 6 renewal periods, all biological results could be relied and reported on the basis of the nominal concentrations. Seventy six to seventy eight eggs were tested per test concentration and control in two parallels per treatment group and control. Based on microscopic observation embryos were at approximately 2 to 128 cell stages at start of treatment.

Environmental parameters (water temperature, pH, LDO) were monitored during the test. There were no deviations from the defined ranges. Total hardness of the test solutions were measured at the beginning and end of the test.

Animals were fed from elimination of the yolk sac (free-feeding stage) to the end of the test with appropriate type and amount of food ad libitum, and thus starvation could not have any effect on the results obtained.

Cumulative mortality (observed from Day 0 to the end of the test on Day 35), mortality observed at embryonic/eleutheroembryonic (i.e. early larval) stage (from Day 0 to the end of hatching on Day 5) and mortality observed at larval/juvenile stage (from Day 6 to the end of the test on Day 35) were statistically evaluated. Statistical significance (p < 0.05) was observed for mortality during embryonic/eleutheroembryonic stage (Day 0 - 5) at concentration of 12.8 mg/L (increased mortality) and larval/juvenile stage (Day 6 – 35) at concentration of 28.7 mg/L (decreased mortality) compared to the control. The observed effects were considered not biologically relevant since the effects were not dose related. Based on this it is considered that the test item do not influence the survival of the test organism (either at embryonic or at larval/juvenile stage).

Number of larvae hatched daily was statistically evaluated on Day 3, Day 4 and Day 5. Statistically significant effect on hatching of the larvae was observed at all concentrations tested on Day 3 (p < 0.05 at concentration of 12.8 mg/L, and p < 0.01 t the other test concentrations), however the effect was considered to be not adverse and not biologically significant: number of hatched animals were statistically significantly increased at all test chambers compared to the control on Day 3 but based on observations on Day 3 (weak chorionic membrane of the embryos which was observed in the control test chambers) it was considered that number of larvae hatched equalized soon after the observation time. No significant difference in numbers of hatched animals was observed on Day 4 or Day 5.

At the end of the test, group body weights were measured. No significant difference compared to the control was observed.

Body length was measured for each animal individually and the data were statistically evaluated. No statistically significant difference compared to the control was observed.

Other sub-lethal effects were monitored to limited extent: numbers of embryos/larvae/juveniles with deformities and/or abnormal behaviour were recorded when observed. No obvious test item related changes in the appearance or behaviour of the animals could be observed.

Under the conditions of this early life stage toxicity study, the test item cesium hydroxide monohydrate had no significant lethal or sub-lethal effects on early life stages of Zebrafish (Danio rerio). The calculated endpoints (35 days LOEC and NOEC) were the following in this test: The 35 d LOEC> 43.0 mg test item/L The 35 d NOEC = 43.0 mg test item/L.

Based on these data, the calculated NOEC (35 d) for cesium hydroxide anhydrous was 38.38 mg/L and the LOEC (35 d) was greater than 38.38 mg/L