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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14 November 2014 - 18 December 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
- Sampling method: Samples were taken from the control, the saturated solution (filtered) and the supersaturated solution (unfiltered) at the start of testing (freshly prepared test media) and at the end of testing (samples taken from additional replicates without daphnids, incubated under the same conditions as the test media with daphnids).
- Sample storage conditions before analysis: All samples were stored protected from light and at ambient temperature before shipment for analysis. Upon receival in the analytical laboratory, they were stored in a refrigerator below 10°C until analysis.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Due to the insolubility of the test item in test water, a saturated solution method of preparation was considered most appropriate.
- A supersaturated solution was prepared with dilution water one day prior to the exposure phase. 100 mg/L of the test item were weighed out and transferred with an appropriate amount of dilution water into a measuring flask. This dispersion was stirred at approximately 1100 rpm for 24 hours at room temperature.
- A saturated solution was obtained by filtering an aliquot of the supersaturated solution through a membrane filter (0.2 µm, RC, Macherey-Nagel) after completion of stirring.
- Both the supersaturated (unfiltered) and the saturated solution (filtered) were used in the test.
- The saturated solution was a clear solution. The supersaturated solution was slightly turbid at t=0h and after 24 or 48 h a white sediment of undissolved test item was observed in the test vessels.
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: Water flea (Daphnia magna)
- Strain/clone: Straus (clone 5)
- Source: in-house laboratory culture, origin: Institut für Wasser-, Boden- und Lufthygiene (WaBoLu)
- Age at study initiation (mean and range, SD): not first brood progeny, 2 to 24 hours old, juveniles were acclimatised at least 2 hours in dilution water
- Feeding during test: no

ACCLIMATION
- Method of breeding: Clone has been bred at Dr. U. Noack Laboratorien in Elendt M4 medium modified to a total hardness of 160 to 180 mg CaCO3/L in a temperature controlled incubator maintaining water temperature at 20 +/- 2°C. Daphnids were cultured in 2-3-L glass vessels with ca. 1.8 L culture medium.
- Lighting cycle: 16 h light and 8 h dark with a light intensity of max. 20 µE/m2/s
- Type and amount of food: ad libitum with a mix of unicellular green algae (e.g. Pseudokirchneriella subcapitata and Desmodesmus subspicatus) with an algae cell density of > 1E+06 cells/mL
- Feeding frequency: minimum 5 times per week
- Gravid adults were isolated the day before initiation of the test such that the young daphnids produced overnight were less than 24 h.
- Diet and diluent water are considered not to contain any contaminant that would affect the integrity or outcome of the study.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
262 mg CaCO3/L
Test temperature:
Water temperature was 21°C at the start of exposure. The temperature in the incubator was 22°C throughout the test.
pH:
New test media:
0 h = 7.99-8.20
Old test media:
48 h = 7.62-7.77
Dissolved oxygen:
t=0 h: 5.71-8.31 mg/L
t=48 h: 7.97-8.44 mg/L
Salinity:
not applicable
Conductivity:
681 µS/cm
Nominal and measured concentrations:
Nominal test concentrations: Control, 100% v/v saturated solution (filtered) with nominal loading rate 100 mg Yb2O3/L, 100% v/v supersaturated solution (unfiltered) with nominal loading rate 100 mg Yb2O3/L.
Measured concentrations at t=0h: < 0.001, 0.231, 34 mg Yb/L (i.e. < 0.001, 0.264, 39 mg Yb2O3/L)
Measured concentrations at t=48h: < 0.001, 0.231, 96 mg Yb/L (i.e. < 0.001, 0.263, 110 mg Yb2O3/L)
Geometric Mean Measured Test Concentration in the filtered saturated solution of Yb2O3 (mg/L) = 0.264 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 50-mL glass beakers filled with 20 mL test solution
- Type (delete if not applicable): covered with glass plates to reduce the loss of water by evaporation and to avoid the entry of dust into the solutions
- Aeration: The test water was aerated prior to the start of the study. No aeration during the study.
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4 (100% v/v filtered saturated test solution), 4 (100% v/v unfiltered supersaturated test solution)
- No. of vessels per control (replicates): 4

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Reconstituted water (ISO medium), 294 mg/L CaCl2.2H2O, 123 mg/L MgSO4.7H2O, 64.8 mg/L NaHCO3, 5.76 mg/L KCl.
- Culture medium different from test medium: yes (culture medium = Elendt M4, modified to a total hardness of 160 to 180 mg CaCO3/L)
- Intervals of water quality measurement: At t=0h, pH, dissolved oxygen, temperature, conductivity and total hardness of the dilution water were measured. Incubator temperature was recorded throughout the test. Dissolved oxygen and pH were recorded at the start and termination of the test.

OTHER TEST CONDITIONS
- Adjustment of pH: not reported
- Photoperiod: 16 h light and 8 h dark
- Light intensity: diffuse light at an intensity of max. 20 µE/m2/s

TEST CONCENTRATIONS
- Control and 100% v/v saturated solution with nominal loading rate of 100 mg Yb2O3/L (filtered) and 100% v/v supersaturated solution (same solution but not filtered)
- Results used to determine the conditions for the definitive study: no, no further study performed

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): immobilisation, after 24 and 48 h (an animal was considered to be immobile if it was not able to swim in the water phase within 15 seconds after gentle agitation of the test vessel)
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % v/v of a saturated solution with a nominal loading rate of 100 mg Yb2O3/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
No immobilisation was observed in any of the test solutions.
The 48-h EC50 was therefore > 100% v/v of a saturated solution with a nominal loading rate of 100 mg Yb2O3/L.
The mean measured dissolved Yb2O3 concentration in the 100% v/v saturated solution was 0.264 mg/L.
Even in a supersaturated solution with a nominal loading rate of 100 mg Yb2O3/L (unfiltered, measured Yb2O3 concentration 39 and 110 mg/L at t=0h and t=48h, respectively), which contains dissolved and undissolved test item, no effects were observed on the exposed daphnids.
No sub-lethal effects were reported.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- EC50/LC50: 24-hour EC50: 1.57 mg/L (95% CI 1.53 - 1.60 mg/L)
- The results from the positive control with potassium dichromate were within the normal range for this reference item.
Reported statistics and error estimates:
No statistics applied.
Validity criteria fulfilled:
yes
Conclusions:
The acute toxicity of diytterbium trioxide to Daphnia magna was investigated in accordance with OECD guideline 202 and conform GLP requirements. Daphnids were exposed to a saturated (filtered) and supersaturated (unfiltered) solution, both with a nominal loading rate of 100 mg/L of the test item. No adverse effects were observed in any of the treatments. The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate of 100 mg Yb2O3/L. The mean measured dissolved Yb concentration in the (filtered) saturated solution was 0.231 mg/L (corresponding to 0.264 mg Yb2O3/L).

Description of key information

The acute toxicity of ytterbium oxide to Daphnia magna was investigated in accordance with OECD guideline 202 and conform GLP requirements (Noack, 2014; Klimisch 1). Daphnids were exposed to a saturated solution with a nominal loading rate of 100 mg/L of the test item. No adverse effects were observed up to and including at the highest concentration tested. The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate of 100 mg Yb2O3/L. This study was assigned key status for endpoint coverage, and based on its results it can be concluded that ytterbium oxide is not harmful to aquatic invertebrates.

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