Dilutetium oxide silicate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 November 2016 - 18 May 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Samples were taken in triplicate. Samples were taken at 0 hours from the control and each test group from the freshly prepared bulk test preparation. Samples taken after 48 hours from the control and the 100% v/v saturated solution were taken from pooled replicates. Additionally, samples were taken after 48 h from the extra samples run alongside the test for the 1.0 and 10% v/v saturated solution test groups.
- Sample storage conditions before analysis: All samples were stored frozen prior to 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.
- Stirring experiment: A nominal amount of test item (525 mg) was dispersed in 5 L of test water with the aid of vigorous magnetic stirring for 96 hours. After 3, 24 and 96 hours, the pH of the media was checked and a sample taken for chemical analysis after filtration through a 0.2 μm Gelman Acrocap filter (initial 100 mL discarded). The results obtained from the stirring experiment indicated that a 96-h stirring period was optimal to ensure solution equilibrium.
- Combined range-finder limit test: A nominal amount of test item (525 mg) was dispersed in 5 liters of test water with the aid of vigorous magnetic stirring for 96 hours. After 96 hours the stirring was stopped and any undissolved test item was removed by filtration through a 0.2 μm Gelman Acrocap filter (first approximate 100 mL discarded in order to pre-condition the filter) to give a 100% v/v saturated solution. A series of dilutions was made from this saturated solution to give further test concentrations of 1.0 and 10% v/v saturated solution. Each prepared concentration was inverted several times to ensure adequate mixing and homogeneity.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea (Daphnia magna)
- Strain/clone: Straus
- Source: in-house laboratory culture
- Age at study initiation (mean and range, SD): < 24 hours
- Feeding during test: no

ACCLIMATION
- Method of breeding: Clone has been bred at the laboratory in Elendt M7 medium in a temperature controlled room maintaining water temperature at 18-22°C.
- Lighting cycle: 16 h light + 8 h dark, 20-min dawn and dusk transition periods
- Type and amount of food: green algae Desmodesmus subspicatus and Tetramin flake food suspension
- Feeding frequency: daily
- 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:

250 mg CaCO3/L

Test temperature:

21-22 °C

pH:

New test media:
0 h = 7.6-7.7
Old test media:
48 h = 7.6-7.9

Dissolved oxygen:

8.6-9.0 mg/L

Salinity:

not applicable

Nominal and measured concentrations:

Nominal test concentrations = control, 1.0, 10 and 100% v/v saturated solution (loading rate 100 mg/L as anhydrous lutetium oxide silicate)
Lu concentrations were only analysed in the control and in the 100% v/v saturated solution.
0 h: < LOQ, 0.492 mg Lu/L (i.e. < LOQ, 0.659 mg/L as anhydrous lutetium oxide silicate)
48 h: < LOQ, 0.431 mg Lu/L (i.e. < LOQ, 0.577 mg/L as anhydrous lutetium oxide silicate)
Note that acidification of the samples was done before filtration, implying that the measured concentrations represent not true dissolved concentrations, and might have included some redissolved precipitated lutetium.

Details on test conditions:

TEST SYSTEM
- Test vessel: 150-mL glass beakers filled with 100 mL of test medium
- 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 saturated solution), 1 (1.0 and 10% v/v saturated 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, 65 mg/L NaHCO3, 5.8 mg/L KCl.
- Culture medium different from test medium: yes (culture medium Elendt M7)
- Intervals of water quality measurement: water temperature was recorded daily, dissolved oxygen and pH were recorded at the start and termination of the test

OTHER TEST CONDITIONS
- Adjustment of pH: The reconstituted water had a pH of 7.8 ± 0.2 adjusted (if necessary) with NaOH or HCl.
- Photoperiod: A 16-hour light to 8-hour dark cycle with a 20-minute transition period (simulation of dusk and dawn)
- Light intensity: between 693 and 714 Lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): immobilisation, daily

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10 (combined range finder-limit test)
- Range finding study: yes (the study consisted of a combined range finder-limit test)
- Test concentrations: control, 1.0, 10, 100% v/v of a saturated solution with nominal loading rate of 100 mg/L
- Results used to determine the conditions for the definitive study: no, no further study performed

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 nominal loading rate of 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

No significant immobilisation was observed in any of the test solutions.
The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate 100 mg/L (as anhydrous lutetium oxide silicate).
The measured dissolved Lu concentrations in the 100% v/v saturated solution were 0.49 mg Lu/L (equivalent to 0.66 mg/L as anhydrous lutetium oxide silicate) and 0.43 mg Lu/L (equivalent to 0.58 mg/L as anhydrous lutetium oxide silicate) at the start and the end of testing, respectively. Note that these dissolved concentrations may have been overestimated because the laboratory acidified the samples before filtration, consequently the measured Lu concentrations might include some redissolved precipitated Lu.

Sub-lethal effects were observed in the 10 and 100% v/v saturated solution test concentrations. In each of these test groups, 1 daphnid was trapped at the water surface during the study.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- 24-h EC50: 0.83 mg/L
- 48-h EC50: 0.64 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 dilutetium oxide silicate to Daphnia magna was investigated in accordance with OECD guideline 202 and conform to GLP requirements. A combined range finder-limit test was performed, in which no adverse effects were observed up to and including the highest concentration tested (i.e., a 100% v/v saturated solution with nominal loading rate of 100 mg/L, as anhydrous lutetium oxide silicate). The 48-h EC50 was therefore > 100% v/v of a saturated solution with a nominal loading rate of 100 mg/L. The measured dissolved Lu concentrations in this saturated solution were 0.49 mg Lu/L (corresponding to 0.66 mg/L anhydrous lutetium oxide silicate) and 0.43 mg Lu/L (corresponding to 0.58 mg/L anhydrous lutetium oxide silicate) at the start and the end of testing, respectively. Note that these concentrations may have been overestimated because acidification was by accident done before filtration, consequently, the measurements may include some redissolved precipitated Lu.

Description of key information

The acute toxicity of dilutetium oxide silicate to Daphnia magna was investigated in accordance with OECD guideline 202 and conform to GLP requirements (Hallett, 2017; Klimisch 1). A combined range finder-limit test was performed, in which no adverse effects were observed up to and including the highest concentration tested (i.e., a 100% v/v saturated solution with nominal loading rate of 100 mg/L, as anhydrous lutetium oxide silicate). The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate of 100 mg/L. This study was assigned key status for endpoint coverage, and based on its results it can be concluded that lutetium oxide silicate is not harmful to aquatic invertebrates at its solubility limit into water.