Digadolinium trioxide

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:

17 October 2016 to 31 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 from the control and each test group at 0 and 48 h. Samples taken at 0 h were taken before addition of the test organisms. Samples taken after 48 h from the control and the 100% v/v saturated solution were taken from pooled replicates. Samples were taken in triplicate.
- Sample storage conditions before analysis: The samples were prepared on the day of receipt. One sample of the triplicate samples was refrigerated at 5°C prior to analysis. The other two samples were stored in the freezer for further analysis if necessary.

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 (500 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 adjusted to approximately pH 7.7-7.8 and a sample taken for chemical analysis after filtration through a 0.2 µm Gelman Acrocap filter (initial 100 mL discarded).
- The results of the stirring experiment indicated that a 24-h stirring period is sufficient to ensure solution equilibrium.
- The actual test solutions were 1.0, 10 and 100% v/v saturated solutions. The 100% v/v saturated solution was prepared as described for the stirring experiment (24 h stirring, 0.2-µm filtered). The 1.0 and 10% v/v saturated solutions were then prepared through serial dilution of the 100% v/v saturated solution.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Scientific name: Daphnia magna
- Strain: Straus
- Common name: Water flea
- Source: in-house laboratory cultures
- Age at study initiation (mean and range, SD): < 24 hours (not a first brood progeny)
- Feeding during test: no

ACCLIMATION
- Method of breeding: Clone has been bred at Harlan Laboratories in Elendt M7 medium in a temperature controlled room maintaining water temperature at 18-22°C.
- Lighting cycle: 16 h light and 8 h dark with 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:

t=0h: 7.5-7.6
t=48h: 7.6-7.8

Dissolved oxygen:

t=0h: 7.9-8.5 mg/L
t=48h: 8.7-8.8 mg/L

Salinity:

not applicable

Nominal and measured concentrations:

Analytically determined concentrations in samples taken during the combined range finder limit test (control, 1.0, 10, 100% v/v saturated solution) were as follows:
0 h: 48 h: 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 gadolinium.

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: prior to the start of the study until oxygen saturation was reached but not 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 435 and 523 Lux.

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

TEST CONCENTRATIONS
- 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.
After 48 h, only 1 daphnid in one replicate in the 100% v/v saturated solution was immobilised.
The mean measured dissolved Gd concentration in the 100% v/v saturated solution was 0.30 mg/L (equivalent to 0.35 mg/L Gd2O3). Note that this dissolved concentration may have been overestimated because the laboratory acidified the samples before filtration, consequently the measured Gd concentration might include some redissolved precipitated Gd.
Sub-lethal effects:
- 1.0 and 10% v/v saturated solution: 1 daphnid covered in debris and 1 daphnid trapped at the surface, respectively, at 24 h (not so at 48 h)
- 100% v/v saturated solution: 2 daphnids in one replicate trapped at the surface at 24 h, 5 daphnids over 2 replicates trapped at the surface at 48 h
Inspection of the data shows no obvious cause for these sublethal effects. Visual inspection of the test media showed no undissolved test item which could have caused these effects. This was considered not to have had an impact on the outcome of the test.

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

Reported statistics and error estimates:

No statistics applied.

Validity criteria fulfilled:

yes

Conclusions:

The acute toxicity of gadolinium oxide to Daphnia magna was investigated in accordance with OECD guideline 202 and GLP. A combined range finder limit test was performed, in which no significant adverse effects were observed up to and including at the highest concentration tested (i.e., a 100% v/v saturated solution with nominal loading rate 100 mg/L). The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate 100 mg/L. The mean measured dissolved Gd concentration in this saturated solution was 0.30 mg Gd/L (corresponding to 0.35 mg/L Gd2O3). Note that this concentration may have been overestimated because acidification was by accident done before filtration, consequently, the measurement may include some redissolved precipitated Gd.

Description of key information

The acute toxicity of gadolinium oxide to Daphnia magna was investigated in accordance with OECD guideline 202 and GLP (Ablitt, 2017, Klimisch 1). A combined range finder limit test was performed, in which no significant adverse effects were observed up to and including at the highest concentration tested (i.e., a 100% v/v saturated solution with nominal loading rate 100 mg/L). The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate 100 mg/L. The mean measured dissolved Gd concentration in this saturated solution was 0.30 mg Gd/L (corresponding to 0.35 mg/L Gd2O3).