Didysprosium trioxide

Short-term toxicity to aquatic invertebrates

Administrative data

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10 July 2017 - 17 August 2017

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Didysprosium trioxide

EC Number:

215-164-0

EC Name:

Didysprosium trioxide

Cas Number:

1308-87-8

Molecular formula:

Dy2O3

IUPAC Name:

dysprosium(3+); oxygen(2-)

Test material form:

solid: particulate/powder

Details on test material:

Name of the test material (as cited in the report): didysprosium trioxide
Physical state: solid
Appearance: (pale) yellow powder
Further information on test item confidential.

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Samples were taken from the control and each test group from the freshly prepared bulk test preparation at 0 hours and from the old or expired pooled replicates at 48 hours for quantitative analysis. Samples were taken in triplicate. Test samples were filtered through 0.2 μm Gelman Acrocap filters (discarding first 10 mL).
- Sample storage conditions before analysis: One set of samples was analysed on the day of receipt and the remaining two sets stored frozen for further analysis if necessary.

Test solutions

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 6-9 (if necessary) 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 96-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 (96 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

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): first instar juveniles < 24 hours old
- Feeding during test: no

ACCLIMATION
- Method of breeding: Clone has been bred at Envigo 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: a mixture of algal suspension (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.

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Test conditions

Hardness:

250 mg CaCO3/L

Test temperature:

22 °C

pH:

New test media:
0 h = 7.6-7.8
Old test media:
48 h = 7.6-7.7

Dissolved oxygen:

t=0 h: 8.5-8.7 mg/L
t=48 h: 8.4-8.5 mg/L

Salinity:

not applicable

Nominal and measured concentrations:

Nominal test concentrations as % v/v saturated solution = control, 1.0, 10 and 100.
Geometric Mean Measured Test Concentration as dysprosium (µg/L) = 0.67, 3.5 and 69
Geometric Mean Measured Test Concentration as didysprosium trioxide (test item) (µg/L) = 0.78, 4.0 and 79
0 h: < LOQ, 0.952, 11.5, 207 µg Dy/L (< LOQ, 1.10, 13.2, 239 µg Dy2O3/L)
48 h: < LOQ, 0.477, 1.05, 22.8 µg Dy/L (< LOQ, 0.549, 1.21, 26.2 µg Dy2O3/L)

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 test solution), 2 (1.0 and 10% v/v saturated 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, 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: Light intensity during the light period was approximately between 388 and 460 Lux.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10 (spacing factor for serial dilutions)
- Range finding study: yes (the study consisted of a combined range finder limit test)
- Results used to determine the conditions for the definitive study: no, no further study performed

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Results and discussion

Effect concentrations

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 100 other: % v/v of a saturated solution with nominal loading rate 100 mg Dy2O3/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 nominal loading rate 100 mg Dy2O3/L.
The mean measured dissolved Dy concentration in the 100% v/v saturated solution was 69 µg/L (equivalent to 79 µg Dy2O3).
Sub-lethal effects:
- 1.0 % v/v saturated solution: 1 daphnid trapped at the surface at 24 h (not so at 48 h)
- 100% v/v saturated solution: 2 daphnids trapped at the surface at 24 h and 48 h

Results with reference substance (positive control):

- Results with reference substance valid? yes
- EC50/LC50: 48-hour EC50: 0.64 mg/L (24-hour EC50: 0.83 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.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The acute toxicity of dysprosium oxide to Daphnia magna was investigated in accordance with OECD guideline 202 and conform GLP requirements. A combined range finder limit test was performed, in which no 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 Dy2O3/L). The 48-h EC50 was therefore > 100% v/v of a saturated solution with nominal loading rate of 100 mg Dy2O3/L. The mean measured dissolved Dy concentration in this saturated solution was 69 µg Dy/L (corresponding to 79 µg Dy2O3/L). The substance can be concluded not to be harmful to aquatic invertebrates in its solubility range.