Dysprosium trinitrate

Long-term toxicity to aquatic invertebrates

Administrative data

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well performed study but considered reliable with restrictions because the reported effect concentrations were calculated based on initial dissolved Dy concentrations whereas they should have been calculated based on mean measured dissolved Dy concentrations. Dissolved Dy was substantially less in old test media compared to new test media, however, a dissolved Dy concentration series was clear both in new and old test media. Therefore, the key long-term NOEC for endpoint coverage was calculated based on the reported dissolved Dy concentrations in old and new test media.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well performed guideline study, however, the original source of the daphnid culture is a lake in the Sudbury region, but it is not reported whether or not this lake is affected by the historical metal contamination in that area, which may affect the sensitivity of the test organisms. In addition, the effect concentrations were expressed based on initial measured dissolved Dy concentrations, whereas a clear reduction of dissolved Dy was observed throughout the tests. Therefore, the study is considered reliable with restrictions but its results should only be used as supporting information.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: Environment Canada standard aquatic biological test method for Daphnia spp. (EPS1/RM/11; EC, 1990)

GLP compliance:

not specified

Analytical monitoring:

yes

Details on sampling:

- Samples were taken 1 day prior to the start of the test (immediately following test solution preparation) and 24 h after the end of the test.
- Dy and inorganic cation concentrations (Ca2+, Mg2+, Na+) were measured in the samples.
- A total volume of 10 mL (5 mL from each replicate) was sampled after stirring the solutions.
- Total and dissolved Dy was measured. For dissolved Dy, filtration through 0.45 µm filter (Tuffryn).
- Samples were preserved with 200 µL of HNO3 (Trace Metal Grade, 70%, approx. 2% acid).
- Samples were stored at room temperature.

Vehicle:

no

Details on test solutions:

- A stock solution of 32 mg Dy/L was prepared from 1000 mg/L Dy atomic absorption standard stabilised in 7% HNO3, and moderately soft medium, and pH was adjusted to 7.3 using KOH.
- Test solutions of 0, 500, 1000, 2000, 4000 and 8000 µg Dy/L were prepared by mixing appropriate ratios of the Dy stock solution and moderately soft medium.

Test organisms (species):

Daphnia pulex

Details on test organisms:

TEST ORGANISM
- Scientific name: Daphnia pulex
- Source: Daphnia pulex culture maintained in the laboratory and originating from McFarlane Lake, Sudbury, ON (no data on contamination history of this lake reported).
- Culture medium: moderately soft medium (Borgmann, 1996), pH adjusted to 7.3 +/- 0.1 using HNO3 or KOH
- Culture conditions: 23°C, 16L:8D
- Feeding: 3x per week, 10 mL algal mixture (Pseudokichneriella subcapitata and Chlorella vulgaris) and 5 mL of yeast, CerophyllTM and trout chow (YCT)
- No feeding during test.
- Age at start of test: neonates < 24 h old

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

Ca2+: 0.562-0.826 mM
Mg2+: 0.146-0.176 mM
Water hardness was therefore roughly between 70 and 100 mg CaCO3/L.

Test temperature:

23°C

pH:

t=0h: 7.5-7.6
t=48h: 7.5-7.7

Salinity:

not applicable

Nominal and measured concentrations:

Nominal test concentrations:
0, 500, 1000, 2000, 4000 and 8000 µg Dy/L

Measured concentrations:
t=0h, total Dy: -4, 474, 946, 1892, 3793 and 7704 µg Dy/L
t=0h, dissolved Dy: -3, 88, 203, 279, 512 and 692 µg Dy/L
t=72h (i.e. 24 h after the end of the test), total Dy: -4, 345, 552, 639, 787 and 1134 µg Dy/L
t=72h (i.e. 24 h after the end of the test), dissolved Dy: -3, 333, 527, 546, 567 and 598 µg Dy/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 400-mL polypropylene beakers
- Type (delete if not applicable): closed (covered with a plastic petri dish to reduce evaporation)
- Fill volume: 100 mL
- Equilibration: all test containers were covered and held under culture conditions for 24 h prior to testing
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 2

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Moderately Soft Medium
- Culture medium different from test medium: no
- Intervals of water quality measurement: pH and temperature were measured at the start and end of testing

OTHER TEST CONDITIONS
- Adjustment of pH: initial yes, to pH 7.3
- Photoperiod: 16L:8D
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): mortality, at the end of the test

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

LC50

Effect conc.:

357 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: 95% CI = 289-435 µg Dy/L

Details on results:

48-h LC50 based on total Dy concentration = 2984 µg Dy/L (2215-3980 µg Dy/L).

Note that effect concentrations reported as free Dy3+ concentration are also available in the thesis (for biotic ligand modelling purposes). However, these results are not included in this study summary.

Reported statistics and error estimates:

Probit analysis was applied to calculate the LC50 data and confidence intervals.

Validity criteria fulfilled:

yes

Conclusions:

The 48-h LC50 of Dy to Daphnia pulex in moderately soft medium at 23°C and pH 7.6 was determined to be 357 µg Dy/L (dissolved concentration). The reliability of the study was considered to have restrictions because the original source of the daphnid culture was a lake in the Sudbury region and it was not reported whether or not the lake under consideration is affected by the historical metal contamination in the Sudbury region, which may affect the sensitivity of the test organisms.

Cross-reference 2

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well performed guideline study. The results obtained in standard moderately soft medium using test organisms from a Hyalella azteca culture originating from a relatively pristine lake can be considered as sufficiently reliable for endpoint coverage. However, these results are considered reliable with restrictions because the effect concentrations were expressed based on initial measured dissolved Dy concentrations, whereas a clear reduction of dissolved Dy was observed throughout the tests.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: US EPA "Methods for Measuring the Toxicity and Bioaccumulation of Sediment-associated Contaminants with Freshwater Invertebrates" (EPA/600/R-99/064; USEPA, 2000)

Version / remarks:

Second Edition

Deviations:

yes

Remarks:

a static 96-h water-only acute test was conducted

Qualifier:

according to guideline

Guideline:

other: Environment Canada's (EC) "Biological Test Method: Test for Survival and Growth in Sediment and Water Using the Freshwater Amphipod Hyalella azteca" (EPS1/RM/33; EC, 2013)

Deviations:

yes

Remarks:

a static 96-h water-only acute test was conducted

Principles of method if other than guideline:

The study was conducted in accordance with the two guidelines cited above. Its aim was also to investigate the impacts of some potential toxicity modifying factors (TMFs) by examining the effects of pH, different concentrations of inorganic cations (Ca2+, Mg2+ and Na+) and dissolved organic carbon (DOC) on the acute toxicity of Dy.

GLP compliance:

not specified

Remarks:

recent publication, however not specifying on GLP compliance

Analytical monitoring:

yes

Details on sampling:

- Samples were taken 1 day prior to the start of the test (immediately following test solution preparation) and at the end of the test in order to measure the concentrations of Dy, inorganic cations (Ca2+, Mg2+, Na+) and DOC (where applicable).

- A total volume of 10 mL (5 mL from each replicate) was sampled after stirring the solutions.
- Total and dissolved Dy was measured. For dissolved Dy, filtration through 0.45 µm filter (Tuffryn).
- Samples were preserved with 200 µL of HNO3 (Trace Metal Grade, 70%, approx. 2% acid).
- Samples were stored at room temperature.

- For DOC analysis, 50 mL of test solution was filtered (0.45 µm, Tuffryn) and stored at 4°C in the dark.

Vehicle:

no

Details on test solutions:

- A stock solution of 32 mg Dy/L was prepared from 1000 mg/L Dy atomic absorption standard stabilised in 7% HNO3, and moderately soft medium, and pH was adjusted to 7.3 using KOH.
- Test solutions of 0, 200, 800, 1600, 3200 and 6400 µg Dy/L were prepared by mixing appropriate ratios of the Dy stock solution and moderately soft medium.
- For the test series investigating the effects of potential toxicity modifying factors (TMFs: Ca2+, Mg2+, Na+, DOC and pH), the required chemicals were added to obtain the required concentration series:
--> Ca2+: 0.5, 1, 2 mM (by adding CaCl2)
--> Mg2+: 0.125, 0.25, 0.5, 2 mM (by adding MgSO4)
--> Na+: 0.505, 1, 2 mM (by adding NaCl)
--> DOC: 4, 8 mg/L (by adding Suwannee River DOC)
--> pH: 6.3, 7.3, 8.3 (by adding MOPS (3-(N-morpholino)propanesulfonic acid), HNO3, KOH)

Test organisms (species):

other: Hyalella azteca

Details on test organisms:

TEST ORGANISM
- Scientific name: Hyalella azteca
- Source: Hyalella's were collected from 4 different locations in Ontario, Canada, and cultivated in the lab. HL, DL, LWL are located close to Sudbury, an area that has historically experienced severe SO2 and metal contamination. FH is relatively pristine.
--> Hanna Lake (HL): 46.443741, -81.038141
--> Daisy Lake (DL): 46.455342, -80.880002
--> Low Water Lake (LWL): 47.152090, -81.694350
--> Eabamet Lake (FH, near Fort Hope): 51.560457, -87.986864
- Culture medium: moderately soft medium (Borgmann, 1996), pH adjusted to 7.3 +/- 0.1 using HNO3 or KOH
- Culture conditions: 5x10 cm pieces of cotton gauze as substrate, 23°C, 16L:8D
- Feeding: 3x per week, 5 mg Tetramin tropical fish food
- Age at start of testing: neonates at day 2-9
- No feeding during test.

- Hyalellas from the four locations (HL, DL, LWL, FH) were tested in the classical tests without investigation of the effects of potential TMFs. Tests investigating the effects of potential TMFs on Dy toxicity were performed only with Hyalellas from FH.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

In the basic tests with moderately soft medium (i.e. classical tests without investigation of potential TMF impacts), Ca2+ concentration ranged from 0.475 to 0.646 mM and Mg2+ concentration ranged from 0.139 to 0.194 mM. As a result, water hardness ranged roughly between 60 and 85 mg CaCO3/L.

In the tests with variations of the potential TMF Ca2+, Ca2+ concentration ranged from 0.475 to 2.048 mM, whereas Mg2+ concentration ranged from 0.126 to 0.180 mM. As a result, water hardness ranged roughly between 60 and 225 mg CaCO3/L.

In the tests with variations of the potential TMF Mg2+, Ca2+ concentration ranged from 0.458 to 0.854 mM, whereas Mg2+ concentration ranged from 0.139 to 2.602 mM. As a result, water hardness ranged roughly between 60 and 325 mg CaCO3/L.

In the tests with variations of the other potential TMFs (Na+, pH, DOC), Ca2+ and Mg2+ concentrations, and consequently water hardness, was similar as in the basic tests with moderately soft medium (see above).

Test temperature:

23°C (incubator)

pH:

Basic tests with moderately soft medium (i.e. classical tests without investigation of potential TMF impacts):
t=0h: 7.4-7.8
t=120h: 7.5-8.2

Tests with variations of the potential TMF pH:
pH 7.5, t=0h: 7.4-7.6, t=120h: 7.5-7.7
pH 6.3, t=0h: 6.7, t=120h: 6.7-6.8
pH 8.3, t=0h: 8.0-8.1, t=120h: 7.9-8.0

Tests with variations of other potential TMFs (i.e. Ca2+, Mg2+, Na+, DOC):
t=0h: 7.4-7.9
t=120h: 7.5-7.9

Nominal and measured concentrations:

Nominal test concentrations:
0, 200, 800, 1600, 3200 and 6400 µg Dy/L

Measured concentrations were approximately 50% or lower at t=0h and decreased with increasing nominal concentration due to Dy precipitation. Also, the concentration gradients for measured total and dissolved Dy concentrations were more pronounced at 0h than at 120h.

In the basic tests in moderately soft medium, total Dy ranged between 96 and 7275 µg Dy/L at t=0h, whereas dissolved Dy ranged from 36 to 1206 µg Dy/L.
At t=120h, total Dy ranged between 52 and 5596 µg Dy/L, whereas dissolved Dy ranged from 43 to 605 µg Dy/L.

Total and dissolved concentrations at 0 and 120 h are available in the publication for each test (with or without varying concentrations of the different potential TMFs) but were not reported here due to the huge number of possible combinations.

Details on test conditions:

TEST SYSTEM
- Test vessel: 400-mL polypropylene beakers
- Type (delete if not applicable): closed (covered with a plastic petri dish to reduce evaporation)
- Fill volume: 250 mL
- Substrate for Hyalella's: 1 piece of 5x10-cm cotton gauze per beaker (pre-soaked for 24 h in test solution)
- Equilibration: all test containers were covered and held under culture conditions for 24 h prior to testing
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 1-2 (for all the pH tests and the second trial with 8 mg DOC/L, there was an additional control without MOPS or DOC, respectively)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Moderately Soft Medium
- Culture medium different from test medium: no
- Intervals of water quality measurement: pH and temperature were measured at the start and end of testing

OTHER TEST CONDITIONS
- Adjustment of pH: initial yes, to pH 7.3 (except in tests investigating the effects of the potential TMF pH where the initial pH was adjusted to the required pH level (6.3 or 8.3))
- Photoperiod: 16L:8D
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): mortality, at the end of the test

Reference substance (positive control):

no

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

376 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, trial 1, 95% CI = 301-477 µg Dy/L

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

372 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, trial 2, 95% CI = 317-430 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

204 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Daisy Lake, trial 1, 95% CI = 174-237 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

276 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Daisy Lake, trial 2, 95% CI = 206-347 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

186 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Low Water Lake, trial 1, 95% CI = 118-252 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

145 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Low Water Lake, trial 2, 95% CI = 90-195 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

146 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Hannah Lake, trial 1, 95% CI = 120-178 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

277 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Hannah Lake, trial 2, 95% CI = 231-326 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

883 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 1 mM Ca2+, trial 1, 95% CI = 735-1037 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

428 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 1 mM Ca2+, trial 2, 95% CI = 359-509 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

266 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 1 mM Ca2+, trial 3, 95% CI = 182-351 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

671 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 2 mM Ca2+, trial 1, 95% CI = 605-751 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

354 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 0.25 mM Mg2+, trial 1, 95% CI = 286-428 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

198 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 0.5 mM Mg2+, trial 1, 95% CI = 155-244 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

474 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 2 mM Mg2+, trial 1, 95% CI = 446-508 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

378 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 1 mM Na+, trial 1, 95% CI = 301-458 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

609 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 2 mM Na+, trial 1, 95% CI = 518-687 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

1 090 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 4 mg/L DOC, trial 1, 95% CI = 835-1397 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

1 868 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 8 mg/L DOC, trial 1, 95% CI = 1500-2355 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

397 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, 8 mg/L DOC, trial 2, 95% CI = 337-501 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

822 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, pH 6.3, trial 1, 95% CI = 546-1142 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

113 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, pH 8.3, trial 1, 95% CI = 90-138 µg Dy/L

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

72 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Fort Hope, pH 8.3, trial 2, 95% CI = 58-87 µg Dy/L

Details on results:

The data obtained with the Hyalellas collected in the pristine location (Fort Hope) during the tests without investigation of the effects of potential TMFs on dysprosium toxicity were identified as key results. The data obtained with Hyalellas from the other locations were not identified as key because the previous history of these Hyalellas could have influenced their sensitivity to dysprosium. Similarly, data obtained in the experiments investigating the effects of potential TMFs on dysprosium toxicity were not identified as key because the test media composition differs from usual standard experimental conditions.

Effect concentrations based on dissolved Dy concentrations are reported in the results box above. Effect concentrations based on total Dy concentrations are reported below this paragraph. Note that the publication also reports effect concentrations expressed as free Dy3+ concentration (for biotic ligand modelling purposes) but these are not reported in this study summary.

Effect concentrations based on total Dy concentrations:
FH MSM trial 1 - 1665 (1352-2077) µg Dy/L
FH MSM trial 2 - 1160 (974-1374) µg Dy/L
DL MSM trial 1 - 723 (593-842) µg Dy/L
DL MSM trial 2 - 985 (691-1319) µg Dy/L
LW MSM trial 1 - 625 (353-895) µg Dy/L
LW MSM trial 2 - 790 (414-1158) µg Dy/L
HL MSM trial 1 - 370 (304-459) µg Dy/L
HL MSM trial 2 - 1945 (1451-2533) µg Dy/L
FH 1 mM Ca2+ trial 1 - 1859 (1421-2465) µg Dy/L
FH 1 mM Ca2+ trial 2 - 1701 (1386-2123) µg Dy/L
FH 1 mM Ca2+ trial 3 - 709 (467-960) µg Dy/L
FH 2 mM Ca2+ trial 1 - 2953 (2478-3597) µg Dy/L
FH 0.25 mM Mg2+ trial 1 - 1881 (1432-2420) µg Dy/L
FH 0.5 mM Mg2+ trial 1 - 1114 (838-1430) µg Dy/L
FH 2 mM Mg2+ trial 1 - 1596 (1374-1843) µg Dy/L
FH 1 mM Na+ trial 1 - 1562 (1130-2068) µg Dy/L
FH 2 mM Na+ trial 1 - 1434 (1131-1784) µg Dy/L
FH 4 mg/L DOC trial 1 - 1705 (1369-2117) µg Dy/L
FH 8 mg/L DOC trial 1 - 2617 (2096-3285) µg Dy/L
FH 8 mg/L DOC trial 2 - 1236 (1042-1581) µg Dy/L
FH pH 6.3 trial 1 - 795 (535-1093) µg Dy/L
FH pH 8.3 trial 1 - 866 (681-1112) µg Dy/L
FH pH 8.3 trial 2 - 621 (496-781) µg Dy/L

- Dy concentrations at the end of the test were not used in the LC50 calculations, due to the lack of clear concentration gradients for dissolved Dy concentrations.
- The sensitivity of H. azteca from the 3 locations in the Sudbury area (DL, LW and HL) was similar among each other but more sensitive than H. azteca from Fort Hope.
- Potential effects of toxicity modifying factors were investigated (Ca2+, Mg2+, Na+, DOC, pH) but the effects were not always very clear:
--> Protection against Dy toxicity was observed with increased quantities of Ca2+ and Na+.
--> Increases in Mg2+ concentration had no effect.
--> DOC provided protection against Dy toxicity at 4 and 8 mg DOC/L but not in the second trial at 8 mg DOC/L which appeared to have no effect on Dy in solution.
--> Lower pH was very effective at increasing Dy solubility (e.g., a drop of 0.9 (to a pH of 6.7) resulted in an 8-times increase of 0h dissolved Dy concentration at 6400 µg Dy/L, while a pH increase of 0.5 (to pH 8.1) caused about a 50% reduction of 0h and 120h dissolved Dy concentrations) but the LC50 values became higher (lower toxicity) with decreasing pH.
- Altogether, based on the linear relationships between calculated Dy3+ concentrations (at the 96-h LC50s) and Ca2+, Na+ and H+ concentration, it seems that Ca2+, Na+ and H+ may effectively compete with Dy3+ for binding sites, thus decreasing Dy toxicity.

Reported statistics and error estimates:

Probit analysis was applied to calculate the LC50 data and confidence intervals.
To compare LC50 values, no overlap of confidence intervals was considered as significantly different. If the confidence intervals overlapped, the Litchfield-Wilcoxon method was used to determine whether there was a statistically significant difference.

Measured Dy concentrations in the test without test organisms (23°C, pH = 7.6, nominal Dy concentrations = 200, 800, 1600, 3200, 6400 µg/L):

Total Dy concentrations at 0h:

189-206 µg/L, 775-792 µg/L, 1563-1588 µg/L, 3171-3217 µg/L, 6270-6387 µg/L

Dissolved Dy concentrations at 0h:

115-126 µg/L, 170-218 µg/L, 325-420 µg/L, 606-688 µg/L, 916-980 µg/L

Total Dy concentrations after 120h:

61-80 µg/L, 535-409 µg/L, 1076-1255 µg/L, 2292-2810 µg/L, 4740-5367 µg/L

Dissolved Dy concentrations after 120h:

40-70 µg/L, 364-486 µg/L, 580-644 µg/L, 565-604 µg/L, 653-688 µg/L

Total Dy concentrations after 120h with 2% acid:

224-237 µg/L, 846-885 µg/L, 1745-1798 µg/L, 3402-3491 µg/L, 6590-6809 µg/L

Dissolved Dy concentrations after 120h with 2% acid:

227-240 µg/L, 854-890 µg/L, 1735-1789 µg/L, 3328-3550 µg/L, 6582-6805 µg/L

Conclusions:

- The increase of dissolved Dy under acidic conditions (i.e. with 2% acid) is a function of primarily increased solubility and to a lesser extent desorption (of adsorbed Dy to test vessel walls).

- The low dissolved Dy concentrations relative to total Dy concentrations were demonstrated - through modelling with Visual MINTEQ 3.1) - to be due to formation of Dy(OH)3 at pH 7.6 and Dy concentrations greater than 800 µg/L.

Validity criteria fulfilled:

yes

Conclusions:

In this study, the toxicity of dysprosium to Hyalella azteca was investigated in moderately soft medium, using Hyalella cultures originating from 3 contaminated and 1 relatively pristine natural source. The latter culture yielded 96-h LC50 values of 372 and 376 µg Dy/L (duplicate tests). These values can be considered as key values from this study. The LC50 values for the other three cultures (i.e. those originating from metal-contanimated locations) were lower, indicating that the previous history of Hyalella cultures from these locations could have increased their sensitivity to dysprosium (or metals in general). Further, in this study, the toxicity mitigating effects of Ca2+, Mg2+, Na+, pH and DOC were investigated. Protective effects were observed for Ca2+, Na+ and H+, and the linear relationships obtained between calculated free Dy3+ concentration (at the 96-h LC50s) and Ca2+, Na+ and H+ concentration indicated that the effects may be due to competition between these cations and Dy3+ for binding at the biotic ligand.

When recalculated to Dy(NO3)3 concentrations, the key 96-h LC50 values obtained in moderately soft medium at pH 7.6 using a Hyalella azteca culture originating from a relatively pristine natural source were 0.798 and 0.806 mg Dy(NO3)3/L.

Data source

Reference

Reference Type:

other: Master Dissertation

Title:

The effects of Water Chemistry and Organism Source on Dysprosium Toxicity to Hyalella azteca

Author:

Lu C

Year:

2015

Bibliographic source:

A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Science in Biology, Waterloo, Ontario, Canada.

Materials and methods

Test guideline

Test guideline 1

Qualifier:

equivalent or similar to guideline

Guideline:

other: Environment Canada's 'Biological Test Method: Test for the survival and growth in sediment and water using freshwater amphipod Hyalella azteca', EPS1/RM/33; EC, 2013

Deviations:

yes

Remarks:

a water-only test was conducted

Test guideline 2

Qualifier:

equivalent or similar to guideline

Guideline:

other: Borgmann and Norwood (1993) procedures for Hyalella azteca chronic sediment toxicity tests

Deviations:

yes

Remarks:

a water-only test was conducted

Principles of method if other than guideline:

The study was conducted in accordance with the two guidelines cited above. Its aim was also to investigate the impacts of potential toxicity modifying factors (TMFs: Ca2+, Mg2+ and dissolved organic carbon (DOC)) on the chronic toxicity of Dy.

GLP compliance:

not specified

Remarks:

recent publication, however not specifying on GLP compliance

Test material

Test material information

Constituent 1

Reference substance name:

Dysprosium

EC Number:

231-073-9

EC Name:

Dysprosium

Cas Number:

7429-91-6

Molecular formula:

Dy

IUPAC Name:

dysprosium

Details on test material:

Dy atomic absorption standard (Inorganic Ventures, Mississauga, ON), stabilised in 7% HNO3, at a concentration of 1000 +/- 10 mg Dy/L was used as test item.

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

- At the start of the test (24 h after solution preparation) two 10-mL samples were collected.
- During the test, samples were collected from both new and old test solutions at least once a week.
- Dy (total and dissolved) and inorganic cation concentrations (Ca2+, Mg2+, Na+) were measured in the samples.
- For dissolved Dy, filtration through 0.45 µm filter (Tuffryn).
- Samples were preserved with 200 µL of HNO3 (Trace Metal Grade, 70%, approx. 2% acid).
- Samples were stored at 4°C prior to analysis.

- For DOC analysis, 50 mL of test solution was taken once a week from both new and old solutions for all treatment concentrations for selected tests only, filtered (0.45 µm, Tuffryn), and stored at 4°C in the dark prior to analysis.

Test solutions

Vehicle:

no

Details on test solutions:

- A 1000 mg/L Dy atomic absorption standard stabilised in 7% HNO3, and moderately soft medium (MSM), were used for test solution preparation.
- Test solutions were prepared one day prior to the start of the test.
- The pH of each test solution was adjusted to 7.3 using KOH.
- All test solutions were stored in sealed 10-L blue plastic carboys for 24 h at about 23°C.
- Depending on the toxicity modifying factor tested, test solutions ranged between 10 and 2000 µg Dy/L.
- In addition to tests in MSM, a few tests were performed investigating the toxicity mitigating effect of Ca2+, Mg2+ and DOC. Hereto, the following chemicals were used for test solution preparation:
--> Test with 2 mM Ca2+: Ca added as CaCl2.2H2O
--> Test with 0.5 mM Mg2+: Mg added as MgSO4.7H2O
--> Tests with DOC (6 mg/L): DOC from White River, ON (WR) or Luther Marsh, ON (LM). LM DOC is a dark colored DOC with high humic ratio (74%) and high specific absorption coefficient (37.8), while WR DOC is lighter in color and has a lower humic ratio.
- Finally, a separate test series was performed at a constant Dy concentration of 500 µg/L and varying Ca2+ concentrations (0.5, 1, 2, 4, 8 mM), to examine the toxicity mitigating effect of Ca2+ on Dy3+ toxicity.

Test organisms

Test organisms (species):

other: Hyalella azteca

Details on test organisms:

TEST ORGANISM
- Scientific name: Hyalella azteca
- Source: Fort Hope (northwestern Ontario), relatively pristine lake
- Culture medium: moderately soft medium (Borgmann, 1996), pH adjusted to 7.3 +/- 0.1 using HNO3 or KOH
- Culture conditions: 5x10 cm pieces of cotton gauze as substrate, 23°C, 16L:8D
- Feeding: 3x per week, 5 mg Tetramin tropical fish food
- Age at start of testing: neonates at day 2-9
- During the test, neonates were fed 5 mg smashed Tetramin tropical fish food immediately after each solution renewal (i.e. 3x/week)

Study design

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

4 wk

Test conditions

Hardness:

Trials in MSM (i.e. classical trials without investigation of potential TMF impacts):
Ca2+: 0.426-0.526 mM
Mg2+: 0.126-0.147 mM
Water hardness roughly between 55 and 65 mg CaCO3/L

Trials investigating the impact of the potential TMF Ca2+ at 2 mM:
Ca2+: 1.869-1.919 mM
Mg2+: 0.126-0.135 mM
Water hardness roughly 200 mg CaCO3/L

Trials investigating the impact of the potential TMF Mg2+ at 0.5 mM:
Ca2+: 0.486-0.501 mM
Mg2+: 0.502-0.510 mM
Water hardness roughly 100 mg CaCO3/L

Trials investigating the impact of variations of the potential TMF Ca2+ at a constant Dy concentration of 500 µg/L:
Ca2+: 0.470-7.921 mM
Mg2+: 0.141-0.151 mM
Water hardness roughly between 60 and 800 mg CaCO3/L

Test temperature:

23°C

pH:

pH of new test solutions: 7.1-7.5
pH of old test solutions: 7.2-8.3 with the exception of the trial investigating the toxicity modifying effects of DOC from WR that showed some abnormally high old solution pH (up to 9.0)

Nominal and measured concentrations:

Nominal and measured test concentrations:
MSM trials (2):
Nominal: 0, 10, 20, 50, 100, 200, 500 µg Dy/L and 0, 50, 100, 250, 500, 750, 1000 µg Dy/L, for trials 1 and 2, respectively
Measured total Dy new test solutions (without control): 4-951 µg Dy/L
Measured dissolved Dy new test solutions (without control): 5-940 µg Dy/L
Measured total Dy old test solutions (without control): 2-612 µg Dy/L
Measured dissolved Dy old test solutions (without control): 1-413 µg Dy/L

2 mM Ca2+ trial:
Nominal: 0, 250, 500, 750, 1000, 1250 µg Dy/L
Measured total Dy new test solutions (without control): 244-1266 µg Dy/L
Measured dissolved Dy new test solutions (without control): 236-1215 µg Dy/L
Measured total Dy old test solutions (without control): 142-873 µg Dy/L
Measured dissolved Dy old test solutions (without control): 61-606 µg Dy/L

0.5 mM Mg2+ trial:
Nominal: 0, 250, 500, 750, 1000, 1500 µg Dy/L
Measured total Dy new test solutions (without control): 229-1467 µg Dy/L
Measured dissolved Dy new test solutions (without control): 223-1333 µg Dy/L
Measured total Dy old test solutions (without control): 126-944 µg Dy/L
Measured dissolved Dy old test solutions (without control): 53-673 µg Dy/L

DOC trials (2):
Nominal: 0, 250, 500, 750, 1000, 1500 µg Dy/L (DOC WR) and 0, 500, 750, 1000, 1500, 2000 µg Dy/L (DOC LM)
Measured total Dy new test solutions (without control): 240-1940 µg Dy/L
Measured dissolved Dy new test solutions (without control): 242-1933 µg Dy/L
Measured total Dy old test solutions (without control): 220-1764 µg Dy/L
Measured dissolved Dy old test solutions (without control): 200-1681 µg Dy/L

Ca2+ trials at constant Dy concentration (500 µg/L):
Nominal: 0, 500 µg Dy/L
Measured total Dy new test solutions (without control): 375-468 µg Dy/L
Measured dissolved Dy new test solutions (without control): 357-477 µg Dy/L
Measured total Dy old test solutions (without control): 198-281 µg Dy/L
Measured dissolved Dy old test solutions (without control): 112-224 µg Dy/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 400-mL tri-cornered polypropylene beakers
- Type (delete if not applicable): closed (covered with a plastic petri dish to reduce evaporation)
- Fill volume: 250 mL
- Substrate for Hyalella's: a piece of 5x10-cm cotton gauze (pre-soaked for 24 h in test solution), not changed during medium renewal
- Equilibration: all test containers were covered and held under culture conditions for 24 h prior to testing
- Renewal rate of test solution (frequency/flow rate): 3x/week
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Moderately Soft Medium
- Culture medium different from test medium: no
- Intervals of water quality measurement: pH and temperature were measured at the start and end of testing - pH was also measured at each renewal in the new and old test solutions

OTHER TEST CONDITIONS
- Adjustment of pH: initial yes, to pH 7.3
- Photoperiod: 16L:8D
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): mortality, at the time of renewal, and growth, at the end of the test (biomass in dry weight after a 6-hour post exposure for gut clearance, only used for further interpretation in case more than 1 Hyalella survived)

Reference substance (positive control):

not specified

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Duration:

4 wk

Dose descriptor:

NOEC

Effect conc.:

5.74 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: MSM trial 1, LOEC = 15.65 µg Dy/L

Effect concentrations 2

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

281 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: MSM trial 1, 95% CI = 226-376 µg Dy/L

Effect concentrations 3

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

268 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: MSM trial 2, 95% CI = 204-337 µg Dy/L, control mortality too high (23.3%)

Effect concentrations 4

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

681 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Ca2+ 2 mM, 95% CI = 596-776 µg Dy/L

Effect concentrations 5

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

548 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: Mg2+ 0.5 mM, 95% CI = 469-636 µg Dy/L

Effect concentrations 6

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

898 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: 6 mg/L DOC WR, 95% CI = 781-1045 µg Dy/L

Effect concentrations 7

Duration:

4 wk

Dose descriptor:

LC50

Effect conc.:

1 215 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

element (dissolved fraction)

Basis for effect:

mortality

Remarks on result:

other: 6 mg/L DOC LM, 95% CI = 1006-1501 µg Dy/L

Details on results:

- The data obtained during trial 1, a classical test without investigation of potential impacts of TMFs, were identified as key results. The data obtained during trial 2 were not considered as key due to the too high control mortality. Data obtained in the experiments investigating potential impacts of TMFs were not identified as key because test medium composition in these tests deviates more from usual standard experimental conditions.

- No NOECs were reported for the endpoint mortality (but could be determined based on the raw data - this was only done for the key test, i.e. trial 1 in MSM medium, for which the NOEC was set at the nominal concentration of 20 µg Dy/L, corresponding to a dissolved concentration of 5.74 µg/L).
- Effect concentrations were only reported based on initial measured dissolved Dy concentrations. However, the key NOEC for endpoint coverage (the NOEC for mortality for MSM trial 1) was expressed based on the geometric mean of the reported dissolved Dy concentration in new and old test media.
- All the TMF tests had significantly higher LC50 values than the MSM tests, indicating protective effects against Dy toxicity. Based on the LC50 data, the strength of protection in order from highest to lowest is: 6 mg/L DOC LM > 6 mg/L DOC WR > 2 mM Ca2+ > 0.5 mM Mg2+.
- Growth was inhibited as dissolved Dy concentrations increased:
--> MSM trial 1: EC25 and EC50 = 296 and 307 µg Dy/L
--> MSM trial 2: EC25, EC50 and LOEC = 27, 85 and 147 µg Dy/L
--> 2 mM Ca2+ trial: EC25, EC50 and LOEC = 251, 354 and 482 µg Dy/L
--> 0.5 mM Mg2+ trial: EC25, EC50 and LOEC = 31, 85 and 223 µg Dy/L
--> 6 mg/L DOC WR: EC25, EC50 and LOEC = 454, 518 and 656 µg Dy/L
--> 6 mg/L DOC LM: EC25, EC50 and LOEC = 531, 813 and 976 µg Dy/L
--> For MSM trial 1 the NOEC and LOEC could not be determined according to the author. For MSM trial 2 it was reported but the control mortality was too high in this test. Therefore, no key values were reported for the growth endpoint in this entry.
- The harmful influence of Dy was inhibited to varying degrees in the tests with different TMFs. Compared to MSM trial 1, both DOC trials and at a lesser extent the 2mM Ca2+ trial demonstrated protective effects against growth inhibition.
- In the presence of 500 µg Dy/L, growth of Hyalella azteca at different Ca2+ concentrations (0.5-8 mM Ca2+) was significantly inhibited relative to the controls. Among the test solutions with different Ca2+ concentrations, the only significant difference was observed between 0.5 mM Ca2+ and 4 mM Ca2+.

Reported statistics and error estimates:

LC50 values were calculated using Probit analysis provided by IBM SPSS Statistics 22.
LC50 values were considered significantly different if their confidence limits did not overlap.
If the confidence intervals overlapped, Litchfield-Wilcoxon method was used to determine significance.
One-way ANOVA test with Dunnett's post hoc comparison was run on IBM SPSS Statistics 22 to find significant differences between dry weights of exposure and control, and to compare water chemistry data.
Regressions and graphs were made by SigmaPlot 12.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

In this study, the chronic toxicity of Dy to Hyalella azteca was investigated in water-only tests over a duration of 4 weeks. The study yielded a key 4-wk NOEC value of 5.74 µg Dy/L (based on the geometric mean of the dissolved Dy concentrations in new and old test solutions). This corresponds to a NOEC of 12.3 µg Dy(NO3)3/L. All potential toxicity mitigating factors studied (Ca2+, Mg2+ and DOC) were observed to protect against toxicity (when based on mortality) to a certain extent. Further, Dy was also observed to have an adverse effect on growth of the test organisms. However, no key NOEC values could be derived for the tests in moderately soft medium. Concerning growth, a toxicity mitigating effect was only observed for Ca2+ and DOC, not for Mg2+.