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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

Administrative data

Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Study period:
2005
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
significant methodological deficiencies
Remarks:
A Klimisch score of 3 was attributed due to the fact that the study does not follow a standardized protocol with respect to the following points: 1) Time duration (7 days) is longer than for classical acute studies. 2) Feeding was allowed during the study. 3) Replicate numbers: the basic experimental design was modified from the classical toxicity test because the authors tested a high number of metal elements. Instead of testing one or a few metals at many concentrations at once, a large number of substances were tested simultaneously at one concentration only (either the maximum concentration of interest, or a concentration close to the predicted toxic threshold) in the first experiment. The concentration of each substance was then either increased or decreased in the next experiment, depending on whether mortality was observed. This procedure was repeated until the toxic range was covered for each substance, or until the substance was demonstrated to cause less than 50% mortality at the highest concentration of interest. Repeat tests were then conducted on either side of the LC50. In spite of the Klimisch score of 3, it was decided to flag this study as a supporting one because it goes in the same direction than the H400/H410 worst-case environmental classification based on previous data obtained on rare earth trinitrates.

Data source

Reference
Reference Type:
publication
Title:
Toxicity of sixty-three metals and metalloids to Hyalella azteca at two levels of water hardness
Author:
Borgmann U., Couillard Y., Doyle P., Dixon G.
Year:
2005
Bibliographic source:
Environmental Toxicology and Chemistry 24(3):641-652

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
This study was performed for the purpose of substances categorization (with respect to their toxicity) under the Canadian Environmental Protection Act (1999). To assist in the categorization process, two federal government laboratories (one using Hyalella and another using Daphnia) have conducted tests for acute lethality using standard methodologies approved by the Canadian stakeholders interested in the process. The present study reports the results of one-week toxicity tests with young Hyalella azteca. Two sets of experiments were run, one in tap water, and another in soft water.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Test material form:
not specified
Details on test material:
- Name of test material: atomic absorption standard containing 1 g terbium/L preserved in hydrochloric acid (HCl) at 2%. Using atomic absorption standard was less expensive than purchasing metals salts, and the stock solutions can be expected to contain fully dissolved terbium.
- Source of test material: obtained from Delta Scientific (Mississauga, ON, Canada).
No other information are available.

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
- Concentrations: Water samples for analysis were not collected for tests conducted in tap water, which were completed first, but were collected from all test solutions at the end of the 7-d exposure in tests conducted in soft water.
- Sampling method: Filtered (0.45 micron) samples were collected using disposable filter cartridges (Acrodiskst, Pall Canada Limited, Mississauga, ON) attached to polypropylene syringes, acidified with high purity hydrochloric acid.
- Sample storage conditions before analysis: Samples were stored in 14-ml capacity Falcont (Becton Dickinson, Franklin Lakes, NJ, USA) polypropylene disposable round bottom tubes with snap caps.

Test solutions

Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Two sets of experiments were run, one in tap water and another in soft water (description of both waters is given in the field named "Details on test conditions"). A solution of 19 parts 1 M NaHCO3 plus 1 part 1 M KOH (similar to the Na:K ratio of the test water) was used to neutralize excess acid in the metal standard and control pH. Sufficient buffer to control pH, if required, was added first, followed by addition of the metal standard. Neutralization was required primarily for tests conducted in soft water. Following addition of neutralizing buffer and metal, the water was aerated gently overnight to allow equilibration of pH and CO2, and any rapid changes in metal speciation that might occur.
- Controls: Three controls and three acid controls were tested. Acid-controls consisted of acid and neutralizing solution additions equal to the amount added in the tests with acidified metal standards.

Test organisms

Test organisms (species):
other aquatic crustacea: Hyalella azteca
Details on test organisms:
TEST ORGANISM
- Common name: Hyalella azteca (freshwater amphipod crustacean).
- Source: Originated from Valens Conservation Area (ON, Canada) in 1985 and cultured in the testing laboratory.
- Age: 1 to 11 days at the start of the test.
- Feeding during test: Yes.
- Food type: Tetra-Mint (Ulrich Baensch, Melle, Germany) fish food flakes.
- Amount: 2.5 mg per feeding.
- Frequency: One feeding at the initiation of the test and another one midweek.
No further data.

Study design

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
7 d
Remarks on exposure duration:
One-week toxicity test: - used because 48-h tests without food are difficult to conduct with young Hyalella, which swim and stick to the surface if not fed. - fits well within a 7-d work week. This 7-d test still should be considered an acute test.
Post exposure observation period:
No

Test conditions

Hardness:
Tap water: 124 mg/L
Soft water: 18 mg/L
Test temperature:
24 to 25°C
pH:
Tap water:
- Control vessel: 7.37
- Exposed vessels: 7.39
Soft water:
- Control vessel: 8.39
- Exposed vessels: 8.21
The above values are mean values obtained from the testing of several metal elements (including terbium).
Dissolved oxygen:
7 to 10 mg/L
Salinity:
No data
Conductivity:
Tap water:
- Control vessel: 46 µS/cm2
- Exposed vessels: 66 µS/cm2
Soft water:
- Control vessel: 311 µS/cm2
- Exposed vessels: 345 µS/cm2
The above values are mean values obtained from the testing of several metal elements (including terbium).
Nominal and measured concentrations:
A range was given for the nominal concentrations tested for all metals in the publication. This range was from 1000 µg/L (soft water) to 3150 µg/L (tap water). There is no information on the precise concentrations tested for terbium.
Details on test conditions:
TEST SYSTEM
- Type of test vessel: 500-ml polyethylene cups (snap-top specimen containers) containing 400 ml of test water.
- Aeration: Test containers were not aerated during the test.
- No. of organisms per vessel: 15
- No. of vessels per concentration (replicates): 1 replicate per concentration (not clear how many concentrations were tested for terbium).
- No. of vessels per control (replicates): 3 replicates for control and 3 replicates for acid control.
No further data.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Two sets of experiments were run, one in tap water and another in soft water:
* Tap water: dechlorinated Burlington City tap water (Lake Ontario, Canada) (hardness 124 mg/L, carbonate alkalinity 84 mg/L, Ca 35 mg/L, Mg 8.7 mg/L, Na 13 mg/L, K 1.6 mg/L, SO4 32 mg/L, Cl 25 mg/L, and dissolved organic carbon [DOC] 1.1 mg/L from January 2001 to October 2003, n 5 69, coefficient of variation 5 3–12%, except DOC, which was 74%).
* Soft water: consisting of 10% tap water and 90% Milli-Qt (Millipore, Bedford, MA, USA) deionized water (soft water measured hardness 18 mg/L, carbonate alkalinity 14 mg/L, Ca 5.6 mg/L, Mg 0.90 mg/L, Na 1.4 mg/L, K 0.15 mg/L, SO4 3.4 mg/L, Cl 2.5 mg/L, and DOC 0.28 mg/L, n 5 17, coefficient of variation 5 5–11%, except for Ca 45%, alkalinity 51% and DOC 69%). Calcium and alkalinity in the soft water were more variable than the other ions and ranged from 10 to 20% of expected concentrations because an airstone was inadvertently used to aerate the test water. Soft water tests were designed to simulate a reasonable worst-case condition for Canada (e.g., dilute waters
of the Canadian Shield with a low DOC content), while still falling within the range tolerated by Hyalella.
- Culture medium different from test medium: dechlorinated Burlington City tap water (Lake Ontario, Canada) was used as culture medium, while both this water and soft water was used as test media.
- Intervals of water quality measurement: After 7 d, the pH, conductivity, and ammonia and oxygen concentrations were measured. Routine major ion analyses were performed on tap water and on each batch of soft water used. In addition, DOC was measured in randomly selected samples of the test containers at the end of the 7-d exposure and averaged 1.4 mg/L (n 5 83, coefficient of variation 31%, range 0.7–3.6). Major ion and DOC analyses were conducted by the National Laboratory for Environmental Testing.

OTHER TEST CONDITIONS
- Adjustment of pH: Neutralization was required primarily for tests conducted in soft water. No information on the need to neutralize pH during the one-week exposure.
- Photoperiod: 16h:8h light:dark photoperiod.
No further data.

EFFECT PARAMETERS MEASURED
After 7 d, the number of survivors was counted.

No further data.
Reference substance (positive control):
not specified

Results and discussion

Effect concentrationsopen allclose all
Duration:
7 d
Dose descriptor:
LL50
Effect conc.:
0.365 mg/L
Nominal / measured:
nominal
Conc. based on:
other: terbium
Basis for effect:
mortality
Remarks on result:
other: (95% CL: 0.252-0.528 mg/L)
Remarks:
Result for soft water
Duration:
7 d
Dose descriptor:
LL50
Effect conc.:
0.792 mg/L
Nominal / measured:
nominal
Conc. based on:
other: anhydrous terbium trinitrate (calculated from molecular weights)
Basis for effect:
mortality
Remarks on result:
other: Result for soft water
Duration:
7 d
Dose descriptor:
LC50
Effect conc.:
0.084 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
other: terbium
Basis for effect:
mortality
Remarks on result:
other: (95% CL: 0.058 - 0.122 mg/L)
Remarks:
Result for soft water
Duration:
7 d
Dose descriptor:
LC50
Effect conc.:
0.182 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
other: anhydrous terbium trinitrate (calculated from molecular weights)
Basis for effect:
mortality
Remarks on result:
other: Result for soft water
Duration:
7 d
Dose descriptor:
LL50
Effect conc.:
0.693 mg/L
Nominal / measured:
nominal
Conc. based on:
other: terbium
Basis for effect:
mortality
Remarks on result:
other: (95% CL: 0.455-1.054 mg/)
Remarks:
Result for tap water
Duration:
7 d
Dose descriptor:
LL50
Effect conc.:
1.504 mg/L
Nominal / measured:
nominal
Conc. based on:
other: anhydrous terbium trinitrate (calculated from molecular weights)
Basis for effect:
mortality
Remarks on result:
other: Result for tap water
Details on results:
No analytical monitoring was performed for the assay in tap water; explaining why there is no result based on measured concentration for this medium. Anyway, the toxicity is higher in soft water and thus this medium represents a worst-case scenario as compared to tap water.
Reported statistics and error estimates:
The concentration resulting in 50% mortality (LC50) and 95% confidence limits were computed using the Trimmed Spearman-Karber method.

Any other information on results incl. tables

The LL50/LC50 for anhydrous terbium trinitrate were calculated from molecular weights; considering a molecular weight for terbium trinitrate of 344.934 g/mol and thus that terbium represents 46.074% of this weight.

Applicant's summary and conclusion

Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of this study, terbium trinitrate is very toxic to Hyalella azteca in soft water: the 7d-LC50 based on measured concentration was 0.182 mg/L when expressed in anhydrous terbium trinitrate (calculated from a 7d-LC50 of 0.084 mg/L when expressed in terbium). The toxicity in tap water was less important.
Executive summary:

This study was performed for the purpose of substances categorization (with respect to their toxicity) under the Canadian Environmental Protection Act (1999). To assist in the categorization process, two federal government laboratories (one using Hyalella and another using Daphnia) have conducted tests for acute lethality using standard methodologies approved by the Canadian stakeholders interested in the process. The present study reports the results of one-week toxicity tests with young Hyalella azteca. Two sets of experiments were run, one in tap water, and another in soft water. While analytical monitoring was performed during the assay in soft water, it was not the case during the assay in tap water. Therefore, there is no result based on measured concentration for this medium. The obtained results are the followings:

Soft water:

Based on nominal loading rate: 7d-LL50 = 0.365 mg/L as terbium = 0.792 mg/L as anhydrous terbium trinitrate

Based on measured concentration: 7d-LC50 = 0.084 mg/L as terbium = 0.182 mg/L as anhydrous terbium trinitrate

Tap water:

Based on nominal loading rate: 7d-LL50 = 0.693 mg/L as terbium = 1.504 mg/L as anhydrous terbium trinitrate

Under the conditions of this study, terbium trinitrate is thus very toxic to Hyalella azteca in soft water (based on measured concentration). The toxicity in tap water was less important.