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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
3 August 2017 - 28 March 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Deviations:
yes
Remarks:
In some instances, the initial and final dissolved oxygen concentrations were outside those recommended in the test guidelines. This was not considered to have affected the results and interpretation of the study.
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Test water: The water used for the test was deionised reverse osmosis water containing less than 1 mg/L Dissolved Organic Carbon.
- Method: Nominal amounts of test item (77, 138.6, 246.4, 431.2 and 770 mg (triplicate replicates of each )) were each separately dispersed in approximately 200 mL of deionised reverse osmosis water and subjected to ultrasonication for approximately 15 minutes followed by magnetic stirring for 24 hours, at room temperature, in order to maximise the dissolved test item concentration. All test vessels were shielded from the light during mixing. Synthetic sewage (16 mL), activated sewage sludge (250 mL) and water were added to a final volume of 500 mL to give the required concentrations of 100, 180, 320, 560 and 1000 mg anhydrous YCl3/L (3 replicates of each).
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Name and location of sewage treatment plant where inoculum was collected: Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK (aeration stage)
- The activated sewage sludge sample was maintained on continuous aeration in the laboratory at a temperature of approximately 21ºC overnight prior to use in the test.
- On the day of collection the activated sewage sludge (12.6 liters) was fed synthetic sewage (630 mL).
- Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 mL) of the activated sewage sludge by suction through a pre-weighed GF/A filter paper (rinsed three times with 20 mL deionised reverse osmosis water prior to drying in an oven) using a Buchner funnel which was then rinsed 3 times with 10 mL of deionised reverse osmosis water and filtration continued for 3 minutes. The filter paper was then dried in an oven at approximately 105ºC for at least one hour and allowed to cool before weighing. This process was repeated until a constant weight was attained.
- Initial biomass concentration: 3.0 g/L


Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Hardness:
cannot be determined based on the available information
Test temperature:
20-21°C
pH:
7.1 - 7.9 (after 0 hours exposure)
7.3 - 8.4 (after 3 hours exposure)
Dissolved oxygen:
The dissolved oxygen concentrations after 30 minutes contact time in all vessels were above 60% of the dissolved oxygen saturation level of 8.9 mg O2/L (i.e. 5.68-8.46 mg/L).
Dissolved oxygen concentrations after 3 h of exposure ranged from 4.2 to 8.9 mg/L.
Final readings (for determination of oxygen consumption rate) ranged from 1.7 to 6.7 mg/L.
In some instances, the initial and final dissolved oxygen concentrations were outside those recommended in the test guideline (7 mg O2/L and 2 mg O2/L respectively). This was considered to have had no adverse effect on the results of the study given that in all cases the oxygen consumption rate was determined over the linear portion of the oxygen consumption trace.
Salinity:
not applicable
Nominal and measured concentrations:
Nominal test concentrations:
- Range finder: Control + 10, 100 and 1000 mg YCl3/L.
- Definitive test: Control + 100, 180, 320, 560 and 1000 mg YCl3/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 500-mL conical flasks containing 500 mL of incubation mixture
- No. of vessels per concentration (replicates): 3
- No. of vessels per blank control (replicates): 6
- Dry matter in the test: 3 g suspended solids/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionised reverse osmosis water containing < 1 mg/L DOC

OTHER TEST CONDITIONS
- Adjustment of pH: The pH of test item stock solutions and test solutions was adjusted to between 7.0 and 8.0 if necessary.
- Photoperiod: normal laboratory lighting

EFFECT PARAMETERS MEASURED
- After 3 hours contact time, an aliquot was removed from each flask and poured into the measuring vessel (250-mL darkened glass Biological Oxygen Demand (BOD) bottle) and the rate of respiration measured using a Yellow Springs dissolved oxygen meter fitted with a BOD probe.
- The contents of the measuring vessel were stirred constantly by magnetic stirrer.
- The rate of respiration for each flask was measured over the linear portion of the oxygen consumption trace (where possible between 7 mg O2/L and 2 mg O2/L). In the case of a rapid oxygen consumption, measurements may have been outside this range but the oxygen consumption was always within the linear portion of the respiration curve. In the case of low oxygen consumption, the rate was determined over an approximate 10 minute period.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8
- Range finding study: yes, control + 10, 100 and 1000 mg YCl3/L
- Results used to determine the conditions for the definitive study: significant inhibition (86-89%) observed at 1000 mg YCl3/L
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
470 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr. (total fraction)
Remarks:
yttrium trichloride anhydrous
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
214 mg/L
Nominal / measured:
nominal
Conc. based on:
element (total fraction)
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
180 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr. (total fraction)
Remarks:
yttrium trichloride anhydrous
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
82 mg/L
Nominal / measured:
nominal
Conc. based on:
element (total fraction)
Basis for effect:
inhibition of total respiration
Results with reference substance (positive control):
The following results were obtained:

3-h EC10 = 0.82 mg/L
3-h EC20 = 1.3 mg/L
3-h EC50 = 5.6 mg/L (95% Confidence Limits 4.1-7.7 mg/L)
3-h EC80 = 24 mg/L

The validation criterion for the reference item EC50 value was fulfilled.
Reported statistics and error estimates:
In order to determine the NOEC, one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf, 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett, 1955) was carried out on the oxygen consumption data after 3 hours for the control and all test concentrations to determine any statistically significant differences between the test and control groups. All statistical analyses were performed using the SAS computer software package (SAS, 1999 - 2001).
Validity criteria fulfilled:
yes
Conclusions:
This activated sludge respiration inhibition test with yttrium trichloride yielded a NOEC and EC50 of 180 and 470 mg YCl3/L, respectively, corresponding to a NOEC and EC50 of 82 and 214 mg Y/L.
Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Data from the related substance yttrium trichloride is used to cover this endpoint. The justification for read across is attached to IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
214 mg/L
Nominal / measured:
nominal
Conc. based on:
element (total fraction)
Basis for effect:
inhibition of total respiration
Remarks on result:
other: This is the 3-h EC50 obtained in the key read across study from Bayliss (2018), expressed as total nominal yttrium concentration.
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
662 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr. (total fraction)
Remarks:
yttrium trinitrate anhydrous
Basis for effect:
inhibition of total respiration
Remarks on result:
other: This 3-h EC50 value was recalculated based on the results (expressed as total nominal yttrium concentration) obtained in the key read across study (Bayliss, 2018) performed with yttrium trichloride.
Remarks:
The results of the study performed with yttrium trichloride, which is a similar water-soluble yttrium compound as yttrium trinitrate, are considered relevant for yttrium trinitrate as well. The read across justification document is attached to IUCLID Section 13.
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
82 mg/L
Nominal / measured:
nominal
Conc. based on:
element (total fraction)
Basis for effect:
inhibition of total respiration
Remarks on result:
other: This is the 3-h NOEC obtained in the key read across study from Bayliss (2018), expressed as total nominal yttrium concentration.
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
253 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr. (total fraction)
Remarks:
yttrium trinitrate anhydrous
Basis for effect:
inhibition of total respiration
Remarks on result:
other: This 3-h NOEC value was recalculated based on the results (expressed as total nominal yttrium concentration) obtained in the key read across study (Bayliss, 2018) performed with yttrium trichloride.
Remarks:
The results of the study performed with yttrium trichloride, which is a similar water-soluble yttrium compound as yttrium trinitrate, are considered relevant for yttrium trinitrate as well. The read across justification document is attached to IUCLID Section 13.

Description of key information

The key read across study from Bayliss (2018) performed with yttrium trichloride, a similar water-soluble compound as yttrium trinitrate, yielded a 3-h EC50 and NOEC of 214 and 82 mg Y/L, respectively. When recalculating these values to yttrium trinitrate concentrations, a 3-h EC50 and NOEC of 662 and 253 mg Y(NO3)3/L were obtained, respectively.

Key value for chemical safety assessment

EC50 for microorganisms:
662 mg/L
EC10 or NOEC for microorganisms:
253 mg/L

Additional information

No useful studies have been identified on the toxicity of yttrium trinitrate to aquatic microorganisms. Therefore, the key study available for yttrium trichloride, a similar water-soluble compound as yttrium trinitrate, was used to conclude on the endpoint. The read across justification is attached to IUCLID Section 13.

Bayliss (2018) performed an activated sludge respiration inhibition test with yttrium trichloride according to OECD guideline 209 and conform GLP requirements. In this study, a 3-h EC50 and NOEC of 470 and 180 mg YCl3/L were obtained, respectively, which is equivalent to 214 and 82 mg Y/L, respectively. When recalculating the latter values to yttrium trinitrate concentrations, a 3-h EC50 and NOEC of 662 and 253 mg Y(NO3)3/L were obtained, respectively. This study is considered reliable without restrictions (Klimisch 1).