Cerium terbium magnesium undecaaluminum nonadecaoxide (hexagonal) ((Ce, Tb)MgAl11O19) and aluminium oxide (Al2O3) from calcination of Al2O3, CeO2, MgO and Tb4O7

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2 December 2011

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances):
1-Litre test bottles were filled with 200 ml of test substance mixtures in Milli-RO water (tap water purified by reverse osmosis) with initial loading rates of 2.5 times the final loading rate. These mixtures were stirred in closed dark brown bottles for approximately 24 hours. The appearance of the loading rates varied from clear and colorless at the lowest loading rate to opalescent with undissolved test substance particles (as precipitate and floating at the surface) at the highest loading rate.
Subsequently, 16 ml synthetic sewage feed, 250 ml sludge and Milli-RO water up to 500 ml were added resulting in the required loading rates. Optimal contact between the test substance and test organisms was ensured applying continuous aeration and stirring.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Preparation of inoculum for exposure:
The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105°C to determine the amount of suspended solids (3.0 g/l of sludge, as used for the test). The pH was 7.7 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.
- Initial biomass concentration: Number of micro-organisms was determined as the amount of Mixed Liquor Suspended Solids (MLSS) per litre test medium = 1.5 g/L of sludge

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

None

Hardness:

No information.

Test temperature:

19.8 - 21.1 ºC

pH:

7.7-7.8 before addition of sludge
7.7 - 8.3 after 3 hrs contact time

Dissolved oxygen:

8.0-8.8 mg O2/L at the start of the study

Salinity:

Not applicable.

Nominal and measured concentrations:

Not applicable.

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: all-glass, 1 liter, filled with 500 ml test solution
- Aeration: yes, using a pipette
- No. of organisms per vessel: 250 ml sludge
- No. of vessels per concentration (replicates): 3 for highest loading rate, 1 for lower loading rates
- No. of vessels per control (replicates): 6
- 1 abiotic controland 1 higest loading rate + nitrification inhibitor

TEST MEDIUM / WATER PARAMETERS
Adjusted ISO medium, formulated using RO-water (tapwater purified by reverse osmosis) with the following composition:
CaCl2.2H2O 211.5 mg/l
MgSO4.7H2O 88.8 mg/l
NaHCO3 46.7 mg/l
KCl 4.2 mg/l

OTHER TEST CONDITIONS
- Adjustment of pH: no

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen recording with oxygen probes connected to a BlueBox, a multichannel measuring and controlling system for a period of approximately 10 minutes. During measurement, the sample was not aerated but continuously
stirred on a magnetic stirrer.

TEST CONCENTRATIONS
In a combined limit/range-finding test loading rates of 10, 100 and 1000 mg/l were tested. The highest loading rate was tested in triplicate, lower loading rates consisted of one replicate. In addition, a blankcontrol (6 replicates) was included. Furthermore, an abiotic control and the highest loading rate with a nitrification inhibitor were tested.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

In the combined limit/range-finding test no statistically significant inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg CAT per litre.
Furthermore, there was no oxygen uptake from abiotic processes and the results at 1000 mg/l with a nitrification inhibitor showed that the heterotrophic inhibition of the respiration rate was comparable to the total inhibition.

Results with reference substance (positive control):

The EC50 of 3,5-dichlorophenol (8.1 mg/l) was in the accepted range of 2 to 25 mg/l for total respiration.

Reported statistics and error estimates:

The NOEC was based on statistical analysis of the data. Data obtained for the test concentrations were compared with those obtained for the control using TOXSTAT Release 3.5, 1996, D.D. Gulley, A.M. Boelter, H.L. Bergman.

Flask	Conc. / loading rate (mg/l)	Temp (°C)	pH before addition of sludge	pH after 3 h contact time	Oxygen conc. at the start (~ mg O2/l)	Respi- ration rate (mg O2/l h)	Respi- ration rate (mg O2/g h)¹	% Inhibition respiration relative to the control (mean value)
C 1	0	21.1	7.8	7.9	8.6	38	25
C 2	0	20.3	7.8	7.9	8.6	39	26
C 3	0	20.5	7.8	7.9	8.0	36	24
C 4	0	20.4	7.8	8.0	8.0	33	22
C 5	0	20.6	7.8	8.0	8.0	34	23
C 6	0	20.6	7.8	8.0	8.0	37	25
Mean						36	24
SD						2	2
CV (%)						6	6
CN (with ATU)	0	20.9	7.8	8.2	8.8	21	14
R 1	5.0	21.1	7.8	8.0	8.8	23	15	36
R 2	12	20.9	7.8	8.1	8.6	13	9	64
R 3	30	20.3	7.7	8.2	8.8	7	5	81
T 1	10	19.8	7.7	7.9	8.1	34	23	6
T 2	100	20.6	7.7	7.9	8.2	38	25	-5
T3a	1000	20.1	7.7	7.8	8.0	39	26	-8
T3b	1000	20.8	7.7	7.7	8.2	38	25	-5
T3c	1000	20.1	7.7	7.7	8.3	41	27	-13
T3 mean						39	26	-9
TA (abiotic)	1000	20.6	7.7	7.4	8.8	1	1	97
TN (with ATU)	1000	20.9	7.7	8.3	8.1	19	13	10^2

C:          Blank Control

CN:        Nitrification control

R:          Reference substance, 3,5-dichlorophenol

T:           Test substance, CAT

CV:         Coefficient of variation

ATU        N-allylthiourea

¹             The amount of suspended solids in the final test mixture was 1.5 g/l.

²              Relative to CN

Validity criteria fulfilled:

yes

Conclusions:

In the combined limit/range-finding test no statistically significant inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg CAT per litre.
Under the conditions of this present test CAT was not toxic to waste water (activated sludge) bacteria at a loading rate of 1000 mg/l (NOEC).

Description of key information

CAT was tested in an activated sludge respiration inhibition test (OECD 209). The substance was not toxic to waste water (activated sludge) bacteria at a loading rate of 1000 mg/l (NOEC).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

CAT was tested in an activated sludge respiration inhibition test (OECD 209). The substance was not toxic to waste water (activated sludge) bacteria at a loading rate of 1000 mg/l (NOEC).