Registration Dossier

Diss Factsheets

Ecotoxicological information

Toxicity to microorganisms

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
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:
yes
Remarks:
(the pH reference substance stock solution was adjusted to 6.75, which is slightly outside the requested range of 7.5±0.5. Since the validity criterion regarding the reference substance was met the integrity or validity of the study was not affected.)
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
not required
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test substance is poorly soluble in water. Weights of the test substance were added to test bottles containing RO (reverse osmosis) water (284 mL), synthetic sewage (16 mL) and antifoam agent (silicone oil in water, 100 µL). Immediately prior to initiation of the respirometer, the required volume of activated sludge (200 mL) was added to each bottle.
- Controls: RO water, synthetic sewage and antifoam agent alone.

The final volume of antifoam was not considered significant and was not accounted for in the final overall volume (500 mL).
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Preparation of inoculum for exposure: Activated sludge was obtained the day before the start of the test. The mixed liquor suspended solids (MLSS) content was determined, synthetic sewage (50 mL/L) was added and the mixture was aerated overnight. On the day of the test, the MLSS content of the sludge was determined and adjusted to 4 g/L by the addition of tap water.
- Pretreatment: none
- Initial biomass concentration: 4 g MLSS/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
21-22 °C
pH:
test start: 7.0-7.1 (adjusted using 0.1M NaOH as required)
test end: 7.4-7.6
Dissolved oxygen:
4.6-6.7 mg O2/L (initial measured dissolved oxygen concentration in the cultures)
Nominal and measured concentrations:
nominal 10, 100, 1000 mg/L
As there was no significant inhibition observed in any test groups, the study was reported as a limit test with no further testing carried out.
Details on test conditions:
TEST SYSTEM
- Test instrument: automated respirometer and associated software (Coordinated Environmental System (CES).
- Test vessel: 500 mL bottles fitted with an oxygen probe, a sinter to deliver air and a nitrogen gas nozzle
- Aeration: oil-free compressed air at 1 L/min
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 5
- Biomass loading rate: 1.6 g/L (MLSS)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reverse osmosis (RO) water

OTHER TEST CONDITIONS
- Adjustment of pH: to 7.0-8.0 with 0.1M NaOH as required

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen concentration after 3 hours contact time

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10
- Range finding study/limit test
- Test concentrations: 10, 100, 1000 mg/L
- Results used to determine the conditions for the definitive study: As there was no significant inhibition observed in any test groups, the study was reported as a limit test.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
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
Details on results:
The highest mean inhibition observed in cultures with the test substance was 12% at both 100 and 1000 mg/L with ranges of -4 to 40% and 1 to 26% (coefficient of variation 19% and 11%, respectively; see Table 1).
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 8.5 mg/L (95% confidence limits 5.5-13.1 mg/L)

Table 1 Specific respiration rates, inhibition and coefficient of variation

 

Group

Nominal Conc. (mg/L)

Bottle No.

Specific respiration rate

(Rs mgO2/gh)

Mean Rs
(mgO2/gh)

% inhibition

Mean % inhibition

Coefficient of variation

(%)

 

 

 

 

 

 

 

 

Control

-

1

24.8

24.5

-

-

6.6

2

23.7

3

24.1

4

23.0

5

27.2

Test Substance

10

6

23.0

24.0

6

2

7.2

7

23.2

6

8

25.2

-3

9

22.4

9

10

26.5

-8

100

11

22.1

21.7

10

12

19

12

14.6

40

13

22.3

9

14

25.4

-4

15

24.0

2

1000

16

20.4

21.6

17

12

11

17

18.3

26

18

22.2

10

19

22.9

7

20

24.4

1

 

The data presented were calculated using unrounded values stored in the computer database. Minor numerical differences may be observed in the respiration rate calculation if rounded values are used to calculate the data. This minor discrepancy is not considered to be significant

Negative inhibition indicates a respiration rate greater than that of the mean control respiration rate

Validity criteria fulfilled:
yes
Remarks:
Control: specific respiration rate>20 mgO2/gh, coefficient of variation <30%. EC50 of 3,5-dichlorophenol was in the accepted range of 2-25 mg/L.

Description of key information

Toxicity to microorganisms: NOEC > 1000 mg/l (OECD 209).

Key value for chemical safety assessment

Additional information

The results indicate that the test material is not toxic to sewage bacteria up to the limits of its water solubility (<1 mg/L) and a NOEC and thus a PNEC cannot be determined.