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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
23 June 1999
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Qualifier:
according to
Guideline:
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Laboratory culture: yes, municipal sludge taken from a laboratory wastewater treatment fed with municipal sewage
- Preparation of inoculum for exposure: The inoculum was washed, brought to a concentration of 5 g/L dry substance and aerated for 24 hours.
50 mL were added to a total volume of 250 mL to obtain a concentration of 1 g/L dry substance in the test.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
30 min
Test temperature:
20 ± 2°C
Dissolved oxygen:
Oxygen concentration during aeration: > 2.5 mg/L
Oxygen concentration immediately before measurement: > 6.5 mg/L
Nominal and measured concentrations:
Nominal: 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: Erlenmeyer-vessel
- Material, size, headspace, fill volume: glass, nominal volume: 250 mL, fill volume 250 mL
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 3

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Synthetic medium: 8 mL/vessel 100-fold concentrated OECD medium

OTHER TEST CONDITIONS
- Adjustment of pH: yes
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
30 min
Dose descriptor:
other: EC20
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
30 min
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Results with reference substance (positive control):
- Results with reference substance valid? yes. EC50 of 3,5-dichlorophenol is in the range of 5-30 mg/L
- Relevant effect levels: 30 min EC20 = ca. 3.0 mg/L; 30-min EC50 = ca 15 mg/L; 30-min EC80 = ca. 50 mg/L (highest concentration tested: 100 mg/L)

Measured data - blank control (BC) and test substance (TS) after 30 minutes incubation time

BC1

BC2

BC3

mv

BC

TS1

Concentration of test substance (mg/L)

-

-

-

-

1001

Added volume of stock solution (mL/vessel)

-

-

-

-

125.0

Direct addition (mg/vessel)

-

-

-

-

-

Oxygen concentration start (mg O2/L)

7.8

8.1

7.9

-

8.1

Oxygen concentration after 6 min (mg O2/L)

6.2

6.6

6.2

-

6.5

Oxygen consumption rate (mg O2/L * 6 min)

1.6

1.5

1.7

1.6

1.6

Oxygen consumption rate (mg O2/L*h)

16

15

17

16

16

Specific oxygen consumption rate ( mg O2/g*h)

16

15

17

16

16

Change in oxygen consumption rate

compared with the blank control (%)

-

-

-

-

0

mv BC = mean value of blank control

pH-values - blank control (BC) and test substance (TS) after 30 minutes incubation time

Vessel no.:

BC1

BC2

BC3

TS1

pH-value before adding the inoculum

before correction:

after correction:

 

6.2

7.3

 

6.2

7.3

 

6.2

7.4

 

6.3

7.4

pH-value after an incubation time of 30 min

-

-

-

7.4

Measured data - reference substance (RS) after 30 minutes incubation time

Vessel no.:

mv

BC

 

RS1

 

RS2

 

RS3

Concentration of test substance (mg/L)

-

1

10

100

Added volume of stock solution (mL/vessel)

-

0.5

5.0

50.0

Oxygen concentration start (mg O2/L)

-

7.8

8.3

8.7

Oxygen concentration after 6 min (mg O2/L)

-

6.3

7.3

8.7

Oxygen consumption rate (mg O2/L * 6 min)

1.6

1.5

1.0

0.0

Oxygen consumption rate (mg O2/L*h)

16

15

10

0

Specific oxygen consumption rate ( mg O2/g*h)

16

15

10

0

Change in oxygen consumption rate

compared with the blank control (%)

-

6

37

100

pH-values - reference substance (RS) after 30 minutes incubation time

Vessel no.:

RS1

RS2

RS3

pH-value before adding the inoculum

before correction:

after correction:

 

6.2

7.2

 

6.2

7.2

 

6.4

7.2

Validity criteria fulfilled:
yes
Conclusions:
No inhibition of respiration was measured at the concentration tested (1000 mg/L).
Executive summary:

The inhibitory effect of N-methylmorpholine oxide on activated sludge respiration was tested according to OECD guideline 209 (version 1999) during an exposure time of 30 min. One replicate of 1000 mg/L test substance was used in a limit test. The final concentration of solids in the test vessels was 1 g/L. Inhibition was not observed, therefore the NOEC is reported to be >= 1000 mg/L and the EC20 is stated to be >1000 mg/L.

The study was valid at the time performed.

Description of key information

There is one study from BASF available. This result was chosen to derive PNEC-STP . The respiration inhibition test from BASF was performed according to a guideline (OECD 209) valid at that time including a test duration of 30 min. The 30 min. EC20 value of > 1000 mg/L is used for the CSA and derivation of the PNEC.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information