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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
November 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Qualifier:
according to guideline
Guideline:
other: The Guideline for the Testing of Chemicals 209, Activated Sludge, Respiration Inhibition Test. MEP, China (2004).
GLP compliance:
yes
Remarks:
HJ/T 155-2004 The Guideline of Good Laboratory Practices on Chemical Testing, MEP, China
Specific details on test material used for the study:
- Analytical purity: 99.9 %
- Lot/batch No.: 301601
Analytical monitoring:
no
Details on sampling:
not applicable
Vehicle:
no
Details on test solutions:
A stock solution was used:
1.2504 g of 1,1-dimethylurea was dissolved in test water and up to 500 millilitre.
12.5 , 25, 50, 100 and ,200 mL of the test substance stock solution were respectively added to the 16 mL of synthetic sewage before adding water to 300 mL and 200 mL microbial innoculum to make a volume of 500 mL.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
Inoculum was collected from the exit of the aeration tank in the Suzhou Wuzhong district urban area sewage treatment plant, located at No.1 of Baodai East Road, Suzhou city. The inoculum batch number was AS-20131106-01.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Post exposure observation period:
Not applicable
Hardness:
no data
Test temperature:
19.0 - 19.9 °C
pH:
7.00 - 7.97
Dissolved oxygen:
0.3051 mg/L DOC
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 62.5, 125, 250, 500 and 1000 mg/L
Details on test conditions:
Duration / contact time: 3 hours during which aeration took place
Vessels: reagent bottle (1 L)
Water: deionised water containing 0.3051 mg/L DOC
Air supply: Clean, oil-free air. Air flow 1 litre/minute
Measuring apparatus: small mouth reagent bottle (500 mL), magnetic stirrer, parafilm
Oxygen meter: HQ40d Multi-Parameter
Nutrient solution: Synthetic sewage
Test substance: The test solution is freshly prepared at the start of the test
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
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
Remarks:
respiration rate
Results with reference substance (positive control):
The EC50 (3h) of 3, 5-dichlorophenol was 8.789 mg/L, and the 95% confidence limits was 7.185-10.669 mg/L, in the accepted range of 5 to 30 mg/L for total respiration.

Table 1: Temperature, pH value, respiration rate and inhibition respiration relative to the control

Groups

Vessel No.

Nominal Concentration

[mg/L]

Temperature []

pH

Respiration rate

[mg O2/L·h]

Inhibition respiration relative to the control [%]

Minimum

Maximum

Before aeration

After 3 h contact time

Controlgroup

C1

0

19.5

19.5

7.06

7.85

20.94

-

C2

0

19.1

19.2

7.07

7.85

20.45

-

Mean

-

-

-

-

-

-

Deviation

-

-

-

-

-

-

Test itemgroup

T-62.5

62.5

19.0

19.3

7.00

7.87

20.56

0.66

T-125

125

19.1

19.4

7.03

7.83

19.99

3.40

T-250

250

19.0

19.9

7.05

7.88

20.31

1.87

T-500

500

19.1

19.5

7.05

7.91

19.36

6.44

T-1000

1000

19.0

19.3

7.05

7.96

18.62

10.02

Reference substance

group

R-2.6

2.6

19.3

19.5

7.01

7.97

16.08

22.30

R-6.4

6.4

19.1

19.4

7.04

7.83

13.53

34.62

R-16.0

16.0

19.5

19.7

7.10

7.78

5.96

71.21

R-40.0

40.0

19.7

19.8

7.09

7.92

3.23

84.40

Maximum

19.9

7.10

7.97

-

-

Minimum

19.0

7.00

7.78

-

-

 Validity of the test:

- The coefficient of variation of oxygen uptake in control replicates was 2.3 %. This does not exceed 15 % and therefore meets the validity requirements of the test.

- The EC50(3h)-value of 3,5-dichlorophenol was 8.789 mg/L, and the 95% confidence limits were 7.185-10.669 mg/L. This lies in the accepted range of 5 to 30 mg/L for total respiration

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this present test, the EC20(3h)-, EC50(3h)-, EC80(3h)-value of 1,1-dimethylurea were higher than 1000 mg/L which was calculated as nominal concentration based on measured inhibition rates.
 
Executive summary:

The influence of 1,1 -Dimethylurea on the respiration rate of activated sludge was investigated in a study accorrding EU Method C.11 ("Biodegradation: Activated Sludge Respiration Inhibition Test").

The respiration rate of an activated sludge fed with a standard amount of synthetic feed was measured after a contact time of 3 hours. The respiration rate of the same activated sludge in the presence of various concentrations (62.5, 125, 250, 500 and 1000 mg/L) of the test sustance under otherwise identical conditions was also measured. The inhibitory effect of the test substance at a particular concentration was expressed as a percentage of the mean respiration rates of two controls. The EC50 value was calculated from percent inhibitory determinations at different concentrations.

Under the conditions of this present test, the EC20(3h)-, EC50(3h)- and EC80(3h)-value of 1,1 -Dimethylurea were higher than 1000 mg/L which was calculated as nominal concentration based on measured inhibition rates.

Description of key information

Under the conditions of this present test, the EC20(3h)-, EC50(3h)-, EC80(3h)-value of 1,1-dimethylurea

were higher than 1000 mg/L which was calculated as nominal concentration based on measured inhibition rates.
 

Key value for chemical safety assessment

Additional information

The influence of 1,1 -Dimethylurea on the respiration rate of activated sludge was investigated in a study according EU Method C.11 ("Biodegradation: Activated Sludge Respiration Inhibition Test").

The respiration rate of an activated sludge fed with a standard amount of synthetic feed was measured after a contact time of 3 hours. The respiration rate of the same activated sludge in the presence of various concentrations (62.5, 125, 250, 500 and 1000 mg/L) of the test sustance under otherwise identical conditions was also measured. The inhibitory effect of the test substance at a particular concentration was expressed as a percentage of the mean respiration rates of two controls. The EC50 value was calculated from percent inhibitory determinations at different concentrations.

Under the conditions of this present test, the EC20(3h)-, EC50(3h)- and EC80(3h)-value of 1,1 -Dimethylurea were higher than 1000 mg/L which was calculated as nominal concentration based on measured inhibition rates.