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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
02-November 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
not required
Vehicle:
no
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, Loughborough, Leicestershire, UK
- Method of cultivation: used on day of collection (maintained on continuous aeration in the laboratory at a temperature of approximately 21 ºC)
- Pretreatment: none
- Initial biomass concentration: SS 3.0 g/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
21 ºC
pH:
6.6-7.5 (the pH at 1000 mg/L was adjusted to 7.1)
Dissolved oxygen:
5.8-8.1 (65-91% of saturation)
Nominal and measured concentrations:
Range finding study: 3 inoculum controls, 3 test concentrations (single at 10 and 100, triplicate at 1000 mg/L), 1 abiotic control, 3 reference substance controls (3.2, 10 and 32 mg/L dichlotophenol )
No main test performed
Details on test conditions:
TEST SYSTEM
- Test vessel: 0.5L glass
- Aeration: 0.5-1.0 L/min
- Biomass loading rate: inoculum concentration 3.0 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionized reverse osmosis water containing less than 1 mg/L Dissolved Organic Carbon

OTHER TEST CONDITIONS
- Adjustment of pH: at 1000 mg/L from 6.6 to 7.1
- Temperature: 21 °C

EFFECT PARAMETERS MEASURED : dissolved oxygen concentration over 30 seconds intervals over 5 minutes post exposure (10 minutes post exposure for positive controls)

TEST CONCENTRATIONS
- Range finding study: 10, 100 and 1000 mg/L
- Test concentrations: no main test performed
Reference substance (positive control):
yes
Remarks:
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
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:
- Adsorption (e.g. of test material to the walls of the test container): none observed
- Blank controls oxygen uptake rate: 38-0-40.8 mg O2/L/h (Specific 26.30 mgO2/dry sludge weight/h)
- Coefficient of variation of oxygen uptake rate in control replicates: 3.09%
Results with reference substance (positive control):
EC50 5.8 mg/L ( 4.4 – 7.7 mg/L)
Reported statistics and error estimates:
NA

Oxygen Consumption Rates and Percentage Inhibition Values after 3 Hours Contact Time in the Range-Finding Test

Nominal
Concentration
(mg/L)

Initial O2
Reading
(mg O2/L)

Measurement Period
(minutes)

Final O2Reading
(mg O2/L)

O2Consumption Rates
(mg O2/L/hour)

%
Inhibition

Control

R1

5.9

6

1.9

40.00

-

R2

5.7

6

1.8

39.00

-

R3

5.6

6

1.8

38.00

-

R4

5.6

5

2.2

40.80

-

Test Item

10

5.2

5

1.9

39.60

0

100

5.2

5

1.8

40.80

0

1000 R1

5.0

5

1.9

37.20

6

1000 R2

5.7

6

2.0

37.00

6

1000 R3

6.1

7

2.1

34.29

13

3,5-dichlorophenol

3.2

6.9

10

2.5

26.40

33

10

7.5

10

5.4

12.60

68

32

8.2

10

7.5

4.20

89

 


R1– R4= Replicates 1 to 4

Validity criteria fulfilled:
yes
Remarks:
see remark on O2 consumption rate
Conclusions:
The NOEC for respiration inhibition of activated sludge is 1000 mg/L.
Executive summary:

In a test according to OECD 209, no inhibition of the respiration of micro-organism in activated sludge was observed at 10, 100 and 1000 mg/L. The NOEC is 1000 mg/L.

Description of key information

In a test according to OECD 209 (Envigo 2017), no inhibition of the respiration of micro-organism in activated sludge was observed at 10, 100 and 1000 mg/L. The NOEC is 1000 mg/L. This confirms the results of an earlier study (RCC 1989) where the inhibition of oxygen at 100 mg/L was 12.4% (IC50 is > 100 mg/L).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information