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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016-11-16 to 2017-06-23
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:
no
Vehicle:
not specified
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Nominal amounts of test item (90, 160 and 280 mg (five replicates of each)) were each separately dispersed in approximately 200 mL of deionized reverse osmosis water and subjected to ultrasonication for approximately 15 minutes followed by magnetic stirring for 24 hours, at temperatures of between 20 °C and 21 °C, in order to maximize the dissolved test item concentration. All test vessels were shielded from the light during mixing. Synthetic sewage (16 mL), activated sewage sludge (250 mL) and water were added to a final volume of 500 mL to give the required concentrations of 180, 320 and 560 mg/L (five replicates of each).
- Controls: maintained under identical conditions but not exposed to the test item
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Name and location of sewage treatment plant where inoculum was collected: from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK which treats predominantly domestic sewage
- Preparation of inoculum for exposure: A synthetic sewage of the following composition, was added to each test vessel to act as a respiratory substrate: 16 g Peptone, 11 g Meat extract, 3 g Urea, 0.7 g NaCl, 0.4 g CaCl2.2H2O, 0.2 g MgSO4.7H2O 2.8 g K2HPO4 dissolved in a final volume of 1 liter of deionized reverse osmosis water with the aid of ultrasonication.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
approx. 21°C
pH:
7.0 - 7.7
Dissolved oxygen:
after 30 min: 5.5-7.0 mgO2/L
after 3 hours: 1.7-2.3 mgO2/L
Nominal and measured concentrations:
180, 320 and 560 mg/L (test item)
Details on test conditions:
TEST SYSTEM
- Test vessel: 500 mL conical flask
- Aeration: with clean, oil-free compressed air via narrow bore glass tubes at a rate of 0.5 to 1.0 liter per minute
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 6
- Sludge concentration (weight of dry solids per volume): 3.0g/L

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

OTHER TEST CONDITIONS
- Adjustment of pH: yes between pH 7.0 to pH 8.0
- Light intensity: normal laboratory lighting
- Details on termination of incubation: after 3 hours contact time an aliquot was removed from the conical flask

Range finding study :
- Test concentrations: 10, 100 and 1000 mg/L.
- Results used to determine the conditions for the definitive study: yes, statistically significant toxic effects were shown at the test concentration of 1000 mg/L
Reference substance (positive control):
yes
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
180 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 560 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks on result:
not determinable because of methodological limitations
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50 = 6.8mg/L

Oxygen Consumption Rates and Percentage Inhibition Values after 3 Hours Contact Time in the Definitive Test

Nominal Concentration (mg/L)

Initial O2 Reading (mg O2/L)

Measurement Period (minutes)

Final O2 Reading (mg O2/L)

O2 Consumption Rates (mg O2/L/hour)

% Inhibition

Control

R1

5.8

5

2.1

44.4

-

R2

5.8

5

2.2

43.2

-

R3

5.9

5

2.3

43.2

-

R4

5.5

5

1.7

45.6

-

R5

5.4

5

1.9

42

-

R6

5.4

5

1.9

42

-

Test Item

180 R1

5.7

5

2

44.4

[2]

180 R2

5.9

5

2.3

43.2

0

180 R3

5.6

5

1.8

45.6

[5]

180 R4

5.5

5

1.8

44.4

[2]

180 R5

5.5

5

1.9

43.2

0

320 R1

5.1

5

1.7

40.8

6

320 R2

4.8

4

2.1

40.5

7

320 R3

5.2

5

2

38.4

12

320 R4

5.5

6

1.8

37

15

320 R5

5.8

6

2

38

12

560 R1

6

7

1.9

35.14

19

560 R2

6

7

1.9

35.14

19

560 R3

6.2

7

2.1

35.14

19

560 R4

6.2

7

2.2

34.29

21

560 R5

6.6

8

2.2

33

24

3,5-dichlorophenol

3.2

6.4

9

1.8

30.67

29

10

7.4

10

4.7

16.2

63

32

8.4

10

7.5

5.4

88

Validity criteria fulfilled:
yes
Conclusions:
The toxicity of the test substance to microorganisms was determined in a GLP study according to OECD 209.
No statistically significant toxic effects were shown at the test item concentration of 180 mg/L.
Executive summary:

The No Observed Effect Concentration (NOEC) after 3 hours exposure was 180 mg/L.

Description of key information

The toxicity of the test substance to microorganisms was determined in a GLP study according to OECD 209. No analytical verification was conducted.

Based on these results the No Observed Effect Concentration (NOEC) after 3 hours exposure was 180 mg/L (nominal).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
180 mg/L

Additional information