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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
GLP compliance:
yes
Analytical monitoring:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The test material was dissolved directly in water.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Water media type:
freshwater
Total exposure duration:
3 h
Test temperature:
21 ± 1ºC
pH:
See table 1
Nominal and measured concentrations:
480, 850, 1500, 2700 and 4500 mg/L (nominal)
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 250 mL darkened glass BOD bottle
- Aeration: Aerated with clean, oil-free compressed air via narrow bore glass tubes at a rate of approximately 0.5 – 1 L per min
-- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2



OTHER TEST CONDITIONS
- Light intensity: Normal laboratory lighting


EFFECT PARAMETERS MEASURED: Oxygen measurement at 0 and 3 h


Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
2 700 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: equivalent to 2401 mg/L cyanuric acid
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 4 500 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: Equivalent to 3402 mg/L cyanuric acid
Results with reference substance (positive control):
- Relevant effect levels: 3 hr EC50 = 8.0 mg/l (95% CL: 6.3-10 mg/l)

Table 1: pH measurements

Substance

Nominal Concentration (mg/L)

pH

0 H

3 H

Control

R1

7.7

8.0

R2

7.7

8.0

Test material

480

8.1

8.1

850

8.2

8.2

1500

8.4

8.3

2700

8.5

8.3

4500

8.7

8.4

3,5-dichlorophenol

3.2

7.7

8.2

10

7.7

8.3

32

7.7

8.3

Table 2: Oxygen consumption rates and percentage inhibition values in the definitive test after 30 minutes contact time

Substance

Nominal Conc. *

(mg/L)

Initial O2 reading

(mg O2/L)

Measurement period

(min)

Final O2 reading

(mg O2/L)

O2 consumption rate

(mg O2/L/min)

% inhibition

Control

R1

6.3

9

2.0

0.48

-

R2

6.1

8

2.0

0.51

-

Test material

480

5.6

6

2.6

0.50

[1]

850

5.6

7

2.4

0.46

7

1500

5.3

7

1.9

0.49

1

2700

4.8

6

1.9

0.48

3

4500

5.0

5

2.2

0.56

[13]

3,5-dichlorophenol

3.2

6.5

10

2.5

0.40

19

10

7.8

10

5.6

0.22

56

32

8.2

10

7.3

0.09

82

[Increase in respiration rate as compared to controls]

* mg test material/L (the equivalent cyanuric acid concentration is 75.6% of this value)

Table 3: Oxygen consumption rates and percentage inhibition values in the definitve test after 3 hours contact time

Substance

Nominal Conc. *

(mg/L)

Initial O2 reading

(mg O2/L)

Measurement period

(mins)

Final O2 reading

(mg O2/L)

O2 consumption rate

(mg O2/L/min)

% inhibition

Control

R1

6.2

9

2.0

0.47

-

R2

5.6

8

1.6

0.50

-

Test material

480

6.4

8

2.8

0.45

7

850

6.2

9

2.4

0.42

13

1500

6.6

10

2.4

0.42

13

2700

6.3

9

2.6

0.41

15

4500

6.5

9

3.0

0.39

20

3,5-dichlorophenol

3.2

6.8

10

3.1

0.37

24

10

7.5

10

5.5

0.20

59

32

8.0

10

7.3

0.07

86

R1 -R2 = replicates 1 to 2

Validity criteria fulfilled:
yes
Conclusions:
The effect of the test material on the respiration of activated sewage sludge micro-organisms gave a 3-hour EC50 of greater than 4500 mg/l equiavlent to 3402 mg cyanuric acid/l). The No Observed Effect Concentration (NOEC) after 3 hours exposure was 2700 mg/l (equivalent to 2041 mg cyanuric acid)

Description of key information

Activated Sludge, Respiration Inhibition study carried out according to OECD 209 with monosodium salt of cyanuric acid.

Key value for chemical safety assessment

EC50 for microorganisms:
3 402 mg/L

Additional information

A study was performed to assess the effect of the monosodium salt of cyanuric acid on the respiration of activated sewage sludge. (Clarke 2007). Activated sewage sludge was exposed to an aqueous solution of the test material at concentrations of 480, 850, 1500, 2700 and 4500 mg/L (equivalent to 363, 643, 1134, 2041 and 3402 mg cyanuric acid/L) for a period of 3 hours at a temperature of 21°C with the addition of a synthetic sewage as a respiratory substrate. The rate of respiration was determined after 30 minutes and 3 hours contact time and compared to data for the control and a reference material 3,5 -dichlorophenol. The effect of the test material on the respiration of activated sewage sludge gave a 3 hour EC50 of >4500 mg/L (equivalent to 3402 mg cyanuric acid/L). The NOEC after 3 hours exposure was 2700 mg/L (equivalent to 2041 mg cyanuric acid/L).