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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21/03/2018 - 27/03/2018
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 (Carbon and Ammonium Oxidation))
Version / remarks:
Adopted: 22 July 2010
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: the test material was weighed directly into the test vessels and diluted with deionised water.
- Eluate: deionised water
- Controls: blank control (equal volume of activated sludge and synthetic medium but not test or reference item), abiotic control (prepared by omitting the inoculum from the test mixtures), positive control (3,5-dichlorophenol)
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): not specified.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Name and location of sewage treatment plant where inoculum was collected: aeration tank of the City of Warsaw's sewage treatment plant ”Czajka”, receiving predominantly domestic sewage.
- Preparation of inoculum for exposure: The sludge was used as collected but coarse particles were removed by settling for a short period and decanting the upper layer of finer solids. The sludge was decanted for a period (15 minutes) to produce a clear supernatant and pellet of sewage solids. The supernatant liquid was discarded and the sludge was resuspended in chlorine-free tap water, with shaking and aeration, and the wash-water was removed by decantation and discarding again. The washing and decantation process was repeated four times. The dry mass of a known volume (100 ml) of the re-suspended sludge was determined and the sludge concentrated by removing liquor or diluted further in chlorine-free tap water to obtain the required sludge solids concentration of 3 g/L. The activated sludge was continuously aerated (3 L/minute) at the test temperature, and was used on the next day. The sludge was fed daily with the synthetic sewage feed (50 mL synthetic sewage feed/L activated sludge) for two additional days.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2ºC
pH:
7.5 ± 0.5
Dissolved oxygen:
60 – 70% saturation
Nominal and measured concentrations:
0.10, 1.0, 10.0, 100.0 and 1000.0 mg/L (nominal).
Details on test conditions:
TEST SYSTEM
- Test vessel: glass beakers
- Material, size, headspace, fill volume: glass, 1000 mL, no, 500 mL.
- Aeration: yes. Clean, oil-free air; air flow 0.5 to 1 L/min.
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- No. of vessels per abiotic control (replicates): 6
- Sludge concentration (weight of dry solids per volume): 1.5 g/L of suspended solids
- Nutrients provided for bacteria: synthetic sewage feed
- Nitrification inhibitor used: N-allylthiourea

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionised water was used for dilution, and chlorine–free tap water for activated sludge washing.

OTHER TEST CONDITIONS
- Adjustment of pH: yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- Inhibition of total oxygen uptake: At the end of 3 hour incubations, samples were withdrawn to measure the rate of decrease of the concentration of dissolved oxygen in a completely filled BOD bottle. The measurements were made individually. A sample from the first aeration vessel was transferred to fill a BOD bottle and the concentration of dissolved oxygen was immediately measured with the self-stirring oxygen electrode. From the data collected, the specific respiration rates of the control and test mixtures were calculated; the percentage inhibition was then calculated.
- Differentiation between inhibition of heterotrophic respiration and nitrification: The use of the specific nitrification inhibitor N-allylthiourea (ATU) enabled the direct assessment of the inhibitory effects of test item on heterotrophic oxidation, and by subtracting the oxygen uptake rate in the presence of ATU from the total uptake rate (no ATU present), the effects on the rate of nitrification were calculated. Two sets of reaction mixtures were prepared, but additionally, ATU was added to each mixture of one set at a final concentration of 11.6 mg/l, which is known to inhibit nitrification completely in sludge with suspended solids concentrations of up to 3000 mg/l. The oxygen uptake rates was measured after the exposure period; these direct values represent heterotrophic respiration only, and the differences between these and the corresponding total respiration rates represent nitrification. The various degrees of inhibition were then calculated.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: geometric series
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol (pure p.a. 100%, Sigma Aldrich, lot: MKBZ0947V)
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 on result:
other: highest concentration tested.
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
678.5 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
< 0.1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: no.
- Effect concentrations exceeding solubility of substance in test medium: no.
- Adsorption (e.g. of test material to the walls of the test container): no.
- Blank controls oxygen uptake rate: above 20 mg O2 per gram of activated sludge (dry weight of suspended solids) per hour.
- Coefficient of variation of oxygen uptake rate in control replicates: below 30%
Results with reference substance (positive control):
- Results with reference substance valid: yes
- Relevant effect levels: the values obtained for the reference item were all within the acceptance criteria, i.e. EC50 (total r.) = 4.57 mg/L (within range 2- 25 mg/L), EC50 (heterotrophic r.) = 8.03 mg/L (within range 5 - 40 mg/L), and EC50 (nitrification r.) = 0.20 mg/L (within range 0.1 - 10 mg/L).

Table 2. Summary of results.

Inhibition

(%)

EC5

(mg/L)

EC10

(mg/L)

EC15

 (mg/L)

EC20

 (mg/L)

EC25

 (mg/L)

Total

< 0.1

< 0.1

138.2

678.5

> 1000

Heterotrophic

0.72

12.85

294.3

>1000

>1000

Nitrification

< 0.1

< 0.1

< 0.1

184.1

866.0

Table 3. Test item total respiration; time related oxygen concentrations (mg/L).

             time, min

bottle #

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1– FB1

8.54

6.80

6.12

5.51

4.93

4.32

3.77

3.20

2.66

2.15

1.64

2 – FT1/0.10 mg/L

8.54

7.07

6.49

5.93

5.37

4.83

4.29

3.75

3.23

2.73

2.10

3 – FT2/0.10 mg/L

8.76

6.84

6.29

5.74

5.21

4.70

4.19

3.71

3.21

2.74

2.25

4 – FT3/0.10 mg/L

8.76

7.32

6.77

6.24

5.72

5.22

4.73

4.23

3.75

3.27

2.83

5 – FB2

8.76

7.23

6.52

5.88

5.32

4.66

4.05

3.50

2.96

2.42

1.88

6 – FT1/1.0 mg/L

8.62

6.24

5.63

5.05

4.53

3.97

3.46

2.96

2.44

1.95

--

7 – FT2/1.0 mg/L

8.55

6.82

6.31

5.75

5.19

4.64

4.13

3.59

3.09

2.58

2.11

8 – FT3/1.0 mg/L

8.19

7.49

6.94

6.40

5.83

5.28

4.73

4.17

3.63

3.11

2.57

9 – FB3

7.82

7.51

6.91

6.36

5.82

5.29

4.74

4.23

3.72

3.20

2.31

10 – FT1/10.0 mg/L

8.80

6.55

5.93

5.35

4.76

4.19

3.62

3.06

2.49

1.95

--

11 – FT2/10.0 mg/L

8.93

6.83

6.23

5.67

5.08

4.48

3.91

3.36

2.79

2.24

1.71

12 – FT3/10.0 mg/L

8.96

7.52

6.90

6.31

5.71

5.14

4.01

3.42

2.89

2.34

1.81

13 – FB4

8.19

5.95

5.22

4.38

3.73

3.04

2.38

1.72

--

--

--

14 – FT1/100.0mg/L

8.15

7.49

6.93

6.31

5.79

5.26

4.72

4.18

3.68

3.14

2.62

15 – FT2/100.0mg/L

6.54

5.77

5.20

4.64

4.11

3.55

3.00

2.51

2.00

1.49

--

16 – FT3/100.0mg/L

7.77

7.08

6.37

5.72

5.19

4.54

4.01

3.35

2.85

2.31

1.80

17 – FB5

9.18

6.76

6.07

5.39

4.75

4.08

3.45

2.79

2.19

1.59

--

18 – FT1/1000 mg/L

8.54

7.13

6.61

6.11

5.61

5.12

4.57

4.11

3.62

3.12

2.63

19– FT2/1000 mg/L

9.16

8.09

7.60

7.11

6.62

6.15

5.68

5.21

4.78

4.32

3.84

20 – FT3/1000 mg/L

8.04

7.43

6.88

6.36

5.88

5.36

4.87

4.39

3.91

3.46

2.98

21 – FB6

7.78

6.80

6.08

5.46

4.84

4.25

3.67

3.10

2.53

1.98

--

Table 4. Test item heterotrophic respiration; time related oxygen concentrations (mg/L).

            Time+ min

bottle #

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1 – FB7

8.20

7.29

6.65

6.11

5.62

5.10

4.60

4.07

3.60

3.10

2.64

2 – FHB1

8.40

7.76

7.45

7.15

6.86

6.57

6.30

6.01

5.74

5.45

5.18

3 – FH1/0.10 mg/L

8.83

8.08

7.79

7.53

7.25

6.97

6.70

6.41

6.13

5.87

5.60

4 – FH2/0.10 mg/L

9.01

8.17

7.83

7.56

7.29

7.01

6.75

6.47

6.20

5.93

5.65

5 – FH3/0.10 mg/L

8.76

7.97

7.70

7.44

7.13

6.88

6.60

6.33

6.06

5.82

5.54

6 – FHB2

8.85

8.23

7.94

7.67

7.39

7.12

6.83

6.53

6.30

6.07

5.79

7 – FH1/1.0 mg/L

8.79

8.26

8.01

7.75

7.48

7.23

6.97

6.70

6.43

6.18

5.96

8 – FH2/1.0 mg/L

8.86

8.33

8.06

7.78

7.51

7.24

6.98

6.71

6.46

6.18

5.96

9 – FH3/1.0 mg/L

8.82

8.14

7.85

7.58

7.32

7.06

6.78

6.52

6.25

5.98

5.75

10 – FHB3

8.45

8.09

7.78

7.48

7.18

6.88

6.61

6.34

6.05

5.82

5.50

11 – FH1/10.0 mg/L

8.86

8.26

8.01

7.76

7.52

7.27

7.04

6.80

6.52

6.32

6.11

12 – FH2/10.0 mg/L

8.74

8.46

8.20

7.92

7.66

7.43

7.19

6.95

6.70

6.44

6.21

13 – FH3/10.0 mg/L

8.91

7.97

7.73

7.46

7.20

6.96

6.70

6.46

6.19

5.95

5.71

14 – FHB4

8.68

8.21

7.87

7.61

7.31

7.05

6.80

6.52

6.26

6.02

5.76

15 – FH1/100.0 mg/L

9.05

8.66

8.38

8.09

7.90

7.65

7.42

7.20

6.97

6.76

6.55

16 – FH2/100.0 mg/L

8.92

8.57

8.31

8.08

7.83

7.59

7.36

7.12

6.87

6.63

6.41

17 – FH3/100.0 mg/L

8.98

8.64

8.42

8.22

7.95

7.71

7.45

7.22

7.00

6.78

6.58

18 – FHB5

8.86

8.35

8.03

7.73

7.42

7.14

6.81

6.53

6.24

5.94

5.68

19– FH1/1000 mg/L

9.27

8.80

8.59

8.42

8.18

7.99

7.78

7.59

7.40

7.21

7.02

20 – FH2/1000 mg/L

9.29

8.81

8.66

8.40

8.20

7.99

7.77

7.57

7.36

7.15

6.96

21 – FH3/1000 mg/L

9.30

8.70

8.52

8.27

8.08

7.90

7.69

7.50

7.31

7.11

6.93

22 – FHB6

8.93

8.49

8.21

7.92

7.63

7.37

7.10

6.84

6.57

6.41

6.20

23 – FB8

8.78

8.36

7.80

7.20

6.77

6.26

5.77

5.28

4.78

4.32

3.83


Table 5. Test item total respiration: values of initial and final pH.

Bottle #

1

2

3

4

5

6

7

8

9

10

11

12

13

14

pH0

7.13

7.18

7.22

7.28

7.20

7.23

7.26

7.40

7.31

7.27

7.27

7.33

7.22

7.29

pHfinal

7.36

7.37

7.27

7.40

7.31

7.31

7.35

7.35

7.24

7.32

7.40

7.44

7.31

7.44

Bottle #

15

16

17

18

19

20

21

 

pH0

7.30

7.29

7.31

7.30

7.30

7.31

7.21

 

pHfinal

7.36

7.39

7.30

7.36

7.43

7.43

7.43

 

Table 6. Test item heterotrophic respiration: initial and final pH.

Bottle #

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

pH0

7.24

7.35

7.41

7.42

7.34

7.42

7.39

7.48

7.38

7.38

7.37

7.43

7.36

7.34

7.46

pHfinal

7.22

7.85

7.84

7.85

7.93

7.74

7.87

7.67

7.54

7.51

7.50

7.65

7.63

7.56

7.62

Bottle #

16

17

18

19

20

21

22

23

 

pH0

7.37

7.37

7.35

7.41

7.53

7.36

7.29

7.19

 

pHfinal

7.58

7.69

7.69

7.52

7.69

7.82

7.75

7.02

 

Table 7. Test item total respiration: oxygen consumption rates.

Bottle #

1

2

3

4

5

6

7

8

9

10

11

Oxygen consumption rate R, mg/Lh

34.88

33.13

30.60

29.55

36.01

32.18

31.40

32.78

38.67

34.50

34.43

Specific respiration rate RS, mg/gh

23.25

22.09

20.40

19.70

24.01

21.45

20.93

21.85

25.78

23.00

22.95

Bottle #

12

13

14

15

16

17

18

19

20

21

 

Oxygen consumption rate R, mg/Lh

35.20

42.84

32.33

34.05

35.78

39.17

30.00

28.03

29.25

36.15

 

Specific respiration rate RS, mg/gh

23.47

28.56

21.55

22.70

23.85

26.11

20.00

18.69

19.50

24.10

 


Table 8. Test item heterotrophic respiration: oxygen consumption.

Bottle #

1

2

3

4

5

6

7

8

9

10

11

12

Oxygen consumption rate R, mg/Lh

31.00

16.89

16.50

16.40

15.90

16.00

15.24

15.36

15.72

16.80

13.92

14.64

Specific respiration rate RS, mg/gh

20.67

11.26

11.00

10.93

10.60

10.67

10.16

10.24

10.48

11.20

9.28

9.76

Bottle #

13

14

15

16

17

18

19

20

21

22

23

 

Oxygen consumption rate R, mg/Lh

14.90

15.48

13.00

14.25

13.05

15.12

11.60

12.40

11.50

13.50

28.89

 

Specific respiration rate RS, mg/gh

9.93

10.32

8.67

9.50

8.70

10.08

7.73

8.27

7.67

9.00

19.26

 


Table 9. The coefficient of variation of oxygen uptake rate in control replicates.

 

FB1

FB2

FB3

FB4

FB5

FB6

FB7

FB8

FHB1

FHB2

FHB3

FHB4

FHB5

FHB6

Oxygen consumption rate R, mg/Lh

34.88

36.01

38.67

42.84

39.17

36.15

31.00

28.89

16.89

16.00

16.80

15.48

15.12

13.50

mean μ , mg/Lh

35.95

29.95

15.63

standard. deviation σ

4.48

1.49

1.26

coefficient of variation

CV = σ/μ, %

12.46

4.98

8.06


Table 10. Test item total respiration inhibition.

Test item total respiration inhibition

Average oxygen consumption rate from FB1 and FB2 equals 35.45 mg/Lh was taken for the calculations

Bottle #

RT, mg/Lh

IT, %

2 – FT1/0.10 mg/L

33.13

6.54

3– FT2/0.10 mg/L

30.60

13.68

4 – FT3/0.10mg/L

29.55

16.64

Average

31.09 ± 1.84

12.29 ± 5.19

Average oxygen consumption rate from FB2 and FB3 equals 37.34 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

6 – FT1/1.0 mg/L

32.18

13.82

7 – FT2/1.0 mg/L

31.40

15.91

8– FT3/1.0 mg/L

32.78

12.21

Average

32.12 ± 0.69

13.98 ± 1.86

Average oxygen consumption rate from FB3 and FB4 equals 39.84 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

10 – FT1/10.0 mg/L

34.50

13.40

11 – FT2/10.0 mg/L

34.43

13.58

12 – FT3/10.0 mg/L

35.20

11.65

Average

34.71 ± 0.43

12.88 ± 1.07

Average oxygen consumption rate from FB4 and FB5 equals 41.01mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

14 – FT1/100.0mg/L

32.33

21.17

15 – FT2/100.0 mg/L

34.05

16.97

16 – FT3/100.0 mg/L

35.78

12.75

Average

34.05 ± 1.73

16.96 ± 4.21

Average oxygen consumption rate from FB5 and FB6 equals 37.66mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

18 – FT1/1000 mg/L

30.00

20.34

19– FT2/1000 mg/L

28.03

25.57

20 – FT3/1000 mg/L

29.25

22.33

Average

29.09 ± 0.99

22.74 ± 2.64


Table 11. Test item heterotrophic respiration inhibition.

Test item total respiration inhibition

Average oxygen consumption rate from FB1 and FB2 equals 35.45 mg/Lh was taken for the calculations

Bottle #

RT, mg/Lh

IT, %

2 – FT1/0.10 mg/L

33.13

6.54

3– FT2/0.10 mg/L

30.60

13.68

4 – FT3/0.10mg/L

29.55

16.64

Average

31.09 ± 1.84

12.29 ± 5.19

Average oxygen consumption rate from FB2 and FB3 equals 37.34 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

6 – FT1/1.0 mg/L

32.18

13.82

7 – FT2/1.0 mg/L

31.40

15.91

8– FT3/1.0 mg/L

32.78

12.21

Average

32.12 ± 0.69

13.98 ± 1.86

Average oxygen consumption rate from FB3 and FB4 equals 39.84 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

10 – FT1/10.0 mg/L

34.50

13.40

11 – FT2/10.0 mg/L

34.43

13.58

12 – FT3/10.0 mg/L

35.20

11.65

Average

34.71 ± 0.43

12.88 ± 1.07

Average oxygen consumption rate from FB4 and FB5 equals 41.01mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

14 – FT1/100.0mg/L

32.33

21.17

15 – FT2/100.0 mg/L

34.05

16.97

16 – FT3/100.0 mg/L

35.78

12.75

Average

34.05 ± 1.73

16.96 ± 4.21

Average oxygen consumption rate from FB5 and FB6 equals 37.66mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IT. %

18 – FT1/1000 mg/L

30.00

20.34

19– FT2/1000 mg/L

28.03

25.57

20 – FT3/1000 mg/L

29.25

22.33

Average

29.09 ± 0.99

22.74 ± 2.64

Test item heterotrophic respiration inhibition

Average oxygen consumption rate from FHB1 and FHB2 equals 16,45 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IH. %

3 – FH1/0.10 mg/L

16.50

          -0.30   

4 – FH2/0.10 mg/L

16.40

                0.30           

5 – FH3/0.10 mg/L

15.90

3.34

Average

16.27 ± 0.32

1.11 ± 1.95

Average oxygen consumption rate from FHB2 and FHB3 equals 16.40 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IH. %

7 – FH1/1.0 mg/L

15.24

7.07

8 – FH2/1.0 mg/L

15.36

                 6.34          

9 – FH3/1.0 mg/L

15.72

4.15

Average

15.44 ± 0.25

5.85 ± 1.52

Average oxygen consumption rate from FHB3 and FHB4 equals 16.14 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IH. %

11 – FH1/10.0 mg/L

13.92

13.76

12 – FH2/10.0 mg/L

14.64

9.29

13 – FH3/10.0 mg/L

14.90

                                                   7.68

Average

14.49 ± 0.51

10.24 ± 3.15

Average oxygen consumption rate from FHB4 and FHB5 equals 15.29 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IH. %

15 – FH1/100.0 mg/L

13.00

14.98

16 – FH2/100.0 mg/L

14.25

6.80

17 – FH3/100.0 mg/L

13.05

14.65

Average

13.43 ± 0.71

12.14 ± 4.63

Average oxygen consumption rate from FHB5 and FHB6 equals 14.31 mg/Lh was taken for the calculations

Bottle #

RT. mg/Lh

IH. %

19– FH1/1000 mg/L

11.60

18.94

20 – FH2/1000 mg/L

12.40

13.35

21 – FH3/1000 mg/L

11.50

19.64

Average

11.83 ± 0.49

17.31 ± 3.45

Table 12. Percentage of test item nitrification inhibition.

Test item concentration, mg/L of test item

IN, %

0.10

18.01

1.0

20.34

10.0

19.68

100.0

19.82

1000

26.08

Table 13. Calculated values of the ECx endpoints for the test item.

Inhibition, %

EC5

EC10

EC15

EC20

EC25

Total

< 0.1

< 0.1

138.2

678.5

> 1000

Heterotrophic

0.72

12.85

294.3

>1000

>1000

Nitrification

< 0.1

< 0.1

< 0.1

184.1

866.0


Validity criteria fulfilled:
yes
Remarks:
see 'overall remarks'.
Conclusions:
Under test conditions, the EC50 values were not determinable because they were above the highest concentration tested. It can be assumed that EC50 > 1000 mg/L.
Executive summary:

A study on the activated sludge respiration inhibition of the test item was carried out according to OECD 209 (GLP study). The respiration rates of samples of activated sludge from a sewage treatment plant treating predominantly domestic sewage (1.5 g/L suspended solids) and fed with synthetic sewage was measured in an enclosed cell containing an oxygen electrode after a contact time (incubation) of 3 hours, at concentrations of 1.0, 10.0, 100.0, 1000.0, 10000 mg/L (nominal). The inhibition of three different oxygen uptakes was determined, total, heterotrophic only and due to nitrification. Blank controls, abiotic controls and positive controls (3,5 -dichlorophenol, tested at 0.01, 0.1, 1.0, 10.0 and 100 mg/L) were run in parallel. All validity criteria were fulfilled.

The following values 3h-ECX (mg/L) were determined:

Inhibition, %

EC5

EC10

EC15

EC20

EC25

Total

< 0.1

< 0.1

138.2

678.5

> 1000

Heterotrophic

0.72

12.85

294.3

>1000

>1000

Nitrification

< 0.1

< 0.1

< 0.1

184.1

866.0

The EC50 values were not determinable because they were above the highest concentration tested. It can be assumed that EC50 > 1000 mg/L for the test item.

Description of key information

Key study. Method according to OECD 209, GLP study. It can be assumed that EC50 > 1000 mg/L for the test item.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
0.1 mg/L

Additional information

A study on the activated sludge respiration inhibition of the test item was carried out according to OECD 209 (GLP study). The respiration rates of samples of activated sludge from a sewage treatment plant treating predominantly domestic sewage (1.5 g/L suspended solids) and fed with synthetic sewage was measured in an enclosed cell containing an oxygen electrode after a contact time (incubation) of 3 hours, at concentrations of 1.0, 10.0, 100.0, 1000.0, 10000 mg/L (nominal). The inhibition of three different oxygen uptakes was determined, total, heterotrophic only and due to nitrification. Blank controls, abiotic controls and positive controls (3,5 -dichlorophenol, tested at 0.01, 0.1, 1.0, 10.0 and 100 mg/L) were run in parallel. All validity criteria were fulfilled.

The following values 3h-ECX (mg/L) were determined:

Inhibition, %

EC5

EC10

EC15

EC20

EC25

Total

< 0.1

< 0.1

138.2

678.5

> 1000

Heterotrophic

0.72

12.85

294.3

>1000

>1000

Nitrification

< 0.1

< 0.1

< 0.1

184.1

866.0

The EC50 values were not determinable because they were above the highest concentration tested. It can be assumed that EC50 > 1000 mg/L for the test item.