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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
GLP - Guideline study. In accordance to the ECHA guidance document “Practical guide 6: How to report read-across and categories (March 2010)”, the reliability was changed from RL1 to RL2 to reflect the fact that this study was conducted on a read-across substance.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION - TEST SUBSTANCE:
- Method: The test substance is non-soluble in water in concentrations needed for the test. For this reason direct dosing of test substance into 100 mL of deionised water was used.
- Differential loading: yes
- Controls: yes
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Method of cultivation:
The activated sludge was collected two days before the day of testing. After the sample collection the sludge was washed with potable water for 0.5 hour and subsequently decanted for 0.5 hour. This procedure was repeated three times in total. Further the sludge was modified by addition of 50 mL of cultivation medium per 2 L of diluted sludge suspension at permanent aeration till the day of the test.

- Preparation of inoculum for exposure:
Before the test the sludge was suspended in water up to concentration about 4000 mg of sludge dry weight per litre. The pH adjustment to 6.0 was carried out. In that way modified sludge suspension was aerated until the use.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
180 min
Test temperature:
20 ± 2 °C
Nominal and measured concentrations:
Main test: 100, 180, 320, 560, 1000 mg/L (nominal)
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Fill volume: 500 mL
- Aeration: filtered compressed-air, airflow rate 0.8 L/min
- No. of organisms per vessel: 207 mL/L of activated sludge (concentration of 4000 mg/L)
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Abiotic oxygen uptake was assessed at the highest test substance concentration (1000 mg/L) in nutrient medium without sludge and with addition of 1 mL of mercury chloride solution.


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of test medium: according to OECD 209
- Source/preparation of dilution water: deionised water
- Culture medium different from test medium: no


OTHER TEST CONDITIONS
- Adjustment of pH: no


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- oxygen consumption


TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8
- Range finding study
- Test concentrations: 46, 100, 220, 460, 1000 mg/L
Reference substance (positive control):
yes
Remarks:
(3,5-dichlorophenol)
Duration:
180 min
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
180 min
Dose descriptor:
EC10
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):
- Results with reference substance valid? yes
- Relevant effect levels: EC50 = 12.2 mg/L (95% CL 10.2 - 15.5 mg/L)
Reported statistics and error estimates:
- 95% confidence intervals for reference substance: QC.Expert 2.5 ©1998-2000 (product of TriloByte Ltd., Czech Republic)

Main test

order of mixtures:

- control 1 and 2: K1 and K2

- reference substance: R1 - R5

- test substance: Z1 - Z5

- abiotic oxygen consumption: Zab

Table 1. Inhibition of respiration in the main test

Containernumber

Label

Conc.

mg.L-1

p1

mg.L-1

p2

mg.L-1

t1

min

t2

min

R

mg.L-1. h-1

Inhibition

%

1

K 1

0

6.50

2.65

0.5

7.5

33.00

0

2

R 1

19

8.02

6.48

0

10

9.24

71.4

3

R 2

14

7.88

5.71

0

10

13.02

59.8

4

R 3

10

7.44

4.08

0

10

20.16

37.7

5

R 4

7.2

7.28

2.95

0

10

25.98

19.7

6

R 5

5.2

6.45

2.51

1.0

9.5

27.81

14.1

7

Z 1

100

6.37

2.47

0.5

7.5

33.43

-3.3

8

Z 2

180

6.39

2.52

1.5

8.5

33.17

-2.5

9

Z 3

320

6.44

2.60

0.5

7.5

32.91

-1.7

10

Z 4

560

6.43

2.63

1.0

8.0

32.57

-0.6

11

Z 5

1000

6.50

2.69

0

7.0

32.66

-0.9

12

K 2

0

6.37

2.67

1.5

8.5

31.71

0

13

Zab

1000

8.66

8.69

0

10

-0.18

-

Average value of K1, K2 = 32.36 mg.L-1. h-1,     SD = 0.912 mg.L-1. h-1

Validity criteria fulfilled:
yes

Description of key information

Cenospheres are not harmful to microorganisms and  the inhibition of the degradation activity of activated sludge is also not anticipated.

Key value for chemical safety assessment

Additional information

One activated sludge study according to OECD 209 is available for the structural related ash (residues), coal. The tested ash was structural related to ash (residues), cenospheres and as cenospheres are a component of fly ash, these results can be used as read across. The NOEC is greater than 100 mg/L (WAF). There is no toxicity in the range of water solubility of ashes and the inhibition of the degradation activity of activated sludge is also not anticipated. It is not expected that cenospheres have adverse effects on microorganisms. In conclusion, cenospheres are not toxic to waste water (activated sludge) bacteria.