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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016-09-15 - 2016-12-07
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Qualifier:
according to guideline
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
GLP compliance:
yes (incl. QA statement)
Remarks:
Rheinland-Pfalz Landesamt für Umwelt, Wasserwirtschaft und Gewerbeaufsicht
Specific details on test material used for the study:
Name Silicic acid Aluminium Magnesium Sodium Salt
Batch no. code # 1107274003
Appearance white powder
Composition Silic acid Aluminium Magnesium Sodium Salt
CAS No. 12040-43-6
EINECS-No. 234-919-5
Purity > 99 %
Homogeneity homogeneous
Vapour pressure not volatile
Stability stable at room temperature
Solubility poor soluble in water
Production date 2011
Expiry date 01. Nov. 2018
Storage room temperature (20 ± 5 °C), dry
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances): Due to the poor solubility of the test item, the test item was weighed directly into the test vessels.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Source: The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant D-67435 NW-Lachen-Speyerdorf.
- Pretreatment: Upon arrival in the test facility, the sludge was filtrated, washed with tap water and re-suspended in tap water. The activated sludge was aerated until usage in the test and fed daily with 50 ml/L synthetic sewage feed.
- Initial biomass concentration: The dry matter was determined as 2.62 g suspended solids/L, giving a concentration of 1.31 g suspended solids/L in the test.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Hardness:
1.08 mmol/L (Analysis of drinking water, Sep 2012)
Test temperature:
20.6 – 21.6 °C
Nominal and measured concentrations:
Nominal: 0, 1, 10, 100 and 1000 mg/L
Reference substance (positive control):
yes
Remarks:
3.5-Dichlorophenol
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
Remarks:
respiration rate
Key result
Duration:
3 h
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
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:
respiration rate
Details on results:
- Results with reference substance valid? yes

Results with reference substance (positive control):
3h-EC50 Positive Control: 8.8 mg/L
All values lie within the recommended range of 2 – 25 mg/L.
Reported statistics and error estimates:
For the estimation of the EC50 of the positive control, the fits showed good statistical correspondence of the data with the dose-response-equation. The positive control gave an EC50 of 8.8 mg/L which lie within the recommended range of 2 –25 mg/L. The coefficient of variation of oxygen uptake rate in control replicates was below 30 % at the end of the test. The oxygen uptake rate of the blank controls was above 20 mg O2 per gram activated sludge in 1 hour.
No observations were made which might cause doubts concerning the validity of the study outcome. The result of the test can be considered valid.

Table O2-Consumption, Inhibition

The values of the O2consumption (which is a measure for the viability of the bacteria) of control, test and positive control vessels and the calculated inhibition are presented in the following table. The measured pH at the end of the test is also stated.


Vessel No.


Content

Concentration in mg/L nominal

O2consump- tion in mg/(L*min)

O2consump- tion in mg/(L*h)


Inhibition in %


pH

1

Blank Control

0

0.6416

38.496

0

7.7

2

Blank Control

0

0.6158

36.950

0

7.8

3

Positive Control

5

0.4499

26.992

30.1

7.8

4

Positive Control

10

0.2788

16.726

56.7

7.8

5

Positive Control

20

0.1558

9.347

75.8

7.8

6

Positive Control

40

0.0870

5.222

86.5

7.9

7

Blank Con- trol

0

0.6484

38.904

0

7.7

8

Blank Con- trol

0

0.6317

37.902

0

7.7

9

Test Item

1000

0.6207

37.239

3.5

7.8

10

Test Item

1000

0.6370

38.219

1.0

7.8

11

Test Item

1000

0.6535

39.211

-1.6

7.8

12

Test Item

1000

0.6311

37.869

1.9

7.8

13

Test Item

1000

0.6579

39.477

-2.3

7.8

14

Test Item

100

0.6334

38.005

1.5

7.8

15

Test Item

10

0.6638

39.826

-3.2

7.7

16

Test Item

1

0.6747

40.481

-4.9

7.7

*17-32

*

*

*

*

*

*

33

Blank Con- trol

0

0.6639

39.832

0

7.7

34

Blank Con- trol

0

0.6575

39.449

0

7.7

Validity criteria fulfilled:
yes
Conclusions:
Silicic acid, Aluminium Magnesium Sodium Salt did not inhibit respiration of activated sludge significantly.

Description of key information

Silicic acid, aluminum magnesium sodium salt (CAS 12040-43-6, SMAS) did not inhibit respiration of activated sludge significantly:


 


3-hour EC50 (inhibition of total respiration) > 1000 mg/L


3-hour NOEC (inhibition of total respiration) >= 1000 mg/L

Key value for chemical safety assessment

Additional information

Since no studies investigating the toxicity of amorphous Silicic acid, aluminum sodium salt (CAS 1344-00-9, NAS) to microorganisms are available, a read-across to the structurally related Silicic acid, aluminum magnesium sodium salt (CAS 12040-43-6, SMAS) was conducted. This read-across is justified within the analogue justification in IUCLID Section 13.