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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:
2001-02-15 to 2001-03-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method:  Tertiary butyl alcohol was used as a solvent in the five lower test solutions. HMDS was dosed directly in the 2 highest concentrations.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
Activated sludge from a domestic sewage oxidation ditch situated at the district of Hazerswoude Dorp, The Netherlands, taken on 5th March 2001.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
The oxygen concentration was recorded every minute during a period of about 10 minutes.
Test temperature:
20 ± 2 °C
pH:
8.1 to 8.3
Nominal and measured concentrations:
Nominal concentrations were 0, 0.10, 0.32, 1.0, 3.2, 11, 39 and 100 mg/l.
Details on test conditions:
TEST SYSTEM
- Test vessel: One litre glass beaker and BOD bottle

- Aeration: All suspensions were aerated vigorously.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Dilution water prepared by adding 1 ml of stock 1 to 4 to each litre of ultrapure water and store at 20 deg C in the dark with aeration. Prescription according to NEN 6634 [3].

- Vehicle: Tertiary butyl alcohol (TBA)

- Particulate matter: Activated sludge = 4.0 g (dw)/l

Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
The two controls had a difference in respiration rate of 2.6%, less than the 15% limit for a valid study.  The validity criteria of the Guideline were fulfilled.
Results with reference substance (positive control):
A positive control test with 3,5-dichlorophenol yielded an EC50 of 13.1 mg/l.  The validity criteria of the Guideline were fulfilled.

No inhibition of the respiration rate was observed within the entire concentration range. Based on nominal test concentrations, the NOEC of HMDS was >= 100 mg/l. The EC50 was >100 mg/l.

Table 1: Results of the activated sludge respiration inhibition test

Test sample

Nominal concentration of test substance (mg/l)

Respiration rate

(mg O2/g/h)

Coefficient of determination

% Inhibition

respiration rate

pH

Hexamethyldisiloxane

 

 

Initial control

0

18.6

-1.0000

-1.3

8.2

Final control

0

18.1

-0.9999

1.3

8.2

0.1

19.8

-1.0000

-0.8

8.2

0.32

20.0

-1.0000

-9.1

8.2

1

19.5

-1.0000

-6.4

8.1

3.2

19.6

-1.0000

-6.9

8.1

11

20.6

-1.0000

-12.0

8.1

39

21.0

-1.0000

-14.1

8.1

100

20.7

-1.0000

-12.9

8.1

 

 

3,5-dichlorophenol

 

 

Initial control

0

15.7

-0.9999

7.0

8.2

Final control

0

18.1

-0.9999

-7.0

8.2

5

14.6

-0.9998

13.7

8.3

12

8.9

-1.0000

47.7

8.3

30

3.5

-0.9743

79.4

8.3

 

Validity criteria fulfilled:
yes
Conclusions:
A NOEC of >=100mg/l and EC50 >100 mg/l for toxicity to microorganisms were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Toxicity to microorganisms: 3hr ASRI NOEC >=100mg/l; EC50 >100 mg/l (OECD 209)

Key value for chemical safety assessment

Additional information

Three reliable studies are available for toxicity to microorganisms.

Two reliable studies are ASRI (activated sludge respiration inhibition) studies. The key study (Mayer 2001) was chosen as the most recent study. This study gave a result of NOEC (3 h) ≥100 mg/l; EC50>100 mg/l. The result from the other reliable ASRI study (Diefenbach 1998) was EC50(3 h) >2000 mg/l.

A reliable study for growth inhibition for Pseudomonas putida is also available (Hanstveit 1999). The result was EC50(17 h) >100 mg/l.