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Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Refer to read across justification provided in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
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
Remarks on result:
other:
Remarks:
Source: CAS 85049-37-2, Oleon, 1995, activated sludge
Conclusions:
No acute toxic effects on microorganisms were found up to the limit of water solubility (OECD 209, activated sludge, RA CAS 85049-37-2).
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
03 Jul 1995
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
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Each test solution was prepared by dissolving a certain amount of test substance in a mixture of 16 mL of the synthetic sewage and 200 mL of mixed liquor. The mixture was then diluted to 500 mL with deionised water.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Laboratory culture: no, activated sludge was obtained from the waste water treatment plant of Bocholt /Germany), which predominantly treats domestic sewage.
- Preparation of inoculum for exposure: The sludge was sieved through 0.5 mm sieve in order to remove large particles. A small amount of the mixed liquor is dried and weighed. From this result, a calculated amount of mixed liquor was suspended in water to obtain an activated sludge with mixed liquor suspended solids level of 4 g/L
- Initial biomass concentration: 1.6 g/L in test solution
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20.0 - 20.3 °C
pH:
Test end: 7.71-7.83
Nominal and measured concentrations:
Nominal: 6.5, 13.7, 26.0, 50.1 and 100.2 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: beakers
- Material: borosilicate glass; Size: 1000 mL; Fill volume: 500 mL
- Aeration: constant supply with clean, oil-free air
- No. of vessels per concentration: 1
- No. of vessels per control: 2

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: aerated tap water

EFFECT PARAMETERS MEASURED : Respiration rate inhibition was recorded after 3 h test duration.
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
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:
- No inhibition of the respiration rate was observed at the highest test concentration of 102 mg/L. Instead, a 16.2% stimulation was observed.
- Effect concentrations exceeding solubility of substance in test medium.
- The two control respiration rates are within 15% of each other.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50(3h) is in the range of 5 to 30 mg/L (21.7 mg/L)
Reported statistics and error estimates:
Logit model of Chou and Chou (1985), determining the median effect

Table 1: Respiration rates of activated sludge in control and % inhibition at different test concentrations:

Test substance [mg/L]

Respiration rate

[mg O2/L*h]

Inhibition [%]

Control 1

18.02

 

Control 2

17.09

 

6.5

19.91

- 13.4

13.7

21.54

- 22.7

26

19.49

- 11.0

50.1

21.89

- 24.7

100.2

20.39

- 16.2

Description of key information

No effects up to the limit of water solubility (OECD 209, activated sludge); read-across

Key value for chemical safety assessment

Additional information

There is no study available assessing the toxicity of the target substance Fatty acids, C16-18, isononyl esters (CAS 91031-57-1) to microorganisms. Therefore, read-across to the structurally related source substance Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters (CAS 85049-37-2) was conducted in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. The source substance is characterized by a similar fatty acid chain length as well as alcohol component and is therefore considered a suitable representative for the assessment of the toxicity of the target substance to microorganisms. A detailed read-across justification is provided in IUCLID section 13.

In the available study, the acute toxicity of Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters on activated sludge was tested according to OECD 209 under GLP conditions. After an incubation time of 3 hours, no inhibition of the respiration rate was observed within the tested concentration range of 6.5 to 100.2 mg/L (nominal), resulting in an EC50(3h) value of >100 mg/L.

Based on the structural and chemical similarity of the target and source substance, the target substance is expected to exhibit a similar ecotoxicological profile. Therefore, it can be concluded that Fatty acids, C16-18, isononyl esters (CAS 91031-57-1) will not exhibit toxic effects to microorganisms up to the limit of water solubility.