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Toxicity to microorganisms

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Reference
Endpoint:
toxicity to microorganisms, other
Remarks:
Toxicity control of ready biodegradability study according to OECD 301F
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Data based on the inhibition control of a ready biodegradability study. This approach is in accordance with the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA 2017).
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
other: Toxicity control from ready biodegradability study according to OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
GLP compliance:
yes (incl. QA statement)
Remarks:
Hessisches Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz, Germany
Analytical monitoring:
no
Details on sampling:
SAMPLING
- Sampling method: The pressure decrease in the reaction vessels was measured daily.
Vehicle:
no
Details on test solutions:
- Composition of medium: according to guideline OECD 301 F
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Source of inoculum/activated sludge: Sewage treatment plant Bensheim, Germany
- Preparation of inoculum for exposure: Activated sludge used for this study was deposited for 15 min and washed by centrifugation. Aliquotes of washed sludge suspension, corresponding to 3.5 g dry material/L were mixed with test water and aerated overnight
- Pretreatment: Sludge was washed by centrifugation, liquid phase was then decanted and solid material was re-suspended in tap water and centrifuged, procedure was repeated 3 times. An aliquot of the final sludge suspension was weighed, dried and ratio of wet sludge to dry weight was determined.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
14 d
Test temperature:
22 °C ± 1 °C
pH:
7.4 - 7.9
Nominal and measured concentrations:
Nominal:. 102.87 mg test item/L
Details on test conditions:
TEST CONDITIONS
- Composition of medium: according to guideline OECD 301 F
- Suspended solids concentration: 28.7 mg sludge/L per flask
- Continuous darkness: yes
- Other: continuous stirring

TEST SYSTEM
- Culturing apparatus: Manometric Test System with test flasks containing a volume of approx. 500 mL.
- Number of culture flasks/concentration: 1
- Measuring equipment: BSB/BOD-Sensor-System, Aqualytic Dortmund, Germany
- Test performed in closed vessels: yes
- Details of trap for CO2: potassium hydroxide solution (45%)


CONTROL AND BLANK SYSTEM
- Inoculum control: 2 flasks
- Abiotic sterile control: 1 flask (poisoned with CuSO4)
- Other: procedure control: 1 flask
Reference substance (positive control):
yes
Remarks:
benzoic acid, sodium salt
Duration:
14 d
Dose descriptor:
NOEC
Effect conc.:
>= 102.87
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks on result:
other: Result of toxicity control from ready biodegradability test
Details on results:
The toxicity control attained 61% biodegradation after 14 d and 62% after 28 d (the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms as degradation was >25% within 14 d.)
Results with reference substance (positive control):
94% biodegradation of reference substance after 14 d and 103% after 28 days.

Since more than 25% degradation occurred in the toxicity control, the substance is with high probability not toxic to aquatic microorganisms. The test item concentration in the toxicity control of 102.87 mg/L can be used as NOEC value for the toxicity to aquatic microorganisms.

Validity criteria fulfilled:
yes
Remarks:
For details see cross-referenced study

Description of key information

NOEC (14 d) ≥ 102.87 mg/L (nominal, toxicity control, OECD 301F, activated sludge)

Key value for chemical safety assessment

Additional information

Since no studies on the toxicity to aquatic microorganisms are available the results of a ready biodegradability study are used to draw conclusion on the toxicity of the substance to aquatic microorganisms. If a compound biodegrades readily in a biodegradability test or does not inhibit at a certain concentration the degradation of a reference substance in the positive control the substance is not considered toxic to microorganisms and the concentration applied in the toxicity control can be set as the NOEC value. This approach is in accordance with the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA 2017).

A substance can be assumed to be not inhibitory to aquatic microorganisms, if in the toxicity control of a ready biodegradation test, more than 25% degradation based on ThOD occurred within 14 days (OECD guideline 301).

For the test item fatty acids, tall-oil, esters with ethylene glycol (CAS 68187-85-9) a biodegradation test according to OECD guideline 301F is available. The test includes a toxicity control, which contains 102.87 mg/L of the test item and 103.69 mg/L benzoic acid. The toxicity control attained 61% degradation after 14 days of incubation. Hence, the substance is considered not toxic to aquatic microorganisms and the test item concentration of 102.87 mg/L can be used as NOEC.