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Toxicity to microorganisms

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toxicity to microorganisms, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
28 Apr - 26 May 2005
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Data based on the inhibition control of a ready biodegradability study.
Reason / purpose for cross-reference:
reference to same study
according to guideline
other: OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
GLP compliance:
Analytical monitoring:
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: 5.15 ml of a stock solution of 10 g/I reference substance and 42.0 mg of the test item were added directly into the vessel
Test organisms (species):
activated sludge
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): activated sludge from the municipal wastewater treatment plant "Breisgauer Bucht"
- Preparation of inoculum for exposure: the activated sludge was washed twice by settling the sludge, decanting the supernatant and re-suspending the sludge in aerated tap water.
- Concentration of sludge: 30 mg dry solids/L
Test type:
Water media type:
Limit test:
Total exposure duration:
14 d
Test temperature:
21.0 - 22.0 °C
Nominal and measured concentrations:
Nominal test substance concentration: 42 mg/L
Details on test conditions:
- Composition of medium: mineral medium acc. to guideline
- Test temperature: 21.0 to 22.0 °C
- Suspended solids concentration: 30 mg dry solids per litre
- Continuous darkness: diffuse light

- Culturing apparatus: Gas wash bottles (2000 ml volume) with lateral connecting pieces for butyl rubber septums were used as reactors.
- Method used to create aerobic conditions: aeration with carbon dioxide free air.
- Details of trap for CO2 and volatile organics if used: 72 9 NaOH were dissolved in 9000ml deionised water in closed recipients (0.2 M NaOH). The inorganic carbon concentration of the 0.2 M NaOH was determined.

- Sampling frequency: On the 4th,7th,11th,14th,21stand 28thday

- Inoculum blank: 3 replicates
- Procedure control: 3 replicates
- Toxicity control: 1 replicate (5.15 ml of a stock solution of 10 g/I reference substance and 42.0 mg of the test item were added directly into the vessel.)
Reference substance (positive control):
benzoid acid, sodium salt
14 d
Dose descriptor:
Effect conc.:
42 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
other: CO2 evolution
Result of toxicity control from ready biodegradability test
Details on results:
The degradation in the toxicity control was 85.9% within 14 days and 82.3% within 28 days
Results with reference substance (positive control):
The reference substance reached > 90% degradation after 14 days.

“If in  a toxicity test, containing both the test and reference substance, less than 35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred within 14 days, the test substance can be assumed to be inhibitory.” (OECD guideline 301)

The degradation rate determined in the toxicity control was 85.9% after 14 days and thus the test substance is with high probability not toxic to aquatic microorganisms. The test item concentration in the toxicity control of 42 mg/L can be used as NOEC value for the toxicity to aquatic microorganisms.

Description of key information

 The assessment of the toxicity of the target substance to microorganisms is based on the results of the toxicity control of the available biodegradation study. A NOEC(14 d): 42 mg/L (based on toxicity control of OECD 301 B) is used as key value for the CSA of the target substance .   

Key value for chemical safety assessment

Additional information

The toxicity of the Ethoxylates (AE) category substances to microorganisms was assessed by read-across based on the grouping of substances (category approach). The available data were used for a general assessment of the toxicity of the Alcohol Ethoxylates (AE) category substances to microorganisms. Based on the available data adverse effects on microbial activity are not expected. The substances of the Alcohol Ethoxylates (AE) category are readily biodegradable. In all studies conducted with a toxicity control, no inhibition of the degradation process by the test substance was observed. The available studies investigating the respiration inhibition of activated sludge organisms and Pseudomonas putida determined no detrimental effects of the tested Alcohol Ethoxylates.