N,N'-methylenedistearamide

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

15 May 2018 to 13 Jun 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Version / remarks:

1992

Deviations:

yes

Remarks:

see 'Any other information on materials and methods incl. tables'

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Name of test material (as cited in study report): N,N'-methylenedistearamide
- Batch No.: VUW 14902
- Purity: 99.5%
- Appearance: White powder
- Expiration date: 31 August 2018
- Storage conditions: Room temperature in the dark

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Obtained on 14 May 2018 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.
- Preparation of inoculum: The activated sewage sludge sample was washed twice by settlement and re-suspension in mineral medium to remove any excessive amounts of Dissolved Organic Carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21 ºC and used on the day of collection. Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 mL) of the washed activated sewage sludge by suction through pre-weighed GF/A filter paper* using a Buchner funnel. Filtration was then continued for a further 3 minutes after rinsing the filter three successive times with 10 mL of deionized reverse osmosis water. The filter paper was then dried in an oven at approximately 105 ºC for at least one hour and allowed to cool before weighing. This process was repeated until a constant weight was attained.

Duration of test (contact time):

28 d

Initial conc.:

10.15 mg/L

Based on:

TOC

Remarks:

replicate 1

Initial conc.:

9.82 mg/L

Based on:

TOC

Remarks:

replicate 2

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: The deionized reverse osmosis water used for the preparation of the mineral medium and the mineral medium used for the test contained less than 1 mg/L Total Organic Carbon (TOC).
- Preparation of the test substance: The test item was dispersed directly in mineral medium. An amount of test item (39.0 mg) was dispersed in approximately 400 mL of mineral medium with the aid of ultrasonication (15 minutes) prior to dispersal in inoculated mineral medium. The volume was adjusted to 3 liters to give a final concentration of 13.0 mg/L, equivalent to 10 mg carbon/L. A test concentration of 10 mg carbon/L was employed in the test following the recommendations of the Test Guidelines.
- Test temperature: 20 - 25 °C
- pH: 7.3 - 7.4
- pH adjusted: Yes. On Day 0 the test and reference items were added and the pH of all vessels measured using a Hach HQ40d Flexi handheld meter and were adjusted to pH 7.4 ±0.2 using diluted hydrochloric acid or sodium hydroxide solution prior to the volume in all the vessels being adjusted to 3 liters by the addition of mineral medium which had been purged overnight with CO2-free air. The inoculum control vessels were prepared in a similar manner without the addition of test item or reference item.
- Aeration of dilution water: Yes
- Suspended solids concentration: 2.4 g/L
- Continuous darkness: Yes
- Other: The test vessels were sealed and CO2-free air bubbled through the solution at a rate of 30 to 100 mL/minute per vessel and stirred continuously by magnetic stirrer.

TEST SYSTEM
- Number of culture flasks/concentration: 2
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Details of trap for CO2 and volatile organics if used: The CO2-free air was produced by passing compressed air through a glass column containing self-indicating soda lime (Carbosorb®) granules. The CO2 produced by degradation was collected in two 500 mL Dreschel bottles containing 350 mL of 0.05 M NaOH. The CO2 absorbing solutions were prepared using purified water.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2
- Abiotic sterile control: 2
- Toxicity control: 1

Reference substance:

benzoic acid, sodium salt

Test performance:

All the OECD test criteria were met. Therefore, the study is considered valid.
- The total CO2 evolution in the inoculum control vessels on Day 28 was 32.83 mg/L.
- The IC content of the test item suspension in the mineral medium at the start of the test (see Table 3) was below 5% of the TC content.
- The difference between the values for CO2 production at the end of the test for the replicate vessels was <20%
- The toxicity control attained 28% biodegradation after 14 days and 54% biodegradation after 28 days thereby confirming that the test item did not exhibit an inhibitory effect on the sewage treatment micro-organisms used in the test.
- Sodium benzoate attained 65% biodegradation after 14 days with greater than 60% degradation being attained in a 10-Day window. After 28 days 113% biodegradation was attained. Biodegradation values in excess of 100% were considered to be due to sampling/analytical variation.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

28 d

Details on results:

No biodegradation of the test substance was observed. A detailed overview of the test results is provided in 'Any other information on restults incl. tables'. The toxicity control attained 28% biodegradation after 14 days and 54% biodegradation after 28 days.

Results with reference substance:

The degree of biodegradation of the reference substance after 14 days was 65 %.

Validity criteria fulfilled:

yes

Remarks:

see 'Test performance'

Interpretation of results:

not readily biodegradable

Conclusions:

The test item attained 0% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B.

Executive summary:

The biodegradation potential of the substance in water was determined in a screening study according to OECD TG 301B (CO2-Evolution Test) and in compliance with GLP criteria (Envigo, 2017). In this study, ~10 mg/L TOC nominal (equivalent to ~13 mg/L test substance) was inoculated with activated sludge from a sewage treatment plant treating predominantly domestic sewage for 28 days under aerobic conditions. During the incubation period the produced carbon dioxide (CO2) was measured and at the end of the test compared with the maximal theoretical CO2 production (ThCO2). Biodegradation was expressed as percentage of the measured CO2 relative to the ThCO2. The test item attained 0% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the terms and conditions of OECD Guideline No. 301B.

Description of key information

Not readily biodegradable according to OECD guidelines.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater

Additional information

The biodegradation potential of the substance in water was determined in a screening study according to OECD TG 301B (CO2-Evolution Test) and in compliance with GLP criteria (Envigo, 2017). In this study, ~10 mg/L TOC nominal (equivalent to ~13 mg/L test substance) was inoculated with activated sludge from a sewage treatment plant treating predominantly domestic sewage for 28 days under aerobic conditions. During the incubation period the produced carbon dioxide (CO2) was measured and at the end of the test compared with the maximal theoretical CO2 production (ThCO2). Biodegradation was expressed as percentage of the measured CO2 relative to the ThCO2. The test item attained 0% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the terms and conditions of OECD Guideline No. 301B.