1-ethylazepan-2-one

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:

27 Feb - 29 Mar 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:

17 Jul 1992

Qualifier:

according to guideline

Guideline:

other: ISO standard 10634

Version / remarks:

"Water quality - Guidance for the preparation and treatment of poorly water-soluble organic compounds for the subsequent evaluation of their biodegradability in an aqueous medium", 1995

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Municipal Sewage Treatment Plant, 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands
- Storage length: The freshly obtained sludge was used immediately.
- Pretreatment: Before use, the sludge was washed with mineral medium.
- Preparation of inoculum for exposure: Magnetic stirring
- Concentration of sludge (susended solids): 3.2 g/L
- Initial cell/biomass concentration: 3 mL/L equal to 9.6 mg/L suspended solids

Duration of test (contact time):

28 d

Initial conc.:

18 mg/L

Based on:

test mat.

Initial conc.:

12 mg/L

Based on:

TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral medium (consisting of solutions A to D according to the guideline) prepared with tap-water purified by reverse osmosis (Milli-RO) and activated carbon
- Test temperature: 22 - 23 °C
- pH: 7.6 (test start), 7.8 (Day 14), 7.4 - 7.5 (Day 28)
- pH adjusted: No. Exception: 1 blank control replicate was adjusted at test start from 7.7 to 7.6 using 1 M HCl.
- Aeration of dilution water: Yes, the test media were aerated with synthetic air during the test.
- Suspended solids concentration at test start: 9.6 mg/L
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: 2 L brown glass bottles
- Preparation of bottles: At the start of the test (Day 0), test and reference item were added to the bottles containing the microbial organisms and mineral components. The volumes of suspensions were made up to 2 L with Milli-RO water.
- Pre-incubation medium: The day before test start (Day -1) the mineral components, Milli-RO water (ca. 80% of final volume) and the inoculum were added to each bottle. This mixture was then aerated over night to purge the system of CO2.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Aeration with synthetic air (CO2 < 1 ppm)
- Measuring equipment: Titration
- Details of trap for CO2 and volatile organics if used: Three CO2-absorber bottles filled with 100 mL 0.0125 M Barium hydroxide (Ba(OH)2) were connected in series to the exit air line of each test bottle. Synthetic air was passed through the scrubbing solutions at a rate of approximately 1 - 2 bubbles per second (30 - 100 mL/min).
- Other: The test media were aerated and stirred continuously.
- Other: At the start of the test (Day 0), the test and reference items were added to the bottles containing the microbial organisms and mineral components. The volumes of the suspensions were made up to 2 L with Milli-RO water, resulting in the mineral medium described before.

SAMPLING
- Sampling frequency: Day 2, 5, 8, 12, 15, 19, 23, and 29
- Sampling method: The CO2-absorber nearest to the test bottle was removed for titration. Each of the remaining two absorbers were moved on position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series.
- Other: The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate. The amount of CO2 produced was determined by titration of the remaining Ba(OH)2 with 0.05 M standardized HCl (1:20 dilution from 1 M HCl). On the penultimate day, the pH of the respective test suspensions was measured and 1 mL concentrated HCl (37%, Merck) was added to the bottles of the inoculum blank and test suspension. The bottles were aerated over night to drive off CO2 present in the test suspension.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 replicates (no test item)
- Procedure control: 1 replicate (reference item sodium acetate)
- Toxicity control: 1 replicate (test item + reference item)

Reference substance:

acetic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

2

Sampling time:

28 d

Remarks on result:

other:

Remarks:

Replicate 1

Parameter:

% degradation (CO2 evolution)

Value:

18

Sampling time:

28 d

Remarks on result:

other:

Remarks:

Replicate 2

Results with reference substance:

The reference item was biodegraded by 85% within 14 d (pass-level: at least 60% within 14 d), thus confirming the suitability of the inoculum and test system.

VALIDITY CRITERIA

The study met all the criteria (Table 1) and was thus considered valid.

Table 1: Validity criteria for OECD 301.

Criterion from the guideline	Outcome	Validity criterion fulfilled
Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.	The difference of duplicate values for % degradation of the test item was ≤ 16% (< 20%).	Yes
Percentage degradation of the reference compound has reached the pass levels by day 14.	The reference item was biodegraded by 84% within 14 d (> 60%).	Yes
The toxicity control should degrade to at least 25% (based on ThOD or ThCO2) within 14 d.	After 14 d, 32% biodegradation was reached in the toxicity control.	Yes
The IC content of the test substance suspension in the mineral medium at the beginning of the test must be less than 5% of the TC.	The IC content of the test item suspension was < 5% of the Total Carbon content.	Yes
The total CO2 evolution in the inoculum blank at the end of the test should not normally exceed 40 mg/L medium.	The total CO2 release in the blank at the end of the test was 31.8 mg CO2/L (63.6 mg CO2 per 2 L of medium).	Yes

 

RESULTS

The relative biodegradation values calculated from the measurents performed during the test period revealed 2 and 18% biodegradation of the test item based on ThCO2, for the duplicates tested. Thus, the criterion for ready biodegradability (at least 60% biodegradation within a 10 -d window) was not met.

In the toxicity control, degradation was 32% after 14 d, which is above the pass level of > 25% in 14 d. Thus, the test item was found not to inhibit microbial activity.

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Interpretation of results:

not readily biodegradable

Description of key information

The substance is not readily biodegradable according to OECD criteria.

Additional information

The ready biodegradability of N-ethylcaprolactam was tested in a study following OECD Guideline 301 B at GLP conditions. Activated sludge of a municipal wastewater treatment plant was used as inoculum. The degradation of the test substance was determined by measuring the CO2 evolution of the inoculum during the test period of 28 days. Biodegradation of 2% and 18 % was determined for the duplicate bottles tested. Thus, the substance is not readily biodegradable according to the OECD criteria.