Fatty acids, C16-18, esters with diethylene glycol

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:

09 Jun - 08 Jul 2015

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)

Deviations:

yes

Remarks:

The temperature in one test vessel containing water which was incubated under the same conditions as the test vessels has a slightly higher temperature on day 5 (25 °C compared to 22 ± 1 °C as recommended in the guideline).

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): A mixed population of activated sewage sludge microorganisms was obtained from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK.
- Laboratory culture: no
- Storage length: Used on the day of collection.
- Preparation of inoculum for exposure: The activated sludge was washed twice by settlement and resuspension in mineral medium to remove any excessive amounts of dissolved organic carbon (DOC). The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approx. 21 °C. The suspended solids concentration was determined to be 3.1 g/L.

Duration of test (contact time):

28 d

Initial conc.:

14.4 mg/L

Based on:

test mat.

Initial conc.:

10 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 22 - 25 °C
- pH: 7.4 - 7.6
- pH adjusted: yes; pH was adjusted to 7.4 ± 0.2 using diluted hydrochloric acid or sodium hydroxide solution prior to the volume in all test vessels being adjusted to 3 L by the addition of mineral medium which had been purged overnight with CO2 free air.
- Aeration of dilution water: yes, aerated overnight
- Suspended solids concentration: 3.1 g/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 5 L test vessels containing 3 L of test solution
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids/L. Approximately 24 h prior to addition of the test and reference items the vessels were filled with 2400 mL of mineral medium and 29 mL of inoculum and aerated overnight.
- Test performed in closed vessels due to significant volatility of test substance: Test vessels were sealed.
- Details of trap for CO2 and volatile organics if used: The CO2 produced 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.
- Other: Vessels were aerated by CO2 free air at a rate of 30-100 mL/min and stirred continuously by magnetic stirrer. The CO2 free air was produced by passing compressed air through a glass column containing self-indicating soda lime granules.

SAMPLING
- Sampling frequency: On day 0, 2, 6, 8, 10, 14, 21, 28 and 29. The appearance of the test solutions was recorded on day 0, 6, 13, 20 and 27.
- Sampling method: 2 mL samples were taken from the first CO2 absorber. The second CO2 absorber vessels were samples on day 0 and 29. On day 28, 1 mL of concentrated hydrochloric acid was added to each vessel to drive off any inorganic carbonates formed. Vessels were resealed , aerated overnight and the final samples were taken on day 29. The samples were analysed by a Tekmar-Cohrmann Apollo 9000 TOC analyser. Each analysis was performed in triplicate.
- Sample storage before analysis: No, immeadiate analysis.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 bottles
- Abiotic sterile control: no
- Toxicity control: yes, 1 bottle
- Other: Reference substance: yes, 2 bottles

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

95

Sampling time:

28 d

Remarks on result:

other: Mean of two replicates

Details on results:

The test item was degraded to 92% after 28 d. After driving off any inorganic carbonates formed a degradation of 95% was recorded after 29 d. The 10-day window was met.

Results with reference substance:

The reference substance was degraded to 85% after 14 d and 84% after 28 d. The result is valid and confirmed the suitability of the inoculum and test conditions.

The toxicity control attained 74% biodegradation after 14 d and 69% biodegradation after 28 d, thereby confirming that the test item did not exhibit an inhibitory effect on STP microorganisms.

Table 1: Percentage biodegradation values

Day	% biodegradation
	Procedure control	Test item	Toxicity control
0	0	0	0
2	53	24	36
6	71	61	60
8	73	63	59
10	75	65	62
14	85	79	74
21	72	74	67
28	79	92	68
29*	84	95	69

* On day 28, 1 mL of concentrated HCl was added to each vessel to drive off any inorganic carbonates formed. The vessels were resealed, aerated overnight and the final samples taken from both absorber vessels on day 29.

Table 2: Validity criteria for OECD 301 B.

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 between the values for CO2 production at the end of the test for the replicate vessels was <20%.	yes
Percentage degradation of the reference compound reached the pass level by day 14 (≥ 60%).	Sodium benzoate attained 85% biodegradation after 14 days.	yes
The toxicity control should degrade to at least 35% (based on DOC) or at least 25% (based on ThOD or ThCO2) within 14 d.	The toxicity control attained 74% biodegradation after 14 days and 96% biodegradation after 28 days.	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 suspension in the mineral medium at the start of the test was below 5% of the TC 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 evolution in the inoculum control vessels on Day 28 was 36.88 mg/L.	yes

 

Validity criteria fulfilled:

yes

Remarks:

See Table 2 in "Any other information on results incl. tables".

Interpretation of results:

readily biodegradable

Description of key information

Readily biodegradable: 95% after 28 d (CO2 evolution, OECD 301B)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

One experimental study is available investigating the ready biodegradability of Fatty acids, C16-18, esters with diethylene glycol (CAS 85116-97-8). The study was conducted according to OECD 301B (GLP) using non-adapted activated sludge as inoculum. 14.4 mg of the test substance were used and incubated for 28 d. The CO2 produced was absorbed in 0.05 M NaOH solution and analysed. On day 28 concentrated hydrochloric acid was added to each vessel in order to drive off any inorganic carbon formed. The final measurement was done on day 29 but refers to the degradation of the substance after 28 d. After 28 d the test substance was degraded to 95% (mean of two replicates). Thus, the substance is concluded to be readily biodegradable according to the OECD criteria.
The toxicity control attained 74% biodegradation after 14 d confirming that the test substance is not inhibitory to the test item.