Dihexyl ether

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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Three different concentrations were tested in this study: 25, 50, 100 mg ThOD/L. One of the two replicates for the 25 mg ThOD/L concentration was excluded from the overall calculation, as after completion of the incubation the test vessel was found to be damaged and thus not being tightly closed, resulting in only 43 % biodegradation after 28 days.

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Name of the test material (as cited in the study report): Nacol ether 6
Physical state: Colourless liquid (at 20°C) with a characteristic odour
Expiration date of the lot/batch: 2018-09-30

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Municipal sewage plant at Taunusstein-
Bleidenstadt
- Laboratory culture: No
- Method of cultivation: Not applicable
- Storage conditions: Directly used after sampling
- Storage length: Not applicable
- Preparation of inoculum for exposure: Washed twice with minearal nutrient solution, aerated for 4 h, homogenised for 2 min and filtered
- Pretreatment: None
- Concentration of sludge: 0.35 mg/L dry mass

Duration of test (contact time):

28 d

Initial conc.:

25 mg/L

Based on:

ThOD/L

Initial conc.:

50 mg/L

Based on:

ThOD/L

Initial conc.:

100 mg/L

Based on:

ThOD/L

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium:
The test solutions contained in a total volume of 1000 mL:
[10 ml] inoculum
[10 ml] Solution A: 8.50 g KH2PO4, 21.75 g K2HPO4, 33.40 g Na2HPO4 · 2 H2O, 0.50 g NH4Cl diluted in 1 L Ultrapure Water
[1 ml] Solution B: 22.50 g MgSO4 · 7 H2O diluted in 1 L Ultrapure Water
[1 ml] Solution C: 36.40 g CaCl2 · 2 H2O (≙ 27.5 g CaCl2) diluted in 1 L Ultrapure Water
[1 ml] Solution D: 0.25 g FeCl3 · 6 H2O diluted in 1 L Ultrapure Water

- Additional substrate: silica gel
- Test temperature: 22°C
- pH: 7.73 - 7.78
- pH adjusted: no
- Aeration of dilution water: Continous stirring
- Suspended solids concentration: ~0.35 mg/L dry matter
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus:
SAPROMAT / Respiromat: Abwassertechnik, IBUK CO, Franziskusweg 12, D-89079 Ulm, Ser.-No.: 0007/05 – 00009
Special flasks for Sapromat: made of glass, 1200 mL and 500 mL volume with special stoppers
Upon biochemical processes in the test solutions the test item is oxidized and oxygen in the liquid phase is consumed. Oxygen in the space above the liquid phase is dissolved in the liquid, resulting in generation of CO2 (from carbon material of the test item) in its place. As this CO2 is absorbed by soda lime, the partial pressure of oxygen in the space and the total pressure decrease. The drop in pressure is detected and converted into an electric signal generating electrolytic oxygen from sulphuric acid copper solution contained in an electrolytic bottle by constant current. This oxygen is supplied to the cultivating bottle and restoration of pressure is detected by means of the manometer, resulting in switching off the relay circuit and stopping the electrolytic process. Thus, the upper space in the cultivating bottle is always kept under a constant pressure of oxygen and the quantity of oxygen consumed in the cultivating bottle is proportional to the quantity of electrolytic oxygen. So the oxygen uptake can be read directly from the manometer.
- Number of culture flasks/concentration: 2 (25 mg ThOD/L), 3 (50 + 100 mg ThOD/L)
- Test item concentrations: 36.1 mg, 33.3 mg, 36.6 mg, 18.4 mg, 24.8 mg, 20.9 mg, 13.0 mg and 11.4 mg of the test item

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 flasks
- Abiotic sterile control: Not included
- Toxicity control: In order to determine a possible bacterial toxicity of the test item one test solution with 20.3 mg test item and 50.8 mg sodium benzoate per 500 mL of test solution was tested in parallel.
- Reference substance: 101.6 mg sodium benzoate/L

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

77.3

Sampling time:

28 d

Remarks on result:

other: ≈100 mg /L ThOD (36.1 mg TS /L) - replicate 1

Key result

Parameter:

% degradation (O2 consumption)

Value:

76.2

Sampling time:

28 d

Remarks on result:

other: ≈100 mg /L ThOD (33.3 mg TS/L) - replicate 2

Key result

Parameter:

% degradation (O2 consumption)

Value:

74.5

Sampling time:

28 d

Remarks on result:

other: ≈100 mg /L ThOD (36.6 mg TS/L) - replicate 3

Parameter:

% degradation (O2 consumption)

Value:

76.7

Sampling time:

28 d

Remarks on result:

other: ≈50 mg /L ThOD (18.4 mg TS/L) - replicate 1

Parameter:

% degradation (O2 consumption)

Value:

80.1

Sampling time:

28 d

Remarks on result:

other: ≈50 mg /L ThOD (24.8 mg TS/L) - replicate 2

Details on results:

79.7 % Degradation, based on O2 consumption, within 28 days, Concentration ≈50 mg /L ThOD (20.9 mg TS/L) - replicate 3
[42.9 % Degradation, based on O2 consumption, within 28 days, Concentration≈25 mg /L ThOD (13.0 mg TS/L) - replicate 1: excluded from overall calculation, test vessel damaged]
77.1 % Degradation, based on O2 consumption, within 28 days, Concentration≈25 mg /L ThOD ( 11.4 mg TS/L) - replicate 2

Results with reference substance:

Concentration ≈170 mg ThOD/L (50.8 mg K/500 mL):
86.4 % Degradation, based on O2 consumption, within 28 days; > 60 % within 3 days

“NACOL ETHER 6” was tested for biodegradability according to ‘Manometric Respirometry Test' (OECD Guideline 301F). The degradation process was followed by the oxygen uptake in the test solutions using three different test item concentrations (corresponding to 25 mg ThOD/L, 50 mg ThOD/L,and 100 mg ThOD/L). With respect to the theoretical oxygen demand (ThOD) of the test item and the measured BOD of the test solutions, the following results were obtained:

• 25 mg ThOD/L, 1* replicate, degradation: 77% (*One of the two replicates was excluded from the overall calculations, as after completion of the incubation the test vessel was found to be damaged and thus not being tightly closed, resulting in only 43 % biodegradation after 28 days.).

• 50 mg ThOD/L, 3 replicates, average degradation was 79%.

• 100 mg ThOD/L, 3 replicates, average degradation was 76%.

The toxicity control showed 81% degradation within 28 days, therefore the test item is not considered to be inhibitory according to the OECD 301F test guideline. The control item sodium benzoate was degraded to an extent of 86% within 28 days, with the threshold of ≥ 60% being met after 3 days and thus fulfilling the required “10-days-window”.

Based on the mean degradation value of the test item, combining all test item concentrations, was 77% and the threshold of “ready biodegradability” obtained within the “10-days-window” and thus the test item is "readily biodegradable".

The test is considered valid, as all validity criteria were met: the positive control was degraded >60% within the 10-days-window and before day 14 (here: after 3 days); variations between the replicates of the test item were < 20%, the oxygen uptake by the blank was < 60 mg/L and pH values were in the required range of 6 -8.5.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The mean degradation of the test item was 77% within 28 days and the threshold of “ready biodegradability” was obtained within the “10-days-window” and thus the test item is "readily biodegradable".

Executive summary:

The biodegradability of the test substance was investigated in a study according to OECD test guideline 301F under GLP. Under aerobic conditions using domestic, non-adapted activated sludge the oxygen uptake was followed over 28 days. The test substance was degraded to 77 % at 25 mg ThOD/l, 79 % at 50 mg ThOD/l, and 76% at 100 mg ThOD/L after 28 days, while all acceptance criteria were fulfilled. The 10-day window was met. Therefore, the test substance is considered to be readily biodegradable.

Description of key information

In a study according to OECD test guideline 301F, the test substance was readily biodegradable (meeting the 10-day windows) with a mean of 77 % biodegradation after 28 days.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The biodegradability of dihexyl ether was investigated in a study according to OECD test guideline 301F under GLP. Under aerobic conditions using domestic, non-adapted activated sludge the oxygen uptake was followed over 28 days. The test substance was degraded to 77 % at 25 mg ThOD/l, 79 % at 50 mg ThOD/l, and 76% at 100 mg ThOD/L after 28 days, while all acceptance criteria were fulfilled. The 10-day window was met. Therefore, the test substance is considered readily biodegradable.

As supporting information, >60 % biodegradation were obtained in another OECD 301 F non-GLP study.