Butyl ethyl 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

Study period:

2017-04-04 to 2017-06-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

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 was used. The treatment plant clarifies predominantly domestic wastewater and has a capacity of 600.000 inhabitant equivalents.
- Pretreatment: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
- Concentration of sludge: 30 mg/L dry solids. The dry solid content of the activated sludge was 5.09 g/L.

Duration of test (contact time):

28 d

Initial conc.:

99.9 mg/L

Based on:

ThOD

Remarks:

The test item was added directly. Therefore 164 mL mineral medium were filled into the test vessels and the test item was pipetted directly into the bottles. 7.75 μL of the test item were added, corresponding to a concentration of 99.9 mg ThOD/L.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium:
For preparation of the mineral medium 10 mL of solution (A) is mixed with 900 mL demineralised water, 1 mL each of solutions (B), (C) and (D) are added and the volume is made up to 1 litre. Before use, the mineral medium is aerated for about one hour.

Mineral medium:
A: Potassium dihydrogenphosphate (KH2PO4): 8.50 g,
Dipotassium hydrogenphosphate (K2HPO4): 21.75 g,
Disodium hydrogenphosphate dihydrate (Na2HPO4 * 2 H2O): 33.40 g, and
Ammonium chloride (NH4Cl): 0.50 g are dissolved in demineralised water and made up to 1 litre.
B: Calcium chloride dihydrate (CaCl2 * 2H2O): 36.4 g is dissolved in demineralised water and made up to 1 litre.
C: Magnesium sulfate heptahydrate (MgSO4 * 7H2O): 22.5 g is dissolved in demineralised water and made up to 1 litre.
D: Iron (III) chloride hexahydrate (FeCl3 * 6H2O): 0.25 g is dissolved in demineralised water, stabilised with one drop of concentrated HCl and
made up to 1 litre.

- Test temperature: The temperature was 21.9 – 22.6°C throughout the whole study.
- pH: 7.4 ± 0.2.
- pH adjusted: yes
- Continuous darkness: not reported


TEST SYSTEM
- Number of culture flasks/concentration: In total three reactors containing the test item. Narrow mouth bottles (500 mL volume) were used. The liquid volume was fixed as 164 mL each.
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Test performed in open system: No


CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, 3 replicates
- Abiotic sterile control: Yes, 1 replicate
- Toxicity control: Yes, 1 replicate
- Other: Reference: 3 replicates

Reference substance:

other: Sodium acetate

Key result

Parameter:

% degradation (O2 consumption)

Value:

72.2

Sampling time:

28 d

Details on results:

Summary of results: Please refer also to the tables 1 and 2 below, shown in "Any other information on results incl. tables"

- Test item:
After a lag-Phase of 4 days with slight negative degradation values, probably due to adaption effects, the degradation of the test item started and reached 60 % of ThOD by day 10 (see table 2 and figure 1 attached). The biodegradation at the end of the test (day 28) was 72.2 % of ThOD (mean of three replicates).
The pH in the test vessels at the end of the test was 7.5.

- Toxicity control:
The degradation in the toxicity control reached 28.6 % within 4 days (see table 2) and was thus above the criterion for inhibition effects to the inoculum (<25 % on day 14). The test item had no toxic effect to the inoculum according to the validity criteria of OECD 301.
The pH in the toxicity control vessel at the end of the test was 8.8.

- Abiotic control:
No abiotic degradation could be detected in the abiotic control. Temporarily, an underflow of the admissible range occurred which means that instead of an oxygen consumption an overpressure was measured. In these cases, the degradation values were equated with 0 (see tables 1 and 2 and figure 1).
The pH in the abiotic control vessel at the end of the test was 9.1.

- Reference item:
The reference compound sodium acetate reached the pass level for ready biodegradability (60 % ThOD within a 10-day window) within 8 days (see table 2).
The pH in the reference vessels at the end of the test was 9.0.

- Blank:
The oxygen consumption of the blanks was 24.4 mg/L in 28 days (mean of three replicates, see table 1).
The pH in the blank vessels at the end of the test was 7.5.

Results with reference substance:

The reference compound sodium acetate reached the pass level for ready biodegradability (60% ThOD within a 10-day window) within 8 days. The pH in the reference vessels at the end of the test was 9.0.

Table 1: Butyl ethyl ether - measured oxygen consumption

	Test item			Toxicity control	Reference item			Blank			Abiotic control
Test item [μL/164 mL]	7.75	7.75	7.75	7.75							7.75
Reference item [mL/164 mL]*				164	164	164	164
ThOD [mg/L]	99.9	99.9	99.9	199.9	100.0	100.0	100.0				99.9
Day	Oxygen consumption [mg O2/L]
0	0	0	0	0	0	0	0	0	0	0	0
4	14.1	11.3	11.3	70.3	70.3	70.3	70.3	14.1	14.1	11.3	0
8	73.2	67.5	70.3	104	90	87.2	90	16.9	16.9	16.9	0
12	87.2	81.6	81.6	135	98.5	95.7	98.5	16.9	19.7	16.9	UFL
16	92.8	87.2	87.2	160	104	104	104	22.5	22.5	22.5	0
20	98.5	92.8	90	172	110	104	110	25.3	25.3	22.5	0
24	101	95.7	92.8	180	110	107	110	25.3	25.3	25.3	0
28	101	95.7	92.8	180	110	107	110	22.5	25.3	25.3	UFL
pH on day 28	7.5	7.5	7.5	8.8	9.0	9.0	9.0	7.5	7.5	7.5	9.1
*stock solution with 128.2 mg/L						UFL: underflow - value is below the admissible range

Table 2: Butyl ethyl ether - Biodegradation in % of ThOD

	Test item			Toxicity control	Reference item			Abiotic control
Test item [μL/164 mL]	7.75	7.75	7.75	7.75				7.75
Reference item [mL/164 mL]*				164	164	164	164
ThOD [mg/L]	99.9	99.9	99.9	199.9	100.0	100.0	100.0	99.9
Day	Degradation (%)
0	0	0	0	0	0	0	0	0.0
4	0.9	-1.9	-1.9	28.6	57.1	57.1	57.1	0.0
8	56.3	50.6	53.4	43.6	73.1	70.3	73.1	0.0
12	69.4	63.8	63.8	58.6	80.7	77.9	80.7	0.0
16	70.3	64.7	64.7	68.8	81.5	81.5	81.5	0.0
20	74.2	68.5	65.7	73.8	85.6	79.6	85.6	0.0
24	75.7	70.4	67.5	77.4	84.7	81.7	84.7	0.0
28	76.7	71.4	68.5	77.8	85.6	82.6	85.6	0.0
*stock solution with 128.2 mg/L

Figure 1: Degradation of butyl ethyl ether in the respirometry test (mean values) refer to "Illustrations" below.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The degradation of the test item within 28 days was 72.2 % of ThOD (mean of three replicates).
The test item reached the criteria for ready biodegradability (60 % ThOD within a 10-d window).
The degradation of the toxicity control after 14 days was >25 %. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline.
No abiotic degradation could be detected.
The test is valid according to OECD 301 F (July 1992).

Executive summary:

A Manometric Respirometry Test according to OECD 301 F (July 1992) was conducted in order to investigate the ready biodegradability of butyl ethyl ether. The biodegradation of butyl ethyl ether was studied in reconstituted water inoculated with activated sludge from a municipal wastewater treatment plant with a concentration corresponding to 30 mg dry solids per litre.The Manometric Respirometry Test determines the ready biodegradability of test items following their oxygen consumption in closed flasks at a constant temperature (±1 °C) in a range of 20 – 24 °C. The consumption of oxygen is determined by measuring the negative pressure in the flasks after absorption of the evolved carbon dioxide in sodium hydroxide. A solution or suspension of the test item in a mineral medium, corresponding to 100 mg/L test item giving at least 50 – 100 mg/L of theoretical oxygen demand (ThOD), is inoculated with activated sludge (30 mg d.s./L) for 28 days. The amount of oxygen taken up by the microbial population during the biodegradation of the test item (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of the ThOD or the chemical oxygen demand (COD). The pass level for ready biodegradability is 60 % of ThOD and must be reached within a 10-d window. The 10-d window begins when the degree of biodegradation reaches 10 %.

The test method is suitable for water soluble and non-soluble test items that are non-volatile and not toxic under the test conditions.

 

The mean degradation rate of butyl ethyl ether was 72.2 % after 28 days. Therefore, butyl ethyl ether is considered to be readily biodegradable based on ThOD.

 

The test is valid according to OECD Test Guideline 301F (July 1992).

• The oxygen uptake of the inoculum blank was in the range of 20 - 30 mg O₂/L and did not exceed 60 mg O₂/L in 28 days.

• The pH value in the test and blank bottles was 7.5.

• The difference of extremes of replicate values was less than 20 %.

• The biodegradation of the reference item reached the pass level of 60% ThOD by day 8.

• The degradation extent in the toxicity control was above 25 % in 14 days based on ThOD.

Description of key information

The mean degradation rate of butyl ethyl ether in a test according to OECD method 301 F was 72.2 % in 28 days. Therefore, butyl ethyl ether is considered to be readily biodegradable based on ThOD.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable