Isobutyl 2-naphthyl 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:

4 October 2016 to 5 December 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

natural water

Details on inoculum:

River water was sampled from the Rhine near Heveadorp, The Netherlands. The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream. The river water was aerated for 7 days to reduce the endogenous respiration. River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.

Duration of test (contact time):

60 d

Initial conc.:

1 mg/L

Based on:

test mat.

Initial conc.:

2.8 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST MEDIA
- The river water used in the Closed Bottle test was spiked per liter of water with 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.4 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg CaCl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was not added to the river water to prevent nitrification.
- Accurate administering of the test substance was accomplished by preparing a solid stock of 3.0 mg of the test substance per g of silica gel in a 50-mL serum flask. To this end, approximately 60 mg of the test substance was dissolved in a few mL of dichloromethane (DCM). The DCM with test substance was dosed on an appropriate amount of silica gel in a 50-mL serum flask to give 3.0 mg test substance/g silica gel. Next DCM was evaporated overnight. After evaporation, the content of the serum flask was thoroughly mixed. An amount of 0.10 g of this silica gel was added to each test bottle. Although no additional oxygen consumption was expected a control with bottles containing silica gel (DCM added and evaporated) was included. The resulting concentration of test substance in the bottles was 1.0 mg/L. Next the bottles were filled with nutrient medium with inoculum and closed. Sodium acetate was added to the bottles using a stock solution of 1.0 g/L

TEST PROCEDURE
- The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.
- Use was made of 10 bottles containing only river water, 10 bottles containing river water and silica gel, 10 bottles containing river water and silica gel with test substance, 6 bottles with river water and sodium acetate. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles were closed and incubated in the dark.

SAMPLING AND ANALYSIS
Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28. One extension from the protocol of the Closed Bottle test was introduced. The Closed Bottle test was prolonged to 60 days by measuring the course of the oxygen decrease in the bottles of day 28 using a special funnel. This funnel fitted exactly in the BOD bottle. Subsequently, the oxygen electrode was inserted in the BOD bottle to measure the oxygen concentration. The medium dissipated by the electrode was collected in the funnel. After withdrawal of the oxygen electrode the medium collected flowed back into the BOD bottle, followed by removal of the funnel and closing of the BOD bottle.

OTHER TEST CONDITIONS
The pH was measured using a Eutech Cyberscan pH11 pH meter. The pH of the media was 8.0 at the start of the test. The pH of the media at day 28 was 7.9 (test and control) and 8.0 (control with silica gel). The temperature was measured and recorded with a sensor connected to a data logger. Temperatures were within the prescribed temperature range of 22 to 24 °C.

Reference substance:

acetic acid, sodium salt

Remarks:

tested at a concentration of 6.7 mg/L (ThOD of sodium acetate is 0.8 mg/mg)

Test performance:

VALIDITY CRITERIA:
The test is valid as shown by an endogenous respiration of 1.2 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 85. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Key result

Parameter:

% degradation (O2 consumption)

Value:

36

Sampling time:

28 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

75

Sampling time:

60 d

Details on results:

The substance is biodegraded by 36% at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test the test substance is biodegraded by 75% at day 60. See 'Any other information on results incl. tables' for additional results on the degradation of the test material.

Results with reference substance:

The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 85.

TOXICITY TO THE INOCULUM

Inhibition of the degradation of a well degradable compound e.g. sodium acetate by the test compound in the Closed Bottle test was not determined because possible toxicity of the test substance to microorganisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected. Therefore, no inhibition of the biodegradation due to the high initial concentration of the test compound is expected.

Table: Biodegradation of the test item (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test.

Time (days)	Biodegradation (%)
	Test substance	Acetate
0	0	0
7	0	76
14	11	85
21	21	-
28	36	-
42	57	-
60	75	-

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The substance is biodegraded by 36% at day 28 and 75% at day 60 in the Closed Bottle test and should therefore be classified as not readily biodegradable. As biodegradation exceeded 60% within the prolonged 60-d test period, the substance can be classified as not persistent.

Executive summary:

In order to assess the biodegradadation of the substance, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study river water was exposed to 1 mg/L of the substance for 28 days under aerobic conditions in the dark. After the standard 28-d test period the study was prolonged to 60 days to assess whether the substance is persistent or not. The test material was biodegraded by 36% at day 28 and should therefore be classified as not readily biodegradable. In the prolonged Closed Bottle test, the test item was biodegraded by 75% at day 60. As biodegradation exceeded 60% within the prolonged 60-d test period, the substance can be classified as not persistent. No inhibition of the biodegradation due to the high initial test substance concentration is expected as inhibition of endogenous respiration of the inoculum by the test substance at day 7 was not detected. Furthermore, the validity criteria of the test were met.

Description of key information

Naph Iso Butyl Ether Beta is not readily biodegradable in an OECD TG 301D test.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

In order to assess the biodegradadation of the substance, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study river water was exposed to 1 mg/L of the substance for 28 days under aerobic conditions in the dark. After the standard 28-d test period the study was prolonged to 60 days to assess whether the substance is persistent or not. The test material was biodegraded by 36% at day 28 and should therefore be classified as not readily biodegradable. In the prolonged Closed Bottle test, the test item was biodegraded by 75% at day 60. As biodegradation exceeded 60% within the prolonged 60-d test period, the substance can be classified as not persistent. No inhibition of the biodegradation due to the high initial test substance concentration is expected as inhibition of endogenous respiration of the inoculum by the test substance at day 7 was not detected. Furthermore, the validity criteria of the test were met.