[2-(1-propoxyethoxy)ethyl]benzene

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:

17-01-2017 until 20-03-2017

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)

Principles of method if other than guideline:

Prolonged duration to 60 days.

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, adapted

Details on inoculum:

Secondary activated sludge was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands, which is an activated sludge plant treating predominantly domestic wastewater. The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 0.40 g Dry Weight (DW)/L of activated sludge was aerated for one week. The sludge was diluted in the bottles to 2.0 mg/L and the inoculum was not pre-exposed to the test substance.

Duration of test (contact time):

60 d

Initial conc.:

2 mg/L

Parameter followed for biodegradation estimation:

O2 consumption

Remarks:

as a percentage of ThOD

Details on study design:

Test bottles:
The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

Nutrients, stocks and administration:
The nutrient medium of the Closed Bottle test contained per liter of deionized water; 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 omitted from the medium 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. Only part of the top layer of the silica gel was brought into contact with the test substance. The serum flask was closed with a screw top with aluminium foil and the content was mixed vigorously. Subsequently 0.2 g of silica gel with the test substance was added to the test bottles. The resulting concentration of test substance in the bottles was 2.0 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:
Use was made of 10 bottles containing only inoculum, 10 bottles containing silica gel and inoculum, 10 bottles containing inoculum, silica gel, and test substance, and 6 bottles containing sodium acetate and inoculum. The concentrations of the test substance, and sodium acetate in the bottles were 2.0 and 6.7 mg/L, respectively. 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. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28. The test was prolonged by measuring the course of the oxygen decrease in the bottles of day 28 using a special funnel which fitted exactly in the BOD bottle. Subsequently, the oxygen electrode was inserted to measure the oxygen concentration. The medium dissipated by the electrode is collected in the funnel and flows back into the BOD bottle after withdrawal of the electrode, followed by removal of the funnel and closing the bottle.

Test conditions:
The pH of the media was 7.3 at the start of the test. The pH of the media at day 28 was 7.3 (controls) and 7.2 (test). Temperatures were within the prescribed temperature range of 22 to 24°C.

Reference substance:

acetic acid, sodium salt

Remarks:

Purity >99%

Test performance:

The validity of the test is demonstrated by an endogenous respiration of 0.7 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 80. 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:

52

Sampling time:

28 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

71

Sampling time:

60 d

Parameter:

% degradation (O2 consumption)

Value:

4

Sampling time:

7 d

Parameter:

% degradation (O2 consumption)

Value:

37

Sampling time:

14 d

Parameter:

% degradation (O2 consumption)

Value:

42

Sampling time:

21 d

Parameter:

% degradation (O2 consumption)

Value:

63

Sampling time:

42 d

Details on results:

Hyacinth body #3 was biodegraded by 52% at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test the test substance is biodegraded by 71% at day 60. A biodegradation in excess of 60% within the 60-day test period allows classification of Hyacinth body #3 as not persistent.

Results with reference substance:

The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 80.

Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of Hyacinth body #3 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 test substance concentration is expected.

Validity criteria fulfilled:

yes

Remarks:

Endogenous respiration on day 28 was 0.7 mg/L; the differences of the replicate values on day 28 were < 20%; the reference compound biodegradation on day 14 was 80; oxygen concentrations were >0.5 mg/L in all bottles during the test period.

Interpretation of results:

not readily biodegradable

Conclusions:

Hyacinth body #3 was biodegraded by 52% on day 28 in the Closed Bottle test. In the prolonged Closed Bottle test the test substance was biodegraded by 71% on day 60. A biodegradation in excess of 60% within the 60-day test period allows classification of Hyacinth body #3 as not persistent.

Executive summary:

In order to assess the biodegradation of Hyacinth body #3, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions (Klimisch 1). In this study, secondary active sludge inoculum was exposed to 2 mg/L of the substance for 60 days. Hyacinth body #3 was not toxic to inoculum because it did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Hyacinth body #3 was biodegraded by 52% on day 28 in the standard Closed Bottle screening test, not being readily biodegradable. In the prolonged Closed Bottle test, the test item was biodegraded by 71% on day 60 (enhanced biodegradability testing). A biodegradation percentage of >60 within a 60-day time period allows classification of Hyacinth body #3 as not persistent.

Description of key information

In order to assess the biodegradation of Hyacinth body #3, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions (Klimisch 1). In this study, secondary active sludge inoculum was exposed to 2 mg/L of the substance for 60 days. Hyacinth body #3 was not toxic to inoculum because it did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Hyacinth body #3 was biodegraded by 52% on day 28 in the standard Closed Bottle screening test, not being readily biodegradable. In the prolonged Closed Bottle test, the test item was biodegraded by 71% on day 60 (enhanced biodegradability testing). A biodegradation percentage of >60 within a 60-day time period allows classification of Hyacinth body #3 as not persistent.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed