Benzoic acid, 2-([1,1'-biphenyl]-4-ylcarbonyl)-

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:

From April 19, 2017 to May 7, 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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)

Deviations:

no

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

TEST SYSTEM

Origin: The secondary effluent microorganisms supplied from the sewage plant for domestic sewage in Veszprém, Hungary.
Conditioning: The secondary effluent used for this study was allowed to settle approximately for an hour, then the decanted effluent was aerated until use (not later than an hour).

TEST UNITS

Type and Size: BOD bottles (300 mL) with special neck and glass stoppers.
Identification: Each test flask was uniquely identified with study code, test group, days of measurement and replicate number.

TEST CONDITIONS

The test was carried out in an incubator and controlled environment room (during the formulation and oxygen measuring) at a temperature of 22±2°C according to guideline. The test flasks were placed into an incubator and kept at 21.4 - 23.4°C, in the dark. The temperature was measured on weekdays during the experiment. The oxygen concentration of test water was 8.8 mg/L at the start of the test. The pH value of the test water was checked prior start of the experiment and was 7.44. The test conditions were measured with suitable instruments and documented in the raw data.

Duration of test (contact time):

28 d

Initial conc.:

ca. 2.6 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

PREPARATION OF THE TEST SOLUTIONS

The respective amount of the test substance was weighed in directly to reach the required concentration of 2.6 mg/L. The chosen test substance concentration was based on theoretical oxygen demand (ThOD) of 2.33 mg O2/mg test substance (calculated according to equation given in the guidelines) and on the performed 14-d preliminary test. The components were applied in the amounts/volumes in the test flasks:

1) Test substance (flasks 1a and 1b)
Based on the theoretical oxygen demand (ThOD) of 2.33 mg O2/mg test substance 8.8 mg of the test substance was thoroughly mixed into 3.40 L of aqueous test medium (corresponding to 2.6 mg/L test substance, with a ThOD of about 6.058 mg O2/L).

2) Procedure Control: Sodium benzoate (flasks 2a and 2b)
Based on the theoretical oxygen demand (ThOD) of sodium benzoate (1.67 mg O2 per mg) stock solution corresponding to 12.24 mg of sodium benzoate was mixed into 3.40 L of aqueous test medium (corresponding to 3.6 mg/L reference substance, respectively a ThOD of about 6.012 mg O2/L).

3) Inoculum Control (flasks 3a and 3b)
Only filtered inoculum was added to 3.40 L of aqueous test medium.

4) Toxicity Control (flasks 4a and 4b)
The test substance (8.8 mg) and the reference substance stock solution (34.0 mL) were mixed into 3.40 L of aqueous test medium corresponding to 2.6 mg/L test substance (ThOD of 6.058 mg O2/L) and 3.6 mg/L reference substance (ThOD of 6.012 mg O2/L).

Microbial inoculum (0.5 mL per litre) was added to each bottle.

COURSE OF THE TEST

Preparation of Test Flasks

Sufficient number of BOD flasks was cleaned with 5 - 10 mL of a wash liquid (2.5 g iodine and 12.5 g potassium iodide per litre of 1% w/v sulphuric acid) by shaking well to coat the bottle walls. After allowing standing for 15 min, the wash liquid was poured off, and the bottles were thoroughly rinsed with tap water and deionised water. Then, the previously described test solutions were filled into the bottles bubble-free until the bottles were completely filled. Then they were tightly closed with glass stoppers.

The Test Bottles

The number of test bottles was the follow:
- 10 bottles containing the test substance and inoculum
- 10 bottles containing the reference substance and inoculum (procedure control)
- 10 bottles containing only inoculum (inoculum control)
- 10 bottles containing the test substance, reference substance and inoculum (toxicity control)

MEASUREMENTS

Measurement of Oxygen
The incubation period of the closed bottle test was 28 d. The oxygen concentrations were measured with an oxygen meter with a stirring O2 electrode. Oxygen measurements were performed in duplicate on Days 0, 7, 14, 21 and 28.

Measurement of temperature: temperature was measured continuously and registered on weekdays.

Reference substance:

other: sodium benzoate

Key result

Parameter:

% degradation (O2 consumption)

Value:

8.3

Sampling time:

28 d

Details on results:

The percentage biodegradation of the test substance reached a mean of 8.3% after 28 d based on the ThOD of the test substance. According to the test guidelines the pass level for ready biodegradability is removal of 60% ThOD. Therefore the test substance is considered not readily biodegradable.

Results with reference substance:

- The reference substance sodium benzoate was sufficiently degraded to a mean of 70.8% after 14 d, based on ThOD, thus confirming the suitability of the used inoculum.
- In the toxicity control containing both, the test substance and the reference substance sodium benzoate, a mean of 37.1% biodegradation was noted within 14 d of incubation.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

Under the test conditions, test substance is considered not readily biodegradable.

Executive summary:

A study was conducted to determine the ready biodegradability of the test substance PBBA according to OECD Guideline 301 D, EU Method C.4 -E and EPA Guideline OPPTS 835.3110, in compliance with GLP. The test substance at 2.6 mg/L was inoculated for 28 d in a pre-aerated microbial system collected from a domestic sewage plant. Biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference substance, sodium benzoate (at 3.6 mg/L) was tested simultaneously under the same conditions as the test substance. Additionally, toxicity and inoculum controls were used.Sodium benzoate was degraded up to 70.8% after 14 d, based on ThOD, thus confirming the suitability of the used inoculum. In the toxicity control containing both the test substance and sodium benzoate, a mean of 37.1% biodegradation was observed within 14 d of incubation. Under the test conditions, the percentage biodegradation of the test substance reached a mean of 8.3% after 28 d based on ThOD. Additionally, the test substance was not considered to have significant inhibitory effects on the secondary effluent microorganisms at the applied concentration level of 2.6 mg/L because degradation was >25 % within 14 d. Under the test conditions, the test substance was not considered to be readily biodegradable (Sipos, 2017).

Description of key information

The test substance is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater

Additional information

A study was conducted to determine the ready biodegradability of the test substance PBBA according to OECD Guideline 301 D, EU Method C.4 -E and EPA Guideline OPPTS 835.3110, in compliance with GLP. The test substance at 2.6 mg/L was inoculated for 28 d in a pre-aerated microbial system collected from a domestic sewage plant. Biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference substance, sodium benzoate (at 3.6 mg/L) was tested simultaneously under the same conditions as the test substance. Additionally, toxicity and inoculum controls were used. Sodium benzoate was degraded up to 70.8% after 14 d, based on ThOD, thus confirming the suitability of the used inoculum. In the toxicity control containing both the test substance and sodium benzoate, a mean of 37.1% biodegradation was observed within 14 d of incubation. Under the test conditions, the percentage biodegradation of the test substance reached a mean of 8.3% after 28 d based on ThOD. Additionally, the test substance was not considered to have significant inhibitory effects on the secondary effluent microorganisms at the applied concentration level of 2.6 mg/L because degradation was >25% within 14 d. Under the test conditions, the test substance was not considered to be readily biodegradable (Sipos, 2017).