2-methyl-4-phenyl-1,3-dioxolane

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:

09 Nov - 09 Dec 1999

Reliability:

2 (reliable with restrictions)

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)

GLP compliance:

yes (incl. QA statement)

Remarks:

Umweltministerium Baden-Württemberg, Stuttgart, Germany

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: effluent from municipal sewage treatment plant, Pforzheim, Germany
- Storage conditions: The effluent was kept under aerobic conditions in the period between sampling and application.
- Preparation of inoculum for exposure: The inoculum was filtered through a coarse filter (Schwarzband, Schleicher & Schüll), the first 200 mL was discarded.
- Storage length: the inoculum was used on the day of collection
- Initial cell concentration: The initial number of microorganisms was determined separately for each batch (blank, test substance, reference and toxicity control) and were as follows: Inoculum blank: 2.4E+02 cells/mL, 7.92 E+05 cells/bottle; Reference: 2.5E+02 cells/mL, 8.25E+04 cells/bottle; Toxicity test: 2.2E+02 cells/mL, 7.26E+04 cells/bottle; Test substance: 2.9E+02 cells/mL; 9.57E+04 cells/bottle

Duration of test (contact time):

28 d

Initial conc.:

2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: mineral medium was prepared from 4 stock solutions containing 8.5 mg/L KH2PO4, 28.5 mg/L K2HPO4*3H2O, 33.3 mg/L Na2HPO4*2H2O, 0.5 mg/L NH4Cl, 22.5 mg/L MgSO4*7H2O, 34.2 mg/L CaCl2*2H2O, and 0.15 mg/L FeCl3.
- Test temperature: 20 ± 2 °C
- pH: 7.4 ± 0.2
- Aeration of dilution water: The medium was strongly aerated for 60 min and allowed to stand for 24 h at the test temperature. The O2 content was measured afterwards.
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: BOD flasks with ground-in-glass stoppers
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: The effluent was kept under aerobic conditions. The mineral medium was aerated for 60 min and allowed to stand for 24 h at the test temperatue.
- Measuring equipment: O2 concentrations were measured with a MTW Microprocessor Oximeter OXI 196 and a calibrated electrode EO 196-1,5. Each of the 3 parallel test assays was measured twice.
- Test performed in closed vessels due to significant volatility of test substance: The test was a Closed Bottle Test according to OECD guideline 301 D. The calculated vapor pressure of the test substance was estimated at 3.8 Pa.

SAMPLING
- Sampling frequency: 0 h, 7, 14, 21, and 28 d
- Sampling method: 3 bottles (assays) per measurement date. Each solution was immediately filled into the test vessels (volume approximately 330 mL) and the O2 concentrations were measured.
- Sample storage before analysis: no

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 3 replicates
- Toxicity control: yes, 3 replicates
- Reference substance: yes, 3 replicates

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

-8.5

Sampling time:

28 d

Details on results:

The negative values of degradation rates result from lower oxygen saturation rates in the test substance study group after aeration.

The determined 28 d degradation rate for the reference substance was 91.8% and 54.2% for the toxicity control (reference substance + test substance).

Results with reference substance:

The reference substance was degraded to 91.8% (mean) within 28 d.

The calculated theoretical oxygen demand (ThOD) of the test substance was 2.34 mg O2/mg test substance.

The calculated theoretical oxygen demand (ThOD) of the reference substance was 1.67 mg O2/mg reference substance.

The calculated theoretical oxygen demand (ThOD) of the toxicity control was 1.00 mg O2/mg substance mixture.

On average, the initial oxygen contents of the aerated test media were as follows:

- 8.9 mg/L inoculum blank

- 8.9 mg/L reference substance

- 8.6 mg/L toxicity control

- 8.6 mg/L test substance

Table 1: Individual calculations of the degradation rates and average values.

	% degradation rates
Bottle n°	Reference				Test substance
	7 d	14 d	21 d	28 d	7 d	14 d	21 d	28 d
1	70.1	73.7	69.5	80.8	-12.8	-16.7	-12.4	-6.4
2	70.1	66.5	64.7	125.7	-17.9	-13.2	-13.2	-9.4
3	68.9	77.2	65.3	68.9	-11.5	-9.0	-11.5	-9.4
average	69.7	72.5	66.5	91.8	-14.1	-13.0	-12.4	-8.4
Bottle n°	Toxicity test
	7 d	14 d	21 d	28 d
1	54.9	56.9	52.9	54.9
2	50.9	53.9	50.9	53.9
3	57.9	53.9	48.9	53.9
average	54.5	54.9	50.9	54.2

Since the pass levels for ready biodegradability are > 60% removal of ThOD within the 28 d period of the test, the test substance cannot be classified as readily biodegradable.

The degradation rate of the toxicity control was > 25% (54.9%) after 14 d. Therefore, toxic efffects of the test substance to the inoculum can be excluded.

 

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

No degradation of the substance was recorded after 28 d of incubation (-8.5% based on O2 consumption). Thus, the substance is not readily biodegradable according to the OECD criteria.

Description of key information

Not readily biodegradable (0% within 28 d, OECD 301 D)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

One GLP guideline study according to OECD 301D is available investigating the ready biodegradability of the substance. A mixed microbial population from the effluent of a local municipal STP was inoculated with a nominal concentration of 2 mg/L test substance and incubated for 28 d under controlled conditions in the dark. Degradation was followed by the determination of dissolved oxygen content after 0 h, 7, 14, 21 and 28 d. An inoculum blank, a procedure control (with 2 mg reference substance/L) and a toxicity control were run in parallel. The derived 28 d degradation rate was -8.5% for the test substance and 54.2% for the toxicity control. The negative value resulted from lower oxygen saturation rates in the test substance study groups after aeration. The pass level for ready biodegradability is > 60% removal of ThOD within 28 d, meeting the 10 d - window. Therefore, the test substance could not be classified as readily biodegradable. Since the degradation rate of the toxicity control was > 25% after 14 d, toxic effects of the test substance to the inoculum can be excluded.