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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
23rd June - 13th September 2005
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. Study read-across from middle fraction of shale oil.
Qualifier:
according to guideline
Guideline:
OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Aerobic activated sludge from a wastewater treatment plant (ARA Ergolz II, Füllinsdorf, Switzerland), treating predominantly domestic wastewater, was incubated in a laboratory wastewater treatment plant (Husmann unit) for one week.
- Storage conditions: The Husmann unit consisted of an aeration vessel (3.3 L) and a settling vessel (5 L). The aeration vessel was continuously aerated with compressed air to maintain aerobic conditions and to keep sludge flocs in suspension. An airlift pump was used to recycle the activated sludge from the settling vessel intermittently back to the aeration vessel.
- Preparation of inoculum for exposure: The water flow through the unit was approximately 0.55 liter per hour resulting in a hydraulic retention time of approximately 6 hours. The sludge was fed with synthetic wastewater which was continuously dosed to the aeration tank at a concentration of dissolved organic carbon (DOC) of approximately 110 to 160 mg/L in the influent.
Three days before the start of the test, the volume of two litres activated sludge were removed from the activated sludge unit. Then, the sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. Then, the sludge was resuspended tap water. Two aliquots of the sludge suspension were weighed, thereafter dried and the ratio of wet to dry weight was calculated. Based on this ratio, the sludge was diluted with test water (see 2.4.1) to obtain a concentration equivalent to 4 g dry material per liter. The sludge was fed once with 50 mL of synthetic wastewater per liter and was kept at room temperature under continuous aeration until use. Two days before the start of the test, the sludge was not fed anymore.
Before the start of the test, the sludge suspension was diluted four times with test water and the content of dry material was determined again. Defined aliquots of the activated sludge inoculum were added to the test flasks to give a final concentration of 100 mg dry material per liter.
- Pretreatment: Over two weeks prior to the test start, the test item was continuously dosed to the aeration tank by means of an organic stock solution in acetone. The concentration of the test item in the water inflow was 15 mg/L.
Duration of test (contact time):
28 d
Initial conc.:
30 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: see materials and methods section
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: 22 ºC
- pH: The pH measured in all flasks at the start of the test was in the range of 7.4 to 7.5. At the end of exposure (Day 28), pH values in the range of 7.0 to 7.4 were measured.
- pH adjusted: yes/no
- CEC (meq/100 g): NDA
- Aeration of dilution water: yes
- Suspended solids concentration: 100 mg/L
- Continuous darkness: yes
- Other: NDA

TEST SYSTEM
- Culturing apparatus: 500-mL Erlenmeyer flasks
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: NDA
- Method used to create anaerobic conditions: NDA
- Measuring equipment: Oxygen consumption was recorded manually by taking a daily reading at least on each working day.
Electro-chemical analysis process:
The biodegradation process consumes the dissolved oxygen in the liquid and generates CO2. The CO2 is adsorbed by soda lime and the total pressure decreases in the airtight test flasks. The pressure drop is detected and converted into an electrical signal by means of an electrode type manometer. The consumed oxygen is replaced by electrolytically generated oxygen from a copper sulfate solution.

CONTROL AND BLANK SYSTEM
- Inoculum blank: inoculum in test medium
- Abiotic sterile control: 30 mg/L test item poisoned with mercury dichloride at 10 mg/L
- Toxicity control: 30 mg/L test item with 30 mg/L positive control

STATISTICAL METHODS: NDA
Reference substance:
benzoic acid, sodium salt
Preliminary study:
NDA
Test performance:
The percent biodegradation in the toxicity control, containing both the test item and the reference item, was calculated based on the sum of the COD of the test item and the ThOD of the reference item (see Sections 2.4.2, 2.5 and 2.6).
In the toxicity control, the biodegradation of the reference item was not inhibited. Within 14 days of exposure, the extent of biodegradation was 45%. Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 30 mg/L because biodegradation in the toxicity control was >25% within 14 days.
Parameter:
% degradation (O2 consumption)
Value:
22
Sampling time:
28 d
Details on results:
The percent biodegradation of the test item was calculated based on the chemical oxygen demand (COD) of the test item of 2.50 mg O2/mg.
A significant biodegradation (>10%) of Shale Oil in the test media was determined after about two weeks test duration. After about three weeks test duration, a plateau of the biodegradation curve was determined. At the end of the 28-day exposure period, the mean extent of biodegradation of Shale Oil was 22%.
Thus, some compounds of the test item were biodegradable. However, the major part of the test item was not biodegraded within 28 days of test duration in this inherent biodegradability test
Parameter:
COD
Value:
2.5 g O2/g test mat.
Results with reference substance:
The percent biodegradation of the reference item sodium benzoate was calculated based on its theoretical oxygen demand of 1.67 mg O2/mg.
In the procedure controls, the reference item was degraded by an average extent of 70% and 72% by exposure days 7 and 14, respectively, thus confirming the suitability of the activated sludge.
Validity criteria fulfilled:
yes
Interpretation of results:
not inherently biodegradable
Conclusions:
At the end of the 28-day exposure period, the mean extent of biodegradation of Shale Oil was 22%. Thus, some compounds of the test item were biodegradable. However, the major part of the test item was not biodegraded within 28 days of test duration in this inherent biodegradability test
Executive summary:

The test item Shale Oil was investigated for its inherent biodegradability in a manometric respirometry test over 28 days based on the OECD Guideline for Testing of Chemicals No. 302 C (1981). The following modifications were made: activated sludge from one source was used and pre-adapted to the test item at the nominal concentration of 15 mg/L for three weeks prior to the start of the test, the test water was slightly changed, and only the biological oxygen demand (BOD) was monitored.

At the end of the 28-day exposure period, the mean extent of biodegradation of Shale Oil was 22%. Thus, some compounds of the test item were biodegradable. However, the major part of the test item was not biodegraded within 28 days of test duration in this inherent biodegradability test.

Based on the rationale for read-across, it is considered acceptable to use this study to address the same endpoint for light fraction of shale oil.

Endpoint:
biodegradation in water: ready biodegradability
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Justification for type of information:
JUSTIFICATION FOR DATA WAIVING
In accordance with Annex XI of the REACH regulation, a ready biodegradability study was considered not to be scientifically necessary due to the availability of existing data. An inherent biodegradability study was felt to already sufficiently cover this endpoint (9.2.1.1).

Description of key information

At the end of the 28-day exposure period, the mean extent of biodegradation of Shale Oil was 22%. 
Thus, some compounds of the test item were biodegradable. However, the major part of the test item
was not biodegraded within 28 days of test duration in this inherent biodegradability test.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

A significant biodegradation (>10%) of Shale Oil in the test media was determined after about two weeks test duration. After about three weeks test duration, a plateau of the biodegradation curve was determined. At the end of the 28-day exposure period, the mean extent of biodegradation of Shale Oil was 22%.


 


Thus, some compounds of the test item were biodegradable. However, the major part of the test item was not biodegraded within 28 days of test duration in this inherent biodegradability test.


 


In accordance with Annex XI of the REACH regulation, a ready biodegradability study was considered not to be scientifically necessary due to the availability of existing data. The inherent biodegradability study was felt to sufficiently cover this endpoint (9.2.1.1).